|posted 1 September 2003|
William H. Calvin, A Brief History of the Mind (Oxford University Press 2004), chapter 4. See also http://WilliamCalvin.com/BHM/ch4.htm
William H. Calvin
monkeys that have adapted to savanna foraging.
The major savanna
resource, however, is grass and large grazing animals.
Homo erectus Ate Well
Adding more meat to the diet fueled the first Out of Africa
While it is natural to focus on survival during downsizings, abilities such as hunting are more likely to be shaped by the opportunities during the aftermath of an abrupt climate change such as a drought. Death on the downside may have more to do with bad luck – being in the wrong place at the wrong time – than it does with not having the right stuff.
Opportunities occur on the upside, the very next year, but only for those with the right stuff. You can only expand into newly burnt territories if you can get by for awhile almost entirely on hunting (a modern example would be the Inuit along the Arctic Circle). So only a fraction of the surviving population can expand; the others stick to the remaining refugia where they can make their living in a more traditional way. The ones that expand are the ones that get the opportunities to become stranded – and occasionally become a new species.
Hunting abilities may provide an optional part of our ancestral diet – there are many studies showing that meat is a minor part of the calories in hunter-gatherer societies – but hunting does get subpopulations into new territories like nothing else, thanks to grass being the low end of the chain of plant succession. This is my major reason for being suspicious of the gathering-is-more-important argument. It assumes efficiency as the main driver, and infers that the major portion of the average diet is more important than the occasional scraps of meat. But dynamics and statics give you different views of the problem, especially when climate changes are so fast that there is a lot of random death followed by a lot of selective opportunity. Having the “right stuff” is, however, quite important in the grassy milieu created by a sudden drought – not just for thriving where others cannot, but for getting into situations where becoming stranded is a common aftermath.
Sustained attention is common in hunting animals. Our cat Brin will spend hours perched atop a fence, watching intently for movements in the grass. She will occasionally dash into the house for food and water, then go right back outside to her “project.”
Not much of chimp and bonobo hunting involves such sustained attention; their hunting is more episodic, spontaneous and opportunistic. If they had some of the moves of the big cats, their diet would likely be more than 5 percent meat.
Certain aspects of intelligence don’t have much effect unless you have the attention span to go with them. Since great apes are not especially known for such sustained attention, we might infer some changes in that direction by the time of Homo erectus when they had adapted to the hunting life. Having both a bigger brain and the hunter’s versatile attention span might have opened up new avenues of mental life.
Joint attention (where an individual directs another’s attention to something and they jointly contemplate it) is not much seen in the great apes but emerges in early childhood for us moderns. Some researchers would nominate it for the prime mover in the transition to behaviorally modern humans (more later).
Another kind of attention might have developed about then, that needed by the nighttime sentry. Back in open woodland, there were still trees in which to nest at night. While a leopard might pick off an occasional sleeping individual, the scattered nature of the nesting sites meant that the others had enough warning to wake up and run. But out on the savanna, there usually aren’t enough trees to go around, making it easy for an entire hominid group to be ambushed, much in the manner that Hadza hunters of Tanzania today ambush groups of baboons that lack trees to nest in.
Occasionally staying awake while others sleep, and having others depend on you to do so – enforced by social sanctions – certainly looks like an advanced social behavior that goes beyond what we share with the chimps and bonobos, yet one that need not wait for language abilities.
The other thing that suggests some social change is the move to a modern amount of sexual dimorphism. Perhaps coalition behaviors were often capable of keeping one big alpha male from excluding the other males from mating opportunities. This loss of the advantage of big male body size might have brought them closer to the modern amount of size difference between males and females.
After the spinoff of the Homo lineage, there may have been a number of different hominid species at the same time – exactly what one expects when a new niche is discovered. The meat-eating niche was, for hominids, such a new niche event. For the next half-million years, variants like Homo rudolfensis and Homo habilis surely tried out their combination of brains and guts, their preferences for closed and open landscapes, and their behavioral methods for fending off predators and competitors.
