The surprising evolutionary relationship between bowerbirds and human art
The surprising evolutionary relationship between bowerbirds and human art
By Matt Ridley | Published: 2025-03-25 14:30:00 | Source: The Past – Big Think
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From the book “Birds, Sex and Beauty” by Matt Ridley. Copyright © 2025 Matt Ridley. Reprinted courtesy of Harper’s, an imprint of HarperCollins Publishers. All rights reserved.
Sexual selection may explain the beginning of art, as Charles Darwin said The descent of man: “The bowerbirds’ playwalks are decorated with brightly colored objects, which indicates that they must get some kind of pleasure from seeing such things.” Great satin jays and bowerbirds that court females with bottle caps and hot peppers are of course driven mostly by instinct, conventional wisdom goes, whereas humans have culture.
Hmm. I think both sides of this claim are partly false: people are driven by instinct more than we care to admit, and bowerbirds have more culture than we assume. Bowerbirds are birds with unusually large brains. Cambridge zoologist John Madden surveyed the behaviors of bowerbirds and concluded that “despite the paucity of data compared with primate studies, bowerbirds can arguably be considered to meet the same criteria on which we base our use of the term culture when applied to our close relatives, the great apes.” For example, a spotted bowerbird that found itself off course due to a storm, and ended up in satin bower country, learned to collect blue items instead of the usual white, green, and red.
As for whether people have instincts, a lot of experiments show that people have innate tendencies and that the way these tendencies often work is by making people more likely to learn some things than others, so culture and instinct are not opposites, but rather work together. Nature works through nurture, not against it. As anthropologist Joe Hinrich has documented, this means, for example, that when people make mistakes they tend to be in an adaptive tendency such as confusing safe animals with dangerous ones rather than the other way around. Learning is a way to develop.
This means that it is very likely that when small-brained human ancestors first began decorating their bodies, homes, clothes, and tools, it was very likely at the request of instinct rather than the result of any kind of rational calculation. Bowerbirds may help us understand how this happened.
Take, for example, the Acheulian axe. This is the name given to a widespread tool mainly used by Homo erectuswhich appear again and again in the archaeological record, over an extremely wide area from Europe to southern Africa to Asia and over an incredibly long period from approximately 1.8 million years ago to just 300,000 years ago. They are tear-drop shaped, symmetrical, and have sharp edges. Years ago, I noticed that the mouse on my desk—which my wife had found on eBay, but which likely came from North Africa originally—was exactly the same size and shape as the computer mouse I was using at the time. This sent a shiver down my spine: two objects designed to fit within a human hand but separated by at least half a million years.
No one is quite sure what Acheulean axes were primarily used for, but skinning animals, chopping vegetables and grinding wood were likely on the list, although it has been suggested that they were thrown as sharp-edged projectiles. It is not immediately clear to us today why this design was well suited to some specific mission, let alone why it worked so well in places as far apart as Africa, Europe, and India.
The much bigger problem the ax poses is why it hasn’t changed much in either space or time. It has experienced more than one and a half million years of severe technological stagnation. Every other technology invented by hominins, from the spear thrower to the Swiss Army knife, has evolved very quickly thanks to innovation. Not the Acheulian axe. That it could be so universal and change so little over such a long period – hundreds of thousands of generations – defies cultural explanation.
If it were a product of culture, it would certainly show fairly rapid change and great geographical diversity: that’s what culture does. However, archaeologists have consistently and universally assumed that Acheulean technology was in fact a pure product of culture: imitation within the tribe according to social conventions. They assumed that because, well, they always assume that about humans. The possibility that we are looking at the product of instinct has never been considered. As four scientists argue for a different explanation: “When non-human animals exhibit complex behaviour, the default is that they are under genetic control. For complex behavior in humans and other hominins, the default is culture, not genes.”
