EVE

A little more than 10 years ago molecular biologists believed that they had found evidence in human genes that all people share a common female ancestor, dubbed Eve, who lived in Africa about 200,000 years ago. The claim has seemingly been challenged on both genetic and fossil evidence, and it had been supported by a repetition of the same kind of analysis. There is an argument that one would expect all current humans to have one common ancestor based on sampling statistics alone.

Then comes corroboration from a different kind of genetic study. While the earlier claim was based on DNA transmitted only through the maternal lineage (mitochondrial DNA), the new report uses DNA transmitted and possessed only by males (the Y chromosome). Michael F. Hammer, a researcher in molecular evolution, reported that his analysis of a part of the Y sex chromosome indicates that modern humans descended from a common male ancestor who lived 188,000 years ago. Although the new report does not say where that ancient man, whom some are calling 'Adam,' lived, his age is close enough to Eve's for this kind of work.

Both analyses are based on counting mutations that distinguish a portion of one modern person's DNA from that of others and using a "molecular clock" that assumes the mutations arise at a known, constant rate.

Even though the studies refer to a single man or woman in the past, they do not imply that those people were a couple or even that they were the only parents of all humans. Their primary significance is in pointing to the time when anatomically modern human beings, Homo sapiens sapiens, evolved from a more primitive ancestor, generally thought to be an archaic form of humans. Many experts propose that the founders of the modern species numbered around 10,000.

Many anthropologists believe this transition happened in Africa and that the subspecies spread to other parts of the world, replacing more primitive forms of humans such as Homo erectus. Others, however, dispute the genetic evidence and argue that modern people evolved in many parts of the world as products both of the people already living there and of immigrants.

There is evidence for this contrary view in fossils. In 1992, for example, researchers found skulls in China that appeared to blend traits of Homo sapiens and the ancestral species, Homo erectus. The skulls are from hominids who they say lived nearly 400,000 years ago, suggesting the transition was happening long before "Adam' or "Eve' could have lived?

Evolutionary or phylogenetic relationships for the hominids are proposed by comparing anatomical features of specimens found in the fossil record and those of still existing species. The available hominid fossils in most cases are partial crania, partial jaw bones, isolated teeth, and infrequently partial upper and lower limbs. Rarely do paleoanthropologists find a complete cranium, let alone a nearly complete skeleton. Typically a hominid species is defined by just a few bone fragments, and many times the remains have been crushed and shattered and damaged prior to fossilization and afterwards deformed by geological processes. Recently two researchers took a look at the reliability of phylogenic analysis by comparing proposed characteristics obtained from gene and protein sequences and those obtained from analysis of cranial and dental features for two currently existing groups of primates, the hominoids (gorillas, chimpanzees, and humans) and the papionins (baboons, mangabeys, and mavcaques). In both cases the molecular phylogenies differed significantly from those derived using cranial and dental characteristics. The researchers concluded that crainodental characteristics cannot be used as reliable indicators of existing primate species evolutionary relationships. "Without a reliable phylogeny, little confidence can be placed in the hypotheses of ancestry..." (Mark Collard and Bernard Wood, "How Reliable Are Human Phylogenetic Hypotheses?" Proceedings of the National Academy of Sciences USA 97 (2000) 5003-6)

Confidence in genetic approaches to this problem should also be tempered by another report. Three British geneticists, led by L. Simon Whitfield, carried out analysis of both mitochondrial DNA and Y chromosome DNA from the same people. The mitochondrial data yielded a time of origin of modern humans between 120,000 and 474,000 years ago. The Y chromosome data indicated the origin was probably between 37,000 and 49,000 years ago. And two more Y chromosome studies using newer techniques and larger sample sizes were reported in "Proceedings of the National Academy of Sciences USA 97 (2000)": report numbers 7354-59 and 7360-65 and they add more evidence for the younger dates. They both support a 50,000 year ago origin for humanity. They also seem to point to a rapid population expansion around 28,000 years ago.

"However, the 50,000 year time may be too long, and the true time may be about 36,525 years, which rounds off to 40,000 years, because it has been shown by Awadalla, Eyre-Walker, and Smith, in Science 286 (24 December 1999) 2524-2525, that "... The assumption that human mitochondrial DNA is inherited from one parent only and therefore does not recombine is questionable. Linkage disequilibrium in human and chimpanzee mitochondrial DNA declines as a function of the distance between sites. This pattern can be attributed to one mechanism only: recombination. ... Many inferences about the pattern and tempo of human evolution and mtDNA evolution have been based on the assumption of clonal inheritance. These inferences will now have to be reconsidered."" (Were Adam and Eve Africans?)

