Michael Cremo - Human Devolution - A Vedic Alternative To Darwin's Theory

2000a).

In the May 26, 1995 issue of Science, Robert L. Dorit of Yale University and his coauthors published a study of the variation in the ZFY gene on the Y chromosomes of 38 humans from various parts of the world. They compared this variation with that found in chimpanzees. In converting the difference in the degree of variation into years, Dorit relied on the assumption that the human line separated from the chimp line about 5 million years ago. This led him to the conclusion that all the humans in his sample had a common ancestor who existed about 270,000 years ago. This differs from the usual age estimate of 200,000 years that comes from mitochondrial DNA studies (Adler 1995). However, a report in Science news (Adler 1995) pointed out that “Dorit and his coauthors acknowledge that factors other than a recent common ancestor could explain their findings” and that their conclusions relied on a lot of “background assumptions.”

In the November 23, 1995 issue of nature, Michael Hammer, of the University of Arizona at Tucson, published a study of Y chromosome variation in eight Africans, two Australians, three Japanese, and two Europeans. He concluded that they all had a common ancestor who lived

188,000 years ago. The geographical location of the common ancestor was not clearly defined. Hammer’s study also suggested that a reanalysis of Dorit’s data would give an age of 160,000 to 180,000 years for the most recent common ancestor of the individuals in the study (Ritter 1995).

In 1998, Hammer and several coauthors published a more comprehensive study of human Y chromosome variation. The time to coalescence for the observed variation was 150,000 years, and the root of the statistical tree was in the African populations. The researchers, using nested cladistic analysis methods, proposed that the Y chromosome evidence showed two migrations. One out of Africa into the Old World, and a movement back into Africa from Asia. “Thus, the previously observed high levels of Y chromosomal genetic diversity in Africa may be due in part to bidirectional population movements,” said the researchers (Hammer et al. 1998, p. 427). Hammer and another set of coworkers reached similar conclusions in a 1997 study of the YAP region of the Y chromosome (Hammer et al. 1997). The movement of Asian populations into Africa is interesting, in light of accounts from ancient Indian historical writings, which tell of the avatar Parasurama driving renegade members of the ancient Indian royal families out of India to other parts of the world, where according to some sources, they mixed with the native populations.

In the November 2000 issue of nature Genetics, Peter Underhill and his coauthors said Y chromosome data suggested that the most recent common male ancestor of living humans lived in East Africa and left there for Asia between 39,000 and 89,000 years ago. By way of contrast, mitochondrial DNA evidence suggested that our common female ancestor left Africa about 143,000 years ago. Underhill simply suggested that the Y chromosome and mitochondrial DNA rates of change are different (Bower 2000a). Henry Harpending of the University of Utah in Salt Lake City thinks the Y chromosome’s mutation rate is slower than Underhill and his coworkers reported. According to Harpending, this would bring Y Guy’s age close to that of Mitochondrial Eve (Bower 2000a). But just as the mitochondrial DNA rate of change is really not known with certainty, the Y chromosome rate of change is also not known with certainty. In an article in Science news, Bower (2000a) says, “The Y chromosome segments in the new analysis exhibit much less variability than DNA regions that have been studied in other chromosomes. Low genetic variability may reflect natural selection, in this case, the spread of advantageous Y chromosome mutations after people initially migrated out of Africa, the researchers suggest. That scenario would interfere with the molecular clock, making it impossible to retrieve a reliable mutation rate from the Y chromosome, they acknowledge.” And geneticist Rosalind M. Harding, of John Radcliffe Hospital in Oxford, England, says, “We don’t know what selection and population structure are doing to the Y chromosome. I wouldn’t make any evolutionary conclusions from [Underhill’s] data” (Bower 2000a). For example, Underhill thought that Africa was the home of the most recent common ancestor of modern humans, because the African populations in his studies showed the most diversity in their Y chromosomes. But Harding points out that this diversity could have arisen not because Africa was the home of the original human population, but because Africa was more heavily populated than other parts of the world. Also, the diversity in populations outside of Africa could have been reduced by the spreading of particularly favorable genes throughout those populations. Bower says (2000a), “If the critics are right, Y guy could be history, not prehistory.” In other words, humans could be millions and millions of years old, and the genetic diversity we see today could simply reflect some recent genetic events in that long history. The earlier results could simply have been erased with the passage of time.

The most recent Y chromosome studies demonstrate that firm conclusions about human origins based on this kind of evidence are still out of reach. A group of Chinese and American researchers (Ke et al. 2001) sampled 12,127 males from 163 populations from East Asia, checking the Y chromosomes for three markers (called YAP, M89, and M130). According to the researchers, three mutations of these markers (YAP+, M89T, and M130T) arose in Africa, and they can all three be traced to another African mutation, the M168T mutation, which arose in Africa between 35,000 and 89,000 years ago. The researchers found that all the East Asian males they tested had one of the three African mutations that came from the African M168T mutation. They took this to mean that populations that migrated from Africa completely replaced the original hominid populations in East Asia. Otherwise, some Y chromosomes without the three African markers should have been found.

As Ke and his coauthors (2001, p. 1152) said, “It has been shown that all the Y chromosome haplotypes found outside Africa are younger than 39,000 to 89,000 years and derived from Africa.” However, they noted that “this estimation is crude and depends on several assumptions.” The assumptions were not directly mentioned in their report. The authors also admitted the possibility of “selection sweep that could erase archaic Y chromosomes of modern humans in East Asia.” Furthermore, they admitted that Y chromosome data is “subject to stochastic processes, e.g., genetic drift, which could also lead to the extinction of archaic lineages.”

Ke and his coauthors (2001, p. 1152) acknowledged another problem, which they said “creates confusion.” They observed that age estimates for a most recent common ancestor arrived at by analysis of variation in mitochondrial DNA and the Y chromosome DNA differ greatly from age estimates derived from analysis of variation in the DNA of the X chromosome and autosomes (chromosomes other than the sex-determining X and Y chromosomes). They said, “The age estimated with the use of autosome/X chromosome genes ranges from

535,000 to 1,860,000 years, much older than the mtDNA and Y chromosome” (Ke et al. 2001, p. 1152). The authors speculate that in the course of population “bottlenecks” during a supposed migration out of Africa, there may have been three or four times as many men as women, leading to the greater diversity in the autosome/X chromosome DNA.

Milford Wolpoff, a committed multiregionalist, says that it’s not surprising that the Y chromosome shows an apparent African origin. Africa had the largest populations for the longest periods of time. Therefore, the African populations were responsible for the greatest number of Y chromosome lineages, which could over time have wiped out other lineages that originally existed along with the African lineages (Gibbons 2001, p. 1052). Ann Gibbons observes that it is difficult to check the reliability of the Y chromosome and mitochondrial DNA evidence. Ideally, one would want to compare this evidence with DNA evidence from many other chromosomes in the nucleus, to see if they all support the same conclusions about the age and geographical origin of anatomically modern humans. But Gibbons (2001, p. 1052) notes: “The dating of nuclear lineages is complicated because most nuclear DNA, unlike that of the mitochondria and the Y chromosome, gets scrambled when homologous chromosomes exchange their genetic material during egg and sperm formation. That makes detection of an archaic lineage so difficult that many geneticists despair they will ever be able to prove—or disprove—that replacement was complete. Says Oxford University population geneticist Rosalind Harding: ‘There’s no clear genetic test. We’re going to have to let the fossil people answer this one.’”