By about 1.8 million years ago, hominids were clearly eating a lot of grass somehow. The ratio of the stable carbon isotopes is different in leaves and fruit (C3 plants) than it is in the African grasses (most of which are C4 types), simply because of somewhat different photosynthesis mechanisms. Animals like gorillas that eat a lot of leaves make bone with the isotopic signature of the C3; a grass-eating animal like a zebra or a warthog acquires the carbon-13 isotopic ratio of the C4 types. And if someone eats a lot of meat from grazing animals, their bones too will look like the C4 types. It may not be true at the level of behavior but at the level of atoms, you are what you eat. (And breathe – inhale deeply, and maybe you’ll get an atom or so that used to reside in a Homo erectus brain.)
So we know that our ancestors shifted from low-grass to high-grass diets before 1.8 million years ago, and it probably wasn’t because they were baking bread. By then, they were not just eating meat occasionally. They were eating a lot of it. They had probably figured out how to bring down big grass-eating animals, and with regularity. Glynn Isaac postulated that Homo erectus had not only attained meat-eating but transport of food and raw materials and the sharing of food. Richard Wrangham suggests that there was a major improvement in diet, perhaps involving food preparation – maybe even cooking the savory stew.
Homo erectus (also known, within Africa, as H. ergaster, but I’ll lump them together for present purposes) was on stage and endured (in east Asia) until only 50,000 years ago.
Many new species of antelope appeared in Africa starting about 2.7 million years ago, adapted to increasingly arid conditions. While this gradual drying of the environment was an important player in the hominid story as well, our ancestors were particularly affected by the opportunities arising from rapid variability in climate, such as droughts and the temporary conversion of forests into grasslands. Static conditions may slowly promote efficiency, but climate dynamics can run pumps. The important point for this brief history of the mind is that the droughts can pump up the population size of any species that feeds, directly or indirectly, on grass – such as Homo erectus.
In a drought affecting the central population, those antelope species specialized for the drier periphery could actually expand their populations at the expense of the more ordinary antelopes that needed a waterhole regularly. You can even see it in the monkeys. Baboons are Old World monkeys adapted to life in the more open woodlands, but they’ll happily invade the forest when the competition allows. The same thing was likely true for hominids. Those capable of making a living on the periphery could likely live anywhere. It’s another example of a potential principle: adaptation to life on the fringes is a good setup for expanding back into the center, especially during droughts.
Grass can grow in places that lack enough rainfall for anything else, such as just south of the Sahara and in the steppes of central Asia. Furthermore, as I mentioned earlier, grass is the first thing to appear in the year after a fire has cleared off everything and restarted the plant succession cycle of grass to bush to forest. This means that cycles of drought and fire can run a pump of sorts.
In the year following a fire, grasslands would greatly expand. Grazing animals can double and redouble their populations in just a few years. Their predators, having a longer time between generations, would more slowly catch up but, if the grass lasted long enough, they too would experience a temporary boom time. As brush and forests return in many places, the grasslands become patchy. Thus some isolated populations of grazers and their predators would develop, only rarely encountering other populations long enough for some gene mixing.
This drought-and-fire cycle does not provide evolutionary advantages for the great apes in general, only for those such as Homo erectus, increasingly able to exploit herds of large grazing animals. That’s one possible answer to the “Why just us?” question. (Most evolutionary arguments such as the advantages of general intelligence tend to apply equally well to other omnivores such as chimpanzees and bonobos.)
Pump the Periphery is a possible principle for hominid evolution. Once there, they may find that plant succession causes grasslands to shrink in a patchy manner, perhaps stranding them in such “islands.” These episodes surely emphasized the importance of such otherwise occasional virtues as cooperation, food preparation for otherwise inedible plants, and hunting efficiency.
As useful as such traits might be to a central population, the crank of Darwinian evolution turns more slowly there. Life on the fringe is, in comparison, a fast track. When deserts get enough rainfall to grow grass, it is the frontier populations that get the extra offspring surviving to adulthood.
Those who survive and thrive on the frontiers also get the chance to expand back into the central population during the next drought. Their new adaptations for grass and drought make it possible for them to make a living in more central places where the more average could not, allowing overall populations to grow. So it doesn’t necessarily take frontier fighting abilities to produce that recurring theme in human history, “from periphery to center, over and over.”