Conclusion: While the results of chromosome research is incredibly exciting, it is still in its infancy and often the findings are overly publicized as is unfortunately often necessary to obtain funding for further research. Hopefully in the future these researchers will consider the true accuracy of their results and will truthfully report their findings without biasing their results by other theories and theological beliefs. We feel that further more accurate research will probably result in more recent dates than any of those discussed above. As has been concluded about one mitrochondrial study, "Many scientists are quite skeptical of the estimated date, ... caution that the mitochondrial clock is none too reliable. "The date is very dubious--it's 135,000 years plus or minus about 300% ..." (from http://web.raex.com/~kitten/origin.htm)

Many scholars have interpreted the Hebrew words translated as "thousand generations" as "a proverbial expression meaning endlessly or forever" and not to mean a literal thousand generations. For the word translated as generations is more properly translated as "a revolution of time" or can also be "an age" as well as a generation. However, possibly one should reconsider that the translation as a literal "thousand generations" is also appropriate, much like for many centuries many "scholars" ignored the translation of "he that sitteth upon the circle of the earth" in Isaiah 40:22 as an indicator that possibly the earth was round.

That men and women are different, everyone knows! But, aside from external anatomical and primary and secondary sexual differences, scientists know also that there are many other subtle differences in the way the brains from men and women process language, information, emotion, cognition, etc.

One of the most interesting differences appear in the way men and women estimate time, judge speed of things, carry out mental mathematical calculations, orient in space and visualize objects in three dimensions, etc. In all these tasks, women and men are strikingly different, as they are too in the way their brains process language. This may account, scientists say, for the fact that there are many more male mathematicians, airplane pilots, bush guides, mechanical engineers, architects and race car drivers than female ones.

On the other hand, women are better than men in human relations, recognizing emotional overtones in others and in language, emotional and artistic expressiveness, esthetic appreciation, verbal language and carrying out detailed and pre-planned tasks. For example, women generally can recall lists of words or paragraphs of text better than men

The "father" of sociobiology, Edward O. Wilson, of Harvard University , said that human females tend to be higher than males in empathy, verbal skills, social skills and security-seeking, among other things, while men tend to be higher in independence, dominance, spatial and mathematical skills, rank-related aggression, and other characteristics .

When all these investigations began, scientists were skeptical about the role of genes and of biological differences, because cultural learning is very powerful and influential among humans. Are girls more prone to play with dolls and cooperate among themselves than boys, because they are taught to be so by parents, teachers and social peers, or is it the reverse order?

However, gender differences are already apparent from just a few months after birth, when social influence is still small. For example, Anne Moir and David Jessel, in their remarkable and controversial book "Brain Sex" , offer explanations for these very early differences in children:

"These discernible, measurable differences in behaviour have been imprinted long before external influences have had a chance to get to work. They reflect a basic difference in the newborn brain which we already know about -- the superior male efficiency in spatial ability, the greater female skill in speech."

But now, after many careful controlled studies where environment and social learning were ruled out, scientists learned that there may exist a great deal of neurophysiological and anatomical differences between the brains of males and females. There are now a number of sophisticated neuroscientific methods which allow scientists to probe minute differences between any two groups of brains. There are several approaches, brought forth by advancements in computerized image processing, such as tomography (detailed imaging of the brain using "slices"):
 

Scientists working at Johns Hopkins University, recently reporting in the "Cerebral Cortex" scholarly journal , have discovered that there is a brain region in the cortex, called inferior-parietal lobule (IPL) which is significantly larger in men than in women. This area is bilateral and is located just above the level of the ears (parietal cortex).

Furthermore, the left side IPL is larger in men than the right side. In women, this asymmetry is reversed, although the difference between left and right sides is not so large as in men, noted the JHU researchers. This is the same area which was shown to be larger in the brain of Albert Einstein, as well as in other physicists and mathematicians. So, it seems that IPL's size correlates highly with mental mathematical abilities. Morphological brain differences in intellectual skills were suspected to exist by neurologists since the times of phrenology (although this was proved to be a wrong approach), in the 19th century. The end of the 20th century has witnessed the first scientific proofs for that.

The study, led by Dr. Godfrey Pearlson, was performed by analyzing the MRI scans of 15 men and women. Volumes were calculated by a software package developed by Dr. Patrick Barta, a JHU psychiatrist. After allowing for the natural differences in overall brain volume which exist between the brains of men and women, there was still a difference of 5% between the IPL volumes (human male brains are, on average, approximately 10 % larger than female, but this is because of men's larger body size: more muscle cells  imply more neurons to control them).

In general, the IPL allows the brain to process information from senses and help in selective attention and perception (for example, women are more able to focus on specific stimuli, such as a baby crying in the night). Studies have linked the right IPL with the memory involved in understanding and manipulating spatial relationships and the ability to sense relationships between body parts. It is also related to the perception of our own affects or feelings. The left IPL is involved with perception of time and speed, and the ability of mentally rotate 3-D figures (as in the well-known Tetris game).

