Humans have always wondered how we came to be on this planet. Virtually every culture and religion has created myths to explain the creation of humans. In the early twentieth century, most scientists believed that the first humans appeared in Asia or Eastrn Europe.Then Dart discove red the Taung skull and provided the first solidevi dence both of an African evolution of the first humanoids and a fossil link between humans and apes, substantiating one part of Darwin’s theories.
This discovery redirected all of human evolutionary research and theory and has served as a corners tone of science’s modern beliefs about the history and origin of our species.Raymond Dartwas born in Queensland, Australia, in 1893 on a bush farm where his family was struggling to raise cattle. He excelled in school and received scholarships to study medicine, specializing in neural anatomy (the anatomy of skull and brain). In 1920 he gained a prestigious position as assistant to Grafton Elliot Smith at the Uni vers ity of Manchester, England. But their relations hipsoured and, in 1922, shortly after his thirtieth birthday, Dart was sent off to be a professor of anatomy at the newly formed University of Witwatersrand in Johannesburg, South Africa.
In the United States, cardiovascular disease leads to one death every 33 seconds and contributes to 70%of total deaths annually. This makes identifying functional foods as potential modifiers of this disease prevalence an invaluable endeavor.
Researchers have investigated whether greencoffeebeanextract (GCBE),which is rich inchlorogenic acid,maybe just such a disease modifier. In one study, two groups were created with 10 people ingesting a green coffee bean extract and 10 ingesting a placebo drink for fourmonths. At the end of the study, the treatment group experienced significant decreases in total plasma homocysteine levels and improvements in vasoreactivity. The ability of GCBE to make an impact on these two independent risk factors for cardiovascular disease progression is significant.
Neither vocalization nor articulation are essentially human. Many of the lower animals, e.g. parrots, possess the power of articulate speech, and birds can be taught to pipe tunes. The essential difference between the articulate speech of the parrot and the human being is that the parrot merely imitates sounds, it does not employ these articulate sounds to express judgments; likewise there are imbecile human beings who, parrot-like, repeat phrases which are meaningless.
Articulate speech, even when employed by a primitive savage, always expresses a judgment. Even in the simple psychic process of recalling the name aroused by the sight of a common object in daily use, and in affixing the verbal sign to that object, a judgment is expressed. But that judgment is based upon innumerable experiences primarily acquired through our special senses, whereby we have obtained a knowledge of the properties and uses of the object. This statement implies that the whole brain is consciously and unconsciously in action. There is, however, a concentration of psychic action in those portions of the brain which are essential for articulate speech; consequently the word, as it is mentally heard, mentally seen, and mentally felt (by the movements of the jaw, tongue, lips, and soft palate), occupies the field of clear consciousness; but the concept is also the nucleus of an immense constellation of subconscious psychic processes with which it has been associated by experiences in the past. In language, articulate sounds are generally employed as objective signs attached to objects with which they have no natural tie.
Charles Robert Darwin was born at Shrewsbury, England, Feb. 12, 1809, of a family distinguished on both sides. Abandoning medicine for natural history, he joined H.M.S. Beagle in 1831 on the five years' voyage, which he described in "The Voyage of the Beagle," and to which he refers in the introduction to his masterpiece. The "Origin of Species" containing, in the idea of natural selection, the distinctive contribution of Darwin to the theory of organic evolution, was published in November, 1859. In only one brief sentence did he there allude to man, but twelve years later he published the "Descent of Man," in which the principles of the earlier volume found their logical outcome.
In other works Darwin added vastly to our knowledge of coral reefs, organic variation, earthworms, and the comparative expression of the emotions in man and animals. Darwin died in ignorance of the work upon variation done by his great contemporary, Gregor Mendel, whose work was rediscovered in 1900. "Mendelism" necessitates much modification of Darwin's work, which, however, remains the maker of the greatest epoch in the study of life and the most important contribution to that study ever made. Its immortal author died on April 19, 1882, and was buried in Westminster Abbey.
I.—Creation or Evolution?
When on board H.M.S. Beagle as naturalist, I was much struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geographical relations of the present to the past inhabitants of that continent. These facts, as will be seen in the latter chapters of this volume, seemed to throw some light on the origin of species—that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, in 1837, it occurred to me that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years' work, I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions which then seemed to me probable. From that period to the present day I have steadily pursued the same object. I hope that I may be excused for entering on these personal details, as I give them to show that I have not been hasty in coming to a decision.
In considering the origin of species, it is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that species had not been independently created, but had descended, like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified so as to acquire that perfection of structure and co-adaptation which justly excites our admiration.
Owing to the lapse of centuries, very little is known with certainty of the life of Hippocrates, who was called with affectionate veneration by his successors "the divine old man," and who has been justly known to posterity as "the Father of Medicine."
He was probably born about 470 B.C., and, according to all accounts, appears to have reached the advanced age of ninety years or more. He must, therefore, have lived during a period of Greek history which was characterized by great intellectual activity; for he had, as his contemporaries, Pericles the famous statesman; the poets Æschylus, Sophocles, Euripides, Aristophanes, and Pindar; the philosopher Socrates, with his disciples Xenophon and Plato; the historians Herodotus and Thucydides; and Phidias the unrivalled sculptor.
In the island of Cos, where he was born, stood one of the most celebrated of the temples of Æsculapius, and in this temple—because he was descended from the Asclepiadæ—Hippocrates inherited from his forefathers an important position. Among the Asclepiads the habit of physical observation, and even manual training in dissection, were imparted traditionally from father to son from the earliest years, thus serving as a preparation for medical practice when there were no written treatises to study.
Although Hippocrates at first studied medicine under his father, he had afterwards for his teachers Gorgias and Democritus, both of classic fame, and Herodicus, who is known as the first person who applied gymnastic exercises to the cure of diseases.
The Asclepions, or temples of health, were erected in various parts of Greece as receptacles for invalids, who were in the habit of resorting to them to seek the assistance of the god. These temples were mostly situated in the neighbourhood of medicinal springs, and each devotee at his entrance was made to undergo a regular course of bathing and purification. Probably his diet was also carefully attended to, and at the same time his imagination was worked upon by music and religious ceremonies. On his departure, the restored patient usually showed his gratitude by presenting to the temple votive tablets setting forth the circumstances of his peculiar case. The value of these to men about to enter on medical studies can be readily understood; and it was to such treasures of recorded observations—collected during several generations—that Hippocrates had access from the commencement of his career.
A disease caused by the protozoan parasite Giardia lamblia, characterized by chronic diarrhea that usually lasts 1 or more weeks. The diarrhea may be accompanied by one or more of the following: abdominal cramps, bloating, flatulence, fatigue, or weight loss. The stools are malodorous and have a pale greasy appearance. Infection without symptoms is also common. As with most other protozoa inhabiting the intestinal tract, the life cycle of Giardia involves two stages: trophozoite and cyst.
Trophozoites stay in the upper small-intestinal tract, where they actively feed and reproduce. When the trophozoites pass down the bowel, they change into the inactive cyst stage by rounding up and developing a thick exterior wall, which protects the parasite after it is passed in the feces.
