The last time we saw Lucy, or Lucy’s great- great- grandmother, she was living about 8 million years ago (MYA), and natural selection was really starting to bug her. The forests all around were shrinking as the warm moist Miocene era came to an end. Ape species were being decimated by competition with the wildly successful monkeys. To make matters worse, monkey digestive tracts were adapted to handle unripe fruit, so the tiny upstarts were able to locate and devour what little fruit there was, before the apes even got a taste. The selective pressure was on.
Ape populations declined, whole species died out, and those remaining were drastically reduced in territory. Ultimately the entire great ape lineage was whittled down to only gorillas and chimps in Africa, orangutans in Sumatra and Borneo, and surprisingly, us, just about everywhere. How did we do it?
In point of fact, we almost didn’t. Geneticists are now sure that humanity passed through at least one extreme evolutionary “bottleneck”, when members of our species (or their forebears) were reduced in number to mere thousands. But humans, it seems, have always had the knack of turning adversity to advantage, and that’s what we did even when endangered. A small founder population living in a very specific environment (dare I say, an aquatic one?) amassed a slightly weird but wonderful set of strange and specific adaptations that prepared them to compete as no species before them ever had. Sparse archeological finds, combined with molecular dating of DNA “clocks” has pieced together at least part of this fascinating story.
Picture this – three hominoid friends are strolling down a forest pathway. They resemble orangutans facially, and are walking partially upright because, as brachiators (tree swingers) their heads are already mounted atop their spines, rather than thrust out front. They are not knuckle-walkers, because this specialized mode of locomotion has yet to evolve in chimps and gorillas. We can call them Orang, Homo and Pan. Orang is destined to die out completely in his African homeland, while Pan will father two sister species (troglodytes and paniscus) that retain a toehold in their ancestral forest home. Homo’s journey will be the strangest of all. But for now, nothing divides them. They are identical, because they are members of the same species.
Abruptly, the friends come to a fork in the pathway. After some hesitation, Orang decides to strike out on his own. It is 8 MYA, and the path he takes leads to a life lived exclusively in the highest tree-tops, in areas where food is so scarce he will rarely see members of his own species, except to mate.
Pan and Homo continue to walk side by side for a while – say, 2 million years. Then they arrive at the edge of the forest. Pan turns back to the familiar world he’s known, but Homo plunges on, (so the current theory goes) out onto the wild, arid, African savannah where, as Elaine Morgan points out in The Descent of Woman, every other creature is faster, bigger, fiercer, or all three. Homo then sprouts a novel set of adaptations, never seen before or since in savannah-dwelling fauna, including hairlessness, fully upright stance, subcutaneous layer of fat, a fleshy nose and descended larynx. He does not develop any natural defences, like claws or fangs. He does not develop canine teeth for tearing raw meat (in fact, his teeth and jaw-size start to shrink), even though he is supposed to be morphing, at this very moment, into a mighty carnivorous hunter.
What he is morphing into is a strangely ill-equipped, small-brained, bi-pedal hominid. Let me emphasize the small-brained part. It is fully 3.5 million years later that his remains are finally found with evidence of tool use – and then it is only crude stone choppers at that. Until that time he somehow managed to survive all comers, outperform lions and cheetahs at hunting, out-scavenge hyenas and, miraculously, remain so consistently well-fed on a high protein diet that he developed a massive energy-consuming brain, for no obvious purpose. It certainly wasn’t for tool use and development, as the “mighty hunter" theorists would have you believe. After its stunning debut, the humble stone-chopper retained its number one spot on the paleo cutting-edge technology hit parade, unchanged, for a million years or so. All the while, our brains continued their slow and steady expansion, in response to …? Some evolutionary advantage must have been conferred, for such a costly appendage to be allowed to develop. (More on that later)
No other savannah-dwelling species took even a vaguely similar evolutionary course.
No other savannah-adapted creature or primate looks anything like us. So yes, it was shocking for scientists to realize just how recently the human and great ape lines had diverged. It was even more shocking to find out how genetically similar we are to orangutans (98%) and chimps (98.5%). How does one explain how very different we look, and are?
I will tell you, but first I have to give a little lecture on how natural selection works. Simply, something in the environment puts pressure on a species, which causes some minor variations to be favoured, and others to die a quick and horrible death. There is nothing mysterious about it at all. Therefore, you should never see anthropologists writing things like “standing and moving upright on the African savannah left our ancestors’ hands free for tool use”. There is nothing forward-looking about evolution; it never produces radical change for some future benefit, or so that other handy sophistications are free to emerge. It produces change because the animal in question will perish without these changes. Even that’s not entirely true: evolution does not “produce” change at all. Life throws up variations through random mutation, and evolution favours some of these variations by “selecting” them to survive. But, pray tell, who or what is doing the “selecting”? Who is in the driver’s seat?
I will tell you who it isn’t. It isn’t us doing the selecting, especially not at this early stage. We were just following our pheromones around as best we could. It isn’t the genes, those clever little strings of base pairs, although they are responsible for the “variation” part, via random copying errors, gene migration and other nifty microscopic shenanigans. Sean B. Carroll nails it in his 2005 book Endless Forms Most Beautiful: The New Science of Evo Devo (and no, despite the title, it’s not THAT kind of book): “Genes per se were not ‘drivers’ of evolution. The genetic tool kit represents possibility – realization of its potential is ecologically driven”. In other words, it’s the environment, stupid.
There is no doubt that the great apes survived by adapting to more specialized habitats: the gorillas staked out mountain areas and lowland scrub. The orangutan died off in Africa altogether, and retreated to the high canopy in Indonesia to become an arboreal specialist. The chimps alone stayed in their traditional forest home. In their little pockets of virgin habitat, they form the primate benchmark against which we must judge how far the other hominoids have come, and how, and why.
Orangutans do not know how to climb and swing at birth. They must be taught labouriously and carefully by their mothers. If not taught, they retreat in frustration from what appears to be their natural habitat. Infant orangs in rehab centres show little aptitude for climbing and even less interest, until food handouts are removed and volunteers coach them on the intricacies of retrieving fruit from the high canopy. Yet their bodies have responded to the evolutionary imperative to change by developing vastly elongated arms and hands, shortened legs, and circular, pivoting hip joints for maximum flexibility. This, combined with the growth of luxurious red hair for camouflage, makes them appear very different from their human cousins. We have seen, in part one, that this apparent difference disappears somewhat when we examine their underlying morphology, biochemistry, behaviour and intellect. By moving into a radically different environment, the orangs faced selective pressure that forced a strange set of new adaptations on them.
Hey! We have strange adaptations too. To produce a radically different-looking and -behaving species (like humans) with relatively little time and genetic innovation (i.e., using the same basic genetic toolbox as chimps and orangs), you need strong pressure applied by a very new and different environment. The savannah just won’t do. But, if we had to choose a new environment at some point, why water?
Am I crazy to find it suggestive that geologists now believe that the Afar Triangle / Great Rift Valley area of Africa (the geographical hotbed of hominid fossil remains) was, at a key point in our evolution, flooded with sea or brackish water, and for significant enough amounts of time to have left salt deposits miles thick in places. Is it too much to hope that rather than going to the sea, the sea came to us?
To be continued…
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