MORE ON "Y-CHROMOSOME ADAM"

See Physical Anthropology: The Core, Chapter 12, pages 297-299;

Physical Anthropology, 6^th edition, Chapter 19, pages 492-495.

In the Fall edition of Physical Anthropology Update we reported on new comparative studies of the human, chimpanzee, gorilla, and orangutan Y chromosome. The reconstructed mutation rates suggested that all modern humans had a common male ancestor around 270,000 years ago. Two new studies propose new dates for a common male relative for all modern humans.

The first study estimates that a common ancestral human Y chromosome existed at around 188,000 years ago.¹ This date is consistent with estimates for "Mitochondrial Eve." The second study places the data of a common ancestral human Y chromosome at a much more recent date of 49,000 to 37,000 years old.²

Although the dates given by these two studies for a common ancestor to all modern humans differ, the authors of both of the new "molecular Adam" studies and those of the "Mitochondrial Eve" studies see their work as evidence for the replacement model of the origins of anatomically modern Homo sapiens.

In the replacement model modern humans evolved in Africa and then moved into Eurasia where they replaced the archaic H. sapiens. The competing hypothesis is the regional continuity modern, also called the multiregional model. This model proposes that H. erectus moved out of Africa a million years ago or earlier; different populations of H. erectus then evolved into modern humans in different regions of the Old World.

The debate continues over these two models. Much of this debate centers on the accuracy of the molecular reconstructions of "Adam" and "Eve" and on the assumptions on which the molecular models of evolution are based. In addition, new fossil discoveries in Asia, discussed in this Update, also seem to be making the story of human evolution more elusive rather than settling old debates.

1 M. F. Hammer, "A Recent Common Ancestry for Human Y Chromosomes," Nature, 378 (November 23, 1995), 376-378.

2 L. S. Whitfield, J. E. Sulston, and P. N. Goodfellow, "Sequence Variation on the Human Y Chromosome," Nature, 378 (November 23, 1995), 379-380.