The Ash Twins Blog

Kanazawa (2007) predicts from evolutionary psychology that attractive parents will have more daughters, and finds evidence supporting his prediction:

The generalized Trivers–Willard hypothesis . . . proposes that parents who possess any heritable trait which increases the male reproductive success at a greater rate than female reproductive success in a given environment will have a higher-than-expected offspring sex ratio, and parents who possess any heritable trait which increases the female reproductive success at a greater rate than male reproductive success in a given environment will have a lower-than-expected offspring sex ratio. One heritable trait which increases the reproductive success of daughters much more than that of sons is physical attractiveness. I therefore predict that physically attractive parents have a lower-than-expected offspring sex ratio (more daughters). Further, if beautiful parents have more daughters and physical attractiveness is heritable, then, over evolutionary history, women should gradually become more attractive than men. The analysis of the National Longitudinal Study of Adolescent Health (Add Health) confirm both of these hypotheses. Very attractive individuals are 26% less likely to have a son, and women are significantly more physically attractive than men in the representative American sample.

Update: Gelman (2006), a statistician, casts serious doubt on Kanazawa’s interpretation of the data:

Physical attractiveness in the survey used by this paper was measured on a five-point scale, from “very unattractive” to “very attractive”. The key result was that 44% of the children of surveyed parents in category 5 (“very attractive”) are boys, as compared to 52% of children born to parents from the other four attractiveness categories. With a sample size of about 3000, this difference is statistically significant (2.44 standard errors away from zero).

In interpreting this statement of statistical significance, however, we should consider the arbitrariness of picking out category 5 and comparing it to 1–4. Why not compare 4 and 5 (“attractive” or “very attractive”) to 1–3? Given the many comparisons that could be done, it is not such a surprise that one of them is statistically significant at the 5% level.

Perhaps the most natural analysis of these data would be a regression of the proportion of boys on the numerical attractiveness measure. Using the data in Fig. 1 of the paper, the estimated regression coefficient is −1.5 with a standard error of 1.4—thus, not statistically significant. (Weighting by the approximate number of parents in each category does not appreciably change this result).

I have little to say about the difficulties of measuring attractiveness except that, according to the paper, interviewers in the survey seem to have assessed the attractiveness of each participant three times over a period of several years. I would recommend using the average of these three judgments as a combined attractiveness measure. General advice is that if there is an effect, it should show up more clearly if the x-variable is measured more precisely. I do not see a good reason to use just one of the three measures.

One way to summarize the multiple comparisons criticism is to consider the number of possible analyses that could have been considered by Kanazawa in comparing different levels of attractiveness. In addition to the linear regression, there is the comparison of category 1 to categories 2–5, the comparison of 1–2 to 3–5, the comparison of 1–3 to 4–5, and the comparison of 1–4 to 5. Any of these, if statistically significant, could have been chosen to be reported. In addition, with three waves of data, the research could report the results from wave 1, wave 2, wave 3, or the average of all three waves. This comes to 5×4=20 possible comparisons. A simple Bonferroni correction multiplies the significance level (p-value) by the number of potential comparisons, so that to achieve statistical significance at the 5% level, one would need an individual comparison with p-value of 0.05/20=0.0025. In comparison, Kanazawa’s reported result is 2.44 standard errors away from zero, which corresponds to a p-value of 0.015 (that is, 1.5%), which would be statistically significant on its own but not as one of 20 possible comparisons. In short, the observed result in this study could easily occur by chance, given the large number of potential comparisons that could be made with these data. (In fact, this p-value is not even statistically significant as one of five comparisons, if we were to ignore the possibility of using data from either of the three waves). . .

[Kanazawa's paper] includes a mistake in interpreting a logistic regression coefficient. The difference reported in this study was 44% compared to 52%—the most attractive parents in the study had an 8% higher rate of girls. One could also say that the proportion of girls was 0.08/0.52=15% higher among the most attractive parents. But the paper reports that “very attractive respondents are about 26% less likely to have a son as the first child”. This appears to be based on an incorrect interpretation of a logistic regression of sex of child on an indicator for whether the parent was judged to be very attractive. The logistic regression coefficient was −0.31. Since the probabilities are near 0.5, the correct way to quickly interpret the coefficient is to divide it by 4: −0.31/4=−0.08, thus a difference of 8 percentage points (which is what we saw above). For some reason, Kanazawa exponentiated the coefficient: exp(−0.31)=0.74, then took 0.74−1=−0.26 to get a result of 26%, which cannot be interpreted in the way suggested in the paper. 26% can be interpreted in terms of the odds ratio (i.e., p/(1−p), where p is the probability), but the statement of “26% less likely” is an incorrect summary of the regression (setting aside the multiple comparisons problems discussed in point 2 of this letter). This is particularly unfortunate since 26% was the number reported in the press.

