Interview with Robert Trivers

«Killing your daughter goes contrary to the tendency to want to pass on one’s genes»

Crafoord Prize in Biosciences

Robert Trivers (Washington D. C., 1943), Crafoord Prize in Biosciences – the equivalent of a Nobel Prize in Biology – has been internationally acclaimed for his work on reciprocal altruism, parental investment, facultative sex ratio determination, parent-offspring conflict, intragenomic conflict, and self-deception. His main books include Social evolution (Benjamin-Cummings, 1985), Natural selection and social theory (Oxford University Press, 2002) and The folly of fools: The logic of deceit and self-deception in human life (Basic Books, 2011). His new work on the evolutionary logic of honor killings was presented in Barcelona at a seminar on «Evolutionary science, family structures and human rights»,1 with biologist Jaume Bertranpetit, microbiologist Mauro Santos, and the members of the Behavioral Sciences Laboratory of Pompeu Fabra University, Toni Bosch and Rosemarie Nagel.

Professor Robert Trivers prefers being addressed as «Bob». I tell him that some caste societies force children to learn four or five courtesy levels, and we agree to avoid not only «professor», but also «usted» (he speaks a little Spanish) or «Sie» in German, a language Trivers is also fluent in.

In his own words: «I have always lived between two worlds. In the German Gymnasium, I was “the American”. In America I was “the German”. I now live in Jamaica, but my kids in the US are “the Jamaicans”. I know what is like to be reminded: “You live here, but you are not one of us. This is our turf”. It is hard. And paradoxically such non-inclusive attitudes are often worse when differences are trivial.»

«Genetic variation may also be our only defense against rapidly-coevolving diseases»

«The narcissism of small differences». And do you not worry that your current focus on Muslim and Hindu honor killings may hinder their inclusion?

Honor killings are practiced against the closely related. So Muslims and Hindus are the victims. Turning a blind eye would show little concern. These killings are often particularly horrific because their purpose is to instill fear to deter disobedience. But I emphasize that horrific crimes are also committed by the distantly related, e.g., in the US, because of fear that white women may fancy individuals like Obama, exhibiting hybrid vigor with intelligence, height, build, health, and good looks.

Male chimpanzees or baboons, and female bonobos or gorillas migrate seeking (as Jaume Bertranpetit noted) to obtain hybrid vigor. Why do humans seek the opposite?

Muslim and Hindu marriages to first cousins, who are themselves the sons of first cousins, etc. multiply illnesses, birth defects and disabilities by ten. But even second and third cousin marriages are avoided by other species and cultures, like the Chinese (who say it makes people dull). Serious conditions like sickle-cell or Tay-Sachs are often transmitted through recessive genes which only express themselves when individuals receive two copies. Endogamy facilitates this. Genetic variation may also be our only defense against rapidly-coevolving diseases, so animals seek hybrid vigor. In normal conditions, however, your daughter has only 50% of your genes, your grandchildren 25%, whilst repeated first cousin weddings can make your descendants over 90% like you. The loss in reproductive success caused by endogamy is outweighed by the more direct gain achieved by having one’s extremely related daughter marry an extremely related cousin and produce extremely related grandchildren.

Photo: Mike McGregor

The more endogamic you have been, the more you gain from further endogamy and nepotism. Animals cannot enforce such extreme endogamy. However, the more endogamic you have been, the more hybrid vigor your daughter can gain through disobedience, and the more related is the daughter.

Yes. Killing your daughter goes contrary to the tendency to want to pass on one’s genes. This is why I am interested in this. It seems to defy evolution, like homosexuality or self-deception. My hypothesis is that you are also so extremely related to other family members that they may matter to you enough to kill your own daughter.

To protect the practice of endogamy or the reputation of these relatives?

Maybe both. There must be benefits because honor killings are also costly for perpetrators, emotionally and legally. To avoid prison, adults often force minors to perpetrate the killings.

The self-deception mechanisms you describe can also make people end up believing their own bluff-threats, to make others take them seriously, as in «give me more or I leave».

Yes. The other says: «you lose more if you leave». You insist: «I swear I will leave», and focus your attention on your reasons to leave until you end up believing your own bluff-threats, and leaving, with massive costs for everyone.

Your current research can help those who argue that arranged marriages to first cousins violate Article 16(b) of the Declaration of Human Rights, which protects the right to form a family with «free and full consent». If girls do not know about the medical costs and connection with honor killings, they are not «fully informed», and if they do, but marry for fear, they are not «free».

Yes. I want to defend the rights of these young girls. Even when they consent, they do it knowing what may happen to them if they disobey. Women (and female mammals, generally) are choosy about mating and can resist forced mating fiercely. Some also know that their children are likely to be born with problems. So in Qatar or Kuwait, the rich go to clinics that screen them genetically to avoid major defects.

