Life on earth is governed by chance

Photo: Jörg Bittner Unna / Wikimedia Commons, CC BY 2.0

P.rinse Hamlet he spent a lot of time reflecting on the nature of chance and probability in William Shakespeare’s tragedy. In the famous speech “To be or not to be”, he notes that we face helplessly “the slings and arrows of outrageous fortune” – although earlier in the play he declares that “there is a special providence in the fall of a sparrow,” By suggesting that everything happens because God wants it to be so.

We can hardly criticize the prince for holding two apparently contradictory views on the nature of the case; after all, it is a puzzle that has plagued humanity through the ages. Why we are here? Or to give the question a little more modern twist, what sequence of events brought us here, and can we imagine a world where we didn’t get to the scene at all?

Biologist Sean B. Carroll is credited with finding a way to take a puzzle that could easily fill volumes (and probably has full volumes) and present it to us in a small, thin, non-technical and fun book, A Series of Lucky Events: Chance and Creation of the Planet, Life and You.

Carroll (not to be confused with physicist and writer Sean M. Carroll) throws the ball with an introduction to the key concepts of probability and game theory, but quickly moves on to the issue at the heart of the book: the role of chance in evolution. Here we meet a key historical figure, 20th-century French biochemist Jacques Monod, who won a Nobel Prize for his work on genetics. Monod understood that genetic mutations play a critical role in evolution, and was struck by the random nature of those mutations.

Carroll quotes Monod: “Pure chance, absolutely free and blind, at the very root of the stupendous edifice of evolution: this central concept of modern biology is no longer one among other possible or even conceivable hypotheses. Today is sole conceivable hypothesis, the only one that corresponds to observed and verified facts. “

Sean B. Carroll
A series of lucky events: chance and the realization of the planet, of life and of you
Princeton University Press, 2020

“There is no scientific concept in any of the sciences”, concludes Monod, “more destructive than anthropocentrism than this”.

From there, it’s a short step to realize that we humans may never have evolved in the first place. As Monod said, “Man was the product of an incalculable number of fortuitous events.” For those who still believed that God was in charge, managing the events of the universe, this was a severe blow. Carroll quotes an American theologian, RC Sproul, who wrote that “The mere existence of chance is enough to snatch God from his cosmic throne.” If we accept that chance plays a role, “it leaves God not only obsolete, but jobless.”

But genetic mutations are just a kind of random occurrence; there are many others that nature sends us. Take asteroids – they usually circle the sun harmlessly between the orbits of Mars and Jupiter, but sometimes one of them hits the Earth. This is what happened at the end of the Cretaceous period, killing dinosaurs and paving the way for the rise of small furry mammals, some of which were our great-great-great (add more great) grandparents.

The story of the asteroid has been told many times, but Carroll adds another less discussed point of view: the asteroid hit the Earth in just the “right” spot: an area of ​​Mexico’s Yucatan Peninsula rich in hydrocarbons and sulfur. then the impact ejected huge amounts of soot and aerosols into the atmosphere that deflected sunlight. Carroll does the math: given the speed of rotation of the Earth, he observes that if the object had been hit 30 minutes earlier or 30 minutes later it would have hit the Atlantic or the Pacific Ocean; still a colossal explosion, but not the kind that would necessarily have given mammals an advantage over dinosaurs. (What-ifs of this kind are fun but perhaps a little arbitrary; for example, why focus on the rotation of the Earth rather than its orbital motion – or the myriad of other factors that had to be “just like that” for the impact to happen. verify where and when it happened?)

The slings and arrows continued after the asteroid; organisms continued to evolve, their fates shaped by genes, environment and natural selection. Carroll details how Darwin’s theory took shape and how it challenged the prevailing worldview in which different species were assumed to be individually created by God. In this new picture, there is no guiding hand; events simply unfold according to the laws of nature. Carroll sums it up: “Look around you for all the beauty, complexity and variety of life. We live in a world of errors, ruled by chance. “

But if chance dominates the day, how are complex organisms born? This is the hard part, and we now understand much better than Darwin how genetic mutation and natural selection work together in a sort of gradual and cumulative process – what Carroll calls “the ladder of evolution.” (Carroll is certainly not the first to describe these processes; Richard Dawkins, for example, devotes much of his 1996 book, “Climbing Mount Improbable,” to the question of how evolution produces complexity.)

There is a lot of microbiology here – Carroll is interested in the details of the mutation – but the historical details are what stuck with me. Like Russian biologist Ilia Ivanov, who, in a project funded by the Soviet Communist Party, tried to create a human-chimpanzee hybrid (a “humanzee”). (The Communists were eager to show that religion was obsolete and that the universe is simply matter interacting with matter, all the way.) The Pasteur Institute in Paris also supported the project. Ivanov eventually managed to inseminate three chimps with human sperm, but they did not get pregnant.

So humans and chimpanzees aren’t as close as Ivanov imagined, but they’re still very close – close enough that viruses that infect one species often jump over the other. Take HIV, the virus that causes AIDS. Carroll explains how a single mutation in the simian immunodeficiency virus (SIV) allowed him to make the leap from chimpanzees to humans, ultimately killing more than 32 million people. Random events brought us here, but random events can kill us too. A chapter on cancer follows, with a detailed exploration of how the effects of cancer involve a mix of genetic and environmental factors and, again, luck.

If the book has a central message, it is that we should thank our lucky stars that we are here. But instead of veering towards philosophy, Carroll chooses lightness; its final section is a cleverly staged imaginary conversation between Monod, Albert Camus, Kurt Vonnegut and no fewer than six comedians – with himself as the moderator. And as he gives himself the last word, I finish with what Ricky Gervais said just before, on the question of why we’re here: “We’re not special, we’re just lucky”, he says “We haven’t.” They haven’t been around for 14 and a half billion years. Then we’re 80 or 90 if we’re lucky, and then we’ll never exist again. So we should make the most of it. “

This article was originally published on Undark. Read the original article.