Pollet & Nettle (2009) present evidence that female orgasm is an adaptation that  motivates females to reproduce with high-status males:

There has been considerable speculation about the adaptive significance of the human female orgasm, with one hypothesis being that it promotes differential affiliation or conception with high-quality males. We investigated the relationship between women’s self-reported orgasm frequency and the characteristics of their partners in a large representative sample from the Chinese Health and Family Life Survey. We found that women report more frequent orgasms the higher their partner’s income is. This result cannot be explained by possible confounds such as women’s age, health, happiness, educational attainment, relationship duration, wealth difference between the partners, difference between the partners in educational attainment, and regional location. It appears consistent with the view that female orgasm has an evolved adaptive function.

From the Economist:

Peter Corning offers a bioeconomic analysis of mole-rat colonies:

One compelling example of a superorganism in nature involves the naked mole-rat (Heterocephalus glaber), a unique African rodent species that lives in large underground colonies (usually numbering 75-80 but sometimes over 200). Naked mole-rats represent a particularly significant illustration of an economic division of labor, because these odd-looking animals — affectionately dubbed “sabre-toothed sausages” — have morphologically-specialized castes and a pattern of breeding restrictions that is both unique among mammals and suggestive of eusocial insects. Typically (but not always), the breeding is done by a single “queen”, with other reproductively suppressed females waiting in the wings. The smallest of the non-breeders, both males and females, engage co-operatively in tunnel-digging, tunnel-cleaning and nest-making, as well as in carrying pups, foraging and the transportation of food (succulent tubers) within the colony’s often extensive tunnel systems. (One investigator, Robert A. Brett, found a tunnel system in Kenya that was more that 3 kilometers long, altogether, and occupied an area equivalent to 20 football fields.) Sherman et al., (1992:75), who have studied these animals extensively, provide the following description of the mole-rats’ co-operative tunnel-building efforts:

The animals line up head-to-tail behind an individual who is gnawing [with it's outsized, powerful front teeth] on the earth at the end of a developing tunnel. Once a pile of soil has accumulated behind the digger, the next mole-rat in line begins transporting it through the tunnel system, often by sweeping it backward with its hind feet. Colony mates stand on tiptoe and allow the earthmover to pass underneath them; then, in turn, they each take their place at the head of the line. When the earthmover finally arrives at a surface opening, it sweeps its load to a large colony mate that has stationed itself there. This “volcanoer” [so-called because its actions appear to an observer outside to resemble miniature volcano eruptions] ejects the dirt in a fine spray with powerful kicks of its hind feet, while the smaller worker rejoins the living conveyor belt.

The vital and dangerous role of defense in a mole-rat colony is also allocated to the largest colony members, who respond to intruders, such as predatory snakes, by trying to kill or bury them and by sealing off the tunnel system to protect the colony. The mole-rats’ “militia” will also mobilize for defense against intruders from other colonies.

Why do mole-rats utilize this highly co-operative survival strategy? Eusociality is relatively rare in nature, and the traditional view has been that a haplodiploid reproductive pattern provides a genetic facilitator. But this is obviously not the case with mole-rats, which are diploid. (Indeed, it seems that haplodiploidy is neither necessary nor sufficient; all species of Hymenoptera are haplodiploid, but most are not eusocial; on the other hand, all termites are eusocial and diploid.) Sherman et al., (1992) provide a bioeconomic (synergy) explanation for the mole-rat strategy: “We hypothesize that naked mole-rats live in groups because of several ecological factors. The harsh environment, patchy food distribution and the difficulty of burrowing when the soil is dry and hard, as well as intense predation, make dispersal and independent breeding almost impossible. By co-operating to build, maintain and defend a food-rich subterranean fortress, each mole-rat enhances its own survival” (p.78). (See also Sherman et al., 1991.) (Although it is not stressed in the mole-rat research literature, another critically important facilitator is a co-operative relationship — and synergy — between the mole-rats and an endosymbiotic bacterium which is able to break down the cellulose in succulent tubers.)

