Among the many confusing tangles of the English language is the dual meaning of “homo”. It is a combining form from the Greek meaning “same” as in homosexual, homologous, etc. Yet, its Latin roots mean “man” as in the ultimate putdown from Pontius Pilate as he presented Jesus Christ with his crown of thorns: “ecce homo” meaning “behold the man.”
Science uses the Latin meaning of man to describe our genus, Homo, which are bipedal primates with large brains. This is an evolutionary branch that separates our species from the bipedal primates with chimp-sized brains, such as Lucy and Ardi.
We’ve seen how our bipedal ancestry extends back to the fossilized specimen of Lucy, the Australopithecus who lived 3.2 million years ago. Then along came the fossilized discovery of Ardi, a bipedal female primate who lived 4.4 million years ago. The evolutionary timeline of the first bipedal primates probably extends back in time even further to Sahelanthropus who lived between six and seven million years ago. The difference in discoveries is in the large volume of fossil evidence for Lucy and Ardi compared to the mere skull, somewhat squashed with decay, of Sahelanthropus.
The fossil records reveal that our family, Homo, emerged in Africa around 2.4 million years ago with Homo habilis which means “handyman”; a name bestowed because of the variety of stone tools discovered alongside it.
“The general interpretation of the fossil evidence is that H. habilis is not only substantially different from Australopithecus but that it represents the beginning of the trends characterizing human evolutionary history, particularly expansion of the brain. Some specimens clearly have a larger cranial capacity than that of Australopithecus, and the capacity increases progressively afterward with H. erectus, archaic H. sapiens, and modern humans. H. habilis is also thought to exhibit the origins of other trends such as smaller teeth and changes in facial structure, especially the nasal region.” (Rightmire 2017)
The horizontal numbers in the chart above illustrate the evolutionary movement of our genus, Homo, toward greater cranial capacity. Natural selection favored the gene mutations for bigger brains and passed those alleles down from one generation to the next. Scientists have identified over 20 species of proto-humans. Moreover, several species of our own big-brained family, Homo, lived at the same time and in the same locales. (to be continued in the next post)