Anthropologist Rob Foley was the first to suggest in the 1980s that Acheulean axes may be partly a product of genetically inherited customs rather than pure cultural learning. It has been largely ignored. Two evolutionary anthropologists, Pete Richerson and Rob Boyd, took up the idea in 2005, describing it as “puzzling” in that it showed so little diversity in cultural traditions. Then four anthropologists from Canada and the Netherlands, led by Raymond Corby of Leiden University, revisited the debate in 2016, adding several new strands of argument.
They note that scientists struggle to explain the sudden arrival of rapidly changing and cumulative stone technology in the Upper Paleolithic after about 300,000 years ago, usually reaching for “cognitive upgrade or increased population size” as a motivation, neither of which is convincing. Instead, Corby says, if earlier technology was largely instinctive, the arrival of cumulative cultural innovation is more easily explained: it was a shift from expressing the instinct to learn something to a pattern that was more dominated by social learning. Corby points out that evolution is fond of endowing even highly intelligent animals, such as bowerbirds, with genetically determined behaviors, if only because it represents a shortcut for the individual to correct that behavior. When I contacted Corby to explore this further, he reminded me that “the relevant database is a fascinating challenge. It includes a few million known axes and billions of unfound axes, according to a conservative estimate.”
Naturally, most cultural anthropologists reacted with disdain to this genetic theory, speaking instead of “preferred cultural conservatism” and “psychological bias toward majority imitation that later became a social norm,” which is little more than a restatement of the problem. Corby responded to his critics by referring to the “Baldwin effect”, an idea proposed by American psychologist James Mark Baldwin in 1896.
Baldwin said that animals that have adopted new habits or found themselves in new environments will find that any genetic mutations that help them adapt to those conditions will be favored. As these mutations spread, new habits become more inherited and instinctive. So what starts out as a completely learned behavior can end up as a partially inherited behavior.
This might superficially resemble the inheritance of acquired characteristics, but it would not be so. In Baldwin’s words: “It will appear as if acquired traits were sunk into the genetic material in a Lamarckian way, but the process will actually be neo-Darwinian.”
Jean-Baptiste Lamarck proposed the famous theory of evolution in which offspring inherit traits acquired during their (their parents’) lifetime: for example, a bodybuilder might have muscular children. But Baldwin’s influence is quite different. For example, by ramping up milk consumption, humans in a few parts of the world inadvertently put themselves in a good position to promote mutations that allowed lactose to be digested in adulthood, and people’s genomes certainly changed. Thus, culture can drive genetic change. I cannot stress enough how difficult it is for most sociologists and most evolutionary biologists to see this point.
Nature works through nurture, not against it.
In the case of hand axes, the importance of this insight is that if early hominins started chopping stone tools, any mutant hominids with a genetic tendency to be good at that skill from the start would flourish, leave more offspring, and so the skill itself would gradually become more heritable. As Corby says: “If apparently plastic individuals repeatedly arise, over hundreds if not thousands of generations, in a technological niche while manipulating stones, provided the cost-benefit ratio is right: wouldn’t long-term selection favor traits of the organism that are worthy of its technological capabilities, and which are crucial to survival?”
This goes against the trend of cultural anthropologists – and most of us – who believe that humans evolve away from instincts and towards culture (…). But evolutionary biologists who have investigated the mechanics agree that the Baldwin effect is a real phenomenon. So even if Homo erectusOur ancestors did not have a genetic inclination to enjoy making stone tools, and their descendants may have had it. Even if the first bowerbirds simply imitated successful competitors, their descendants found themselves with very specific instincts to (learn) the construction of very specific bowers. It is not fanciful to assume that Homo erectus He had an instinct for making hand axes more than the Satin Bowerbird had an innate instinct for making very complex bowers of a particular design.
At the very least, the hypothesis should be taken seriously. This does not mean that making axes does not require any learning; Bowerbirds still have to learn how to master bower building by watching others and practicing. But it directs learning towards an instinctive and adaptive end. I repeat: a lot of learning is like this: nurturing and enhancing nature, rather than conquering it.
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