It makes for good TV though…
Listen to my BBC radio chat with Malcolm. We discuss our Human ancestors after 2 minutes of ridiculous intro chat in this clip:
[audio http://www.brookes.ac.uk/lifesci/runions/DrMolecule/20120814 – Human evolution and Florence Nightingale.mp3]
I grew up watching televised accounts of our ‘cavemen’ ancestors battling giant man-eating dinosaurs. In fact, those battles didn’t happen – not even close. Dinosaurs went extinct 65 million years ago and our ancestors have evolved to walk on two legs and look something like us only in the last 2-3 million years. The very earliest primates started to evolve from early mammals 85 million years ago and would have overlapped with the dinosaurs somewhat.
We all – excepting Simon Schama – experience this sort of historical time dilation when thinking about things that happened before we were born. At its extreme, the child who asks, ‘Mommy, when you were little did you see dinosaurs’ to the usual adult confusion about what century events happened in. Modern humans of our species, Homo sapiens, have only been around for the last 400,000 years, and have only started to behave modernly during the last 50,000 years. It is during that period that we see the rise of symbolic culture and language.
Charles Darwin and Alfred Russell Wallace shocked Victorian sensibilities
when they proposed that Humans had evolved from apes. The very idea was lampooned in ‘the ascent of Man’ images of the sort that are now known to depict one of the most brilliant and impactful scientific ideas ever. Evolution is a fact. I proceeds so slowly, however, that it is difficult to observe in action. The giraffe that might benefit from having a longer neck doesn’t just grow a longer neck. Over hundreds or thousands of generations, giraffes that have slightly longer necks are slightly more successful at foraging in trees than their slightly-shorter-necked contemporaries. These more successful foraging giraffes are likely more fit and are better able to pass their genes into the next generation. By a series of very small increments, giraffe offspring in subsequent generations will have slightly longer necks. That process continues until the longer necks are no longer an advantage, i.e. until they become too heavy or breathing becomes difficult. Evolution is a slow process which results in ‘fitter’ organisms but it regulates against ‘runaway’ selection – it is just physically impossible for a giraffe to have a neck any longer than they now are – the animal would become ‘unfit’ in many other respects.
Back to Human evolution. It really isn’t as simplistic as the idea illustrated that a chimpanzee turned into a caveman etc. After all, chimpanzees still exit. Why? The answer is that in the deep dark past – millions of years ago – we shared a common ancestor that resembled a small primate. Some offspring of the ancestor began to evolve towards Human form while others evolved towards modern chimpanzee form. Evolution is a branching process and one of the biggest drivers of branching is when offspring find themselves in different environments where different characteristics will help them survive and reproduce better. What was the original main distinction between the Human branch and the chimpanzee branch? Answer – the ability to walk upright in our branch (or to walk on a branch in the chimp’s case, get it?). The Human branch moved onto the savannah where individuals who could stand or walk upright had a definite surveillance and hunting advantage just by being able to see further. The chimp branch remained in the forest where climbing ability and smaller stature were an advantage (have you ever seen a chimp climb – holy baloney?). Gradually and over thousands of generations, animals in each branch evolved to more closely resemble either modern Humans or chimpanzees.
So, let’s consider the Human branch. Why did it stop branching along the way? That’s a trick question. The answer is that it didn’t stop branching. As Human ancestors spread out of Africa into Asia and Europe, populations became isolated. Remember, we’re talking about migrations that take generations – you didn’t just jump on Air Africa and fly to London in those days. Isolated populations gradually differentiate – as you well know if you’ve ever sat in a pub with a Scotsman, an Irishman, a Welshwoman, and an Englishwoman. Language is one of the first things to start changing and differences are obvious over very fine geographical scales. Physical attributes take longer to evolve but they do and they have resulted in many branches of the original one that lead to modern Humans. Look at an enlarged view of the image to the left – we (Homo sapiens) are only one of several different species which have existed and even co-existed during the last 2 million years. Most recently, we shared Europe with Homo Neanderthalis – and I mean in relatively modern times, until about 30,000 years ago.
So what ever became of the Neanderthals? Well, they went extinct. This often happens when closely related species try to co-exist. Perhaps
we could have continued to co-exist but similar species usually require what is called a ‘niche’, that is, they need to have their own environment, or food source, or method of survival. Remember that Humans and chimpanzees can co-exist because they get the trees and we get everything else. If the chimpanzees tried to use our resources, a Planet-of-the-Apes situation might ensue. More likely, however, is that they would go the way of the Neaderthals and not be heard from again. Hey, we’re not even very tolerant with members of our own species who try to take our land from us.
A debate continues about just how close our species and the Neanderthals really were. We still harbour a good deal of Neanderthal DNA and scientists are trying to work out whether that’s because, as some think likely, the species interbred where their ranges overlapped (in Paris after a romantic night out on the left bank, for example), or whether that’s just leftover DNA from our common ancestor back at the ranch point.
In any case, ‘no Sweetheart, Mommy didn’t see dinosaurs when she was little.’ She was closer to meeting Human-relatives of a completely different species but even that’s probably pushing it a bit. How old do you think Mommy is, anyway!?