A few weeks ago I finished The Monkey's Voyage: How Improbable Journeys Shaped the History of Life by Alan de Queiroz. It was a fascinating read, detailing how the voyage of plants and animals between the continents has changed the world in which we live. Even, de Queiroz asserts, something that is both random and highly unlikely in and of itself is nearly inevitable over millions of years of life, whether it is a new plant colonizing an island or monkeys from Africa crossing into South America. The book made me think once more about how randomness shapes the history of life. If we know anything from science, it is that humans are not the inevitable outcome of evolution. Neither our dominance as a species nor even our existence were assured. Random and improbable events led us to where we are.
Think about just a few of the moments where, had something been different, life would have taken another path. Whatever natural disaster caused the human population to bottleneck around 100,000 years ago could have driven us to extinction instead. The extinction that killed the non-avian dinosaurs paved the way for the rise of mammals. Without that extinction event, perhaps our mammalian ancestors would have remained eternally in the periphery, hiding from and being hunted by dinosaurs as they continued their own evolution? Whatever event it was that sparked life might not have occurred, leaving our planet empty. Any number of events might have led us to an earth without us in it. To paraphrase Stephen Jay Gould, if one replays the tape of life over again, it is highly probable that we would not again be the end result.
Random events have a strong influence on the history of life, and the history of our civilizations. It plays, perhaps, a larger role than we are inclined to give credit for; it is certainly something that may make us deeply uncomfortable at the very least. This must surely account at least in part for the stubborn persistence of Young-Earth Creationism well into the 21st Century. Certainly fundamentalist religious beliefs, lack of good science education, and unscrupulous people willing to take advantage of the gullible for financial gain all play a role. Yet I have to think many people refuse to accept the reality of evolution because it implies that random forces play a role in our lives, forces that are near-completely out of our control. While natural selection itself isn't random, it is random mutation in our genes that provides the material for evolution to work with. Evolution, at last, removes humans from their privileged position among the animals. We are the result of evolution, but not the inevitable outcome.
Some may shy away from the findings of modern science because they prefer to see us as special creations; they fear an impersonal universe indifferent to our existence and imagine it a cold and joyless place. For me, however, this is a source of wonder. How amazing it is to think about what led us to this moment! How remarkable it is to ponder our existence when you think that our ancestors survived famines, plagues, predators, and extinctions, all the way back in an unbroken line to the beginnings of life. Surely knowing that the molecules that make up our bodies came from dying stars, that we are related to every living thing on this planet, from the lowest moss to the elephants and lions that roam the savanna, is adequate compensation for accepting the serendipity of life? Wonder is the appropriate response, not fear! Understanding and accepting that randomness plays a great role in the history of life is the beginning of uncovering this wonder, of discovering the magisterial history of life on this planet.
The tree of life, depicting the inter-relatedness of all living things
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