Most of the Flynn effect seems to occur on the lower end of the IQ spectrum moving upwards. Source. This is highly consistent with education, nutrition and diseases hypotheses, but it is difficult to see how to reconcile this with a sexual selection hypothesis.
It reconciles quite well, actually.
The greater the genetically-determined status differential between a woman’s husband and her a potential lover, the more differential advantage to the woman’s offspring in replacing the husband’s genes with those of a higher-quality male. So the lower the status of the husband, the greater the incentive to replace his genes with another’s.
Assuming for a moment IQ is 100% heritable and IQ is linear in advantage, the woman with an IQ of 85 and a husband of IQ 85 will see her kids have an IQ of 85 if she’s faithful, and 115 with a lover of 145, for a net advantage to her kids of +30 IQ if she strays. If a woman and her husband are IQ 100, the same lover will raise the IQ +22.5; her kids get less advantage than Mrs. 85. In the case of Mr & Mrs. IQ 115, the advantage is only +15. For Mr & Mrs. IQ 130, the advantage to cheating is only +7.5. For Mr. & Mrs. IQ 145, cheating with a lover of IQ 145 doesn’t benefit her kids at all, while for Mr & Mrs. IQ 160, she wants to avoid having kids by a lover of IQ 145.
So, it is precisely the women on the low end that have the greater incentive to cheat “up”, which we would expect would result in more cheating, and thus the low end where IQs would increase the most.
Also, the lower status the woman’s husband, the easier it is to find a willing lover of higher status, and thus the greater the opportunity to replace the husband’s genes with another’s. Mrs. 85 can find a lover with IQ 100 more easily than Mrs. 100 can find a lover with IQ 115, even though the both have the same incentive to find a lover of +15 IQ points. Mrs. 115 has even more difficulty finding a lover of IQ 130, and so on.
So, it is precisely the women on the low end that have the greater opportunities to cheat “up”, which we would expect would result in more cheating, and thus the low end where IQs would increase the most.
One commonly expected form of common infidelity would be generally with strong males while trying to get a resource rich males to think the children are there’s
Assuming monogamous and assortative marriage, there’s a serious limit to how high resource/high status a male a woman can marry relative to her own status. Assuming she’s already landed the best husband she can manage, it is then in her subsequent interest to acquire the best genes for her kids she can. Insofar as better genes result in higher status, this would translate to favoring high-status males as lovers to produce kids supported by the best-she-can-manage husband. If status correlates better with IQ rather than strength in human societies, well, we’d expect that to select for IQ.
The fraction of the population which engages in infidelity even in urban environments is not that high. Infidelity rates in both genders are around 5-15%, but only about 3% of offspring have parentage that reflects infidelity.
Ahah. My data on this was substantially out-of-date. That is a serious blow to the hypothesis.
(Hmm. Except that in modern welfare states, the government has replaced the husband as supporter on the low end of the socioeconomic ladder, so maybe the effect is now most strongly happening among the children unmarried women, which would cause a drop-off in children of infidelity corresponding to the rise of out-of-wedlock births? Meh.)
I’m not aware of any obvious way to test your hypothesis.
A test would be to look wether there is a correlation between cheating and IQ and whether this correlation is influenced by sex. Also, asymetrical incidence of STDs with respect to the sexes could also be an indicator.
It reconciles quite well, actually.
The greater the genetically-determined status differential between a woman’s husband and her a potential lover, the more differential advantage to the woman’s offspring in replacing the husband’s genes with those of a higher-quality male. So the lower the status of the husband, the greater the incentive to replace his genes with another’s.
Assuming for a moment IQ is 100% heritable and IQ is linear in advantage, the woman with an IQ of 85 and a husband of IQ 85 will see her kids have an IQ of 85 if she’s faithful, and 115 with a lover of 145, for a net advantage to her kids of +30 IQ if she strays. If a woman and her husband are IQ 100, the same lover will raise the IQ +22.5; her kids get less advantage than Mrs. 85. In the case of Mr & Mrs. IQ 115, the advantage is only +15. For Mr & Mrs. IQ 130, the advantage to cheating is only +7.5. For Mr. & Mrs. IQ 145, cheating with a lover of IQ 145 doesn’t benefit her kids at all, while for Mr & Mrs. IQ 160, she wants to avoid having kids by a lover of IQ 145.
So, it is precisely the women on the low end that have the greater incentive to cheat “up”, which we would expect would result in more cheating, and thus the low end where IQs would increase the most.
Also, the lower status the woman’s husband, the easier it is to find a willing lover of higher status, and thus the greater the opportunity to replace the husband’s genes with another’s. Mrs. 85 can find a lover with IQ 100 more easily than Mrs. 100 can find a lover with IQ 115, even though the both have the same incentive to find a lover of +15 IQ points. Mrs. 115 has even more difficulty finding a lover of IQ 130, and so on.
So, it is precisely the women on the low end that have the greater opportunities to cheat “up”, which we would expect would result in more cheating, and thus the low end where IQs would increase the most.
Assuming monogamous and assortative marriage, there’s a serious limit to how high resource/high status a male a woman can marry relative to her own status. Assuming she’s already landed the best husband she can manage, it is then in her subsequent interest to acquire the best genes for her kids she can. Insofar as better genes result in higher status, this would translate to favoring high-status males as lovers to produce kids supported by the best-she-can-manage husband. If status correlates better with IQ rather than strength in human societies, well, we’d expect that to select for IQ.
Ahah. My data on this was substantially out-of-date. That is a serious blow to the hypothesis.
(Hmm. Except that in modern welfare states, the government has replaced the husband as supporter on the low end of the socioeconomic ladder, so maybe the effect is now most strongly happening among the children unmarried women, which would cause a drop-off in children of infidelity corresponding to the rise of out-of-wedlock births? Meh.)
Yeah, me neither.
A test would be to look wether there is a correlation between cheating and IQ and whether this correlation is influenced by sex. Also, asymetrical incidence of STDs with respect to the sexes could also be an indicator.