In contrast, Lucy’s skeleton is 40 percent complete and dates to about 3.2 mya.
Lucy’s pelvis is more humanlike, and the design of her knee joint suggests that she walked upright in a manner similar to that of modern humans.
These are thought to belong to the same species as the remarkably complete 1.6-million-year-old skeleton named “Turkana Boy,” found at nearby Nariokotome.
The nature of the association between the two finds is not yet completely evident, as even partial hominin skeletons are almost vanishingly rare as researchers delve deeper into the past to a time before the introduction of burial practices.
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.
They had small (ape-sized) braincases and rather protruding faces.
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.
All these features would have made them agile upright foragers among tree branches, where they presumably sought food by day and sheltered at night even though they moved on two legs while on the ground.
The environments in which these early hominins lived suggest that (1) they were still comfortable in the forest and (2) they were largely active at the forest edges and in the woodlands where the forest graded into more open savanna—a type of habitat that was expanding in their African homeland after about 7 mya as climates became drier and more seasonal.
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.