Hominid Species Time Line
Notes on this account:
For purposes of describing the fossil evidence and interpretations of it as briefly and as coherently as possible, I have grouped the main specimens into three large categories:
(1) The most ancient and ape-like hominids, ranging in age from approximately 7 million years to 3 million years in age. These finds are quite recent and give us glimpses of our hominid family history back to, or almost to, the point of divergence of hominids from the line that led to chimpanzees. Unfortunately, the specimens in this category are tantalizingly incomplete, consisting of the remains of only a few individuals or even a single individual, and some have not yet been fully studied.
(2) The more recent Australopithecine/Paranthropus species [the “southern apes” who co-existed with or “lived beside”] members of our genus 3 million years ago and after; these species represent collateral lines that developed in different directions than our ancestors and became extinct.
(3) Members of the genus Homo, our closest relatives, including direct ancestors but also some collateral lines.
I use these three categories simply for convenience in describing a large group of items. I group the fossil evidence in this manner both to make sense of a formidable list of species, and also to highlight unresolved issues and questions about our origins, family history, and lines of descent. The only rationale for these divisions in the body of knowledge itself is the presumed appearance of the first members of the genus Homo some time between 2 and 3 million years ago.
1. Hominid vs. hominin. I need to point out that in this discussion I follow the older usage, “hominid” in talking about our family of species. The recent terminology change (replacing “hominid” with “hominin” makes perfect sense to specialists, but is confusing to everyone else.)
The change in terminology was prompted by the discovery, on genetic evidence, that the African apes (chimps and gorillas) are more closely related to humans than they are to the Asian apes. So, the term “hominid” was appropriated to designate us and our group of ape cousins and to distinguish them from Asian apes. Meanwhile, “hominin” was coined to distinguish groups of species within our taxonomic category. “Hominin” refers to that family of species that split off from the ancestral chimp line, walked upright, lost their fighting canines, and eventually developed big brains (that is, our gang). That is, hominin is a term used to distinguish us from our closely related cousins, chimps and gorillas. In the recent scientific literature, “hominin” refers to the extended family (or “tribe”) of upright, “man-like” creatures to which we belong. That is what the term “hominid” has conveyed for some time. Since my intention is to address only non-specialists, I use the older term.
If you are confused by my discussion of these terms, see http://www.madsci.org/posts/archives/2003-04/1050350684.Ev.r.html
2. I use the word “human” to describe only those species within our own genus, Homo.