If the bioeconomics — the functional synergies — provide an important part of the explanation for the naked mole-rat survival strategy, the “political” aspects are equally important, and are also well-documented. As is the case with many other socially-organized species, naked mole-rats exhibit a combination of self-organized co-operation (pre-programmed individual “volunteerism”) and orchestrated social controls that are policed by various coercive means. The control role of the breeding queen is of central importance. The queen is usually the largest animal in the colony (size usually determines the dominance hierarchy), and she aggressively patrols, prods, shoves and vocally harangues the other animals to perform their appointed tasks. Indeed, it has been observed that her level of aggressiveness varies with the relative urgency of the tasks at hand. In addition, the queen acts to suppress breeding and reproduction on the part of non-queen females, who are always ready to take over that role. (Occasionally other females are allowed to share the breeding function with the queen; why this is so is not known.) The queen also intervenes frequently in the low-level competition that goes on among colony members over such things as nesting sites and the exploitation of food sources. And when the reigning queen dies, there is a sometimes bloody contest among the remaining females to determine her successor.

All of this control activity is facilitated by an elaborate communication system that includes 17 distinct categories of vocalizations — alarms, recruitment calls, defensive alerts, aggressive threats, breeding signals, etc. In fact, the mole-rats’ communication system rivals that of some primate species in its level of sophistication. Thus, a naked mole-rat colony may be characterized as a superorganism. . .

From Richard Dawkins’s The Selfish Gene:

Memes and genes may often reinforce each other, but they sometimes come into opposition. For example, the habit of celibacy is presumably not inherited genetically. A gene for celibacy is doomed to failure in the gene pool, except under very special circumstances such as we find in the social insects. But still, a meme for celibacy can be successful in the meme pool. For example, suppose the success of a meme depends critically on how much time people spend in actively transmitting it to other people. Any time spent in doing other things than attempting to transmit the meme may be regarded as time wasted from the meme’s point of view. The meme for celibacy is transmitted by priests to young boys who have not yet decided what they want to do with their lives. The medium of transmission is human influence of various kinds, the spoken and written word, personal example and so on. Suppose, for the sake of argument, it happened to be the case that marriage weakened the power of a priest to influence his flock, say because it occupied a {199} large proportion of his time and attention. This has, indeed, been advanced as an official reason for the enforcement of celibacy among priests. If this were the case, it would follow that the meme for celibacy could have greater survival value than the meme for marriage. Of course, exactly the opposite would be true for a gene for celibacy. If a priest is a survival machine for memes, celibacy is a useful attribute to build into him. Celibacy is just a minor partner in a large complex of mutually-assisting religious memes.

Salon’s Glenn Greenwald offers another useful critique of the Politico reporter Mike Allen’s abuse of anonymous sourcing. Those of you who have seen Season 5 of The Wire are familiar with another serious problem with off-the-record status that often goes ignored: The journalist could be just inventing the quotation out of whole cloth. While it shouldn’t be difficult to find a former Bush administration official to bash Obama, it is even easier to just invent a colorful Obama-bashing quotation and print it as an anonymous statement. It may also be presumed that Politico‘s journalists are familiar with the quotation characteristics that would be conducive to being linked at the Druge Report, and an invented statement can better comply with those characteristics. After the fact, of course, Allen can dodge any questions about the validity of the statement by relying on journalistic  principles of source anonymity.

From How Stuff Works, I give you “How Cannibalism Works“:

“Well-built men, 18-30, who would like to be eaten by me” was the typical advertisement Armin Meiwes took out on personals Web sites [source: Harper's]. After hundreds of false starts, he found a willing partner in 43-year-old Bernd-Jurgen Brandes. The two men met on March 9, 2001. It would be an odd night for both of them.

With Brandes high on painkillers and schnapps, yet consenting, Meiwes removed the man’s penis with a knife. He flambéed it, and the two ate it together. Bleeding heavily, Brandes took a bath. He eventually lost consciousness, whereupon Meiwes slit his throat, butchered him and ate a little more of­ the man’s flesh. Over the course of the next few months, Meiwes consumed 44 pounds of Brandes’ dead body [source: Speigel].

The cannibal was eventually arrested and tried amid a media frenzy. But at the time of Meiwes’ prosecution, Germany, like some other Western nations, had no law prohibiting cannibalism. Instead, Meiwes and other cannibals like him, including serial murderers Albert Fish and Jeffrey Dahmer, was convicted of the killing, not the eating. Murder is illegal; cannibalism exists beyond the law. It is taboo. . .

Forty years later, four men on a yacht named the Mignonette sailing from England to Australia were stranded in a lifeboat after the yacht sank in the Atlantic. They remained adrift for more than two months and exhausted the meat of a sea turtle they’d captured. One of the men — a sailor named Richard Parker — drank seawater out of desperate thirst. As his health declined, his shipmates opted to kill and eat him rather than wait for the young man to die naturally. In an excruciating twist of irony, a sailor named Richard Parker was eaten by his fellow castaways after they’d eaten a tortoise in a 1838 Edgar Allen Poe short story, “The Narrative of Arthur Gordon Pym” . . .