People become infected either directly by hand-to-mouth transfer of cysts fromfeces of an infected individual or indirectly by drinking feces-contaminated water. After the cyst is swallowed, the trophozoite is liberated through the action of digestive enzymes and stomach acids, and becomes established in the small intestine.
Epidemiology.
Giardiasis occurs worldwide. Surveysconducted in the United States have demonstrated Giardia infection rates ranging from1 to 20%, depending on the geographic location and age of persons studied. In community epidemics caused by contaminated drinking water, as many as 50 to 70% of the residents have become infected. Outbreaks also occur among backpackers and campers who drink untreated stream water. Both human and animal (beaver) fecal contamination of stream water has been implicated as the source of Giardia cysts in waterborne outbreaks. Giardia species in dogs and possibly other animals are also considered infectious for humans.Epidemics resulting from person-to-person transmission occur in day-care centers for preschool-age children and institutions for the mentally retarded. Infants and toddlers in day-care centers are more commonly infected than older children who have been toilet-trained. Why some people become ill when infected with G. lamblia and others do not has not been fully explained. Host immunity undoubtedly plays a role, but the exact immune mechanisms involved have not been identified. A number of other factors, such as the number of Giardia cysts swallowed (dose), varying virulence between Giardia strains, and origin of the parasite (human or animal), have been postulated, but not proved, as having an influence on the clinical course of infection.
Diagnosis.
The diagnosis of Giardia infection is most commonly made by identifying the causative agent, G. lamblia, in the feces. It is also possible to identify the parasite in digestive juices or biopsy material taken from the small intestine. In individuals with watery diarrhea, trophozoites are most commonly found in stools, but a few cysts may also be present. After the acute stage has passed, stools are more often semiformed or formed, and contain the more hardy cyst form of the parasite. Because Giardia cysts are passed in the feces on an intermittent basis, a minimum of three stool specimens (one every other day) should be obtained and examined to minimize the chance of missing an infection. The parasites may be stained in iodine or by more permanent staining methods for purposes of differentiating them from other bowel-inhabiting protozoa.
Treatment.
Three drugs are available in the United States for the treatment of giardiasis: quinacrine, metronidazole, and furazolidone. Quinacrine is considered the drug of choice for adults and older children. Although quinacrine is effective in young children, the drug frequently causes vomiting in this age group. Metronidazole gives cure rates similar to quinacrine, and is generally well tolerated by both adults and children. Furazolidone is also an effective drug; it is the only anti-Giardia preparation that is supplied in pediatric suspension.
The asexual creation of a genetic copy, a capability possessed by plants but not by most animals. Thus, plants generate genetic copies spontaneously, and rooting “cuttings” is widely used by horticulturists to propagate millions of clones annually. In animals, only some lower invertebrates can be cloned by “cutting”; for example, earthworms when bisected will regenerate the missing half, resulting in two whole, genetically identical individuals.
However, asexual reproduction and cloning do not normally occur in vertebrates except for the special case of identical twinning. This is despite the fact that individual cells, called blastomeres, within the very early embryo are totipotent; that is, each is capable, if evaluated on its own, of developing into a viable termpregnancy and infant. A major scientific interest in cloning revolves around the question of whether the hereditary material in the nucleus of each cell remains intact throughout development, regardless of the cell’s fate.
On a more practical level, the production of genetic copies of mammals could support the rapid improvement of livestock herds by propagation of valuable founder animals, the creation and production of disease models or transgenic animals for biomedical research, and the preservation of the genetic contribution of a particularly valuable animal, even after death. Therapeutic cloning, a variation that involves the isolation of embryonic stem cells, may provide new cell-based medical approaches to the treatment of human diseases or degenerative conditions. Reproductive cloning. Scientific inquiry into reproductive cloning in animals began with a “fantastical experiment” suggested by Hans Spemann in 1938 that involved the insertion of a nucleus into an ovum bereft of its own genetic material.
This experiment was eventually conducted in 1952 by Robert Briggs and Thomas King in an amphibian, the northern leopard frog, and the technology was quickly extended to a number of other lower vertebrates and invertebrates, and eventually to mammals. The first step in mammalian reproductive cloning is removal of the genetic material from an egg by micromanipulation to create an enucleated egg called a cytoplast. Then genetic material from a donor cell is added, in the form of an intact cell or an isolated nucleus, to produce a diploid, reconstructed embryo.
The cell cycle of the nuclear donor cell may be temporarily slowed or stopped in advance of nuclear transfer. Development of the nuclear transfer embryo is triggered chemically, and the cloned embryo is subsequently transferred into a host mother in order to establish a pregnancy .
A subspecialty of medicine based on the use of radioactive substances in medical diagnosis, treatment, and research. Cyclotron-produced radioactive materials were introduced in the early 1930s, but the invention of the nuclear reactor during World War II made carbon-14, hydrogen-3, iodine-131, and later technetium-99m available in large quantities. Today most biomedical research and the care of many patients depend on the use of radioactive materials.
The most widely used radionuclides are technetium-99m, iodine-123, carbon-11, and fluorine-18. The latter two require a cyclotron near the site of radiotracer production because of their rapid radioactive decay (carbon-11 decays with a half-life of 20 min, fluorine-18 with a half-life of 110 min). The short half-life of the radioactive tracers makes it possible to administer the radiotracers to individuals without the harmful effects of radiation. Tracer principle. The most fundamental principle in nuclear medicine is the tracer principle, invented in 1912 by Nobel laureate G. Hevesy, who found that radioactive elements had identical chemical properties to the nonradioactive form and therefore could be used to trace chemical behavior in solutions or in the body. One of the important consequences of the use of tracers was to establish the principle of the dynamic state of body constituents.
Prior to the development of radioactive tracer methods, the only way to study biochemical processes within the body wastomeasure the input and output of dietary constituents and examine concentrations of molecules at autopsy. With radioactive tracers, the movement of labeled molecules could be followed from the processes within organs, to excretion. In essence, the use of radioactive tracers makes it possible to study the biochemistry within the various organs of the human body.
According to the principle of the constancy of the internal environment, the concentration of chemical constituents in body fluids is usually kept within a very narrow range, and disturbances of these values result in disease. This concept has been one of the foundations of modern biochemistry. Nuclear medicine makes it possible to examine regional physiology and biochemistry in ways that at times surpass the perception of surgeons during an operation or pathologists during an autopsy. Imaging methods make it possible to measure regional as well as overall organ function, and to portray the results in the form of functional or biochemical pictures of the body in health and in disease. Such pictures enhance the information about structure that is obtained by other imaging methods, such as computerized tomography (CT) or magnetic resonance imaging (MRI), often providing unique, objective evidence of disease long before structural changes are seen.
