Last of the Hominids
As hunter-gatherers, we roamed the plains & forests in search of wild foods & game. But in order for this way of living to be sustainable, tribes had to stay geographically dispersed. Because of these hominids rising dominance within the food chain, a population too dense in one area for too long would deplete the supply of game, sometimes to the point of extinction. To exceed what the land could provide in this way meant starvation. And so territory was fiercely guarded from rival tribes. This was nothing new within Earth's history, but rather a common adaptation of many top predators.
These isolated populations acted like evolutionary incubators, each with not only their own gene pools, but also with their own language and culture. Unique branches diverged and morphed through the millennia. Often these branches of evolution withered into extinction. For a time though, we shared the Earth with multiple species and subspecies of hominid.
The most famous of our evolutionary relatives were the Neanderthals, now thought to be a subspecies of Homo sapien. They were a shorter but more robust hominid, with a protruding brow, more capable of weathering frigid ice-age climates. But in the end, whether aided by shifting climate or through direct confrontation, Homo Sapiens out-competed these evolutionary relatives. They disappear from the fossil record around 30,000 years ago. But recent findings also suggest that at times our ancestors saw Neanderthals as potential mates. Some of their genetic code lives on within us today.
Up until as recently as 13,000 years ago, on a small island within what we now call Indonesia, evolved Homo Floresiensis. The species is thought to descend from Homo Erectus and Homo Ergaster, common ancestors of modern humans. Given the colloquial name of the "Hobbits", H. Floresiensis was only about three and a half feet tall at maturity. This kind of island dwarfism is a common phenomena throughout earth's history, occurring when species struggle for food within a limited ecosystem, so that only the smaller individuals who need less resources tend to survive. But ultimately the Hobbits also drifted into extinction, leaving Homo sapiens as Earth's sole surviving hominid.
Extinction of the Megafauna
For millions of years Earth's animals had been wholly dependent upon the natural ebb and flow of their ecosystems, unable to move beyond the constraints of the food chain. But with our growing brains & the use of tools, prehistoric humans came to completely dominate their prey. By the end of the Paleolithic era we had spread to six continents. And in a perverse consequence of our superior adaptation, we drove a majority of Earth's large mammals into extinction. This has come to be known as the Quaternary Extinction Event.
Those species most susceptible to human's stone-age weapons were the megafauna. Their huge mass was once a strong protection from predators, but even the Wooly Mammoth and Mastodon were of no match for a coordinated tribe of well armed humans. And the slow gestation times of these large beasts meant their populations couldn't be quickly replenished. Competing predators like Smilodon (the saber-toothed cat), dependent on the same prey that we targeted, were also driven into extinction. Amplifying this wave of extinctions was a warming climate. With the equilibrium thrown out of balance, food chains collapsed. Across the six continents that humans had come to inhabit, a multitude of species disappeared into the fossil record. Upon the continent of Africa species had the chance to co-evolve in tandem of humans growing hunting abilities, so the pace of extinction was slowed. Within the Americas and Australia however arrival of humans was sudden, and the species there will ill-prepared for the threat they posed.
Evolution vs. Extinction
Mass extinction events had pulsed throughout Earth's history before the coming of Homo sapien, whether from impacts by meteorites, disease, ice ages, and other environmental changes like the the oxygen catastrophe. Such extinctions are part of the normal process of evolution, a burning away of the underbrush to allow for new growth, a pruning of the evolutionary tree. At the same time though, it's historically rare that just one species can have such a profound impact upon so many diverse ecosystems.
In the grand scheme of things, across the expanse of time and space, our role in driving other species into extinction may have little significance. So maybe it's possible to see humanity as part of a continuum, not as just another species, but as a catalyst for another global shift. Yet from a closer vantage point it can also seem cataclysmic. Entire lines of species that took millions of years to evolve have vanished.
With the food-chain under strain, even those species that survived were met with immense challenges, and we humans found our food supply waning. In this way the extinction of the megafauna was of particular significance in shaping human civilization. Faced with declining game, we were forced to adapt. And in response a wave of change swept around the globe. It was the Neolithic Revolution.