New evidence underscores the theory of human origin that suggests humans most likely share a common ancestor with orangutans, according to research from the University of Pittsburgh and the Buffalo Museum of Science. Reporting in the June 18 edition of the Journal of Biogeography, the researchers reject as "problematic" the popular suggestion, based on DNA analysis, that humans are most closely related to chimpanzees, which they maintain is not supported by fossil evidence.

Jeffrey H. Schwartz, professor of anthropology in Pitt's School of Arts and Sciences and president of the World Academy of Art and Science, and John Grehan, director of science at the Buffalo Museum, conducted a detailed analysis of the physical features of living and fossil apes that suggested humans, orangutans, and early apes belong to a group separate from chimpanzees and gorillas.

A recent high-profile article in the journal Nature released the results of a study with implications that shocked the scientific community because they contradict long-held claims of human-chimp DNA similarity.

The title of the recent journal article accurately sums up the research findings: "Chimpanzee and Human Y Chromosomes are Remarkably Divergent in Structure and Gene Content."

From a large-scale perspective, the human and chimp Y chromosomes were constructed entirely differently. On the human Y chromosome, there were found four major categories of DNA sequence that occupy specific regions. One can think of this in terms of geography. Just as a continent like Europe is divided into countries because of different people groups, so are chromosomes with different categories of DNA sequence.

Not only were the locations of DNA categories completely different between human and chimp, but so were their proportions. One sequence class, or category containing DNA with a characteristic sequence, within the chimpanzee Y chromosome had less than 10 percent similarity with the same class in the human Y chromosome, and vice versa. Another large class shared only half the similarities of the other species, and vice versa. One differed by as much as 3.3-fold (330 percent), and a class specific to human "has no counterpart in the chimpanzee MSY [male-specific Y chromosome].

The Nature article expressed the discrepancy between this data and standard evolutionary interpretations in a rather intriguing way: "Indeed, at 6 million years of separation, the difference in MSY gene content in chimpanzee and human is more comparable to the difference in autosomal gene content in chicken and human, at 310 million years of separation."