Sapiosexual Aliens: Why Sexual Selection for Mental Fitness Indicators Drives the Evolution of Most Extraterrestrial Intelligence

Geoffrey Miller
University of New Mexico, USA

‘Sapiosexual’ people are sexually attracted to intelligence. I suspect that most intelligent aliens are sapiosexual too: their cognitive and communicative abilities evolved mostly for reproductive benefits through attracting mates, not just for practical survival benefits. 

‘Fitness indicators’ are exaggerated traits such as the peacock’s tail that evolve to signal the fitness of one organism to another organism. Fitness indicators rely on game-theoretic signalling principles: they must be conspicuously large, costly, complex, and/or precise so they are hard to fake, or other organisms would evolve to ignore them. Many fitness indicators deter predators, intimidate rivals, or solicit parental care. But the most elaborate ones evolve through sexual selection to attract mates. In turn, mate choice evolves to focus on the most informative indicators that maximize the expected fitness of offspring.

Some of these sexually-selected fitness indicators are physical ornaments, but many are behavioral/psychological ornaments such as bird song or human music. In our lineage, sexual selection for these ‘mental fitness indicators’ – such as intelligence, language, creativity, humor, art, and music – has played a major role in the tripling of our brain size in the last two million years, and in driving the emergence of our unusual minds.

Sexual-selected mental fitness indicators might sound like a fluke of DNA-based terrestrial biology.  But there are deep evolutionary and information-theoretic reasons why they are likely to be the royal road from mute, marginally-intelligent aliens to conscious, articulate, creative aliens. Evolution through cumulative selection on heritable variation is the only known process that can produce complex adaptations, including those that would underlie extraterrestrial intelligence. Every genetic transmission system must strike a balance between replication fidelity (or else the gene pool would disintegrate) and random variation/mutation (or else evolution would stagnate). For complex organisms that depend on large amounts of genetic information, most mutations are neutral or harmful (because disruptions are more likely than improvements) -– regardless of their habitat, econiche, physical basis, genetic infrastructure, or phenotypic form. Without regularly mixing genes with other individuals (e.g., through sexual recombination), asexual lineages suffer ‘mutational melt-down’– a runaway entropic catastrophe – and go extinct quickly. Thus, sexual reproduction is the main way that lineages of complex organisms can persist. Given sampling errors in mutations and sexual recombination, there will be variation in genetic quality across individuals. Given sexual reproduction and genetic variation, there are incentives for organisms to select their mates carefully by paying attention to fitness indicators – and for the fitness indicators to become ever larger, more complex, more precise, and more attractive. 

Cognitive and communicative abilities make especially informative fitness indicators because their underlying computational systems must be especially complex and precise, so uniquely vulnerable to harmful mutations, uniquely informative about fitness, and uniquely likely to get caught up in a signaling arms race that drives a runaway elaboration of intelligence. Thus, we can expect that extraterrestrial intelligence is most likely to emerge among life forms that are sexually reproducing, choosy about their mates, and a bit obsessed with each other’s mental fitness indicators.


Geoffrey Miller is an evolutionary psychologist best known for his books The Mating Mind (2001), Mating Intelligence (2008), Spent (2009), and Mate (2015).He has a B.A. in Biology and Psychology from Columbia University and a Ph.D. in Cognitive Psychology from Stanford University, and he is a tenured professor at University of New Mexico. He has 116 academic publications (cited 8,000+ times), addressing sexual selection, mate choice, signaling theory, fitness indicators, intelligence, creativity, language, art, music, humor, emotions, personality, psychopathology, and behavior genetics. He has given 175 talks in 15 countries, reviewed papers for 50+ journals, and also worked at NYU Stern Business School, UCLA, and the London School of Economics. His research has been featured in Nature, Science, The New York Times, The Washington Post, New Scientist, and The Economist, on NPR and BBC radio, and in documentaries on CNN, PBS, Discovery Channel, National Geographic Channel, and BBC. His podcast series The Mating Grounds has logged more than 3 million downloads. He has been a passionate science fiction reader since childhood, and loves the Iain M. Banks Culture series. He’s co-authored 17 previous papers with Peter Todd.