Do the subjects of life on Earth and of Earth’s place in the cosmos (and the place of us human beings, too) interest you? If so, it might be worth your while to spend 20 minutes listening to an episode of the WNYC radio show “Radiolab”. The episode is called “Cellmates”. It is about how complex life first arose on Earth. The “cells” in question are single-celled organisms, not prison cells!
Click here for the show. The first and last parts of the show are promotional stuff. The stuff we are interested in starts at the 1:30 mark, and ends at the 22:00 mark. But here is the gist of the show:
For two billion years after life first appeared on Earth, living things were limited to very simple, single-celled organisms, such as bacteria and a different group of simple organisms that nevertheless are fundamentally different from and larger than bacteria, known as archaea. Then, somehow, life appeared whose cells were much more complex.
The theory is that a single bacterium was absorbed by a single archaeon and, by a freak accident, both survived the merger. Indeed, the bacterium thrived and reproduced (by division) within the archaeon. The archaeon also thrived and reproduced (by division). The bacteria-in-an-archaeon combination was able to process energy more robustly than either organism could singly, in ways that allowed for more complex life to develop. The descendants of that first bacterium are now the “mitochondria” of complex cells, where the energy production of those cells occurs.
The simple life forms that existed prior to this merger were bound by their physical limitations. They could get no bigger, and no more complex. Thus they had been essentially static for two billion years. This one freak merger broke life free from that static situation. Every single complex life form on Earth, from jellyfish to redwood trees to human beings — indeed, every form of life that you can see with your eyes (bacteria and archaea are microscopic) — comes from that one freak merger.
How do we know this? For one, there is the similarity of all the cells found in complex life. Whether the cells are in jellyfish, redwoods, or humans, they have the same structure. For another, there is DNA shared by all complex cells, across all complex life forms. We share certain DNA with jellyfish and redwoods that points to this one single merger.
This relates to astronomy. According to Nick Lane, professor at the University of London and author of The Vital Question: Energy, Evolution, and the Origins of Complex Life (W.W. Norton, 2015), who is the central figure in “Cellmates”, this merger was “so breathtakingly improbable that only once did it ‘take’”. Therefore, there is in the universe “no trajectory towards necessary complex life”. There is “nothing about the way evolution has worked on Earth to suggest that complex life is an inevitable outcome”. (This discussion appears at about the 20:00 mark.)
If this freak event had not happened, then Earth would have continued to be home to simple life forms only, just like it had been for a couple billion years. And therefore, “we will probably find life elsewhere [than Earth], but it will probably be microbial.” No space aliens, no “Star Wars cantina”, etc.
So that is the gist. But here’s something important to keep in mind: We have no idea how even primitive life forms arose on Earth in the first place. We cannot reproduce this in a lab. We do not find it re-occurring in nature. Life does not generate from inanimate matter.
Of all the things that I have learned in my time with the Vatican Observatory, studying the history of science and telling you readers of Sacred Space Astronomy about it, perhaps the most amazing thing is how much our ideas have changed over time regarding how life comes to be. At the dawn of modern astronomy, in Galileo’s and Kepler’s day, people though that life was a natural product of matter. They had thought this for centuries. Life — even complex life — was thought to be spontaneously generated straight from the lifeless dirt. For example, the ancient Jewish scripture commentary, the Mishnah, discusses whether dirt that generates a mouse would be unclean, since Leviticus 11:29 declares mice unclean:
A mouse which is half flesh and half earth, the man who touches its flesh is unclean, (but the man who touches) the earth, is clean. (Chullin 126b:11)
That idea of spontaneous generation of life is a big part of the idea of life on other worlds. If mice are a natural product of matter, and if Jupiter is made of the same matter as is Earth (and why wouldn’t it be, if it circles the sun, like Earth, and has moons circling it, like Earth?), then Jupiter will have mice, or its version of mice. So will all the other planets that orbit the sun. So will all the planets orbiting other suns. Science and logic come together to tell us that the Earth is probably a very ordinary place. There are worlds like Earths, creatures like mice, and even intelligent creatures like humans, everywhere. Hence, the Star Wars cantina.
But the theory of spontaneous generation slowly died off in the centuries after Galileo and Kepler. It had its last gasps in the late nineteenth century. Now we have no idea how life arises. We cannot reproduce life in a lab. No mice spring from lifeless dirt, no matter what we do. Not even the humblest bacteria do. Whatever the process may be by which life first comes into existence, it is not something that happens easily.
And now, this merger theory says that the formation of complex life hinges on a “breathtakingly implausible event”. We have gone from thinking that the life we see is a regular, natural product of matter, to thinking that it is the product of two irreproducible events — of two miracles, in essence. Thus, today science and logic come together to tell us that the Earth, with its complex life, is probably a very unusual place. You won’t find another anywhere nearby.
Science does change (obviously). So, maybe in 50 years we will have discovered how life arises from matter, and have found that the single-bacterium-archaeon merger theory is all wrong. But as things stand now in science, the change from the days where science told us the Earth is just another world is breathtaking. And that change has left popular culture — with its Star Wars universes, its belief in space alien UFOs, and the like — utterly in the dust.