A petition in says that in Spain 400 ten-to-sixteen-year-old girls are forced to marry every year, and we recently criminalized such marriages, but the last honor killing reported in the Spanish media was the 1928 crime of Níjar, that inspired García Lorca’s Blood wedding. In Níjar, Paca la Coja ran away with her cousin to avoid marrying the brother of her sister’s husband, which is what her sister wanted in order to take her inheritance. It was not really about honor, and neither were they part of the population of over two million Muslims and 35,000 Hindus now living in Spain.

Sure. Even if it is about genes, the social context and institutions can make a difference. UK Hindus, for example, cannot practice honor killings because they lack the Hindu institutions that sanction them.

Steep taxes on third children, besides helping us deal with climate change, could also stop honor killings if, as Mauro Santos noted, these killings make no sense in small families.

Yes, it would make no sense to make an example of a daughter, if you lack others who will then marry who they are told. Third-child taxes typically yield a son and a daughter per family, which could perhaps stop the killings.

«My lab research showed that homophobes were much more turned on by gay sex than liberals»

And is this not the most likely scientific explanation of the story of the Virgin Mary?

I studied the Bible as a child, and still pray in a certain way and meditate, but do not know what you have in mind.

Allegedly Anne, the mother of the Virgin Mary, was a widow with only one daughter, Mary. Marrying her daughter to a wealthier older man must have been her best survival option. Being, allegedly, only thirteen at that time, it would have been normal for her to prefer a young local boy over a distant old man. But we also know that the Romans took advantage of young girls in the occupied territories, treating them as servants and promising them protection and prosperity. Mary reports encountering a man (no wings or other angelic features are mentioned in her description) who calls her pretty and makes such promises. Mary gives in, accepting she is a servant (Luke 1:26). Moses’s law required Mary to be stoned for her out-of-wedlock pregnancy, so Anne would have lost her only daughter had she not used her temple influence to allege that the pregnancy involved no sex.

And the rest is history! Romans were practicing crucifixions and other gruesome punishments to instill fear and secure obedience. So both rejecting a Roman and being pregnant out of marriage could have cost Mary her life. Women are sometimes punished for rejecting a man’s advances, for failing to reject a man’s advances, or even for being raped.

The Bible says that Joseph decided not to make an example of Mary and was going to repudiate her secretly (Matthew 1:19). But as you explain, the offended man may forgive, but the community will not. So to save her life, he had to go along with Anne’s version of the facts. Fortunately, Mary had a relative, Elizabeth, finally pregnant at an advanced age (perhaps from extramarital sex with a fertile man) who backed up her story. Jesus then grows up to oppose stoning women caught in extramarital sex, though he usually avoids saying so for fear of getting in trouble (John 8).

It makes sense. In those days, having large families, killings and severe punishments, in general, and against women, were far more common than today.

In Spain almost a thousand women were killed in the last fourteen years, and men also kill around six children yearly, either to hurt the women who leave them or because they are jealous of the kids, as in the recent case of a Spanish man in Germany. People living abroad (Spanish in Germany, British in Spain, etc.) are often overrepresented in these crimes, perhaps because on top of all the «you are not one of us», «we are better», etc., when their wives leave them, their status goes down even further.

Women respond to infidelity or fear of abandonment with tears or feigned indifference, but always more rationally, with efforts to become more attractive. Men become aggressive and drunk. The less secure men are, the more they will fear infidelity, and as their status goes down, they may become more angry and aggressive, which women dislike. It is a vicious circle. The greater the fear of abandonment, the more unpleasant and aggressive they become, trying to retain her by fear. Sometimes, jealousy makes men become not only violent and unpleasant but also aroused, and so prone to rape the woman who is leaving them. We see this in other species too. Even ducks raped by groups of males are often re-raped by their own partner immediately after, presumably to introduce sperm that can compete with the sperm already inside.

Sperm competition exists also in chimpanzees and bonobos.

Well, men (not women) find the thought of their partner having sex outside the couple arousing. Women dislike the thought, and the men who fake love to obtain sex and who destroy something important for mere variety. Men, by contrast, often find the flirtatious, indomitable girlfriend more alluring and fantasize about her being with other men. Being both attracted to her and furious with her, confused, angry men may do crazy things, including murder, even if murdering your girlfriend and kids again defies evolutionary logic.

Photo: Mike McGregor

Adaptive strategies can backfire. Diarrhea can save us from food poisoning, but one can also die of diarrhea. But are men like this when their partner is a man?

Men often have to deceive themselves into thinking they love the woman they want sexually in order to deceive her too. But men need not fake love to have sex with other men. This aspect of some gay communities made me doubt the traditional evolutionary story about gay people benefiting family members enough to contribute to the survival of their genes as much as if they had reproduced. In San Francisco, gay men were partying rather than babysitting or financing nephews. We have now identified two genetic markers for male homosexuality, one on the X chromosome, the Xq28 region. This explains why gayness is more common in some families, though hormonal factors in pregnancy and environmental factors after birth also matter.