Survival cannibalism is a last resort. In the case of one group adrift in a lifeboat, 116 days passed without food before the party turned to eating human flesh. In most cases, anything even remotely resembling food was first eaten. Dogs, candles, leather, shoes and blankets are all consumed first before cannibalism becomes the only recourse for survival. . .

The Fore peoples of Papua New Guinea had a strongly codified type of endocannibalism as part of funerary rites. In this tribe, women and children played the largest role in cannibalism among deceased Fore males. The society allowed certain relations to eat certain parts of the deceased. A woman, for example, ate the brain of her dead brother. A sister-in-law ate the hands of her husband’s dead brother or the buttocks, vulva and intestines of her dead sister-in-law. . .

Nigerian Rukuba chiefs draw power by eating the flesh of an infant from their tribe. . .

This last example is the case with the Mianmin, a mountain-dwelling group in Papua New Guinea. The group was well-known for practicing exocannibalism, the result of raids on neighboring villages. When a visiting anthropologist questioned the Mianmin on why they carried off dead Atbalmins, who lived nearby, the Mianmins told the scientist they considered them “good meat.” To the Mianmins, the Atbalmins (who exist outside their kin group and culture), were their “game” . . .

During World War II, Chinese military members reportedly ate the flesh of executed enemies [source: Chong]. In another case, an American priest reported witnessing a Chinese Nationalist general cut out and consume the heart of a captured communist in the context of this war [source: Chong]. Both Iroquois and Fiji Island cultures ritualized similar acts of cannibalistic rage (called battle rage, when found in the context of war). In both cultures, captured warriors were subjected to torture and mutilation before a crowd, before ultimately being killed and parts of their bodies eaten [source: Sanday]. Even more recently, Congolese rebels stood accused by the United Nations in 2003 of eating murdered pygmies [source: Los Angeles Times]. The rebels were also accused of a more obscure form of cannibalism: forced autocannibalism. . .

The most famous case of autocannibalism came in 1934, when a group of about 2,000 white Southerners sent invitations and announced in local newspapers around Jackson County, Florida, that they intended to sacrifice a black man. Members of the group captured Claude Neal and sacrificed him. Neal’s penis and testicles were cut off and he was made to eat them. Other parts of his body were cut off (and some saved as mementos), before Neal was skinned and burned. . .

Materialists argue that ritualized cannibalism took shape after acts of survival cannibalism. A scarcity of food sources from a widespread and long-lasting drought in an area may have forced cultures to attack and eat one another. From a prolonged bout of survival cannibalism, a culture could seek to justify or support a practice their ancestors would have found abominable by framing it within the context of religion. With the Aztecs, this context was framed by feeding of the sun with blood through sacrifice and communing with a higher power through anthropophagy [source: Ortiz de Montellano]. By ritualizing the consumption of human flesh, it becomes something more than a meal; it becomes spiritual. . .

In the 1950s and ’60s, anthropologists studying the Fore people of Papua New Guinea documented an outbreak of kuru, a degenerative spongiform brain disease. The Fore contracted the disease by consuming the brain of their relatives as part of a funerary ritual. Kuru, which is the human version of mad cow disease, is highly contagious. If kuru could nearly wipe out the Fore in the 20th century, it’s possible it could have also wiped out the Neanderthals millennia earlier. . .

When examining ancient evidence of anthropophagy, there’s ultimately one clear indicator that actual consumption of human flesh by another human has occurred; this evidence is found in the stool. Human muscle contains a unique protein called myoglobin that can survive cooking and eating. If myoglobin is present in human feces, the only explanation is that one human consumed, digested and excreted another human. This very evidence was found in 1994 in Colorado at an Anasazi people cave site, dated around A.D. 1150. Coprolite, fossilized human feces, was discovered in the cave alongside a cooking pot with remnants of human tissue, bones bearing butcher marks and butcher tools stained with human blood. . .

Because we fear the concept of cannibalism, it becomes an easy tool for exploiting other cultures. When Columbus described the Carib indians as “sub-human eaters of men,” he effectively placed the culture firmly below Europeans [source: Anguilla Guide]. Labeling a culture cannibalistic animalizes it, and, in the context of colonization, justifies murder and land-grabbing. . .

