Now it is time to clear up some of the confusing bits in Part One. How I shall do that is by confusing you all the more so that that last part does not look as confusing. At least, let us say comparatively less confusing. Anyway, there we were with hominins and hominids, so let’s pick up there again.
So hominins include hominids so that Homo antecessor, Homo eragaster, Homo erectus, Homo floresiensis, Homo habilis, Homo heidelbergensis, Homo naledia, Homo neanderthalensis, Homo rudolfensis and Homo sapiens are the most recent. Then a bit earlier there were Australopithecus afarensis, Australopithecus africanus, Australopithecus anamensis, Australopithecus bahrelghazali, Australopithecus garhi, Australopithecus sediba and the closely related but geographically far removed Ardipithecus kadabba and Ardipithecus ramidus. Perhaps earlier but maybe at roughly the same time, give or take a millennium or two either way, there is another long since extinct genus of hominin, Paranthropus, containing two widely accepted species, Paranthropus robustus and Paranthropus boisei. Mind you, the validity of Paranthropus as a separable genus is contested because it is sometimes considered synonymous with Australopithecus, so are sometimes referred to as robust Australopithecines. Are you with me? Just so that you know, I have no idea about palaeontological timelines, so I have played safe by listing them alphabetically. It also saves me getting my fingers burned by playing with fire in the debates about which came before another.
Given the vast length of time and the few bones found that identify those ‘people’, such things as cranial measurements that brains were smaller and mess developed than ours, they would at best have distinguishable sounds but would have been unable to use what we call a language and apart from a few bits and pieces at a stage when artefacts began to appear, they did not live in organised societies as we know them. In other words, no civilisations. For my favourite tribe, the Ah¡buts, this where humans put on this planet by them, alternatively Homo sapiens being the outcome of some kind of breeding experiment, those visitors would have had to be extremely patient, if not simply indulgent, to spend countless millennia on refining species of primate to the imperfect creature we still are. So, next bit.
Now we get really going. Our supposed evidence of the origins of modern Homo sapiens is quite frequently revisited and revised. Much of what we know, at least assume, is thanks to a Swiss physician, Friedrich Miescher, who discovered a microscopic substance in the pus of discarded surgical bandages in 1869. What, one might wonder, was a doctor doing messing about with used, bloody bandages full of infection? He did it, so it does not really matter or, more the point, I have no idea whatsoever. Fast forward and a lot of examination of that kind of substance we arrive at Francis Crick and James Watson, who are often wrongly named as the people who discovered DNA, completed their model, which is now accepted as the first correct model of the double helix of DNA. At the beginning of 1953 Crick went to The Eagle, a pub in the centre of Cambridge that I know well, which is beside the point, where he announced that Watson and he had discovered the ‘secret of life’, by which he meant that double helix model of DNA. DNA, or deoxyribonucleic acid, is the hereditary material found in human beings and almost all other ‘living’ organisms.
Almost every cell in somebody’s body has the same DNA. A genome, which is all the genetic information of an organism, is inherited from parents, half from the mother and half from the father. The gametes, which are an organism’s reproductive cells whereby female gametes are called ova and male gametes sperm, are formed during a process called meiosis. Like the genome, each gamete is unique, which explains why siblings are not identical. That genome is mostly the same in everybody although there are variations across the genome. It accounts for about 0.001% of a person’s DNA contributing to different physical attributes and health. Closely related people have similar DNA which helps using mathematical models to show us that we all share ancestors and how recently they lived. So somewhere along the line a vast number of greats before grandparent should get us to the line at which we took a different track to our closest relatives who became bonobos, chimpanzees, gorillas and other primates. Got it? Now for a bit of something marginally easier to understand; so, here we go.
