An evolutionary eye on - the Capitol riots

Why do people go all-in for the in group?

Ghost in the machine by Dr. David Baird is the newsletter of, which provides daily updates on the latest research across the human nature sciences.

This issue brings you:

  1. An evolutionary eye on - the Capitol riots. Why do people go all-in for the group?

  2. This week in human nature research

    • Why fecundity is a mystery to us

    • Concerned conservatives and alarmed liberals

    • Moral inheritance

    • Homo saltator - the dancing human

    • Small prey gave us big brains

  3. Latest articles on Human Nature News

    • Birth pangs of a new religion? QAnon and its historical parallels

    • Public honesty inspections promote dishonesty

    • When balancing altruism and selfishness, it's me first

    • How demagogues persuade people to vote against their own beliefs

    • Conspiracy theories affect your behaviour, whether or not you believe them

    • Ancient mercantile links between Exeter and Europe

    • Adaptation to malaria in hunter-gatherers 7000 years ago

An evolutionary eye on - the Capitol riots

Until the thing turned tragic, what struck me most was the popcorn angle. Seditionary riot as TV entertainment. And the entertainment value, I have to admit, was the fascination of watching people wrecking their own lives, live on TV.

Nobody, by that time, was seriously concerned that law and order, democracy, and the American Way of Life ™ was under any threat at all from these jokers. Watching the live footage, it sometimes seemed there were more journalists and cameras than seditionists. It was certainly clear that this was a lunatic fringe, not a mass movement. It must have been clear even to the lunatic fringists themselves.

So the question is, why did they take part at all? Under the glare of TV lights, live-streaming their illegalities on their own phones, the thing was an evidentiary goldmine. Anyone involved had to know they'd be taken down.

What these people were doing was self-sacrificial. They were in a kind of ecstasy, giving up their personal self-interest for the good of the group.

Why is the group so important?

When I was a grad student in the 1990s, E.O. Wilson's "Sociobiology" (1975) was a foundational text in evolution departments. But in the rest of the academy, his relatively brief discussion of human social behaviour was still very contentious. Even within evolutionary biology, the argument hadn't quite died down. It was all very well describing how evolution shaped animal societies. But humans are different. Somehow.

The field of evolutionary psychology, essentially sociobiology applied to humans, was still in its infancy in the 90s, and still being disparaged as a refuge for lazy-thinking, armchair bigots.

And group selection? That was taboo. Group selection was to evolutionary biology as aether was to physics - an embarrassing mistake we'd rather just not talk about.

I found the polemic all rather bewildering. Wasn't this the place where people debate pure ideas, purely on their merit? Well, no. It was a place where humans have arguments, just like everywhere else. Appeals to authority, ad hominem attacks, character assassination, straw men, the whole gamut of rhetorical tricks were put into service beneath a thin veneer of academic civility that fooled no-one.

Anyway, Wilson won out, because his fundamental idea was simply this - humans are biological. And in the famous words of Theodosius Dobzhansky in 1973:

Nothing in Biology Makes Sense Except in the Light of Evolution


In the social context, that means our societies can only make sense in the light of evolution. Our politics can only make sense in the light of evolution. Our morality can only make sense in the light of evolution.

And our riots.

This, if you like, more radical formulation of the basic premise, remains contentious in parts of academia today, although not nearly as contentious as it would have been not so long ago. Evolutionary approaches are still a minority pursuit across the humanities and social sciences, but they do exist in most fields, and they seem to be gaining currency.

For me, these ideas are foundational. If they reveal things that I would rather were not so, then so be it. The world is like that. There is nothing deterministic in these ideas. If they expose uncomfortable truths, then we are free to take action to change the world for the better.

So this is the lens through which I view the Capitol riots. Setting aside the (straightforward) rights and wrongs of the thing, it offers a clear case study of the power of the group. What we saw were people behaving like worker ants.

(Totally coincidentally, ants just happen to be E.O. Wilson's favourite study animal).

Social insects appear almost monstrous to us because of the recklessness with which the individual's life is spent for the benefit of the group. But it turns out, humans are not so different from ants. Once you start looking for it, you see examples of reckless self-sacrifice all around us. In the Capitol riots, we saw people not simply risking, but almost guaranteeing, criminal records, judicial penalties, lost jobs and future employment opportunities, all for the brief thrill of committing fully to the group.

