Immunological Time Scale for Hominid Evolution

TLDR

Immunological studies show that ape and human serum albumins are extremely similar, yet evidence indicates that albumin has evolved at a steady rate rather than slowing after ape‑human divergence. The study proposes that apes and humans share a more recent common ancestor than traditionally believed. Using micro‑complement fixation, the authors confirm the close albumin similarity and estimate that humans and African apes diverged only about 5 million years ago, in the Pliocene.

Abstract

Several workers have observed that there is an extremely close immunological resemblance between the serum albumins of apes and man. Our studies with the quantitative micro-complement fixation method confirm this observation. To explain the closeness of the resemblance, previous workers suggested that there has been a slowing down of albumin evolution since the time of divergence of apes and man. Recent evidence, however, indicates that the albumin molecule has evolved at a steady rate. Hence, we suggest that apes and man have a more recent common ancestry than is usually supposed. Our calculations lead to the suggestion that, if man and Old World monkeys last shared a common ancestor 30 million years ago, then man and African apes shared a common ancestor 5 million years ago, that is, in the Pliocene era.