It is difficult to say how the wide variety of early hominins were interrelated.Moreover, although these ancient forms were clearly members of the same larger group, discerning exactly how any of them may have been connected to later species is problematic because of incomplete fossil evidence or different interpretations of the same evidence.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.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.may have originated as early as about 2.8 mya, though the record during this time is tantalizingly fragmentary.A variety of incomplete or broken fossils from the period between about 2.5 and 2.0 mya have been placed in the category of “early .
However, other skeletal elements indicate that she spent much of her time clambering through the branches of trees.
Some paleoanthropologists extend the span of this species far back into time to include many anatomically distinctive fossils that others prefer to allocate to several different extinct species.
In contrast, a majority of paleoanthropologists, wishing to bring the study of hominins into line with that of other mammals, prefer to assign to molecular clocks to calculate how long species had been separated from a common ancestor.
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.
These fossils, along with the slightly older trails of footprints found at Laetoli, Tanzania, prove that early hominins were upright bipeds when on the ground.