Another previous study by the same group led by Dr. Godfrey Pearlson has shown that two areas in the frontal and temporal lobes related to language (the areas of Broca and Wernicke, named after their discoverers) were significantly larger in women, thus providing a biological reason for women's notorious superiority in language-associated thoughts. Using magnetic resonance imaging, the scientists measured gray matter volumes in several cortical regions in 17 women and 43 men. Women had 23% (in Broca's area, in the dorsolateral prefrontal cortex) and 13% (in Wernicke's area, in the superior temporal cortex) more volume than men.

These results were later corroborated by another research group from the School of Communication Disorders, University of Sydney, Australia, which  was able to prove these anatomical differences in the areas of Wernicke and of Broca . The volume of the Wernicke's area was 18% larger in females compared with males, and the cortical volume the Broca's area in females was 20% larger than in males.

On the other hand, additional evidence comes from research showing that the corpus callosum, a large tract of neural fibers which connect both brain hemispheres, is enlarged in women, compared to men , although this discovery has been challenged recently.

In another research, a group from the University of Cincinnati, USA, Canada, presented morphological evidence that while men have more neurons in the cerebral cortex, women have a more developed neuropil, or the space between cell bodies, which contains synapses, dendrites and axons, and allows for communication among neurons . According to Dr. Gabrielle de Courten-Myers, this research may explain why women are more prone to dementia (such as Alzheimer's disease) than  men, because although both may lose the same number of neurons due to the disease, "in males, the functional reserve may be greater as a larger number of nerve cells are present, which could prevent some of the functional losses."

The researchers made measurements on slices of brains of 17 deceased persons (10 males and seven females), such as the cortex thickness and number of neurons in several places of the cortex.

Other researchers, led by Dr. Bennett A. Shaywitz, a professor of Pediatrics at the Yale University School of Medicine, discovered that the brain of women processes verbal language simultaneously in the two sides (hemispheres) of the frontal brain, while men tend to process it in the left side only. They performed a functional planar magnetic resonance tomographic imaging of the brains of 38 right-handed subjects (19 males and 19 females). The difference was demonstrated in a test that asked subjects to read a list of nonsense words and determine if they rhyme . Curiously, oriental people which use pictographic (or ideographic) written languages tend also to use both sides of the brain, regardless of gender.

Although most of the anatomical and functional studies done so far have focused on the cerebral cortex, which is responsible for the higher intellectual and cognitive functions of the brain, other researchers, such as Dr. Simon LeVay, have shown that there are gender differences in more primitive parts of the brain, such as the hypothalamus, where most of the basic functions of life are controlled, including hormonal control via the pituitary gland. LeVay discovered that the volume of a specific nucleus in the hypothalamus (third cell group of the interstitial nuclei of the anterior hypothalamus) is twice as large in heterosexual men than in women and homosexual men, thus prompting a heated debate whether there is a biological basis for homosexuality . Dr. LeVay wrote an interesting book about the sex differences in the brain, titled "The Sexual Brain" .

During the development of the embryo in the womb, circulating hormones have a very important role in the sexual differentiation of the brain. The presence of androgens in early life produces a "male" brain. In contrast, the female brain is thought to develop via a hormonal default mechanism, in the absence of androgen. However, recent findings have shows that ovarian hormones also play a significant role in sexual differentiation.

One of the most convincing evidences for the role of hormones, has been shown by studying girls who were exposed to high levels of testosterone because their pregnant mothers had congenital adrenal hyperplasia . These girls seem to have better spatial awareness than other girls and are more likely to show turbulent and aggressive behaviour as kids, very similar to boys'. But do these differences mean a superiority/inferiority relationship between men and women?

"No", says Dr. Pearlson. "To say this means that men are automatically better at some things than women is a simplification. It's easy to find women who are fantastic at math and physics and men who excel in language skills. Only when we look at very large populations and look for slight but significant trends do we see the generalizations. There are plenty of exceptions, but there's also a grain of truth, revealed through the brain structure, that we think underlies some of the ways people characterize the sexes."

Dr. Courten-Myers concurs: "The recognition of gender-specific ways of thinking and feeling -- rendered more credible given these established differences -- could prove beneficial in enhancing interpersonal relationships. However, the interpretation of the data also has the potential for abuse and harm if either gender would seek to construct evidence for superiority of the male or female brain from these findings."

The conclusion is that neuroscience has made great strides in the 90s, regarding the discovery of concrete, scientifically proved anatomical and functional differences between the brains of males and females. While this knowledge could in theory be used to justify misogyny and prejudice against women, fortunately this has not happened. In fact, this new knowledge may help physicians and scientists to discover new ways to explore the brain differences in the benefit of the diagnosis and treatment of diseases, the personalized action of drugs, different procedures in surgeries, etc. After all, males and females differ only by one Y chromosome, but this makes a real impact upon the way we react to so many things, including pain, hormones, diseases, medicines, etc.

Conclusion: The female was not created as just a "clone" of the male with appropriately different reproductive organs, physically and psychologically there are many differences which to date have not been sufficiently studied and documented by the sciences.

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