But, to jump ahead for a moment, the advent of herding grazing animals on a commons, rather than merely preying on them, makes one very vulnerable to theft, where the accumulation of a lifetime can be lost overnight. People become very worried about appearing weak and so violently “defend their honor” at the slightest provocation. And organized theft can also become a way of life:
The successive waves of “barbarians” [from the steppes of northeast Asia] who overran the formerly Roman lands for more than a thousand years… were toughened by having lived an outdoor life in harsh, unforgiving surroundings. They were experienced in making war. They were hungry, whether for grazing lands or for plunder.
– David Fromkin, 1998
So what do such large-animal predators need, compared to great apes in general? Cooperative behaviors are usually important to such predation. Indeed, even if a lone hunter kills a large antelope, it is too much meat for even a single family. The obvious strategy is to give most of it away and count on reciprocity tomorrow. Tolerated scrounging can develop into more elaborate forms of reciprocal altruism.
Sharing has a long growth curve, unlike most things that evolution operates on. You can share more things, with more people, over longer periods of time – all for additional payoffs. Human-level cooperation has come to emphasize a delayed reciprocity in which each partner risks short-term costs to achieve a long-term mutual advantage.
There are a number of ways to hunt but the one with the long growth curve is accurate throwing. Twice as far, twice as fast, twice as accurate – they are all likely to mean your family eats high-calorie nontoxic food for additional days of the month. Set pieces (like the modern dart throw or basketball free throw) are not as useful for hunting as a versatile throwing capability, able to improvise on the spot. And once you can reliably hit moving targets, things again improve.
But accurate throwing (as opposed to, say, the chimp’s fling of a branch) is a difficult task for the brain. During “get set” one must improvise an appropriate-to-the-target orchestration of a hundred muscles and then execute the plan without feedback. While there are hundreds of ways to throw that would hit a particular target, they are hidden amidst millions of wrong answers, any one of which would cause dinner to run away. Planning it right the first time, rather than trying over and over, has real advantages.
Since the great apes are not noted for their planning skills, we might infer that hominid planning skills were improving out in the grasslands. It’s not clear when this intensified, but it is a long road from the occasional accuracy of a chimp fling to the right-on-target high velocity skills of a baseball pitcher.
The improvement doesn’t mean there was a bump developing on the skull that we might label “hand-arm planning center.” Nor is there a reason to expect it to rate a “for the exclusive use of” label. In modern stroke patients, one sees a lot of overlap between hand-arm and oral-facial planning (also, and this may prove important, they both overlap with language). Though the natural selection payoff might be the hand-arm planning that orchestrates a brief ballistic movement, the same improved neural machinery is likely available for planning on longer time scales and other muscle groups. (Just remember curb cuts for wheelchairs and their free use for skateboards.)
Homo erectus promptly spread out of Africa into Asia by 1.7 million years ago. It was still in east Asia only 50,000 years ago, in the middle of the most recent ice age. Homo erectus was a very successful species. Why did it endure?
Perhaps they had learned to delay food consumption as well as to hunt, to prepare plant foods by pounding and soaking them first. Some think that cooking was also invented early in the H. erectus era. Such forms of preparation considerably expand the diet, important in hard times when the choice has become restricted. (Though Japanese monkeys can be seen to wash the sand off of food, and even to throw handfuls of grain mixed with sand into the water so as to eat what floats, the name of their game is still immediate consumption, not an intermediate product.)
Together, hunting and food preparation are probably what allowed Homo erectus to live in the more arid areas with only occasional trees – say, on the “shores” of the Sahara and in the steppes of central Asia.
By about 1.5 million years ago, the almost designed-looking “Acheulean” toolkit developed, the second big step up in toolmaking. Making an Acheulean handaxe required a lot more sustained effort, with an unseen goal (that flattened teardrop shape, edged all around) held in mind. In captivity, apes can shatter rocks to get a sharp edge, and use it to cut the rope that keeps a box of bananas closed. But making something to a certain design seems to be another matter, likely requiring a great deal of tutoring and more of an attention span than apes usually have.