The physiological and biochemical orientation of nuclear medicine provides a better approach to understanding disease. The body is viewed as a complex array of coordinated chemical and physical processes that can become impaired before signs of disease develop. This has led to the concept of chemical reserve. It is now known that chemical abnormalities, such as a reduced rate of glucose metabolism in Huntington's disease or a marked deficiency of a neurotransmitter such as dopamine in Parkinson's disease, can occur long before the onset of symptoms. This makes possible the detection of disease far earlier than symptoms or structural abnormalities can. In focal epilepsy, for example, chemical abnormalities are often detectable before structural changes occur.
Diagnosis. In a typical examination, a radioactive molecule is injected into an arm vein, and its distribution at specific time periods afterward is imaged in certain organs of the body or in the entire body. The images are created by measuring the gamma-ray photons emitted from the organs or regions of interest within the body. Nuclear medicine imaging procedures differ from ordinary x-rays in that the gamma rays are emitted from the body rather than transmitted across the body, as in the case of x-rays. As in most modern imaging, the principle of tomography is used, that is, the person is viewed by radiation detectors surrounding the body, or by rotation of a gamma camera around the body.
Such procedures include single-photon emission computed tomography (SPECT), based on the use of iodine-123 or technetium-99m, and positron emission tomography (PET), based on the use of carbon-11 and fluorine-18. The latter two elements are short-lived (carbon-11 half-life is 20 min; fluorine-18 half-life is 110 min) and therefore must be produced near the site where the studies are performed. The nature of the injected material, called a radiopharmaceutical, determines the information that will be obtained. In most cases, either blood flow or biochemical processes within an organ or part of an organ are examined. The essence of a nuclear medicine examination is measurement of the regional chemistry of a living human body.
Examples of commonly used procedures in nuclear medicine using the tracer principle are examination of the blood flow to regional heart muscle with thallium-201- or technetium-99m-labeled radio pharmaceuticals, imaging the regional movements of the ventricles of the heart, detection of blood clots in the lung or impaired lung function, detection of breast and prostate tumors, detection of acute inflammation of the gallbladder, and examination of practically all organs of the body. Positron emission tomography and single-photon emission computed tomography are used to study regional blood flow, substrate metabolism, and chemical information transfer. In the last category, positron emission tomography has been used to establish the biological basis of neurological and psychiatric disorders, and may help improve the drug treatment of depression, Parkinson's disease, epilepsy, tardive dyskinesia, Alzheimer's disease, and substance abuse. Advances in PET and SPECT and the use of simple detector systems may help in the monitoring of the response of an individual to drug treatment, and perhaps reduce the incidence of side effects. These methods can also provide information on the physiologic severity of coronary stenosis and myocardial viability, especially after thrombolytic therapy or other forms of treatment.
One of the most important areas of research in nuclear medicine is the study of recognition sites, that is, the mechanisms by which cells communicate with each other. For example, some tumors possess recognition sites, such as estrogen receptors. Another area is in assessment of the availability of receptors that are the primary site of action of many medications. Specific effects of a drug begin by the binding of the drug to specific chemical receptors on specific cells of the body. For example, the finding that Parkinson's disease involves the neurotransmitter dopamine led to the development of L-DOPA treatment, which relieves many of the symptoms of the disease. Measurement of abnormalities of predopaminergic neurons makes it possible to characterize the abnormalities of pre-synaptic neurons in individuals with Parkinson's disease early in their illness at a time when the progress of the disease might be halted.
Treatment. In some diseases, radiation can be used to produce a biological effect. An example is the use of radioactive iodine to treat hyperthyroidism or cancer of the thyroid. The effects of treatment can be assessed with nuclear medicine techniques as well. For example, the metabolism of pituitary tumors can be used as an index of the effectiveness of chemotherapy with drugs that stimulate dopamine receptors. Reference : McGraw - Hill Encyclopedia of Science and Technology
One of a series ofbeta-lactam antibiotics, all of which possess a four-ring beta-lactam structure fused with afive-membered thiazolidine ring. These antibiotics are nontoxic and kill sensitive bacteria during their growth stage by the inhibition of biosynthesis of their cell wall mucopeptide.
The antibiotic properties of penicillin were first recognized by A. Fleming in 1928 from the serendipitous observation of a mold, Penicillium notatum, growing on a petri dish agar plate of a staphylococ-cal culture. The mold produced a diffuse zone which lysed the bacterial cells. Commercial production of penicillin came from the pioneer work of E. Chain and H. W. Florey in 1938, first in England and then in the United States, where it was developed from an academic project into a collaborative war effort between industry and government research. Penicillin (as penicillin G) was made available to the allied troops in Europe in the latter part of the World
War II.
Penicillin is produced from the fungal culture P. chrysogenum that was isolated from a moldy cantaloupe. The pharmaceutical industry uses highly mutated strains cultured in large, highly aerated, stirred tank fermentors controlled to optimize antibiotic production and to efficiently use raw materials such as corn syrup, corn steep liquor, and cottonseed flour. Temperature, pH, dissolved oxygen, soluble nitrogen and ammonia levels, and sugar feed rates are important control factors. The biosynthesis of penicillin is known in detail, and all the enzymes involved in the formation of this secondary metabolite have been isolated and purified.
Penicillin G, the most commonly fermented penicillin, is produced by the addition of a precursor phenylacetic acid to the growing culture. Use of phe-noxyacetic acid as a precursor produces penicillin V Both penicillins are recovered by extraction into organic solvents at acid pH and precipitation as their potassium or sodium salt.
Penicillin G is generally given by injection against penicillin-sensitive streptococci such as pneumo-cocci (meningitis), and in treatment of endocarditis and gonorrhea. Penicillin G procaine salt is used for intramuscular injection to provide quick distribution of the antibiotic. Penicillin G benzathine salt is used for slower release. Penicillin G can be given in combination with probenecid, a compound which delays urinary excretion. Penicillin V is acid stable and is usually given orally. It is effective in the treatment of upper respiratory infections and periodontal work.
More effective semisynthetic penicillins are produced by coupling different side chains to the active penicillin nucleus 6-aminopenicillanic acid. This nucleus is produced from either penicillin G or penicillin V by using specific immobilized enzymes. The various side chains confer different antibiotic properties on the penicillin.
The fermented penicillin G and penicillin V are susceptible to destruction by an enzyme (beta-lactamase) produced by certain bacteria which makes them resistant. The penicillins methicillin, oxacillin, nafcillin, cloxacillin and dicloxacillin all are resistant to hydrolysis by beta-lactamases and are used to treat staphylococcal infections. Cloxacillin and dicloxacillin are used orally. Ampicillin and amoxicillin are penicillins with extended spectra as they are effective against many gram-negative bacteria. They are used mainly orally against streptococci and other respiratory-tract pathogens, including Haemophilus influenzae,in the treatment of sinusitis, bronchitis, and pneumonia. They are used extensively in pediatrics and against Listeria mono-cytogenes and Salmonella spp.
