In Power: Limits and Prospects for Human Survival, Richard Heinberg looks at humanity’s power over nature and the power that some people have over others. This book demonstrates that we must relearn the lessons of power if humanity is to have a thriving future and is essential reading for everyone who calls planet Earth home. Today, we share an excerpt from the book that talks about how power developed during the Pleistocene epoch.
Excerpt from the Book
The story of humanity’s development of its awesome and unique array of powers likely began, ironically, with climate change. About 13 million years ago, several centuries of drought ravaged the forests of east Africa. As a result, many tree-dwelling primates were forced to adapt to living in expanding savannahs. The primates that stayed in the shrinking forests were the ancestors of today’s nonhuman great apes— gorillas, chimps, and bonobos. The primates that came down from the trees evolved into several lineages of hominins (i.e., proto-humans). One of those lineages ultimately led to us.
It’s still unclear whether the savannah dwellers developed an upright stance, walking on two legs instead of four (a process that must have taken millions of years), before, during, or after leaving the forest. Nevertheless, living in grasslands rewarded the trait of bipedalism. It was now advantageous to stand tall, so as to peer over high grass to see predators and potential food. Crucially, this increasingly upright posture conferred power in several other ways:
- Bipedal hominins burned fewer calories as they foraged, compared to knuckle-walking forest primates (walking on two legs isn’t calorically superior to the quadrupedal locomotion of deer or horses, at least over short distances— but our ancestors weren’t directly competing with those kinds of animals; instead, they were competing with other apes).
- Hominins and their descendants could walk and run long distances at a constant speed. This enabled them to chase down prey such as deer that could sprint much faster, but tired quickly.
- Hominins’ (and later humans’) ability to walk long distances also helped them to spread out geographically— ultimately hiking, boating, and sledding their way throughout all the Earth’s continents except Antarctica.
- Crucially, bipedalism freed hominins’ front limbs for tasks other than locomotion. Meanwhile, life on the savannah required more emphasis on long-distance vision. As their sense of sight increasingly predominated over other senses, proto-humans began to coordinate their eyesight with small, controlled movements of their freed-up hands. Even though the hands of other primates are anatomically similar to those of humans, new neural pathways in hominins helped in the development of the muscle control necessary for grasping, manipulating, and throwing— using what paleoanthropologists appropriately call the “power grip.”
But walking upright imposed costs and required adaptations. Notably, it created the need for a thicker pelvis; and this, in turn, resulted in changes to the process of childbirth. Babies were born smaller, so they required more lengthy parental care before they could fend for themselves. And that period of extended care promoted extended families— which offered more opportunity for social interaction and for the development and transmission of culture.
Increased social contact contributed to one more crucial change in hominins and their descendants: a substantial growth in brain size. Bigger brains co-evolved with walking; with finer, more controlled hand movements; and with increased social interaction. Each of these developments compounded the others. Big brains, for example, also reinforced changes in childbirth, already underway as a result of bipedalism: because of their larger crania, babies had to be born in a less mature state, and were even more dependent on long-term familial care.
Meanwhile, more social interaction required more memory and thought— hence bigger brains. Walking, the development of better hand-brain coordination, bigger brains, and increased social interaction, in effect, together constituted a self-reinforcing evolutionary feedback loop. Over nearly seven million years our brains tripled in size, with most of that growth occurring in the past two million years. And, during that same period, humans became some of the most social creatures on the planet.
Crucially, it’s important to remember that these changes were occurring among several prehuman and human species. Even after the appearance of true humans (genus Homo), perhaps three million years ago, several distinct species persisted.
- The earliest known of the true human species was Homo habilis, which must have emerged nearly three million years ago; all known signs of this species are restricted to Africa.
- Signs of Homo erectus date from two million years ago; this human species emerged in Africa but then spread to Eurasia. It may have survived in Java as late as 70,000 years ago.
- Homo denisova, which probably appeared in Africa at least 400,000 years ago, migrated northeast to Siberia, and southeast to Indonesia and New Guinea. Denisovans persisted longest in their southeastern range; genetic evidence suggests they may have interbred with Homo sapiens in New Guinea as recently as 15,000 years ago.
- Homo neanderthalis, with which we share about 99.8 percent of our genetic code, emerged in Africa at least 400,000 years ago and spread north and northwest to the Middle East and Europe; and later eastward, where Neanderthals probably interbred with Denisovans. Neanderthals had similar-sized brains (perhaps even slightly bigger), on average, to those of sapiens. But the formation of Neanderthal skulls suggests that there may have been differences in how this large brain was organized and used, compared to ours. Neanderthals died out by about 40,000 years ago.
There were other human species as well. Homo ergaster, which may have been a variant of Homo erectus or a separate species (experts disagree on this point), lived in southern Africa between 1.9 and 1.4 million years ago. Two species, Homo soloensis and Homo floresiensis, have been identified just in Indonesia, where human fossils seem to have survived particularly well. Homo naledi lived in part of southern Africa 300,000 years ago. Homo heidelbergensis preceded Neanderthals in Europe, and persisted alongside them for a time (it may have been the common ancestor of Homo neanderthalis and Homo sapiens).
All the species mentioned are simply ones whose remains happened to be preserved and were later discovered by modern researchers; there may have been more, evidence of which hasn’t been found. What’s crucial to our story is the clear fact that none of them survived to the present— except one.
Homo sapiens first appeared in Africa roughly 300,000 years ago, then spread out from that continent in at least three waves, the first of which occurred over 250,000 years ago, and another about 100,000 years ago. Sapiens individuals who were part of those early migratory waves interbred with Neanderthals and probably with Homo erectus as well. But these sapiens evidently died out. A later wave of migration began about 70,000 years ago. This time sapiens survived and flourished nearly everywhere it went. All humans outside Africa who are alive today— Asians, Pacific Islanders, Europeans, and Native Americans— descended from that last migratory wave. Meanwhile, in the process of flourishing, sapiens profoundly altered landscapes nearly everywhere it went, wiping out many large mammal and bird species. This was a uniquely powerful kind of primate.
During the last three million years, as these various human species came and went, the environment was in a state of enormous flux. Ice ages lasting tens of thousands of years were interrupted with shorter warming periods during which the ice retreated, opening up space for grasslands and forests. Then the ice would return. Some of these shifts were fairly abrupt, punctuated by sudden, cataclysmic floods and extreme weather events. Neurophysiologist William H. Calvin has theorized that these repeated bouts of climate change acted as an evolutionary pump, forcing humans to adapt repeatedly to dramatically altered circumstances, thereby selecting for larger brain size. The notion is hard to prove or disprove, and it raises the question whether there were equivalent evolutionary impacts on other animals. However, it also offers food for thought about our future human response to the climate change that we ourselves are now causing. But— back to our story.
All human species walked upright. All used their opposable thumbs to make and use tools. Why did the last great migration of Homo sapiens out of Africa succeed, when earlier ones didn’t? It would appear that sapiens had acquired some crucial power advantage in the meantime that enabled it to outcompete all other human species, either deliberately or inadvertently driving them to extinction.
The prime candidates for this hypothetical new source of power, according to most paleoanthropologists, are the fabrication and use of more sophisticated tools, control of fire, and language-based social skills. Spoiler alert: the question of how and why other human species died out is still open and the evidence is inconclusive. Nevertheless, it’s worth exploring these three advantages one by one, as they profoundly shaped who we are today. Whether or not they enabled sapiens to outcompete other sorts of humans, these were unquestionably the sources of power that ultimately led our kind to dominate the rest of the biosphere.