The demographic transition as parasitic castration

Or how the memes spayed us for their own benefit.

The demographic transition is a change in the life history of homo sapiens, where we transitioned from a high-death high-birth regime, to a low-death low-birth one. Here I will explain the change in birth rates, but not the change in death rates.

Orthogonal transmission and virulence

The memes have taken over the genes as "parasites" of the human host. Over time, thanks to greater population density, there was more sociocultural interaction outside of groups of shared genetic lineages.¹ The genetic "parasite" requires "vertical transmission", i.e. ordinary biological human reproduction down a genetic lineage. And for the longest time, the memes were constrained by the same transmission regime, in the form of culture being passed on down a lineage. But with a greater population, memes switched from propagating in parallel to the genes, by vertical transmission, to propagating orthogonally, by horizontal transmission.

Horizontal transmission of parasites results in greater virulence, where the greater part of the host's lifecycle is cannibalised, and resources diverted to memetic, instead of genetic propagation.

Parasitic castratation

In some cases, even the reproductive part of the host's lifecycle is cannibalised. We call this parasitic castration. It may involve liquidating the gonads, or even behavioural modification. Often this leads to host gigantism, where we have a physically larger, but sterile host. This is because the usual lifecycle of the host, which involved reproduction, is now modified to just the indefinite maintenance of the host’s adult body, naturally benefitting the parasite by provisioning it with greater metabolic resources.

In nature, the parasitic barnacle Sacculina carcini castrates its mud crab host so that it has more of the host resources for itself. Because Sacculina itself does not require its host's gonads in order to reproduce. In fact, in rather theatrical fashion the parasite reprograms its host to carry out its own genetic interests instead:

Despite being castrated, the crab doesn’t lose its urge to nurture. It simply directs its affection toward the parasite. A healthy female crab carries her fertilised eggs in a brood pouch on her underside, and as her eggs mature she carefully grooms the pouch, scraping away algae and fungi. When the crab larvae hatch and need to escape, their mother finds a high rock on which to stand, and she bobs up and down to release them from the pouch into the ocean current, waving her claws to stir up more flow. The knob that Sacculina forms on a crab sits exactly where the brood pouch would be, and the crab treats the parasite knob as if it were its own pouch. She strokes it clean as the larvae grow, and when they are ready to emerge, she forces them out in pulses, shooting out heavy clouds of parasites. As they come spraying from her body she waves her claws to help them on their way.²

The human body, and by extension the human brain, is but a vehicle for the propagation of replicators. For most of human history, this has been a vehicle for the reproduction of genes. But with a bigger brain and social behaviour, we have a new replicator upon the scene. The memes, parasitically hijacking the vehicle of the human host, parasitically castrating it to spend less time raising children and more time as participants of culture.

Arms race

Why would the genes just stand back and allow this? Surely the genes would defend their own interests in the host phenotype and engineer counter-adaptations to neutralise the castrating effects of the memes?

We can conceive of genes and memes being part of an arms race to exert control over a shared phenotype of the human host. The question then becomes: what in general would tend to cause one side to persistently lose in such an arms race? Why do genes allow for memetic parasitic castration?

In The Extended Phenotype, Dawkins considers just this question where he invokes the Life-Dinner Principle. It states that predators run for their food, but prey run for their lives. In the arms race between predator and prey, the predator wants to hunt better, and the prey wants to escape better. It is crucial for the prey to succeed, and less so for the predator. A prey which gets eaten is a genetic dead end. A predator which fails to catch its prey has other opportunities for getting fed. As Dawkins writes about the cuckoo:

The cuckoo is descended from a line of ancestors, every single one of whom has successfully fooled a host. The host is descended from a line of ancestors, many of whom may never have encountered a cuckoo in their lives, or may have reproduced successfully after being parasitised by a cuckoo.³

A meme is an obligate parasite, it does not have a vehicle of its own construction (otherwise known as an organism) to produce copies of itself. To complete its lifecycle, it must jump to another human host's brain (or some widely consumed recorded medium) in order to replicate. The onus is thus greater on the parasite memes in their arms race with the genes to manipulate human reproductive behaviour in ways conducive to their own means of propagation.

Selection

Memetic success, like its genetic counterpart requires relative differential reproduction: i.e. host-castrating memes should spread better than non-host-castrating memes. However, we actually don't have to track the frequencies of memes with no effect on human reproductive investment. For our purposes, we are actually only interested in the phenotype of having more or less children. Even though the memes (or alleles) for or against having children might not be relatively abundant relative to memes having nothing to do with children, it is the relative frequencies between them which drives the demographic transition.