With its flattened-teardrop symmetry, the Acheulean handaxe has long invited cognitive explanations. It is the earliest hominid tool that seems “designed” in some modern sense. Yet for most of the “Swiss Army knife” multipurpose suite of proposed uses (defleshing, scraping, pounding roots, and flake source), an easy-to-make shape would suffice – and indeed the simpler tools continued to be made. None of these uses adequately addresses the “design aspects.” Why is the handaxe mostly symmetric, why mostly flattened, why the seldom-sharp point, why sharpened all around (when that interferes with gripping the tool for pounding uses)?
Nor does a suite of uses suggest why this form could remain the same from southern Africa to western Europe to eastern Asia – and resist cultural drift for so long. The handaxe technique and its rationale were surely lost many times, just as Tasmanians lost fishing and fire-starting practices. So how did Homo erectus keep rediscovering the enigmatic handaxe shape, over and over for nearly 1.5 million years? Was there a constraining primary function, in addition to a Swiss Army knife collection of secondary uses?
Elsewhere I describe the handaxe’s extraordinary suitability for one special-purpose case of projectile predation: attacking herds at waterholes on those occasions when they are tightly packed together and present a large, stampede-prone target. Briefly, in the beginner’s version that uses a tree branch rather than a stone, the hunters hide near a waterhole. When the herd is within range, the branch is flung into their midst. The lob causes the herd to wheel about and begin to stampede. But some animal trips or becomes entangled by the branch. Because of jostling and injury by others as they flee, the animal fails to get up before hunters arrive to dispatch it.
One can imagine that tree branches were soon in short supply near waterholes. If our waterhole hominids resorted to second best, lobbing a rock into the herd’s midst, it would not trip animals but it might knock one down. Because of the delaying action of the stampeding herd, this too might allow an animal to be caught. Even when you miss, the herd will be more tightly packed together on its next cautious visit to the water’s edge – a sea of backs with few gaps makes it even harder to miss.
What rocks would work best? Large rocks, but also rocks whose shape had less air resistance. Most rocks tumble, but flat rocks (say, from a shale outcrop) will sometimes rotate in the style of a discus or frisbee, keeping the thin profile aligned to the direction of travel and thereby minimizing drag. Because animals will keep their distance when under heavy predation, range would become increasingly important. (Throwing farther is not the problem so much as the increased accuracy needed. Twice as far is about eight times as difficult.)
Hunters might also have noticed that stones with sharp edges were more effective in knocking an animal off its feet, even when not heavy. Withdrawal reflexes from painful stimuli, such as a sharp prick from an overhanging thorn tree, cause a four-legged animal to involuntarily squat. Even if the spinning stone were to hit atop the animal’s back and bounce free, it might cause the animal to sit down. It is the sudden pain that is relevant, not any actual penetration of the skin. That’s my theory for why handaxes are somewhat pointed (it will snag in a pushed-up roll of skin), sharpened all around, and flattened.
The handaxe would also be useful for that “Swiss Army knife” suite of secondary uses (defleshing, scraping, pounding roots, and flake source) but none of those uses tells you why it is shaped the way it is: unless damaged and reused, it is like a flattened teardrop, edged all around.
So what cognitive ability was needed by early Homo erectus for handaxe design? Not much more than for shatter-and-search. Rather than being seen as an embarrassing exception to 50,000-year modernity, the handaxe can be seen – once the singular controlling use is appreciated – as having a very pragmatic shape, where deviations from the flattened teardrop are more likely to result in dinner running away. The step up to staged toolmaking (first shape a core, then knock off flakes) at 400,000 years ago is far more impressive as evidence of enhanced cognition.
So the thought processes of Homo erectus were surely different from what is seen in great apes – there was likely more sharing and planning – but there is still no evidence of increased creativity or art, and I’d discount the otherwise suggestive handaxe evidence as suggesting esthetic design in toolmaking.
In appearance, they were almost human. In intellect, they were likely only apes of a superior sort, not even halfway there – but with all the moves of an accomplished hunter and sophisticated gatherer.
The River That
copyright ©2003 by William H. Calvin