Cambridge zoologist Arik Kershenbaum, author of Zoologist’s Guide to the Galaxy (2021), thinks that convergent evolution here on Earth can offer us guides to what must happen on other planets that can support life. “Convergent evolution” means that radically different life forms arrive at the same solutions. He told science writer Dan Falk in an interview:
Sometimes this “convergence” of traits is for something obviously useful, like wings. But sometimes convergence produces bizarrely similar creatures that share so many characteristics, it can be hard to believe they’re not closely related. The recently extinct thylacine [a large predatory marsupial native to Tasmania and mainland Australia], for example, could easily be mistaken for a peculiar breed of dog, but it’s much more closely related to a kangaroo! And yet living a life similar to that of modern coyotes or jackals meant that it evolved many similar characteristics convergently.Dan Falk, “Why Extraterrestrial Life May Not Seem Entirely Alien” at Quanta (March 18, 2021)
Kershenbaum believes that “laws of evolution” govern what can possibly happen, due to the physics of the universe. He told Falk:
On Earth, flight evolved four different times in four different groups: in birds and bats and pterosaurs and insects. The fact that they all use wings isn’t because they evolved on Earth; it’s because it was advantageous to fly, and wings are just about the only way to fly. And so we can expect these constraints to be operating everywhere in the universe.Dan Falk, “Why Extraterrestrial Life May Not Seem Entirely Alien” at Quanta (March 18, 2021)
Such laws, in his view, govern human behavior as well. But that introduces a fatal conundrum for his argument:
It could be that animals on other planets will cooperate simply for mutualistic reasons, because it benefits them both. But much of the cooperation on Earth, much of the sociality, is driven by relatedness. We cooperate because we’re related. We feed our children, we help our parents, we befriend our siblings. All of these things are well founded in evolutionary theory. The way our characteristics, our traits, our behaviors are passed down from generation to generation is through our genes. And if our genes make us tend to cooperate with our siblings, then we’ll be more successful, and so will they, and we’ll all pass on our related genes.Dan Falk, “Why Extraterrestrial Life May Not Seem Entirely Alien” at Quanta (March 18, 2021)
Kershenbaum admits a difficulty:
The trouble is, we don’t know what aliens have for genes. So this is something we can’t say is quite as universal as some of the other constraints of biology on Earth. It may be that the way that alien life forms are related to each other is completely different, and so their sociality may be completely different as well.Dan Falk, “Why Extraterrestrial Life May Not Seem Entirely Alien” at Quanta (March 18, 2021)
But wait. It’s not clear that convergent evolution is a law, as opposed to merely a tendency. And there is a much bigger difficulty…
With intelligent life forms, like humans, it’s not just genes. Co-operation is not based entirely on relatedness. People co-operate for a variety of reasons, including team, workplace, union, alumni, civic, political, or religious loyalty. Or else it’s group philanthropy directed at humans, animals, or the environment — usually based on philosophical or religious beliefs.
These beliefs are immaterial and may or may not originate in genes, as opposed to culture. If extraterrestrials are smart enough to be in touch with us, why shouldn’t we assume that they are not governed wholly by genes either but also by immaterial beliefs?
Kershenbaum’s viewpoint is one end, if you like, of a spectrum: He thinks we can predict that extraterrestrial life will be like based on convergent evolution on Earth. At the other end are those who warn that we really have no idea how extraterrestrial intelligences might think, for example even whether they would be friendly or hostile — or they might have emotions we don’t even understand.
It’s a fascinating discussion. Convergent evolution is real but whether it is a “law” is unclear. And it may or may not govern the world of ideas. Any such an argument must be, and probably will be, made separately.
See also: SETI director warns: Those aliens could be malevolent Harvard astronomer agrees: We’ve sent a lot of signals in recent years; they may have got them. But now what? Astronomer Avi Loeb has a low-risk practical idea: Look for alien debris on our still, lifeless, atmosphere-free Moon
Why some experts hope we don’t find life on Mars. Many thinkers worry about what will happen if the extraterrestrials land. But will they feel worse if we never find ET?