Kin recognition in humans

Following Tuesday's discussion on kin recognition in animals, here is an excerpt from J. Philippe Rusthon's article, "Genetic similarity, human altruism, and group selection," (pp. 505-506) on kin recognition in humans:

Human behavior also seems to follow lines of genetic similarity with respect to kin preference. For example, among the Ye'Kwana Indians of South America, the words "brother" and "sister" cover four different categories ranging from individuals who share 50% of their genes (identical by descent) to individuals who share only 12.5% of their genes. Hames (1979) has shown that the amount of time the Ye'Kwana spend interacting with their biological relatives increases with their degree of relatedness, even though their kinship terminology does not reflect this correspondence. Anthropological data also show that in societies where certainty of paternity is relatively low, males direct material resources to their sisters' offspring (to whom their relatedness is certain) rather than to their wives' offspring (Kurland 1979). [See also Hartung: "Matrilineal Inheritance" BBS 8 (4) 1985.] An analysis of the contents of 1,000 probated wills revealed that after husbands and wives, kin received about 55% of the total amount bequeathed whereas nonkin received only about 7%; offspring received more than nephews and nieces (Smith et al. 1987).

When the level of genetic similarity within a family is low, the consequences can be serious. Children who are unrelated to a parent are at risk; a disproportionate number of battered babies are stepchildren (Lightcap et al. 1982). Also, unrelated people living together are more likely to kill each other than are related people living together (Daly & Wilson 1988) [see also here]. Converging evidence shows that adoptions are more likely to be successful when the parents perceive the child as similar to themselves (Jaffee & Fanshel 1970) [see also here].

See also: "Kin Recognition", "Olfaction and human kin recognition", and the Face Research Lab at the University of Aberdeen.

Kin recognition in animals

Following yesterday's discussion on the topic of kin selection, here is an excerpt from J. Philippe Rushton's article, "Ethnic nationalism, evolutionary psychology and Genetic Similarity Theory" (pp. 493-494):

In order to favour near kin over distant kin and distant kin over nonrelatives, the organism must be able to detect degrees of genetic similarity in others. Hamilton (1964 and 1971) proposed several mechanisms by which detection could occur: (1) location or proximity to self as in the rule ‘if it’s in the nest, it’s yours’; (2) familiarity, which is learning through social interaction; (3) similarity-to-self through imprinting on self, parents or nest mates as in the rule ‘look for physical features that are similar to self’ – dubbed the ‘armpit effect’ by Dawkins (1976); and (4) ‘recognition alleles’ or innate feature detectors that allow detection of genetic similarity in strangers in the absence of any mechanism of learning – dubbed the ‘green beard effect’ by Dawkins (1976). In this latter, a gene produced two effects: (a) creating a unique trait such as a green beard, and (b) preferring others who also have that trait. Hamilton and Dawkins both favoured an imprinting mechanism, which Hamilton (1971) suggested would be most effective if it occurred on the more heritable traits because these best indicate the underlying genotype.

There is dramatic evidence that many animal species do detect and then act on genetic similarity (Fletcher and Michener 1987; Hauber and Sherman 2001). In a classic study of bees, Greenberg (1979) bred for fourteen degrees of closeness to a guard bee, which blocks the nest to intruders. Only the more genetically similar intruders got through. A classic study of frog tadpoles separated before hatching and reared in isolation found the tadpoles moved to the end of the tank where their siblings had been placed, even though they had never encountered them previously, rather than to the end of the tank with non-siblings (Blaustein and O’Hara 1981). Squirrels produce litters that contain both full-siblings and half-siblings. Even though they have the same mother, share the same womb, and inhabit the same nest, full–siblings fight less often than do half-siblings. Full-siblings also come to each other’s aid more often (Hauber and Sherman 2001).

Similarity detection is also required for assortative mating, which occurs in insects, birds, mammals and even plants. Optimal outbreeding in some plants is promoted by acceptance of pollen from source plants that are neither too similar nor too dissimilar molecularly from the host plant’s own pollen (see Hauber and Sherman 2001, for review). Even in species that disperse, the offspring typically show strong aversion to mating with close relatives. One study of wild baboons showed that paternal kin recognition occurs as frequently as maternal kin recognition even though identifying paternal kin is much more difficult in species where the mother mates with more than one male (Alberts 1999).

See more on kin recognition here and here.

Kin selection, inclusive fitness and altruism

- "A chicken is just an egg's way of making another egg."

- "[L]egend has it that in a pub one evening Haldane told his friends that he would jump into a river and risk his life to save two brothers, but not one, and that he would jump in to save eight cousins, but not seven."

All organisms are "survival machines" for genes -- and the primary "function" of these survival machines is to facilitate the successful propagation of copies of the genes into future generations.

From any particular gene's point of view, it does not matter if copies of it are made by its own "survival machine" (i.e. by the individual in which it resides) or by another survival machine -- or even machines -- that shares copies of that gene (typically a relative or relatives of the individual in question):

[I]n 1964 W. D. Hamilton showed that because close relatives of an organism are likely to share more genes in common (not to be confused with "common genes," the opposite of scarce genes), the gene can also increase its evolutionary success by promoting the reproduction and survival of these related individuals. This leads individuals to behave in a manner maximizing their inclusive fitness, rather than their individual fitness. [link]

Thus, in an (not necessarily conscious) effort to aid in the propagation of their own genes, individuals show altruism and favoritism toward relations with whom they share some portion of their genes.

From Steve Sailer:

One of the basic laws of modern evolutionary science, quantified by the great Oxford biologist William D. Hamilton in 1964 under the name "kin selection," is that the more close the genetic relationship between two people, the more likely they are to feel loyalty and altruism toward each other. Natural selection has molded us not just to try to propagate our own genes, but to help our relatives, who possess copies of some of our specific genes, to propagate their own.

See also: W.D. Hamilton works