Day 299: The Story Of The Human Body

Are you worried about rapid global climate change today? If not, you should be, because rising temperatures, altered rainfall patterns, and the ecological shifts they cause imperil our food supply. Yet, as we have already seen, global climate change has long been a major impetus in human evolution because of its effects on the age-old problem of “what’s for dinner?” It turns out that getting enough food in the face of global climate change also triggered the age of humans.

Getting dinner (or, for that matter, breakfast and lunch) probably does not dominate your list of daily concerns, yet most creatures are almost always hungry and preoccupied with the quest for calories and nutrients. To be sure, animals also need to find mates and avoid being eaten, but the struggle for existence is often a struggle for food, and until recently the vast majority of humans were no exception to this rule. Consider also that acquiring food is even more taxing when your habitat alters dramatically, causing the foods you normally eat to vanish or become less common. As we saw, the challenge of finding enough to eat sparked the first two major transformations in human evolution. As Africa became cooler and drier many millions of years ago, fruit became more scattered and scarce, favoring those ancestors who were better able to forage by standing and walking upright. Additional evolutionary responses were big, thick cheek teeth and large faces well suited to eating foods other than fruit, including tubers, roots, seeds, and nuts. Yet, as important as these transformations were, it is hard to think of Lucy and other australopiths as human. Although bipeds, they retained ape-sized brains, and they didn’t speak, think, or eat like us.

Our bodies and the way we behave evolved to be much more recognizably “human” at the dawn of the Ice Age, a truly pivotal period of change in the earth’s climate that was initiated by continued global cooling between 3 and 2 million years ago. Over this period, the earth’s oceans cooled about 2 degrees Celsius (3.6 degrees Fahrenheit). Two degrees may seem trivial, yet as an average of global ocean temperatures, it represents an enormous quantity of energy. Global cooling involved many back and forth shifts, but by 2.6 million years ago the earth had chilled sufficiently to cause ice caps at the poles to expand. Our ancestors had no idea that gigantic glaciers were forming thousands of miles away, but they certainly experienced cycles of habitat change that were intensified by tumultuous geological activity, especially in eastern Africa. Because of a massive volcanic hotspot, the entire region was pushed upward like a soufflé, and then (like some soufflés) the central portion collapsed, forming the Great Rift Valley. The Rift Valley created an extensive rain shadow, drying out much of eastern Africa. The Rift Valley also harbored many lakes, which to this day continue to fill up and then drain out in cycles. Although eastern Africa’s climate was constantly changing, the overall trend was that forests shrank while woodlands, grasslands, and other more arid, seasonal habitats expanded. By 2 million years ago, the region looked much more like the set of The Lion King than Tarzan.

Imagine being a hungry hominin about 2.5 million years ago, living in a shifting mosaic of grasslands and woodlands, and wondering what to eat. How would you cope as preferred foods, like fruits, became scarcer? One solution, which we saw in the big-faced and humongous-toothed robust australopiths, was to focus even more intensively on increasingly prevalent tough, hard foods like roots, tubers, bulbs, and seeds. These hominins must have spent many hours a day arduously chewing, chewing, and chewing. Fortunately for us, natural selection seems to have also favored a second, revolutionary strategy to cope with changing habitats: hunting and gathering. This innovative way of life involved continuing to gather tubers and other plants but incorporated several new, transformative behaviors that included eating more meat, using tools to extract and process foods, and cooperating intensively to share foods and other tasks.

The evolution of hunting and gathering underlies the evolution of the human genus, Homo. Moreover, the key adaptations that were selected to make this ingenious way of life possible among the first humans were not big brains, but modern-shaped bodies. More than anything else, the evolution of hunting and gathering spurred your body to be the way it is.

