Sunday, October 25, 2009

Missing Link?

Human evolutionary theory has suffered a shock recently with the release of details of a possible direct human ancestor dating from 6 million years ago – Ardipithecus ramdius – or Ardi for short.

Finding a specimen that old is surprising enough in itself; yet the real surprise is the revelation that Ardi lived in a well-forested and tropical environment and walked upright.

So, what' so surprising about that?

Previous theories about man's evolution have focussed on the idea that bi-pedal locomotion developed in response to a move to the dryer grasslands and away from the trees. This always seemed unlikely to me. The theory was that in order to see predators from a distance evolution favoured our ancestors who could stand and walk so they could see over the grass and spot the lions before the lions spotted them. Sounds good, until you stop and think about it.

In order for this theory to hold water you would have to have evidence that the environment was changing quite rapidly and that staying close to the trees was not really an option – unless you are a chip or orang-outang. This clearly flies in the face of obvious logic. Why would you choose a very precarious existence out on the plains when you could stay very close to the trees? Tough one that old Ardi may be able to shed light on.

According to the scientists involved in Ardi's discovery, she was up and about a long time before her descendants moved out onto the plains. Why? They speculate that by freeing up her hands she (and more particularly the “he” versions) were more able to gather food and return it to their mates, thereby providing the evolutionary advantage of walking upright a long time before we left the trees for good. Sounds fairly appealing.

But, in common with all theories – it's only a theory, and there are problems.

First, and I confess that I didn't really fully understand this before, the fossil evidence for Ardi and most of the other possible human ancestors you can find on the family tree is really very scanty. So scanty that we have many more fossils of, say, sabre-tooth cats than we have of humans. Therefore the analysis of human fossils remains and the extrapolation of the fossil evidence to form a theory about human evolution is based on very slim fossil evidence, to say the least. In Ardi's case the actual discovery of the fossil bones was made some 8 years ago and the field workers have been busy ever since in trying to firm up the evidence by using a variety of techniques and sources. We are just short of evidence. Very short! Why?

In my view, this is the key question.

Just stop and consider, we are talking about millions of years of human evolution. During that long period we have only a very few skeletal remains upon which to base any theory. Even given that the base populations in Africa were probably quite small, millions of years still adds up to millions of years of potential fossils. That's a lot of potential human carcasses lying about willing and able to form ancestor fossils.

They either are not there or we haven't found them yet. If they aren't there, why not?

Simple. What most of the researchers seem unable or unwilling to deal with is the place early man occupied in the food chain. Ardi and her cousins had very small brains – some only just slightly larger than a chimp. Their lives were short and brutal. They were prey species for all the large to medium predators. Think about the function of the hyenas and vultures on the plains of Africa today. They clean up. They clean up everything. They most certainly would have cleaned up any human remains they found. Result? Some very small, very chewed bone fragments.

After every rain (and these are fairly infrequent!) the scientists return to the valley where Ardi was found and search for newly uncovered bones. They may find some more evidence for Ardi and her kind. We wish them luck. Fortunately, the cause of evolution and, in particular, Darwinian evolution does not depend on their discoveries.

What evidence there is forced the scientists into formulating a new theory to account for the advent of bi-pedalism so early in the evolutionary saga. They came up with sex. Postulating that the males, by freeing up their hands, were able to gather food on the forest floor and near the edge of the savannah and carry it back to the females – thereby providing the earliest equivalent of the ubiquitous box of chocolate on record!! These males were successful in mating and evolution provided the rest.

This pre-supposes that early hominids were very unlike their simian relatives in mating behaviour. Even before the advantages of males co-operating in hunting activities may have “forced” them to be co-operative in mating, our ancestors were (seemingly) avoiding the potential fatal consequences of fighting to secure mates for a more equitable and sociable outcome. This gave us the real advantage over the other branches of the family. We work together and share the females. This behaviour is passed on to our offspring.

Every dog (or indeed proto-human) really does, therefore, have his day.

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