Some societies showed a willingness to participate in anthropophagy in certain circumstances but absolutely not in others. One New Guinea tribe views cannibalism as “‘an inhuman, ghoulish nightmare, or as a sacred, moral duty,’ depending on context” [source: The New York Times]. This dichotomy isn’t as strange as it seems. Western society contradicts itself in how it views cannibalism. While it abhors the consumption of human flesh, Western society sanctions organ transplants and blood transfusions. And in the Eastern Chinese society, the organs, skin and eyes of executed prisoners are sold for transplant operations . . .

Dal Martello & Maloney (2006) find that kin recognition signals are processed from the upper half of the human face:

We report two experiments that aimed to determine where in the face the cues that signal kinship fall. In both experiments, participants were shown 30 pairs of photographs of children’s faces. Half of the pairs portrayed siblings and half did not. The 220 participants were asked to judge whether each pair of photographs portrayed siblings. We measured the effect on kin recognition performance of masks that covered the upper half or the lower half of the face (Experiment 1) and the eye region or the mouth region (Experiment 2). In Experiment 1, we found that the signal detection estimate of performance decreased only 5.3% (ns) when the lower face was masked but by more than 65% when the upper face was masked. We tested whether the combination of kinship information from the two halves of the face can be treated as optimal combination of independent cues and found that it could be. In Experiment 2, we found that masking the eye region led to only a 20% reduction (ns) in performance whereas masking the mouth region led to a nonsignificant increase in performance. We also found that the eye region contains only slightly more information about kinship than the upper half of the face outside of the eye region.

Source: http://journalofvision.org/6/12/2/DalMartello-2006-jov-6-12-2.pdf

Here’s an odd news tibdit from 2003:

Pygmy activists from Congo have demanded the United Nations set up a tribunal to try government and rebel fighters accused of slaughtering and eating Pygmies who are caught in the country’s civil war.

Army, rebel and tribal fighters – some believing the Pygmies are less than human or that eating the flesh would give them magic power – have been pursuing the Pygmies in the dense jungles, killing them and eating their flesh, the activists said at a news conference yesterday.

There have been reports of markets for Pygmy flesh, the representatives alleged.

“In living memory, we have seen cruelty, massacres, genocide, but we have never seen human beings hunted and eaten literally as though they were game animals, as has recently happened,” said Sinafasi Makelo, a representative of the Mbuti Pygmies in Congo.

“Pygmies are being pursued in the forests … people have been eaten,” said Makelo, a delegate to the UN Permanent Forum on Indigenous Issues, which is meeting at UN headquarters.

“This is nothing more, nothing less than a crime against humanity,” he declared. “This is a certain kind of genocide.”

Njuma Ekundanayo, an expert member of the Permanent Forum, said attacks against the Pygmies “are not only coming from the army but also from other groups”.

“We don’t understand why the military practises cannibalism against the Pygmies,” she said.

The fighters also rape and sexually assault Pygmy women, and sexually transmitted diseases are spreading in Pygmy communities, the activists said.

About 600,000 Pygmies are believed to live in Congo, which is in the midst of a five-year-old civil war fuelled by deep-seated ethnic and tribal hatreds. Original inhabitants of Congo, the Pygmies continue to live deep in the forests, eking out an existence by hunting and gathering food from small, nomadic base camps.

Earlier this year, human rights activists and UN investigators confirmed that rebels cooked and ate at least a dozen Pygmies and an undetermined number of people from other tribes during fighting with rival insurgents. There have been no reports of Congolese Army soldiers engaging in similar activity. . .

Jean-Pierre Bemba, the group’s leader, has said he was “shocked” by reports that his troops ate people.

Addressing the UN Permanent Forum on Indigenous Issues yesterday, Makelo told the body to ask the Security Council, the UN Committee on Human Rights and other bodies to recognise acts of cannibalism as a crime against humanity and acts of genocide.

Hibbing & Alford (2004) present interesting findings from experiments testing psychological responses to decisions by authorities:

[P]eople’s reactions to a given outcome are heavily influenced by the procedure employed to produce the outcome.We find that subjects reactmuch less favorably when a decision maker intentionally keeps a large payoff, thereby leaving the subject with a small payoff, than when that same payoff results from a procedure based on chance or on desert. Moreover, subjects react less favorably to outcomes rendered by decision makers who want to be decision makers than they do to identical outcomes selected by reluctant decision makers. Our results are consistent with increasingly prominent theories of behavior emphasizing people’s aversion to being played for a “sucker,” an attitude that makes perfect sense if people’s main goal is not to acquire as many tangible goods as possible but to make sure they are a valued part of a viable group composed of cooperative individuals.

Source: http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1008&context=poliscifacpub