a very kind reader points me to a fairly newly published book (pub. last month) titled Our Political Nature: The Evolutionary Origins of What Divides Us by avi tuschman (thank you, very kind reader! (^_^) )

the very kind reader thought i might be interested in the book since it’s got sections on inbreeding and outbreeding … and altruism. yes, indeed! that’s right up my alley!

i’ve only glanced through the book, but this caught my eye … sounds vaguely familiar [from chapter 10]:

“Inbreeding Increases Altruism

“There’s another potential positive-feedback mechanism that promotes inbreeding in animal populations: inbreeding can increase altruism. Altruism is the force that causes an individual to reduce his or her own fitness while increasing the fitness of another. But what’s the connection to mate choice?

“Inbreeding raises the genetic relatedness of the members of the group. Since inbreeders share a higher percentage of their genes with one another, they act less selfishly toward one another. By helping closely related individuals, inbreeders are helping to propagate copies of their own genes. Chapter 19 explains in greater detail this particular phenomenon, which is called ‘kin selection.’

“If specific alleles associated with altruism exist in (or mutate into) a population, then inbreeding can increase the frequency of these ‘altruistic’ alleles until they are ‘fixed’ in the population; that is, they can become permanent, contingent on continued inbreeding.

“In a random mating system, in contrast, altruism is likely to be lower because individuals share fewer genes in common with each other. In an outbred population, two nonrelatives may reproduce. Half of their offspring’s DNA would come from the mother, and half from the unrelated father. Among inbreeders, however, parents already share a proportion of their DNA with one another. Therefore, the inbred offspring have *more* than half of each parent’s genes. The longer a population’s history of continuous inbreeding, the higher the genetic overlap becomes. Having a child that shares more than 50 percent of one’s DNA is an easy way for a parent to increase the propagation of its genes, and therefore to gain greater fitness — without even expending any additional reproductive effort.

“Although sustained inbreeding in a human population can increase altruism among the in-group, it can also *decrease* altruism toward out-groups. This hostility may particularly occur when colonies of inbreeders live side by side but do not outbreed. Separation by a reproductive boundary would entail a sharp drop in genetic relatedness between the two groups. So altruism would be high within the groups but very low between them.”


like i said, i’ve only glanced through the book, but i couldn’t see anywhere where mr. tuschman connects inbreeding or outbreeding with family types. or that long-term mating patterns and their downstream effects on social structures (like on family types) likely influence selection within populations.

still, looks like a very interesting book! i shall definitely be having a read of it. (^_^)

edit: from chapter 19:

“Yet regardless of political orientation, close family members tend both to behave more altruistically toward each other than toward distant kin and to treat distant kin better than non-kin. When we translate Hamilton’s Rule from biology into the language of politics, kin-selection altruism toward close kin becomes ‘nepotism’ and the preferential treatment of distant kin becomes ‘tribalism.'”


see also: OurPoliticalNature.com

previously: practically everything on the blog and mating patterns, family types, social structures, and selection pressures

(note: comments do not require an email. citizens against altruism!)