Group selection has made a comeback in recent years. The idea is straightforward, and in this age where we talk about multiple levels of selection, from gene, to cell, to organism, with various subsystems potentially involved as well, it's much less contentious to just keep on going up the organisational chart.

It helps that straightforward experimental demonstrations are available. For instance, if you rear chickens in cages and select the biggest individual from each cage to breed the next generation, you end up with super-aggressive murderer chickens. But if instead you select the cage with the largest total body weight of chickens and breed from all of the individuals in the selected cage, you end up with chilled, egalitarian chicken peaceniks [1].

The idea is not that group selection has led to peaceful humans. Far from it. But the group is our super-power. We are nothing without the group to support us. No human is an island. We would, almost all of us, simply die if we were abandoned, and not just because we lack the skills to survive. We owe our lives to the group, and we are very often willing to pay the price.

At its most extreme, we will send our children to war when the group asks us to. Our whole genetic investment in the future. Now, that sentence may not quite capture the emotional experience you have when you think about your children, but as far as evolution is concerned, that's what they are. And yet, we will send them. In all societies, throughout the ages. It's a human universal. Evolution has favoured those human groups that consisted of individuals willing to sacrifice everything for the group.

That history leaves us with a legacy of fanatical commitment to the group. Whatever group we form an attachment to, we will die on that hill.

So the next time you're considering attacking the Capitol, ask yourself what's really going on. Maybe this is all about a fight to the death between pre-human hunter-gatherer tribes a couple of million years ago. Maybe you’d be better off sitting at home watching TV.

[1]. W.M. Muir (1996), Group Selection for Adaptation to Multiple-Hen Cages: Selection Program and Direct Responses. Poultry Science, 75(4):447-458,

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This week in human nature research

This week we have new research from:

  • Human Nature (volume 31, issue 4, December 2020)

  • Evolution and Human Behavior (in press)

  • Quaternary (volume 4, issue 1, March 2021)

  • Yearbook of Physical Anthropology (in press)

Why fecundity is a mystery to us

The human reproductive system has evolved some unusual characteristics. One of these is concealed fecundity.

Concealed fecundity has three main characteristics. First, women are generally unable to consciously recognize their own fertile period. This is different from most mammals, including primates, where females are only sexually receptive during their fertile period. Second, the timing of ovulation is highly variable. That is, it’s unpredictable. And third, there is good evidence that women unconsciously transmit cues about their fecundity. For instance, men find women more attractive during their fertile period.

Why would such a constellation of features evolve? One hypothesis is that as females evolved the capacity for analysis and decision-making, they became capable of altering their own fertility according to their own self-interest. The investment that human and pre-human females must make in their offspring is so extreme that there is plenty of motivation for individuals to delay reproduction until the time is right.

This intellectual capacity set up a conflict between the self-interest of the individual and the selfishness of genes. In this paper, Philip H. Crowley develops a model that explains the evolution of self-deception in the human female reproductive cycle as an outcome of this evolutionary conflict.

Crowley, P.H. Self-Deception about Fecundity in Women. Hum Nat 31, 421-442 (2020).

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Concerned conservatives and alarmed liberals

What scares us depends on evolution, culture, development and experience. It also depends on politics. The general finding in the literature is that conservatives are more fearful. But in this paper, Peter K. Hatemi & Rose McDermott argue that conclusion is due to bias in the fears that investigators have chosen to test.

Instead, Hatemi & McDermott show that non-political fears correlate with political ideology across the spectrum. Libs and cons are all fearful, just of different things.

Their data on non-political fears show that those who are more socially conservative are more fearful of sharp objects, graveyards, and urinating in public. Those who are concerned about pollution and immigration are more fearful of suffocation and swimming alone. Those who are against immigration are more fearful of thunderstorms.

What does it all mean? Well, that's a question for another day. But the fact that the differences vary systematically with ideology is certainly intriguing.

