Welcome, all, to the first evening of ‘deep questions.’ Gauguin’s first one, phrased in French back in 1897 and placed in the upper left corner of that extra-wide Tahiti painting, was: Where do we come from?
The short answer, we now know, is ‘Out of Africa.’ Repeatedly. The second wave took over the whole world. The Eurasian descendants of the first wave, such as the Neanderthals, were gone by 40,000 years ago, replaced by the new guys from Africa, Homo sapiens.
Though, because the Neanderthals interbred with the successful newcomers, some of us non-African Homo saps still carry around Neanderthal sequences in our DNA. Migrations matter.
But ‘from’ is not just a series of places along the hominin timeline, nor the migrations between them. ‘From’ is also a series of transformations, each created by an evolutionary process. It’s nature’s wordless version of a cake recipe, the series of things you have to do to make something happen.
The travelogue is interesting but what’s extraordinary are those mindless turn-the-crank processes that reshaped the fifth great ape into a modern human. And in the last half of that up-from-the-apes story where brain size triples, we see evolution operating on a fast track, one that is rarely seen.
So, the plan is first to cover the major transformations for all three deep questions, and then come back to flesh them out on subsequent evenings.
Where to start? Since I’m interested in the three episodes when the ancestor’s brain enlarged more than its body size did, 34 million years ago is a good place to begin. That’s when the apes parted company with the monkeys, having lost the tail, acquired a more versatile arm and shoulder, and on top of that, got a brain almost twice the size of what sufficed for the monkeys.
But we need not linger long at 34 million, as we know very little about how those changes occurred, only that they appeared alongside the earliest of the Old-World monkeys, making apes more of an alternative to monkeys than their evolved offspring.
Where did this enlargement happen?
This first episode in brain enlargement apparently happened in Africa — at least, that’s where the earliest ape fossils are found. But then the evolutionary action may have shifted to the forests of Europe during the gradual cooling and drying spanning 23 to 5 million years ago, back in the period that the geologists call the Miocene. In a more humid Europe, there must have been a lot of tropical fruit trees.
[Picks up postcard.] Here’s my picture-postcard version of our family tree, with some dates for when new branches got started. And my personal choice of mug shots for the surviving species.
I see you have depicted humans as hikers? As in trekking “Out of Africa”?
No. I meant humans as using symbols — such as that icon seen on the off-brown national park trail sign, pointing the way. A very big development indeed, quite different than bashing rocks together, however skillfully, the way Homo erectus is depicted.
When was the second enlargement episode?
The second big step in brain enlargement, the one that makes an ape ‘great,’ is first seen in an ape skull discovered in Hungary from about 12 million years ago. That was a time when the global winds reorganized; before, Europe was humid and the winds were northeast to southwest like the modern trade winds. Afterwards, westerlies developed to the north of the Mediterranean, leaving it dry for a long period. But we need not linger long at 12 million either, again because the data is still thin.
Only for lack of data. The great apes evolved from earlier apes with smaller brains — the siamang and the various gibbons are their closest living stand-ins. The orangutan’s skull−it’s the only surviving Eurasian great ape−looks a lot like the fossil skulls from those first Miocene great apes in Europe and Asia, having brains twice as large as those of the lesser apes.
The other surviving great ape species — gorilla, chimp, bonobo, and us — are all in Africa but their ancestors can be seen in Germany at 9.7 million years ago — about as far north as apes went. Today, after a lot of climate change, the surviving ‘African apes’ can only be found hugging the equator.
The genetics says that bonobos are our closest living relatives among the four surviving great apes, with chimps nearly as close. Judging from the genetic clock, we last shared a common ancestor with both of them about 6 to 7 million years back, with gorillas at about 8, and with orangs back about 12 to 15 million years ago. bipedal woodland apes.
So, we humans are the fifth great ape. When that branch split off about 6 to 7 million years ago, did the brain enlarge again?
Apparently not. Even at 2.5 million years, the pre-Homo skulls are not much larger than those of the great apes.
Most of the evolutionary action before 2.5 million — or at least what we see in the fossil bones for the australopithecines — was in the lower body, converting the great ape’s occasional upright stance into an efficient bipedal stride, routinely able to cover long distances. These ‘bipedal woodland apes’ lived in the fringes of forests where grasslands mixed with clusters of trees — that’s the definition of woodland.
They walked with a stride like ours by about 3.6 million years ago, well before the brain boom began at 2.3. By 3.6, the ape foot had been remodeled into human form, its ‘lower thumb’ having become our big toe, important for maintaining balance as we fall forward.
As the expanse of trees across Africa began to thin out and break into patches during the Pliocene, woodland became the growth habitat, where there was always additional land becoming available for the next cohort of grandchildren to inhabit. But only if you were an ape able to thrive in such a woodland setting, rather than a chimpanzee.
In woodlands the bushes and trees have more underground storage organs — roots, tubers, and such. They also have meat on the hoof. Thought that meant that there were also the herbivore’s traditional predators to deal with, such as lions and hyenas.
Home sweet home.
At least, there were still some trees in which to take refuge. And sleep at night.
Farther out into open country, there were few trees — and those lovely acacia trees out there in the savanna, kept trimmed from below by the tallest giraffes, happen to be thorn trees, creating the original procrustean bed if one chose to sleep up in a tree.
The tongue of a giraffe adapted to thorns but the hide of a human did not?
Yes, but focus on what lured a woodland great ape so far out into open country. It was probably acquiring meat that served as a driver for evolving our more effortless stride. Once out in open country, you can see meat — or, at least, circling vultures — many miles away. Even if you don’t spot the birds, there are the dust trails kicked up by the hyenas, running at top speed from miles away. They are coming from various directions, pointing the observer toward the hidden site of the action. So, getting there quickly is important.
Chimps would have to stop and rest many times. A great ape waddles like a duck, rotating the hips if not the entire body, with each step. [Demonstrates.] Very tiresome.
But what replaced that?
A stride that’s quite daring, actually. Standing upright, we allow ourselves to fall forward, swinging one leg ahead to stop the fall. [Demonstrates.]. That fall creates forward momentum that, encountering the stiff forward leg, helps elevate you again. Recall, if you will, the head bobbing up and down a little, seen in someone striding along.
Thanks to conserving that forward momentum from the fall forward, you don’t have to pull yourself ahead with a leg, as when walking slowly without striding. And so you don’t tire as quickly.
Once the momentum carries our center of gravity in front of that foot which caught us, we fall again — only to catch ourselves with the other leg. Our running is an exaggerated version of this stride. It’s a simple process, beloved by physiologists like me, capable of endless repetitions with a minimal expenditure of calories.
My favorite depiction of this human stride is that bronze λ sculpture by Alberto Giacometti which I first saw at the Art Institute in Chicago, back when I was an undergraduate at Northwestern. Here’s my tourist picture of L’Homme qui marche that resides at the Louisiana Museum of Modern Art in Denmark.
 Begun book
 Lutz, H., Engel, T., Lischewsky, B. & Berg, A. von (2017): A new great ape with startling resemblances to African members of the hominin tribe, excavated from the Mid-Vallesian Dinotheriensande of Eppelsheim. First report (Hominoidea, Miocene, MN 9, Proto-Rhine River, Germany). — Mainzernaturwissenschaftliches Archiv 54: xx-xx, 14 figs.; Mainz.