David Queller recently proposed the hypothesis that xenophobia evolved due to "isolation mismatch" - David's proposed name for the idea of cross-species incompatibility and infertility.
Having "mule" offspring is sometimes harmful - worse than having no offspring at all. Queller proposes that analogous cultural mismatches can produce broadly similar harmful effects - as memes battle with incompatible companions and generally fail to work together. He gives examples and argues that mechanisms to avoid these bad outcomes could result in xenophobia - via genetic and/or cultural evolution.
David's ideas here are obviously important and worthwhile - but I'm rather skeptical about whether "isolation mismatch" is largely responsible for xenophobia. Humans cooperate in part due to reciprocity and cultural kin selection. In the absence of those effects they can behave pretty badly. If you are a caveman, you don't bash in the brains of a member of a neighboring tribe because you are concerned about cultural mismatch. You do it because they are a competitor and would likely do the same to you given half a chance. Xenophobia is pretty well explicable as a baseline state that arises when the mechanisms responsible for cooperation are absent. That's not to say that divergent selection as a result of cultural mismatches due to isolation is unimportant, but that it may be only a small part of the story of the origins of xenophobia.
Much the same argument applies to explanations for xenophobia that invoke the cost of producing genetic mules. Mules do exist and do have significant costs, but a lot of xenophobic behavior is not directly associated with the production of mules. That hypothesis would predict more female xenophobia - since females bear most of the cost of bearing mule offspring. In fact, xenophobia is more likely to be exhibited by males (see reference below). Rivalry and competition for mates seem like more appropriate explanations for that than the costs of producing mules.
Finally, I'm completely onboard with David when he writes:
Indeed understanding the roots of xenophobia might provide ways to mitigate it.
This is one of the ways in which cultural kin selection is of great social and political importance. Aside from it being of scientific interest, there's also the issue of it providing scope for improving the scope of human cooperation by engineering and promoting shared memes.
Here Rob argues that the idea cooperation between humans which is not due to kinship must be due to reciprocity is wrong. That's correct. There are also manipulation and virtue signalling to consider - to mention just two other mechanisms.
Hi. I'm Tim Tyler and this is a video about manipulation. More specifically it's about the role of manipulation in producing cooperative behaviour.
Manipulation involves a biological entity skilfully influencing another biological entity - for its own ends.
Manipulation can be deceptive or honest. A manipulator may be forceful or subtle. They can target their victim's body, their perceptions or their environment. Manipulators may use rewards or punishments to help to elicit the behaviour they desire. Or they might use weapons, drugs or misdirection.
Manipulation one of the types of biological interaction which is capable of producing cooperative behaviour. A classic example of manipulation producing cooperation involves cuckoo foster parents. Through their own feeding behaviour, the hosts take a reproductive hit on behalf of a non relative with no hope of it being repaid. They do this because they are being manipulated. The cuckoo chick fools them into mistakenly believing that it is one of their own offspring.
Although, in this example, kin recognition is involved, manipulation is a different idea from kin selection. It need not involve relatedness. The example of a cuckoo chick shows that it can take place between individuals of different species. The creatures involved need not have much in common. Manipulation is also a different idea from reciprocity: with manipulation, the victim need not benefit - and quite often they don't benefit.
The definition of manipulation I gave mentioned that it took place between "biological entities". That's a intended as a broad category that can include anything from individual genes to entire governmental departments.
Manipulation is common. Parents frequently manipulate their offspring - for example by punishing them. In turn, offspring manipulate their parents - for example by crying when they want attention. Sellers try and manipulate buyers into thinking their products have high value. Buyers try to manipulate sellers into thinking they are short of funds but might still go for the right deal. Manipulation is also a common mechanism which produces cooperative behaviour. It helps to keep workers in eusocial colonies in line. It helps avoid genes on chromosomes defecting against each other by bypassing meiosis. However, despite manipulation being widespread, it is much less well known as a source of cooperation than kin selection or reciprocity.
Manipulation is common in symbiotic relationships. Some parasites manipulate their hosts into contact with other hosts - since parasites require contact between hosts to facilitate their own reproduction. To give three examples: Toxoplasmosis makes rodents more likely to interact with cats; the rabies parasite promotes contact with other prospective hosts and malaria-carrying mosquitoes are more likely to bite humans.
Humans also manipulate other humans for their own benefit - and for the benefit of friends and relatives. Some biologists have called some sorts of manipulative behaviour among humans "Machiavellian" - after the writer Niccolò Machiavelli, who appeared to endorse political strategies involving cunning and duplicity.