Hatemi, P.K., McDermott, R. Dispositional Fear and Political Attitudes. Hum Nat 31, 387-405 (2020).

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Moral inheritance

In this paper, Kevin Smith & Peter K. Hatemi presented their subjects with a set of moral dilemmas. They found strong evidence for the heritability of morality.

This is not unexpected. Current intuitionist theories of human morality assume a significant role for inheritance. (Intuitionist models describe how moral behaviours emerge from unconscious processes, rather than as the outcome of a rational, conscious analysis).

Indeed, one of the strongest general results in psychology is that about 50% of the variation in any behavioural trait is heritable.

However, the only previous test of the heritability of morality failed to demonstrate an inherited component. That was a big problem for the intuitionist theories.

So Smith and Hatemi's work rescues the intuitionist theories, at least for the moment. With only two papers in the field, each coming to opposite conclusions, clearly more work needs to be done.

But there is an intriguing hint of something more. The methodology Smith and Hatemi used is associated with Dual Process Theory, which holds that moral behaviours are the outcome of competition between a fast-thinking, unconscious/emotional process, and a slow-thinking, conscious rational process. Whereas the previous study, which failed to demonstrate heritability, used self-reporting questionnaires. That is a technique associated with Moral Foundations Theory, which holds that morality emerges from five or six thematic modules - care/harm, fairness/cheating etc. - each of which has evolved in response to specific selection pressures.

With a sample size of two, one testing each of the main competing theories, we clearly can't come to any conclusions about which theory is true. But it does point the way for future work.

Watch this space.

Smith, K., Hatemi, P.K. Are Moral Intuitions Heritable? Hum Nat 31, 406-420 (2020).

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Homo saltator - the dancing human

Dance is a human universal. In a vast diversity of culturally specific ways, we all do it.

It seems pretty clear that dance is about communication. Individuals dance to impress potential mates. Group dances give off a bunch of social signals, both within and between groups. For instance, the organisational capability on display during a group dance can signal the capacity for the group to act in concert in other circumstances - perhaps during conflict with other groups. If we can fight as well as we can dance, best not mess with us! And the whole process of organising, learning, and performing a group dance is a powerfully cohesive force for the group.

All of this has been widely documented in the ethnographical literature. What Fink and co-authors propose here is that dance evolved from simpler movements that originally had no informational content. As group sizes increased, and as groups interacted more frequently with other groups, there was a need to communicate social information accurately. The sophisticated content of dance movements provides the medium for that accurate communication.

So despite the great diversity in dance movements and contexts, wherever and however dancers jiggle and gyrate, they're probably sending much the same sorts of signals.

Bernhard Fink, Bettina Bläsing, Andrea Ravignani, Todd K. Shackelford. Evolution and functions of human dance. Evolution and Human Behavior 2021;

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Small prey gave us big brains

Human trophic level

The human trophic level (HTL) has received relatively little systematic attention from researchers, despite its implicit importance in many explanations of human evolution. Discussion of the HTL tends to proceed from the assumption that humans are a kind of super-flexible omnivore, able to adapt easily to widely varying ecological situations. Some hand-waving analogies are drawn with (20th century) hunter gatherer societies, and that's about it.

In [1], Ben-Dor and co-authors reconstruct the HTL during homininan (humans and our closest ancestors) evolution, drawing evidence from human physiology and genetics, archaeology, paleontology, and zoology.

Starting from a low trophic level (more plant material, less animal material) Homo habilis, the human line evolved towards increasing carnivory, peaking with Homo erectus in the Lower Palaeolithic. Homo erectus was most likely a hypercarnivore (obtaining more than 70% of its diet from animal sources), and specialized on megafauna.

The emergence of Homo sapiens was not immediately associated with a reduction in the trophic level. However, by the Late Upper Palaeolithic, a significant shift had taken place, with Homo sapiens adopting a much more generalist diet.

This history suggests that Homo sapiens retains a suite of specializations for carnivory, including behavioural, physiological, and anatomical adaptations. To name just a few of many examples, our longer small intestine and shorter large intestine, weak jaws, high body fat, metabolic adaptations to a high-fat diet, low sensitivity to insulin, early weaning, food-sharing, and acidic stomachs are all strongly associated with carnivory. Table 2 in [1] presents a fascinating summary of the evidence which you should definitely go look at. The paper is open access.

