Although we have no clue how life began, and no way to estimate the odds, many astrobiologists believe life gets going easily on earthlike planets and so will be widespread in the universe. It is then possible that some of those planets might have evolved intelligent beings.
For 50 years, a band of heroic astronomers has been sweeping the skies with radio telescopes in the hope of stumbling across a message from an extraterrestrial civilization. Known as SETI – the Search for Extraterrestrial Intelligence – this enterprise is predicated on the assumption that intelligence is an expected product of biological evolution. But is it?
With only one sample of life to go on, it’s hard to draw general conclusions. However, looking back at the evolution of life on Earth, some features, for example eyes and wings, have evolved independently many times, presumably because they have good survival value.
We might therefore expect alien life to possess these characteristics too. But other features, like the elephant’s trunk, seem to be baroque aberrations – the result of rare evolutionary accidents.
When it comes to human-level intelligence, is that a wing-like or a trunk-like property? There is no agreement among scientists, but Charles Lineweaver of the Australian National University has pointed out that advanced intelligence evolved only once, in Africa, even though it could have arisen independently in several other isolated land masses, for example Australia or America.
Moreover, dinosaurs, which famously “ruled the Earth” for 200 million years, never evolved to make tools, build cities or fly to the moon (as far as we know). These facts suggest that human-level intelligence is a rare quirk of fate rather than the inevitable product of natural selection. If that is so, it is bad news for SETI.
Arguments about the likelihood of intelligent aliens is made murkier by disagreement concerning the nature of the evolutionary process. For some decades after the acceptance of Darwin’s theory, there was a popular belief that life on Earth gets progressively more complex over time.
Some philosophers regarded humans as the culmination of that ladder of progress. If there were indeed a directionality in evolutionary change, one could imagine that high intelligence is an expected, even inevitable, product of biological evolution, given sufficient time.
Sadly for SETI, most contemporary biologists don’t think evolution is heading anywhere in particular; there is no inbuilt biological arrow of time, they claim, no innate drive towards complexity or braininess.
True, life on Earth started out with simple microbes, but the emergence of greater complexity was merely the product of a meandering exploration in the vast space of biological possibilities, and not a systematic trend. The idea that intelligence is somehow “waiting in the wings” for a chance to arise is dismissed as mystical nonsense.
Defending that view, Lineweaver invokes what he calls “the Planet of the Apes fallacy”. In the original movie starring Charlton Heston, humanity gets wiped out and the apes become the dominant species by rapidly evolving human level intelligence. The story is portrayed as if there is “an intelligence niche” that became vacated by the demise of Homo sapiens, with the apes being next in line to fill it.
But this runs completely counter to mainstream Darwinism, according to which if some catastrophe destroyed our species, there is no reason to expect that in 20 million or even 100 million years another terrestrial species would be building radio telescopes or launching spacecraft.
All of which casts grave doubt on whether, even in a universe teeming with life, there are any advanced alien civilisations sending out radio messages.
There is, however, a glimmer of hope for SETI.
Evolutionary theory remains a work in progress, and in recent years some contrarian biologists have challenged the dogma that there is no directionality in evolution.
They have identified several mechanisms whereby characteristics acquired during the lifetime of an organism seem to be passed on to their offspring, a process known as epigenetic inheritance. This is in stark contrast to standard Darwinism, according to which mutations in offspring arise from purely random errors unconnected to the circumstances of the parent.
If epigenetic inheritance plays a significant role in the evolution of brains, it is possible to imagine a sort of accelerating IQ phenomenon.
In fact, the fossil record points to an upward trend in the encephalisation quotient – a measure of brain size relative to body mass – among hominins over the past few million years. Assuming something similar works itself out on other planets too, maybe we are not alone after all.
Paul Davies is Regents' Professor and Director of the Beyond Centre for Fundamental Concepts in Science at Arizona State University. He is also a prolific author, and Cosmos columnist.
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