Friday, December 21, 2007

our ancestors

the earliest discovered human portait

Okay, it's time to get cracking on homo sapiens, our nearest and dearest, and our ancestors, as I recently promised myself.

First, we're primates. There are over 230 living primate species divided among 13 families. Most primates are arboreal, but a few species such as our own are described as terrestrial. I'm going to be using all sorts of nomenclature here to try to make connections between families, suborders and the like [for example, I’ve only just heard of cladistics], and much of this stuff is contested, so I should say at the outset that this is all provisional. Humans belong to the family Hominidae in the suborder Haplorrhini. At one time, humans were described as the only hominids, but more recent genetic and molecular research has placed chimps, gorillas and orang-utangs in the same family [though there's still some dispute re the latter. As to the rare and endangered bonobo [Pan paniscus], my favourite, it's our closest living relative along with the chimpanzee [Pan troglodytes], sharing some 98.4% of our DNA [though that figure, long quoted, belies the complexity of the differences between our genetic material and that of the Pan species, as revealed through the chimpanzee genome project]. The common chimpanzee and the bonobo, also known as the pygmy chimpanzee, are the only two species of the genus Pan, though there are a number of subspecies of chimps. I'm very much tempted to dwell on the bonobo, but I'll save it for another post. Anyway, in spite of differences, some authorities claim that bonobos, chimps and humans should all be classified within the genus Homo. Others suggest that humans should be reclassified as Pan sapiens, but none of this seems likely to happen in the foreseeable.

To quote from Wikipedia [which I’m pretty confident is reliable in this instance]:

Recent DNA evidence suggests the Bonobo and Common Chimpanzee species effectively separated from each other less than one million years ago. The chimpanzee line split from the last common ancestor with the Human approximately four to six million years ago. Because no species other than Homo sapiens has survived from the human line of that branching, both Pan species are the closest living relatives of humans, and cladistically exactly equally close to humans.

Now to the Homo genus. This is complicated. The Homo genus belongs to the sub-tribe Hominina, and is the only extant genus in that subtribe, one of two subtribes under the tribe Hominini. The other subtribe is Panina, which includes the chimps, but this classification is recent and not entirely accepted. In any case, other members of the Homo genus, such as Homo habilis, Homo ergaster [and/or Homo erectus] and Homo neanderthalensis, are all extinct. Interestingly, no remains have yet been identified of any extinct species of the closely related Pan genus.

It’s obviously difficult to tease out the relations between species and subgroups here, and to date them and determine patterns of movement and development. The fossil record, as everyone knows, is scant and heavily contested, as the ongoing debate about ‘Homo floresiensis’ has shown. The current orthodoxy, in any case, seems to be that Homo habilis is the earliest known member of our genus, and that the species flourished in Africa some two million years ago. Homo habilis seems to have been contemporaneous with the Australopithicines [such as A robusta and A boisei], an extinct genus, possibly the first bi-pedal genus, but not directly related to ourselves, though part of the Hominid family.

Homo erectus seems to have first emerged about 2 million years ago [thus making it contemporaneous with H habilis], and survived till about 400,000 years ago. Its brain size was some 55% larger than H Habilis, and it's believed to have been the first human species to have migrated out of Africa into colder regions. Sexual dimorphism [the size difference between the sexes within a species] became less pronounced over time, and some pundits have argued that these changes represent significant social and behavioural changes. All conjectural, however. The date of the migration out of Africa is also a subject of much dispute. Homo erectus was also contemporaneous with the later 'robust' Australopithicines.

The transition from H erectus to Homo sapiens is as highly contested as all the other transitions. Individual fossils have proved difficult to classify between late H erectus, H sapiens and Homo neanderthalensis. Neanderthals cloud the picture even further, and some classify them as Homo sapiens neanderthalensis [which explains why we are sometimes classified as Homo sapiens sapiens].

The so-called Cro-Magnon man, discovered in France and dating to 28,000 years ago, was an early representative of Homo sapiens sapiens outside of Africa. The earliest known example of H sapiens sapiens is 130,000 years old, and was found in East Africa.

The sites of discovery of H s sapiens show an increasingly accelerated development in tool-making and cultural artefacts. The Lascaux caves date from 15000 to 17000 years ago, and provide evidence of complex ritual and hunting practices, as well as artistic skills. The image accompanying this post is 26,000 years old, and is the oldest 'naturalistic' human portrait yet discovered. More stylised depictions date back to at least 32,000 years ago.

It's an almost impossibly complex story. and one worth updating continually in the light of new research, new dating techniques and new hypotheses. At least I have slightly more of a handle on it than I did before starting this post, which is all I could've hoped for.



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