Declining prey size

So, we're carnivores. But we evolved during a time when our preferred prey, megafauna, were in decline.

The debate about megafauna decline during the Pleistocene centers around the question of whether humans were responsible. Much less attention has been paid to how humans responded to this ecological change. Megafauna were slower, easier to track, were present in much higher biomass density, were less energetically costly to hunt, and had a higher fat content (important to balance a diet high in proteins). Their disappearance would have had a significant impact on humans.

We had to get better and better at catching more and more of the remaining smaller and smaller prey. Clubs and pointy sticks were fine for bringing down lumbering giants. But we had to get a lot smarter if we wanted to catch enough of these little scurrying, hiding, running and jumping beasties to keep the wolf from the door.

So, we invented new physical technologies, such as projectile weapons and traps. We learned new skills, like speculative (predictive) tracking, and the manipulation of materials. We observed our environment more closely, to understand the ecology of diverse prey species on land, in the air, and under water.

The smartness we evolved to maintain our hypercarnivore diet in the face of disppearing megafauna enabled us later on to harness plant material with sufficient efficiency to shift away from our hypercarnivore diet. We invented grinding stones, gathering strategies, and eventually developed gardens and agriculture.

Hominin brain size steadily increased over 2 million years - most of the Pleistocene. That trend then reversed at the end of the Pleistocene. Both observations require explanation.

The prevailing idea is that first, we bootstrapped our brains, then at the end, we fine-tuned them. Our societies became more complex, requiring bigger brains, supporting more complex social relations, requiring bigger brains, reductio ad infinitum. Finally, when our brains were big enough, but very expensive, we fine-tuned them, getting rid of excess weight. But not, of course, reducing function. That would mean stone-age hunters were smarter than us, and that would never do.

And even if the social bootstrapping theory is correct, it still begs the question - what for? What was the advantage of more complex societies?

In the context of declining prey size, one advantage of bigger brains and complex societies was to support technological and intellectual developments associated with hunting smaller prey. Tracking, in particular, is a highly intellectual exercise, requiring the acquisition of skills, the development of hypotheses, and the transfer of knowledge both about the ecology and behaviour of target species, and the tactical process during the hunt itself. Other advantages included: the use of fire, to maximise the extraction of calories; the development of fine blades, to process small prey items; sharing behaviour, requiring inhibitory control, which bigger brains are better at.

The prey size hypothesis also fits the observed reduction in brain size at the end of the Pleistocene, when we started domesticating animals and raising plants. It doesn't require a huge amount of real-time intellectual processing to catch a domesticated animal or harvest a crop.

Neanderthal extinction may also be explained by the prey-size hypothesis. Neanderthal diets were largely composed of megafauna, which supply relatively more fat to supplement Neanderthal's energy intake. Neanderthal's large body size would have required a higher energy intake than Homo sapiens, especially during the cooler period when their numbers declined. Neanderthals therefore may have been particularly dependent on larger prey species, just when such species were in decline.

The shift to agriculture itself requires explanation. It wasn't inevitable. It happened at different times in different places. It wasn't a single event that then reverberated around the world. The prey-size hypothesis notes that as prey animals become smaller, the proportion of fat also reduces. Humans cannot obtain all of their calories from protein. They need to supplement their diet either with fat, or carbohydrate. There is some evidence that fat, not protein, was a limiting resource in pre-agricultural communities. It may be that the scarcity of fat helped drive human societies towards agriculture.

The prey size hypothesis offers a powerful new synthesis for human evolution. It generates testable predictions that don't suffer from the circular logic of the social bootstrapping hypothesis. We may be witnessing the birth of a new paradigm.

[1] Ben-Dor, M, Sirtoli, R, Barkai, R. The evolution of the human trophic level during the Pleistocene. Yearbook Phys Anthropol. 2021; 1- 30.

[2] Ben-Dor M, Barkai R. Prey Size Decline as a Unifying Ecological Selecting Agent in Pleistocene Human Evolution. Quaternary. 2021; 4(1):7.

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