Hetacillin, pivampicillin, and bacampicillin are effective pro drug forms of ampicillin. Amoxicillin is formulated with a beta-lactamase inhibitor clavu-lanic acid as Augmentin for the treatment of ampicillin-resistant infections. Carbenicillin, ticar-cillin, azlocillin, mezlocillin, and piperacillin were developed to combat pseudomonad, enterobacter, and serratia infections resistant to ampicillin. They are used mainly to treat urinary Pseudomonas aeruginosa infections, sepsis from burns, and chronic infections of the respiratorytract. Reference : McGraw - Hill Encyclopedia of Science and Technology
Cells that have the ability to self-replicate and to give rise to mature cells. The concept of stem cells was originally based on renewing tissues. Many adult tissues, such as the skin, blood, and intestines, consist of mostly mature and short-lived cells that must be continuously replaced. Stem cells were postulated as the source of the self-renewal. In the early 1960s, Canadian scientists Ernest A.
McCulloch and James E. Till provided the first experimental proof of the existence of stem cells in the blood system. They revealed that a type of cell in bone marrow possesses the capacity to replicate itself and to differentiate to various lineages of mature blood cells. Self-renewal, together with the capacity for differentiation, defined the properties of stem cells. This definition is generally used in stem cell biology today.
Stem cells can be found at different stages of fetal development and are present in a wide range of adult tissues. Many of the terms used to distinguish stem cells are based on their origins and the cell types of their progeny. There are three basic types of stem cells. Totipotent stem cells, meaning that their potential is total, have the capacity to give rise to every cell type of the body and to form an entire organism. Pluripotent stem cells, such as embryonic stem cells, are capable of generating virtually all cell types of the body but are unable to form a functioning organism. Multipotent stem cells can give rise only to a limited number of cell types. For example, adult stem cells, also called organ- or tissue-specific stem cells, are multipotent stem cells found in specialized organs and tissues after birth.
Their primary function is to replenish cells lost from normal turnover or disease in the specific organs and tissues in which they are found.
Totipotent and embryonic stem cells.
Totipotent stem cells occur at the earliest stage of embryonic development. The union of sperm and egg creates a single totipotent cell. This cell divides into identical cells in the first hours after fertilization. All these cells have the potential to develop into a fetus when they are placed into the uterus. [To date, no such totipotent stem cell lines (primary cell cultures) have been developed.] The first differentiation of totipotent cells forms a sphere of cells called the blastocyst, which has an outer layer of cells and an inner cell mass. The outer layer of cells will form the placenta and other supporting tissues during fetal development, whereas cells of the inner cell mass go on to form all three primary germ layers: ectoderm, mesoderm, and endoderm. The three germ layers are the embryonic source of all types of cells and tissues of the body.
Embryonic stem cells are de-rivedfrom the inner cell mass of the blastocyst. They retain the capacity to give rise to cells of all three germ layers. However, embryonic stem cells cannot form a complete organism because they are unable to generate the entire spectrum of cells and structures required for fetal development. Thus, embryonic stem cells are pluripotent, not totipotent, stem cells.
Embryonic germ cells.
Embryonic germ cells differ from embryonic stem cells in the tissue sources from which they are derived, but appear to be similar to embryonic stem cells in their pluripotency. Human embryonic germ cell lines are established from the cultures of the primordial germ cells obtained from the gonadal ridge of late-stage embryos, a specific part that normally develops into the testes or the ovaries. Embryonic germ cells in culture, like cultured embryonic stem cells, form embryoid bodies, which are dense, multilayered cell aggregates consisting of partially differentiated cells. The embryoid body-derived cells have high growth potential. The cell lines generated from cultures of the embryoid body cells can give rise to cells of all three embryonic germ layers, indicating that embryonic germ cells may represent another source of pluripotent stem cells.
Growing mouse embryonic stem cells.
Much of the knowledge about embryonic development and stem cells has been accumulated from basic research on mouse embryonic stem cells. The techniques forsep-arating and culturing mouse embryonic stem cells from the inner cell mass of the blastocyst were first developed in the early 1980s. To maintain their growth potential and pluripotency, mouse embryonic stem cells can be grown on a feeder layer, usually consisting of mouse embryonic fibroblast cells. The feeder cells support embryonic stem cells by secreting a cytokine growth factor, the leukemia inhibitory factor, into the growth medium. Alternatively, purified leukemia inhibitory factor can be added to the growth medium without the use of a mouse embryonic feeder layer. (The leukemia inhibitory factor serves as an essential growth factor to maintain embryonic stem cells in culture.) A line of embryonic stem cells can be generated from a single cell under culture conditions that keep embryonic stem cells in a proliferative and undifferentiated state. Embryonic stem cell lines can produce indefinite numbers of identical stem cells. When mouse embryonic stem cells are integrated into an embryo at the blas-tocyst stage, the introduced embryonic stem cells can contribute to cells in all tissues of the resulting mouse. In the absence of feeder cells and the leukemia inhibitory factor in cultures, embryonic stem cells undergo differentiation spontaneously Many studies are focused on directing differentiation of embryonic stem cells in culture. The goal is to generate specific cell types. Formation of cell aggregates with three-dimensional structure during embryonic stem cell differentiation in culture may allow some of the cell-cell interaction to mimic that of in vivo development. The culture conditions can be designed to support and select specific cell types. With these experimental strategies, preliminary success has been achieved to generate some cell types, such as primitive types of vascular structures, blood cells, nerve cells, and pancreatic insulin-producing cells.
Growing human embryonic stem cells.
Since 1998, research teams have succeeded in growing human embryonic stem cells in culture. Human embryonic stem cell lines have been established from the inner cell mass of human blastocysts that were produced through in vitro fertilization procedures. The techniques for growing human embryonic stem cells are similar to those used for growth of mouse embryonic stem cells. However, human embryonic stem cells must be grown on a mouse embryonic fibro-blast feeder layer or in media conditioned by mouse embryonic fibroblasts (see illustration).
There are anumber of human embryonic stem cell lines being generated and maintained in laboratories in the United States and other nations, including Australia, Sweden, India, South Korea, and Israel. The National Institutes of Health has created a Human Embryonic Stem Cell Registry, which lists stem cell lines that have been developed and can be used for research. Human embryonic stem cell lines can be maintained in culture to generate indefinite numbers of identical stem cells for research. As with mouse embryonic stem cells, culture conditions have been designed to direct differentiation into specific cell types (for example, neural and hematopoietic cells).
Adult stem cells.
Adult stem cells, also referred to as somatic stem cells, occur in a wide variety of mature tissues in adults as well as in children. Like all stem cells, adult stem cells can self-replicate. Their ability to self-renew can last throughout the lifetime of individual organisms. Unlike embryonic stem cells, though, it is usually difficult to expand adult stem cells in culture. Adult stem cells reside in specific organs and tissues but account for a very small number of the cells in tissues. They are responsible for maintaining a stable state of the specialized tissues. To replace lost cells, stem cells typically generate intermediate cells called precursor or progenitor cells, which are no longer capable of self-renewal. However, they continue undergoing cell division, coupled with maturation, to yield fully specialized cells. Such stem cells have been identified in many types of adult tissues, including bone mar-row,blood, skin, gastrointestinal tract, dental pulp, retina of the eye, skeletal muscle, liver, pancreas, and brain. Adult stem cells are usually designated according to their source and their potential. Adult stem cells are multipotent because their potential is normally limited to one or more lineages of specialized cells. However, a special multipotent stem cell that can be found in bone marrow, called the mesenchymal stem cell, can produce all cell types of bone, cartilage, fat, blood, and connective tissues.
