From Cambrian Explosion to First Farmers: How Climate Made Us Human
Details Blur As We peer back through millions of years, but the outline of the story is clear enough. During the past 2– 3 million years, our hominin forebears had to cope with an increasingly variable and cooling climate. Across those 100,000 Homo generations, survival and reproduction depended on maintaining biological and behavioral compatibility with constantly changing climatic and environmental conditions. Hence much of modern human biological versatility and adaptability, including several unique aspects of brain function, comes from evolution’s selective winnowing within those ancient predecessor populations. The genes of the survivors, those best able to reproduce, are part of our genetic inheritance today. That climate change has been a major source of natural selective pressure has long been known. Alfred Russel Wallace, the overshadowed younger contemporary of Charles Darwin and codiscoverer of evolution by natural selection, wrote that, among the variations occurring in every fresh generation, survival of the fittest occurred in response to the “changes of climate, of food, of enemies always in progress.” The corollary, of course, is that since biological evolution must focus on surviving the present, oblivious of the future, it provides no guarantee against extinction. Even so, a multivalent brain that enables cultural and behavioral adaptability and strategic forward thinking would surely help an animal species cope better with subsequent environmental changes. Indeed, it seems to have worked sufficiently well for our Homo genus ancestors during two million years of ever- changing climatic conditions for at least one Homo species to have carried the baton of survival into the present. In the next two centuries, our species faces a new challenge of greater, faster, and protracted climate change. Since the Cambrian Explosion of new life forms around 540 million years ago, there have been five great natural extinctions and many lesser ones. The earliest extinction of multicellular life, though less destructive than its successors, occurred around 510 million years ago, apparently due to acute sulfurous shrouding, cooling, and oxygen deprivation caused by a massive volcanic eruption in northwest Australia. Most of these catastrophic transitions were marked by climate extremes, volcanic activity, and altered ocean chemistry, especially rapid surface acidification of shallow coastal waters.
COVID-19 and future pandemics: a global systems approach and relevance to SDGs