So consider just those memes which successfully induce their hosts to a pronatalist⁴ behaviour of having more children. This implies their hosts are more busy raising children than actually spreading the memes for having more children. As a result such memes would be far less successful than the antinatalist memes for having less children. Do not underestimate the time and effort it takes to effectively spread a meme. It is an empirical fact⁵ that humans preferentially imitate the more prestigious individuals, and it takes a lot of investment, e.g. in education or career advancement, to develop a certain amount of prestige. Which only serves to increase the payoff in memetic propagation of time spent not raising children, provided it is fruitfully spent on cultivating the prestige required to more effectively spread antinatalist ideas.

Note that even though in other cases hypocrisy might be involved, i.e. a distinction between belief and action, the successfully castrating meme actually has to affect the host's reproductive behaviour: if they don't spend less time raising children, they cannot spend more time spreading antinatalism, which means no greater relative propagation of our castrating meme. Arguably, hypocrisy would also compromise the contagion of the meme, as the background human aversion against hypocrisy would penalise ideas for which their hosts do not practice what they preach.

But we also wouldn't want to be invoking group selection: why would one meme "altruistically" take on the responsibility of castrating the host? Why not let some other meme do it, and reap the benefits of greater cultural participation for free? However, again it is not quite true that all memes would stand to gain if the human host decides to spend less time on having and raising children, and more time on cultural participation. When we restrict our interests to the phenotype⁶ of having more or less children, then the antinatalist memes/alleles do spread better than the pronatalist ones. No matter the frequencies of other memes indifferent to reproductive investment, when it comes to the phenotype of having fewer or more children, the antinatalist memes/alleles will out-propagate the pronatalist memes/alleles, thus parasitically castrating the human host.

Once again the problem of individual benefit versus group benefit arises, and in an acute form. A protozoan is so small in comparison with a beetle larva that a single protozoan, on its own, could not muster a sufficient dose of hormone to affect the beetle. Hormone manufacture must be a group effort by large numbers of individual protozoa. It benefits all individual parasites in the beetle, but it must also cost each individual something to add his tiny contribution to the group chemical effort. If the individual protozoa were genetically heterogeneous, consider what would happen. Assume a majority of protozoa cooperating in synthesising hormone. An individual with a rare gene that made him opt out of the group effort would save himself the cost of synthesis. Such a saving would be of immediate benefit to him, and to the selfish gene that made him opt out. The loss of his contribution to the group synthesis would hurt his rivals just as much as it hurt him. In any case the loss to the group’s productivity would be very small, though it would represent a major saving to him. Therefore, except under special conditions, taking part in a cooperative group synthesis together with genetic rivals is not an evolutionarily stable strategy. We must therefore predict that all the Nosema in a given beetle will be found to be close relatives, probably an identical clone.⁷

Also the assumption is that an atomic meme is sufficient, and a composite memeplex unnecessary, to reprogram the host to have less children. Hence there can be no free-riding invasion of the evolutionary stable strategy, because as soon as an allele of the atomic meme stops castrating the host it immediately loses the benefit of greater propagation.

Memeplex

Having established that humans will have less children, what of the other memes which do not pertain directly on whether or not to have children? They would certainly want to "free-ride" on those hosts which forgo biological reproduction in favour of cultural participation. But again, all is not equal. The more successful free-riders must be compatible with the antinatalist memes and incompatible with pronatalist memes, i.e. to participate in an antinatalist "memeplex". This could be memes for the value of education and career advancement, atheism, women's rights, etc.⁸ And so we have the other concomitants of the demographic transition.

1. Endogenous Growth and Demographic Transition in a model of Cultural Transmission, Zakharenko, Roman

Found via Tim Tyler at https://on-memetics.blogspot.com/2011/12/memes-and-demographic-transition.html

2. Zimmer, Carl. Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures (pp. 81-82). Atria Books. Kindle Edition.

3. Dawkins, Richard. The Extended Phenotype (Oxford Landmark Science) (p. 107). OUP Oxford. Kindle Edition.

4. I use "pronatalist" and "antinatalist" here loosely to refer to a general preference for having children and am not referring to the philosophical positions.

5. Richerson, Peter J. and Boyd, Robert (2005) Not by Genes Alone: How Culture Transformed Human Evolution. University of Chicago Press: Chicago, IL.

6. Here I think Dawkins in The Extended Phenotype focuses too much on regions of reality/spacetime in defining a lineage's extended phenotype, and less so on whatever aspects/properties of reality which produces their differential propagation. Though to be fair, he does emphasise the point on correlated variation.

7. Dawkins, Richard. The Extended Phenotype (Oxford Landmark Science) (pp. 328-329). OUP Oxford. Kindle Edition.

8. Note that this doesn't have to be group selection. It is simple frequency-dependent selection, where some memes do better when other memes in the "environment" are already present, and vice versa, in a mutually reinforcing manner.