Blood stem cells.
Blood stem cells, or hematopoietic stem cells, are the most studied type of adult stem cells. The concept of hematopoietic stem cells is not new, as it has been long realized that mature blood cells are constantly lost and destroyed. Billions of new blood cells are produced each day to make up the loss. This process of blood cell generation, called hematopoiesis, occurs largely in the bone marrow. The presence of hematopoietic stem cells in the bone marrow was first demonstrated by E. A. McCulloch and J. E. Till in a mouse model in the early 1960s. The first experimental work on stem cells was an unexpected outcome from their study for measuring the effects of radiation. They found that the blood system of a mouse that has been subjected to heavy radiation can be restored by infusion of bone marrow. The stem cells responsible for reconstituting the blood system generate visible cell colonies on the spleen of the recipient mouse. Each of the spleen colonies consists of one or more types of blood cells, and all the cells in a colony are derived from a single cell. Self-renewal capacity of the colony-forming cells is demonstrated by their ability to form secondary spleen colonies. Such blood stem cells, known as colony forming unit-spleen cells, qualify as pluripotent hematopoi-etic stem cells because they can replicate and give rise to multiple types of mature blood cells. A definitive proof of blood stem cells is their ability to reconstitute the blood system. Bone marrow transplantation demonstrates the restorative powers of blood stem cells in humans.
Isolating blood stem cells.
Like other adult stem cells, blood stem cells are rare and difficult to isolate. Only about1in100,000cellsin the bone marrow is a stem cell. Scientists have used cell-sorting methods to enrich and purify blood stem cells. Stem cells differ from mature cells in their surface markers, which are specific protein molecules on the cell membrane that can be tagged with monoclonal antibodies. By using a set of surface markers, some expressed mainly on stem cells and others on mature blood cells, nearly pure populations of stem cells can be separated from bone marrow. The stem cells purified by this approach can engraft (begin to grow and function) and reconstitute the blood system in the recipient. In animal studies, as few as 30 purified stem cells can rescue a mouse that has been subjected to heavy radiation. Besides the bone marrow, a small number of blood stem cells can be found in circulating blood. In addition, stem cells in the bone marrow can be mobilized into the bloodstream by injecting the donor with certain growth factors or cytokines. This approach can result in a large number of stem cells circulating in peripheral blood, from which they can be collected and used for transplant therapy. Umbilical cord blood and cord blood banks.
An alternative source of blood stem cells is human umbilical cord blood, a small amount of blood remaining in the placenta and blood vessels of the umbilical cord. It is traditionally treated as a waste material after delivery of the newborn. However, since the recognition of the presence of blood stem cells in umbilical cord blood in the late 1980s, its collection and banking has grown quickly. Similar to bone marrow, umbilical cord blood can be used as a source material of stem cells for transplant therapy. In 1989, the first successful cord blood transplant was reported for treating a 6-year-old boy suffering from Fanconi's anemia (an inherited disease that primarily affects the bone marrow, resulting in decreased production of blood cells) in Paris. Since then, over 6000 cord blood stem cell transplants have been performed worldwide, mainly in patients with blood conditions and in some cancer therapies. However, because of the limited number of stem cells in umbilical cord blood, most ofthe procedures are performed on young children of relatively low body weight. A current focus of study is to promote the growth of umbilical cord blood stem cells in culture in order to generate sufficient numbers of stem cells for adult recipients.
Many blood banks have been established to collect and cryopreserve cord blood cells. Commercial banks offer services of storing cord blood of healthy newborns for potential future use by themselves or their siblings. Although it is considered a biological insurance, the chance ofa child using his or her own cord blood is estimated at 1 per 20,000 collections. Of the estimated 6000 cord blood transplants, only 14 were performed using autologous sources. Public banks encourage donation of cord blood for unrelated transplants. The Stem Cell Research and Therapeutic Act of 2005 (H.R. 2520) established a national umbilical cord blood program, providing federal funding to collect and store cord blood for blood cell transplants. The program functions to provide a national inventory of 150,000 cord blood units for public use and to establish a registry network integrated with the national marrow donor registry administered by the National Marrow Donor Program (NMDP).
Mesenchymal stem cells.
Mesenchymal stem cells (MSCs) are a type of multipotent adult stem cells, and they are defined by the capacity to give rise to a variety of connective tissue lineages, including bone, cartilage, tendon, muscle, and fat cells. Classic studies found a type of cells in bone marrow stroma capa-bleofgenerating fibroblast-like cell colonies. These clonogenic cells were termed colony forming unit-fibroblasts (CFU-F). CFU-F share some characteristics of MSCs. MSCs appear as fibroblast-like spindle-shaped cells. CFU-F assay is still used to evaluate MSCs in cell cultures. MSCs can be distinguished and isolated from other cells based on phenotypic characteristics. Typically, MSCs express specific surface antigens SH2, SH4, and STRO-1 and lack blood cell markers CD45 and CD34. MSCs can replicate as multipotent cells. The mesenchymal cell lineage potential can be demonstrated in vitro with appropriate culture conditions. Differentiation can be induced to osteocytes by dexamethasone and ascorbate, to chrondrocytes by transforming growth factor-^3, or to adipocytes by dexamethasone and insulin. MSCs are primarily obtained from bone marrow stromal cells. They are also found in small numbers in umbilical cord blood. In addition, adipose-derived stem cells (ASCs) have been shown to be similar to MSCs. Fat tissue is of mesenchymal origin and contains stromal components. ASCs can be isolated from fat tissue by the method of liposuction. Human ASCs have been shown to exhibit the capacity to give rise to fat, bone, cartilage, muscle, and possibly neurons. Thus, ASCs may provide a potential source of multipotent adult stem cells. Neural stem cells. Neural stem cells, the multipotent stem cells that generate nerve cells, are a new focus in stem cell research. Active cellular turnover does not occur in the adult nervous system as it does in renewing tissues such as blood or skin. Because of this observation, it had been dogma that the adult brain and spinal cord were unable to regenerate new nerve cells. However, since the early 1990s, neural stem cells have been isolated from the adult brain as well as from fetal brain tissues. Stem cells in the adult brain are found in the areas called the subventricular zone and the ventricle zone. Brain ventricles are small cavities filled with cerebrospinal fluid. Another location of brain stem cells occurs in the hippocampus, a special structure of the cerebral cortex related to memory function. Stem cells isolated from these areas are able to divide and to give rise to nerve cells (neurons) and neuron-supporting cell types in culture.
