This diagram, lifted from a lively paper by the astrobiologist Charles Lineweaver, is the tree of life on earth. The “root” at the center is the last common ancestor of all life. Toward the bottom left, you’ll find the genus “Homo”, to which you and I belong, at the end of a twig representing animals. The two neighboring twigs, ending in Zea (i.e. corn) and Coprimus, represent plants and fungi, our two closest relatives.
Professor Lineweaver offers this diagram as an antidote to the superstition that evolution has some tendency to converge on intelligence; his criterion is that we ought not say that evolution “converges” toward some feature unless we observe that feature arising independently in at least two or more twigs. By that same criterion, evolution has no tendency even to converge on heads, which (says Dr. Lineweaver) are likely to be prerequisite for anything like human intelligence.
If human-like intelligence is a fluke, then presumably the ability to build radio telescopes is also a fluke, which stands as a cautionary note for those who expect to communicate with extraterrestrial civilizations.
Now it’s certainly true that if you magnify that animal twig to display separate branches for birds, dolphins and carnivores, you can fool yourself into thinking that intelligence has emerged independently along a multitude of pathways. After all, the last common ancestor of birds and men had a very small brain; after 310 million years of independent evolution, birds and men both have much larger brains. The last common ancestor of dolphins and men had a small brain; after 85 million years of independent evolution, both dolphins and men have much larger brains. But Dr. Lineweaver observes that the “independence” is illusory. By the time we and the dolphins went our separate ways, we were already endowed with highly similar biochemical neural pathways and constraints that left us both with (in Dr. Lineweaver’s words) a finite number of highly evolved “toggle switches” that could be successfully tinkered with.
Moreover, even if evolution were biased toward intelligence, there’s no reason to suppose that intelligence would be the sort we can communicate with across interstellar distances:
About 600 million years ago, two kinds of metazoans, protostomes and deuterostomes, diverged from each other. Both evolved independently for ~600 million years and were very successful. Today there are about a million species of protostomes and about 600,000 species of deuterostomes (of which we are one). We consider ourselves to be the smartest deuterostome. The most intelligent protostome is the octopus. After 600 million years of independent evolution and despite their big brains, octopi do not seem to be on the verge of building radio telescopes.
Doctor Lineweaver closes with an endorsement of the Search for ExtraTerrestrial Intelligence, on the grounds that it’s cheap and he might be wrong. Do you agree with him?