The most recent genetic data now shows we really are all descended from one mother: ‘mtEve’, in full ‘mitochondrial Eve’. She lived something like 200,000 years ago. There is also ‘Y-Adam’, ‘Y-chromosome Adam’. They are not the biblical Adam and Eve. To support the DNA modelling, fossil evidence including carbon dating shows us that they were part of a whole population of our ancestors who were definitely not alone in some kind of Garden of Eden. Instead of living anything between 3000 and 6000 years ago as some people still believe, although the most recent concession has accepted 10,000 years, DNA suggests they definitely lived considerably more than 100,000 years ago. To really put the biblical version back in its box, the evidence also tells us that it is unlikely they lived in the same place and even less likely at the same time. So, mtEve is maybe as long as 200,000 years ago and Y-Adam up to 338,000 years back. Anyway, because of the way DNA works, it is not possible to actually trace it back that many thousands of years. So scientists can only use the Y-chromosome to find Y-Adam and mtDNA to find mtEve. Males have one X and one Y chromosome (XY) while females have two X chromosomes. However, there were vast problems searching for Y-Adam’s age. To begin with there is none of Y-Adam’s DNA to compare with. We had to figure out what his chromosome looked like on the basis of the DNA of living men. They could not look at the Y chromosome of every man in the world, so scientists they used a sample of about 70 men from different areas of the world to represent as many living people as possible. A computer takes these DNAs and puts them in order of ancestry based on their similarities and differences. The result is a phylogenetic tree (which we shall get back to later) that shows which Y chromosomes are mutated versions of others.
We can see that with all of this going on we are running out of space in time and explanations about civilisations before humans. So, on we go. Boldly, of course.
Most recently the notion that humanity exclusively emerged in the Olduvai Gorge in Tanzania is a little less certain than before with the discovery of Neanderthal mitochondrial DNA (mtDNA) in many Europeans. They appear to have contributed approximately in the range one to four percent of the genomes of non-African originating modern humans, Homo sapiens. ‘Modern humans’ of about 40,000 years ago, at the time Neanderthals became extinct, have been found to have between six and nine percent of their mtDNA. Then to make it more difficult, or easier to confound those who already do not understand such as Creationists who cannot see back further than the Garden of Eden no more than 10,000 years ago, in 2008 a molar and finger bone were discovered in a cave in Denisova in Siberia. Now we have what is yet not firmly classified Homo denisova or Homo altaiensis that we know as Denisovans. They were contemporary to Neanderthals, but in their case seem to have died out about 50,000 years ago. There are controversial views that they were still just hanging on as recently as 20,000 and in extremis only 10,000 years ago. Without hard evidence we do not know. What we can say with some certainty is that they were not Homo sapiens, nor they did not have civilisations before humans, there again they were contemporaneous with what became modern humans so the theory, if there is one, would hold no water at all.
There is enough new evidence to suggest Homo sapiens also interbred with those recently discovered Denisovans who ranged across parts of Asia given that it now appears that as recently as 15,000 years ago ‘we’ shared caves with them. Now only Pacific islanders and Southeast Asians have substantial Denisovan mtDNA, up to five or even seven percent. Anyway, most people in other parts of mainland Asia have less than 0.05 percent Denisovan ancestry. There is one little blip in that Icelanders, who are the descendants of Nordic settlers, have a tiny amount of that mtDNA as well. More complicated than that is possible evidence that Neanderthals and Denisovans might have interbred because a recent find seems to indicate they used the same shelter at the same time, more or less at least, so might have had a bit of fun with each other. This naturally opens another can of genetic worms with the question as to whether there might have been more cross breeding between Denisovan-Neanderthals and Homo sapiens. If aliens were involved then it must have been a very interesting ‘laboratory’. It is a pity they did not leave a few useful notes behind to instruct us how to improve what we are, at least dispose of our tendencies toward belligerence and self-destruction. It could also help reduce governmental health service budgets that receive a great deal of governmental criticism from the very same politicians who make those cuts. Perhaps the aliens might like to call in some time to put that problem right. Anyway, let’s go on. You will have to wait until next week though.
Featured image by Gerhard Schmid via Creative Commons Licence.