The Ice Age precipitated the evolution of hunting and gathering along with modern bodies in several species of early Homo, but the most important is H. erectus. This consequential species has figured prominently in our understanding of human evolution since 1890, when Eugène Dubois, an intrepid Dutch army doctor inspired by Darwin and others, set off to Indonesia to find the true missing link between humans and apes. Blessed with good luck, Dubois found a fossil skullcap and a femur within months of arriving and promptly named it Pithecanthropus erectus (“upright apeman”). Then in 1929, comparable fossils were found in a cave near Beijing (then Peking), China, and named Sinanthropus pekinensis. In the ensuing decades more fossils of a similar nature started turning up in Africa, at Olduvai Gorge in Tanzania, and in places like Morocco and Algeria in North Africa. As with the Peking Man fossils, many of these finds were initially given new species names, and it wasn’t until after World War II that scholars came to the conclusion that the far-flung specimens actually belonged to a single species, H. erectus. According to the best evidence currently available, H. erectus first evolved in Africa by 1.9 million years ago and then rapidly started to disperse from Africa into the rest of the Old World. H. erectus (or a closely related species) shows up in the Caucasus Mountains of Georgia by 1.8 million years ago and in both Indonesia and China by 1.6 million years ago. In parts of Asia, the species persisted until less than a few hundred thousand years ago.

As you might expect for a species that endured for almost 2 million years on three continents, H. erectus came in a variety of shapes, much as we still do. They ranged from 40 to 70 kilograms (88 to 150 pounds) in weight, and from 122 centimeters to more than 185 centimeters (4 feet to almost 6 feet) in height. Many of them were the size of humans today, but females were at the smaller end of the human range, as was an entire population discovered in Georgia (at a site named Dmanisi). If you met a group of H. erectus on the street, you’d probably recognize them as being extremely humanlike, especially from the neck down. Unlike australopiths, their bodies had modern human proportions with relatively long legs and short arms. They had tall, narrow waists and completely modern feet, but their hips flared out more to the side than ours. Like us, they had low, wide shoulders and broad, barrel-shaped chests. But their heads were not entirely like ours. Although H. erectus didn’t have snouts, their faces were tall and deep, and males especially had an enormous, barlike browridge above their eyes. H. erectus brains were intermediate in size between australopith and human brains, and their skulls were long and flat on top and angled out at the back instead of being round like ours. Their teeth were nearly identical to human teeth today, but just a little larger.

~~The Story Of The Human Body : Evolution, Health, and Disease -by- Daniel Lieberman.

Day 87 : Book Excerpt : Ideas: A History

Much more controversial, however, are the reasons for why agriculture developed, why it developed then, and why it developed where it did. This is clearly of major importance in understanding mankind’s mental development. It is also an even more interesting question than it looks when you consider the fact that the hunter-gathering mode is actually quite an efficient way of leading one’s life. Ethnographic evidence among hunter-gatherer tribes still in existence shows that they typically need to ‘work’ only three or four or five hours a day in order to provide for themselves and their kin. Skeletal remains of Stone Age farmers reveal more signs of malnutrition, infectious diseases and dental decay than those of their hunter-gatherer predecessors. Why, therefore, would one change such a set of circumstances for something different where one has to work far harder? In addition, reliance on grain imposed a far more monotonous diet on early humans than they had been used to in the time of hunting and gathering. In any case, when people first domesticated crops, these remained a minor part of the diet for centuries, possibly more than a thousand years. Again, why the change?

One theory is that the switch to agriculture was made for ritualistic or social reasons, because the new foods were rare luxuries, which gradually spread, the way designer goods do in our own day. Lentils, for example, grow just two per wild plant and would hardly have staunched the hunger of a Stone Age family. Yet lentils are among the first crops of the Near East. Some palaeontologists feel beer was the most important end-product of these grains, the importance of alcohol in a ritual feast being obvious.