Plasticity. Stem cell plasticity refers to the phenomenon of adult stem cells from one tissue generating the specialized cells of another tissue. The longstanding concept of adult organ-specific stem cells is that they are restricted to producing the cell types of their specific tissues. However, a series of recent studies have challenged the concept of tissue restriction of adult stem cells. Much of the experimental evidence is derived from transplant studies with blood stem cells. Bone marrow stem cells have been shown to contribute to liver, skeletal muscle, and cardiac cells in human recipients. In mouse models, purified blood stem cells have been demonstrated to generate cells in nonblood tissues, including the liver, gut, and skin. Although the stem cells appear able to cross their tissue-specific boundaries, crossing occurs generally at a low frequency and mostly only under conditions of host organ damage. The finding of stem cell plasticity is unorthodox and unexpected (since adult stem cells are considered to be organ/tissue-specific), but it carries significant implications for potential cell therapy. For example, if differentiation can be redirected, stem cells of abundant source and easy access, such as blood stem cells in bone marrow or umbilical cord blood, could be used to substitute stem cells in tissues that are difficult to isolate, such as heart and nervous system tissue. However, the concept of plasticity has been the subject of controversy.
The observed frequency of lineage conversion is generally low. An alternative explanation to plasticity is the phenomenon of fusion of host and donor cells. Recent findings suggest that blood cells contribute to other tissues by fusing with preexisting cells rather than by converting to other cell lineages.
Potential clinical applications.
Stem cells hold great potential for developing cell therapies to treat a wide range of human diseases. Already in clinical use is blood stem cell transplant therapy, well known as bone marrow transplant therapy for the treatment of patients with certain types of blood diseases and cancers. The discovery of stem cells in various adult tissues, stem cell plasticity, and human embryonic stem cells brings new excitement and opportunities. Stem cells offer the possibility of cell replacement therapy for many human diseases, such as Parkinson's and Alzheimer's diseases, spinal cord injury, diabetes, heart disease, and arthritis, that result from loss or damage of cells in a specialized tissue of the body. Stem cell therapy might revolutionize the treatment and outcome of these diseases. Stem cell science is still in the very early stage. Much more research is required to understand the biological mechanisms that govern cell differentiation and to identify factors that direct cell specialization. Future cell therapy will depend largely on advances in the understanding of stem cell biology and the ability to harness the process of stem cell growth and differentiation. Somatic cell nuclear transfer (SCNT) stem cells. SCNT involves a micromanipulation procedure in which the nucleus of an egg is removed and replaced by a nucleus taken from somatic cells, typically skin cells. Successful nuclear transfer requires reprogramming of the donor nucleus. The cells so created may divide in cultures to generate embryonic stem cells that can initiate embryogenesis. This is the technique being used in cloning animals, such as the first cloned mammal, Dolly the sheep. However, cloning by nuclear transfer is observed with extremely low efficiency, probably due to faulty and incomplete reprogramming of the donor nucleus. The mechanisms governing the transition from a differentiated genome to a totipotent state remain largely unknown. A major interest in SCNT is the prospect of creating patient-specific embryonic stem cells. These cells would be genetically identical to the nuclear donor except for maternal mitochondrial deoxyribonucleic acid (mtDNA) of the oocyte. Therefore, the problem of graft rejection would be avoided if the cells could be used for transplant therapy for the donor patients. The concept of using SCNT to generate customized stem cells for cell therapy is also referred to as therapeutic cloning. However, there are hurdles and limitations to using embryonic stem cells in clinical applications. A major challenge is to achieve the directed differentiation and controlled growth before stem cells can be used for transplant therapy. Another issue on SCNT in human stem cells is the sourcing of human eggs. The procedure requires a large number of eggs from women, and poses an ethical and technical challenge.
The success in producing embryonic stem cell lines by the SCNT technique has been demonstrated in mice. In an article published in Science in 2005, a team led by Hwang Woo Suk of South Korea claimed the establishment of patient-specific stem cell lines by using the SCNT technique. However, the paper was later retracted as the results were fabricated and the claim a fraud. The field is still left uncertain if somatic nuclear replacement is feasible in humans. Ethical and regulatory issues. The use of human embryonic stem cells raises ethical, social, and legal issues. The major concern centers on the source of stem cells. Human embryonic stem cell lines are made from the inner cell mass of a blastocyst stage embryo. Most embryos used to produce stem cells are left over from in vitro fertilization (TVF) treatment. The embryos are destroyed by the procedure of extracting stem cells. The early embryo has the biological potential to develop into a person. However, society has not reached consensus on when human life begins. The attention on stem cell research and cloning calls for regulation and legislation from governments. In the United States, current policy allows federal funds to be used for research only on existing human embryonic stem lines. The human embryonic stem cell lines that meet the eligibility criteria are listed in the Human Embryonic Stem Cell Registry by the National Institutes of Health (NIH).
One concern about SCNT is that it may lead to the reproductive cloning of humans. In theory, the embryo created via SCNT could be used to clone a human if it were implanted into a womans uterus. In the United States, the legislators in the House of Representatives and the Senate have introduced bills proposing a ban of all forms of cloning, including research cloning, or inhibiting reproductive cloning while preserving therapeutic cloning research. However, these bills have not been passed, and no federal law has been established on human embryonic stem cell research. The Canadian Parliament has passed Bill C-6 that prohibits creation of a human clone, sale of sperm or ova, and commercial surrogacy. The bill permits the use of stem cells obtained from discarded products of in vitro fertilization, that is, excess and unused embryos. In the United Kingdom, a law permits the use of embryos in research and therapeutic cloning research but bans reproductive cloning, and implanting a cloned embryo in a human uterus is liable to criminal prosecution. Cloning research must be licensed from the Human Fertilization and Embryology Authority that governs embryonic and stem cell research in the United Kingdom. Reference : McGraw - Hill Encyclopedia of Science and Technology
A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from prior levels of function and interferes with the ability to perform routine daily activities (for example, balancing a checkbook or remembering appointments).
Alzheimer's disease is the most common form of dementia, affecting 5% of individuals over age 65. The onset of the dementia typically occurs in middle to late life, and the prevalence of the illness increases with advancing age to include 25-35% of individuals over age 85. Memory loss, including difficulty in remembering recent events and learning new information, is typically the earliest clinical feature of Alzheimer's disease. As the illness progresses, memory of remote events and overlearned information (for example, date and place of birth) declines together with other cognitive abilities.
In the later stages of Alzheimer's disease, there is increasing loss of cognitive function to the point where the individual is bedridden and requires full-time assistance with basic living skills (for example, eating and bathing). Behavioral disturbances that can accompany Alzheimer's disease include agitation, aggression, depressive mood, sleep disorder, and anxiety.
The major neuropathological features of Alzheimer'sdisease include the presence of senile plaques, neurofibrillary tangles, and neuronal cell loss. Although the regional distribution ofbrain pathology varies among individuals, the areas commonly affected include the association cortical and limbic regions. Deficits in cholinergic, serotonergic, noradrenergic, and pep-tidergic (for example, somatostatin) neurotransmitters have been demonstrated. Dysfunction of the cholinergic neurotransmitter system has been specifically implicated in the early occurrence of memory impairment in Alzheimer's disease, and it has been a target in the development of potential therapeutic agents. A definite diagnosis of Alzheimer's disease is made only by direct examination of brain tissue obtained at autopsy or by biopsy to determine the presence of senile plaques and neurofibrillary tangles. A clinical evaluation, however, can provide a correct diagnosis in more than 80% of cases.