Unfortunately, manipulation is poorly-understood as a mechanism capable of producing cooperation. Martin Nowak fails to mention manipulation on his list of mechanisms favouring cooperation in his book SuperCooperators. Karl Sigmund doesn't mention manipulation in The Calculus of Selfishness either. Gintis and Bowles don't treat the topic in A Cooperative Species. Manipulation was slow to be understood historically as a mechanism responsible for producing cooperative behaviour and still today remains an under-appreciated force.
In cultural evolution, memes induce pro-social behaviours in humans by manipulating them. It seems likely that they do this partly because human friendship promotes the contact between their hosts that they need to spread. Memes use promises, threats, sex, desire, misinformation - and numerous other tricks to manipulate humans into being nice to other humans. Memes may be engineered to do this (e.g. by prospective human recipients) - or they may evolve via natural selection to behave in this way.
Manipulation is implicated in the evolution of eusociality. A queen will often manipulate their offspring to make them better serve her. This manipulation typically results in colony-level cooperation. Manipulation also is the basis of the symbiont hypothesis of eusociality. Originally developed to explain cooperation between termites, the symbiont hypothesis holds that host eusociality arose, in part, because it facilitated the transfer of symbiotic microbes down the generations. Each symbiotic microbe must regularly find new hosts. They do this by finding their way into young termites - where they rapidly multiply and adapt - successfully repelling subsequent invaders. This requires contact between hosts, which the symbionts facilitate by manipulating their hosts.
Memes are well known for doing something similar. They colonise the minds of children, and once established there are hard to displace. From the perspective of memes, children's minds represent especially valuable real estate to control. An early beach head in a host can avoid direct combat with a fully-developed immune system; there are fewer existing inhabitants to compete with for resources; a young mind offers the most time for adaptation to the host's environment - and there's a lifetime's opportunities ahead to spread to others. Memes get into children's heads partly by manipulating the behaviour of adult instructors.
If cultural evolution's effects are sufficiently strong, phenotypic effects due to nuclear DNA might be swamped by the effects of cultural variation. Perhaps egalitarian memes might act to eliminate variation at the level of DNA. Or maybecultural tags and tribal identifiers evolve quickly and generate so much phenotypic variation that the effects of nuclear DNA are swamped. In either case, population bottlenecks at the level of DNA might not matter much.
On balance, it seems unlikely that cultural variation makes the effect of recent population bottleneck on the variation in human DNA irrelevant. A good rule of thumb is that around half the variation in a typical trait is down to DNA. Cultural variation is important, but not so important that DNA doesn't matter.
Matthew Zimmerman is someone who has a reasonable understanding of cultural evolution. Matt's publications include a paper on the topic of this video: Cooperation, Evolution of - Matthew Zimmerman, Richard McElreath, Peter J Richerson. I commented on the paper here.
Egalitarian memes have made great strides during the last few thousand years. Consider the rise of memes suppressing:
Nepotism;
Slavery;
Racism;
Sexism;
Ageism.
...and favouring:
Monogamy;
Democracy;
Gay marriage;
Taxation.
It should also be pointed out that other memes are simultaneously promoting inequality. Wealth inequality is still enormous - bigger than ever before in some areas. I think what's going on there is pretty obvious - progress is unevenly distributed and provides elites with the means to keep their wealth out of the hands of others.
The pro-egalitarian memes are a little more puzzling. It seems as though the memes of the down-trodden majority have been progressively getting the upper hand over time - at the expense of the memes of the elites. But why? The elites control a lot of broadcasting machinery. They can hire propaganda experts. They can build churches and educational institutions. Why are their memes doing so badly?
I don't have a complete answer. Part of the answer may be that progress happens to disproportionally favour networking and social technology - which helps the masses to organize. Part of the answer may be that humans have genetically-encoded egalitarian preferences, and cultural progress has resulted in memes pandering to these preferences - much as cultural progress has resulted in greater satisfaction of our preferences for ice cream and chocolate gateau.
Memetics suggests asking the question: "what's in it for the memes?" Especially in such cases such as this - where the reproductive interest of genes of human hosts are being systematically suppressed.
In this case, it looks as though the pro-egalitarian memes are mostly just being used by one group of humans to manipulate other humans for their own benefit. In other words, this looks like one of those cases where the meme's eye view doesn't buy us too much.
David Queller recently proposed the hypothesis that xenophobia evolved due to "isolation mismatch" - David's proposed name for the idea of cross-species incompatibility and infertility.
One issue for 
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