But the most basic of the economic arguments stems from the fact that, as has already been mentioned, some time between 14,000 and 10,000 BP, the world suffered a major climatic change. This was partly a result of the end of the Ice Age which had the twin effects of raising sea levels and, in the warmer climate, encouraging the spread of forests. These two factors ensured that the amount of open land shrank quite dramatically, ‘segmenting formerly open ranges into smaller units and arranging the niches for different species by altitude and type of vegetation . . . Sedentism and the reduction of open range encouraged territoriality. People began to protect and propagate local herds, a pre-domestication practice that can be referred to as food resource management.’ A further aspect of this set of changes was that the climate became increasingly arid, and the seasons became more pronounced, a circumstance which encouraged the spread of wild cereal grasses and the movement of peoples from one environment to the next, in search of both plants and animal flesh. There was more climatic variety in areas which had mountains, coastal plains, higher plains and rivers. This accounts for the importance of the fertile crescent. Grasses were naturally prevalent in this Near Eastern region (wild stands of emmer and einkorn wheat, and barley, exist there to this day). But it is not difficult to work out what happened. ‘The harvested batch of seeds would be selected in favour of non-shattering and uniform maturation. As soon as humans began to sow the seeds they had harvested, they automatically – even if unintentionally – initiated a process of selection in favour of the non-shattering genotype.’

Mark Nathan Cohen is the most prominent advocate of the theory that there was a population crisis in pre-history and that it was this which precipitated the evolution of agriculture. Among the evidence he marshals to support his argument is the fact that agriculture is not easier than hunter-gathering, that there is a ‘global coincidence’ in the simultaneous extinction of mega-fauna, the big mammals which provided so much protein for early humans, a further coincidence that domestication emerged at the end of the Pleistocene Age, when the world warmed up and people became much more mobile, and that the cultivation of wild species, before agriculture proper, encouraged the birth of more children. It is well known, for instance, that nomads and hunter-gatherers control the number of children by not weaning them for two years. This limits the size of a group that is continually on the move. After the development of sedentism, however, this was no longer necessary, and resulted, says Cohen, in a major population explosion. Cohen also claims that evidence for a population crisis in antiquity can be inferred from the number of new zones exploited for food, the change in diet, from plants which need less preparation to those which need more, the change in diet from larger animals to smaller (because larger ones were extinct), the increasing proportion of remains of people who are malnourished, the specialisation of artefacts which had evolved to deal with rarer and rarer animals and plants, the increased use of fire, for cooking otherwise inedible foodstuffs, the increased use of aquatic resources, the fact that many plants, though available as food in deep antiquity, were not harvested until around 12,000 BP, that grass (cereals) is a low priority in food terms, and so on and so on, all of which Cohen contends is corroborated by archaeological excavation. For him, therefore, the agricultural revolution was not, in and of itself, a liberation for early humans. It was instead a holding action to cope with the crisis of overpopulation. Far from being an inferior form of life, the hunter-gatherers had been so successful they had filled up the world, insofar as their lifestyle allowed, and there was no place to turn.

It is another attractively simple hypothesis but there are problems with it. One of the strongest criticisms comes from Les Groube, who is the advocate of a rival theory. According to Groube, who is based in France, it is simply not true that the world of deep antiquity was in a population crisis, or certainly not a crisis of overpopulation. His argument is the opposite, that the relatively late colonisation of Europe and the Americas argues for a fairly thinly populated Earth. For Groube, as man moved out of Africa into colder environments, there would have been fewer problems with disease, simply because, from a microbial point of view, the colder regions were safer, healthier. For many thousands of years, therefore, early man would have suffered fewer diseases in such places as Europe and Siberia, as compared with Africa. But then, around 20,000 years ago, an important coincidence took place. The world started to warm up, and man reached the end of the Old World – meaning that, in effect, the known world was ‘full’ of people. There was still plenty of food but, as the world warmed up, many of the parasites on man were also able to move out of Africa. In short, what had previously been tropical diseases became temperate diseases as well. The diseases Groube mentions include malaria, schistosomiasis and hookworm, ‘a terrible trinity’. A second coincidence also occurred. This was the hunting to extinction of the mega-fauna, which were all mammals, and therefore to a large extent biologically similar to man. All of a sudden (sudden in evolutionary terms), there were far fewer mammals for the microbial predators to feast on – and they were driven to man.

~~Ideas: A History -by- Peter Watson