The clinical diagnosis of Alzheimer's disease requires a thorough evaluation to exclude all other medical, neurological, and psychiatric causes of the observed decline in memory and other cognitive abilities. Although the cause of Alzheimer's disease is unknown, a number of factors that increase the risk of developing this form of dementia have been identified. Age is the most prominent risk factor, with the prevalence of the illness increasing twofold for each decade of life after age 60. Research in molecular genetics has shown that Alzheimer's disease is etiologically heterogeneous. Gene mutations on several different chromosomes are associated with familial inherited forms of Alzheimer's disease.
A major strategy for the treatment of Alzheimer's disease has focused on the relation between memory impairment and dysfunction of the acetylcholine neurotransmitter system. other treatment strategies to delay or diminish the progression of Alzheimer's disease are being explored. Behavioral and pharmacological interventions are also available to treat the specific behavioral disturbances that can occur in Alzheimer's disease.
Everyone has heard it said of somebody or other that he (or she) was born to be a genius. Can such an assertion ever be correct? A simple 'yes or no' answer has to be negative, because sophisticated inborn capabilities simply cannot exist.
Outside mythology, nobody begins life having proclivities that can guarantee the emergence of high abilities.That does not necessarily mean that the idea of being born to be a genius must be entirely false. People are not born identical, and some of the ways in which they differ at birth can have consequences that affect the course of their whole lives. One widely accepted view is that certain individuals begin life possessing innate gifts or talents that predispose a person towards exceptional attainments in a particular area of ability. Another common belief is that a person's intelligence level, which has a major role in determining the likelihood of substantial achievements, is largely fixed at birth.
This chapter examines some of the evidence that has a bearing on the possible involvement of innately-determined influences on variability, among the numerous contributing forces that combine to enable certain individuals to become exceptionally capable.All human individuals are affected in many ways by the particular combination of genetic resources they inherit. That the influences of genetic differences between people can extend to the manner in which lives are experienced is easily verified. Just watch the contrasting ways in which people at a party react to the entrance of a spectacularly beautiful individual and to a man or woman of ordinary appearance. Those differing responses will certainly affect the individuals who elicit them. Indeed, the manner in which others react to people can have an impact on many of their experiences. One beautiful woman has her education enriched as a consequence of influential people being drawn to her company; another fails to make the most of her opportunities because of repeated experiences of getting her wishes without having to make an effort. An ordinary-looking man loses out because the teacher who might have been able to help him prefers to spend time with other pupils.
Another plain man eventually thrives because his failure to gain attention fuels his determination to do well. It is not at all uncommon for the degree of success a young person experiences to be partly decided by genetic characteristics even when the genetically influenced characteristics that are crucial are ones that have no direct effects on the person's capabilities as such. In the performing arts, for example, it is not unknown for stage directors to select the prettiest of a group of equally competent young ballet dancers for a starring role. Those examples illustrate just a few of the many ways in which our lives are affected by the particular genetic material we happen to inherit. Note, however, that the eventual nature of the influences that originate in genetic variability is typically unpredictable and far being from straightforward. It is easy enough to see that people's appearances can affect how others respond to them, but it is not usually possible to predict the long-term consequences of that.
That unpredictability is highly significant, because in order to establish that there was something real in the notion of a person being 'born to be a genius' it would be necessary to go a stage beyond merely confirming that individuals are influenced by their genes, and demonstrate that a consequence of people's differing genetic compositions is to affect their abilities in a clearly predictable manner.Do differing generic materials have predictable influences on individuals' attainments, or not? In the first part of this chapter I examine evidence relating to the frequent claim that such direct influences stemming from people's genes do indeed exist, and take the form of innate talents or gifts.
These, it is often claimed, are possessed by some young people but not others. A common assumption is that a person must possess gifts or talents in order to be capable of reaching the highest levels of expertise. Afterwards, I investigate the related possibility that innate variability in general intelligence makes a big contribution to the likelihood of individuals gaining exceptional capabilities. Finally, I take a broader look at the issues, and reach some conclusions concerning possible genetic influences on the likelihood of someone becoming a genius. In the minds of many people it is a clear and simple fact, not to be questioned, that certain men and women have been born with innate talents that make them capable of high attainments. I call that viewpoint 'the talent account'.
Does it greatly matter whether the talent account is true or false? It matters immensely, not only because efforts to explain creative achievements can never succeed if they depend upon faulty assumptions about the origins of a person's unusual capabilities, but also because important practical issues are involved. The fact that the talent account is widely believed in has consequences that affect the lives of numerous young people. Within certain fields of expertise, such as music, unquestioning acceptance of the talent account is almost invariably accompanied by the belief that excellence is only attainable by those children who are innately talented. A frequent result of teachers and other influential adults having this combination of beliefs is that when scarce educational resources or opportunities are being allocated they are likely to be directed exclusively towards those young people who are thought to possess a special talent. Young children who are believed to lack innate talents are denied resources that are vital in order for a child to gain any chance of succeeding.
If the talent account was shown to be correct, it might be argued that a selection process that is based upon it makes sense, because it directs limited resources towards those individuals who are most capable oftaking advantage of them. But if the talent account is wrong, and innate talents are fictional rather than real, a policy of denying facilities to young people because they are deemed not to possess such talents is clearly wasteful and unjust. It could still be argued that those children who are selected as being talented are the ones who are most likely to succeed anyway, since their above-average early progress still may be a good predictor of eventual success even if the inference that such progress points to an innate talent being present is wrong. It makes sense, in other words, to have a selection policy that favours young people who have already done well.
Even so, a policy of totally denying learning facilities to any child who (because he or she has not yet made unusual progress) is thought to lack a vital innate talent can hardly be justified unless there are convincing reasons for assuming that such talents do indeed exist. There is no item of evidence that single-handedly confirms or refutes the talent account, but various kinds of information have a bearing on the issue. A number of findings have been seen as offering support. First, for instance, there is some evidence that appears to show that skills appear inexplicably early in a few children. Second, some other findings seem to point to the possible existence of special inborn capacities in a smallnumber of individuals. Third, various scientific results appear to indicate the involvement of biologically transmitted mechanisms in exceptional skills.
A number of reports of extraordinarily precocious development in early childhood have appeared. These accounts are certainly consistent with the possibility that some children are born possessing special qualities that raise the likelihood of their becoming exceptionally capable. Of course, the sheer fact that a particular child turns out to be a prodigy does not in itself demonstrate that there must have been anything unusual about that child at the time of birth. However, if unusual capabilities were seen to emerge in the very earliest months of life, it would be hard to see how the child could possibly have acquired them through the kinds of learning that ordinary children are capable of. In that event the conclusion that some special innate causes were involved would seem unavoidable.
