Is it what we have lost that makes us human?
A study published in the March issue of Nature indicates that at a genetic level, it is not necessarily what we have gained, but what we have lost that may have made us (by way of our ancestors of course) human. The study indicates that numerous genetic sequences relating to the regulation of gene expression, sequences that are highly conserved between Pan and other mammals, have undergone deletion in the human genome at some time in our evolutionary history.
The study found that deletions of regulators involved in the phenotypic expression of penile spines (present in chimpanzees, though barely so) and in suppression of brain expansion had occurred in our evolutionary past. This of course provides an explanation of why humans do not possess the penile spine trait and goes some of the way to explain how human brain expansion came about (see my previous post on microcephaly research).
The most interesting thing about the article however, is that some 510 such deletions have been found. While many fall within regions currently believed to be non-coding, there are certainly others that have direct relationships with traits that define the genus Homo. I will be awaiting with anticipation further studies that are able to identify which other human defining phenotypes are found to be influenced by the deletion of regulatory sequences.
“Human-specific loss of regulatory DNA and the evolution of human-specific traits”
McLean, C., Reno, P., Pollen, A., Bassan, A., Capellini, T., Guenther, C., Indejeian, V., Lim, X., Menke, D., Schaar, B., Wenger, A., Bejerano, G. & Kingsley, D.
Nature 471, 216–219 (10 March 2011)