Humans are both very like and very different from other species we find on Earth. At the sub-cellular and biochemical level, the similarities, the almost universality of the DNA code and its property of self-duplication and storage of genetic information is breathtaking. On the other hand, no other species has succeeded in the scope and breadth of it’s colonization of this planet. Much of the “success” in growing a population that now exceeds seven billion individuals can be attributed to our being a social species. Sociability and its evolutionary roots have been well studied. However there does seem to be something missing. The rapid runaway expansion of human culture and the extraordinary flowering of human art, which might be attributed in turn to the literal expansion of the human brain seem to require further explanation.
The human brain is a very power-hungry organ. This paper states an adult brain consumes 25% of resting metabolism, over double that of our primate cousins and vastly more than the 3 -5 % of non-primate mammals. The paper goes on to describe how the acceleration in brain size seems to occur with the emergence of Homo erectus starting around 1.6 million years ago. It suggests some causes such as climate change, changes in diet and foraging behaviour, increased cooperation as possible factors. But did Homo erectus really need to be so brainy?
The antiquity of modern language and speech capacities, going back to at least the last common ancestor of Neandertals, Denisovans and modern humans some half a million years ago, raises new and interesting questions concerning the nature of the linguistic design space, the relationship between biological and cultural evolution, and the time frame for the emergence of modern human traits, and language in particular.
The paper does not seem to consider why brain size increase, a prerequisite for the much later flowering of human art and culture and the other evolutionary attributes (the changes to the hyoid bone for example) seem to occur so rapidly and so long before the dawn of human civilization which we might put at around 10,000 or so years ago.
Step forward, Geoffrey Miller, psychologist and author of a book published in 2000, The Mating Mind: How Sexual choice Shaped the Evolution of Human Nature (There’s a detailed précis of the book here.) Miller’s hypothesis, that human braininess evolution was driven at least in part by sexual selection, if true, explains both rapid increase in brain size and the early development of language.
He points out one difficulty in his hypothesis; that of a lack of pronounced sexual dimorphism in humans which would be expected if just women (or just men?) were doing the choosing. He then proposes
…the idea of sexual ornaments as costly, reliable indicators of fitness, and argues that our most distinctive mental traits evolved through mutual mate choice as fitness-indicators.
[I’m quoting Miller from his précis linked above]
In the last four chapters of his book, Miller suggests the following uniquely human mental traits that appear to have evolved under mate choice: art, morality, language, and creativity.
For art, Miller suggests the sexual element could be artistic and artisanal skill as a fitness indicator saying (in his précis):
This beauty-as-virtuosity theory also helps make sense of the hand axe, which can be viewed as a sexually-selected feature of hominid extended phenotypes for over 1.5 million years.
Morality, according to Miller is hard to explain in evolutionary terms. In chapter 9, ‘Virtues of Good Breeding’ he sets out the difficulty:
Psychologists sometimes fail to understand how circular it is to ‘explain’ moral behavior in terms of moral preferences. Of course, one can always say that we are kind because we choose to be kind, or it feels good to be kind, or we have brain circuits that reward us with endorphins when we are kind. Such responses beg the question of why those moral preferences, moral emotions, and moral brain circuits evolved to be standard parts of human nature.
He goes on to reject reciprocal altruism as sufficient to explain the roots of morality. He mentions a study on Arabian Babblers that behave apparently altruistically, but closer observation shows that what is happening is fitness displays driven by sexual selection. There’s lots more in the chapter that is persuasive polemic, building on the idea that human altruism has an evolutionary origin in fitness displays. He even manages to suggest giving to charity is rooted in this behavior.
It’s in chapter 10 that language becomes woven into Miller’s argument. The title ‘Cyrano and Scheherazade’ sets the tone. Miller should be pleased to see the paper News linked to. When he wrote his book, whether Neandertal’s spoke a language was still speculation. Miller again argues for sexual selection with language skills, singing, poetry and declamation as weapons to be deployed in courtship and seduction. Near the end of the chapter he asserts:
Language evolved as much to display our fitness as communicate useful information. To many language researchers and philosophers, this is a scandalous idea. They regard altruistic communication as the norm, from which our self-serving fantasies might sometimes deviate. But to biologists, fitness advertisement is the norm, and language is an exceptional form of it.
I hope some have been interested enough to get this far and I look forward to any comments.