The published reports include some accounts of quite remarkable development in the first year of a child's life. One boy is reported to have begun speaking at five months of age and to have gained a fifty-word vocabulary by six months and the capacity to speak in three languages by the age of three years. Another child is said to have begun to speak in sentences at three months, hold conversations at six months, and read simple books by his first birthday. However, the reliability of these accounts as sources of evidence is doubtful, because they are all retrospective and anecdotal. In the case of the boy who was reported to speak in sentences at three months, he was not actually seen by the psychologist who wrote about him, David Feldman, until reaching the age of three.
The parents told Feldman that they had been amazed by their son's progress in his first year, and yet Feldman himself confessed to being just as astounded by the parents' absolute dedication to accelerating the child's development and their unending quest for ways to stimulate him. In all likelihood the child's early achievements were indeed exceptional, but strong doubts about the likelihood of their emerging spontaneously and without any parental prompting are raised by the fact that all that we know about the actual circumstances comes from the testimony of parents who were extraordinarily committed to stimulating their child's progress. Reference : "Genius Explained" De Michael J. A. Howe
The widely publicized Human Genome Project has been a massive undertaking requiring enormous computing power. Its goal has been to produce an accurate map of the chemical structures that make a person a person—the blueprint of human life, involving several billion pieces of information.
Along the way, the project has also become a test case for weighing the benefits of private versus public science represented on each side by highly visible scientists with charismatic personalities, with the largely government-funded public project at the U.S. National Institutes of Health led by Francis Collins competing head-to-head with a for-profit commercial operation led by 1. Craig Venter of Celera Genomics to crack the code first. Each group has claimed victor)' on several occasions as new milestones have been reached; most observers seem to accept the proposition that the project would not have advanced as quickly as it did were it not for the intensity of the competition.
The rivalry may have peaked during a joint presentation at the 2001 American Association for the Advancement of Science meeting at which Venter's Celera group , publishing in a issue of Nature that was literally hot off the presses when it arrived at the meeting, simultaneously revealed similar "draft" human genome maps. (Actually, neither map was entirely complete, and the work of both groups continues.) While the rivalry may indeed have spurred both groups to work harder and faster, it also spurred a heated debate about the conflict between the preservation of commercial patent rights, based on keeping details proprietary, and the advancement of public science, based on a policy of open information sharing.
Knowing most of the genetic code, or even all of it, does not, however, mean understanding it and does not translate directly into effective therapies for genetics-related problems. Genes with specific known effects must still be identified, defined, and distinguished from the amorphous chunks of code. Many traits are believed to be the result of the interaction of multiple genes and often reflective of environmental influences as well. Even identical twins do not always have the same personalities, problems, or diseases. Nevertheless, the project is an important and highly visible step in the direction of linking genetic heritage with a variety of conditions. This step has also raised people's awareness of the profound social and ethical issues associated with the complete mastery of human genetics that the project appears to promise in the not-so-distant future. The issues include the following: • Genetic testing and privacy: What will employers and insurance companies do with the information about individuals' susceptibility to particular diseases? • The question of "designer babies": Is it right for parents to choose their children's gender, height, weight, coloration, athletic ability, or intelligence? • I he essential nature of human individuality and identity: Should the code ever be duplicated to produce a new human, and if it is, will this clone be the same person, or a new one? • The relations between genetics and ethnic identity, genetics and personality, and genetics and human behavior: How much of our decision making is based in biology and how much is actually a matter of choice ?
Against this backdrop, public controversies have raged about the heritability of homosexuality (the "gay gene" idea), of obesity (the so-called "fat gene"), and of individual predispositions to mentally disturbed, aggressive, or criminal behavior. The idea that SO much of human behavior might be "in the genes" represents an assault on the Western legal system (and some Western theology) by undermining the presumption that humans make behavioral choices that are free and that may be rationally determined.
Some worry that the kind of genetic determinism that this line of research seems to reinforce will blind us to the social and environmental determinants of behavior, such as learned social values, economic influences, and family dynamics. At the same time the eventual promise of the project may be to enable us to transcend the tyranny of biology, making possible the achievement of human control over human evolution and destiny to an unprecedented degree. But the minute we have the capability to correct defective genes, we will be faced with the dilemma of having to choose which human characteristics actually fall in the "defect" category. As the old saying goes, we must be careful what we ask for—we might get it.
Despite the ethical challenges that a complete knowledge of human genetics may eventually engender, there are some cases where social consensus on the right course of action is more likely than in other cases. If diseases such as cystic fibrosis or diabetes can be treated with gene therapy, if dysfunctional organs can be replaced with substitutes from modified animals, or if nerve cells or other critical human tissues can be made to regenerate themselves, the benefits would appear overwhelming.
In fact, most people in both North America and Europe (the areas where opinion data are generally available) are much more supportive of medical biotechnology than of agricultural biotechnology, most likely because the benefits to the quality of human life are so readily apparent for medical interventions. Yet in each of these examples - gene therapy , xenotransplantation , and the use of stem cells substantial controversy has arisen.
The ALLEGED BENEFITS of the " Mozart effect" have produced something like a gold rush , with parents hoping to strike musical pay dirt for their children.Te original source of enthusiasm was a 1993 study by Frances Rauscher at the University of California in Irvine and colleagues.It found that college students who listened to 10 minutes of a Mozart piano sonata had improved performance of spatial-temporal tasks , those involving mental imagery and time sequences , immediately afterward.
Somehow this finding became distorted into a claim ( not Rauscher's) that listening to the music of Mozart made babies smarter.Eventually , then-Gov . Zell Miller of Georgia propsed the idea of providing every newborn Georgia peach with a Mozart compact disc and today the state of Florida mandates the school children listen to classical music every day. Some recent attempts to replicate the original findings , including those by researchers at the University of Windsor in Canada and Appalachian State University in North Carolina , have failed to do so.Rauscher , now an assistant professor of cognitive development at the University of Wisconsin in Oshkosh retorts that the design of these experiments did not conform to that of the original.
Meanwhile , preschoolers are listening to all kinds of music as part of the Early Childhood Music Project at Cornell University's Early Childhood Center.Elisabeth Stilwell , the center directory , is enthusiastic about the benefit of music for children."We've always know that music is great for kids," she say, " but now research shows that music should be an essential part of early childhood.It's fun,creative, and it's proven ways to develop areas of the brain for later academics tasks such as reading and math."
The research Stilwell refers to is a study published in March 1999 that found that second graders in Los Angeles scored 27 percent higher than other children on proportional math and fractions tests after they were given four months of keyboard training on the piano.
A disease caused by the protozoan parasite Giardia lamblia, characterized by chronic diarrhea that usually lasts 1 or more weeks. The diarr...
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Brain zaps improve math
Need to improve your math skills or do your taxes faster? Try zapping your brain with electricity. Researchers have shown that administering a small electrical charge to the brain may enhance a person's ability to process numbers for up to 6 months. The team says the approach, which it claims is harmless, could one day restore numerical skills in people suffering from degenerative diseases or stroke, and it may even improve the math abilities of the general population More: Science Magazin
What are the most effective forms of renewable energy?
