Historically, this process has been considered a more or less direct series of assumed improvements within a single lineage that eventually culminated in the burnished “perfection” of .As flattering to the modern human ego as this picture may be, it is evidently quite wrong.
The molecular clock concept is based on an assumed regularity in the accumulation of tiny changes in the genetic codes of humans and other organisms.
Use of this concept, together with a reanalysis of the fossil record, moved the estimated time of the evolutionary split between apes and human ancestors forward to as recently as about 5 mya.
It had long been known that human beings physically resemble the primates more closely than any other known living organisms, but at the time it was a daring act to classify human beings within the same framework used for the rest of nature.
Linnaeus, concerned exclusively with similarities in bodily structure, faced only the problem of distinguishing is a matter of active debate.
Given these apelike cranial proportions, it is hardly surprising that many paleoanthropologists have characterized these early hominins as “ from Hadar, Ethiopia.
Ardi’s skeleton, which is more than 50 percent complete, dates to about 4.4 mya.
Fossils found since the early 1990s have begun to hint at just how complex the hominin bush was in the three million years or so following the time of , both known from South and East African sites.
This early radiation (diversification) of hominins, of which the latest survivors lived as recently as about 1.5 mya, made for a rather motley assortment.
Instead, human evolution has been throughout its long history a matter of experimentation, with new species being constantly spawned and thrown into the ecological arena to compete and, more often than not, become extinct.