Could these findings support gay rights?

It could help in arguing against those claiming that it is entirely a matter of choice and easily changeable. But we have not found genetic markers for lesbians (perhaps because their explanation is hormonal rather than genetic) and it would be absurd to claim that male and female homosexuals should be treated differently because of that.

«The main religions are overwhelmingly patriarchal in logic and structure»

Of course. The fact that homophobic men are sexually aroused by images of gay men also shows that at least some physical reactions are involuntary.

Yes, my lab research showed that homophobes were much more turned on by gay sex than liberals. They had erections they did not identify with.

Dissemination of such scientific findings could turn homophobia into a sign of gayness, perhaps deterring the expression of homophobic sentiments. Dissemination of your findings regarding depressed immunity could also help.

Our studies show that concealing your homosexual identity multiplies your chances of getting HIV and doubles your chances of cancer and infectious diseases such as bronchitis and sinusitis. Coming out also has cardiovascular benefits. So the former US Army policy of «don’t ask, don’t tell» was very bad for gay people. Imagine having to permanently conceal your spouse, your family, your past life, your friends and associates, having to change the pronoun with which you refer to your loved ones, carry no picture or letter from them to the front line, and close the door and talk quietly if any friend calls. Such permanent anxiety about being caught and rejected is devastating and it damages people’s immune response. It is outrageous to impose such a burden on people who volunteer to defend us.

Sure, volunteers and non-volunteers should not be sent to areas of high risk of disease and infection with unnecessarily depressed immune systems.  I like it when students trust me enough to tell me they are gay within days of knowing me. Jamaican students must be more reluctant.

As I explain in Wild life, Jamaican gays suffer terrible attacks, including corrective rapes. People know I am part of a vigilante group that protects homosexuals. One day they will come for me for defending them, but I am willing to risk it.

Repressed homosexuality in priests has been linked to abuse in religious schools in Spain, and a campaign is now asking for criminal liability not to expire after just a few years. By the time the kids leave school and can come before a judge, it is often too late. People don’t understand why they cannot testify sooner.

Children subject to very serious abuse may be killed by their abusers in order to secure their silence. To survive, they must persuade their oppressor that they are harmless, accept the abuse, and will keep quiet about it. They cannot give away signs of resentment, or a desire to fight back or call for help, and so they have to go into a state of induced self-denial, including cases of dissociation where one side of the mind hides the information from the other side. This allows the child to show a good front and smile at their oppressor, as if what happened was forgotten, accepted, or unimportant. They have to deceive themselves to deceive the abuser. If the abuser is a caregiver (such as a tutor, who is both a teacher, a priest and somebody who acts as a father-surrogate), the amount of time required for the child to remember is much greater. Typically, the closer the abuser to the abused, the more time is required. So if the criminal liability of caregivers expires faster than the crimes can be prosecuted…

«Abused children have to deceive themselves to deceive the abuser»

It is practically like not prosecuting them at all. It makes sense not to destroy the life of a hardworking parent for a minor theft he committed when young and unemployed (the argument for property crimes having limited liability). But pedophilia and other sex crimes have a strong tendency to be repeated, particularly if the schools and churches hide them and criminal liability expires.

They may well continue if all else does. The main religions are overwhelmingly patriarchal in logic and structure, which is why the Catholic church claims that celibacy does not contribute to priestly pedophilia, but homosexuality does. More priest homosexuality will show a greater percentage of molestation of boys over girls, rather than a change in molestation rates. But what can be more conducive to sex with children than a complete prohibition of sex with adults? And what could be more conducive to abusing boys than an all-male priesthood that presumably attracts men who like men?

Don’t we know from the army, and all-male expeditions, that young men deprived of women, and crammed together with other young men, will look at each other sexually more than they would otherwise?

Hmmm… Having childless priests may reduce nepotism, but reduces catholic numbers, which they then hurry to pump up by controlling women’s reproduction and banning family planning and abortion even in cases of incest and rape. It is a bad system for everyone.

«It is strange that feminists should reject evolutionary biology, when we offer so much research they could use»

A typical image you may associate with Spain is that of priests in golden robes speaking loudly from a pulpit about vanity, arrogance, wrath, violence, lasciviousness, and coveting one’s neighbor’s wife… to kneeling mothers and grandmothers in black, whose problems are more likely to be low self-confidence, having to invent headaches, etc.

Clearly men are more likely to commit what Catholics deem deadly sins. It is men who have a 20% inflated self-image, who wrongly think women fancy them, who have more anger management issues, who think more about sex, who are willing to have it with strangers, and who are more likely to kill or rape.

Women make great teachers, theologians, psychologists, and social workers. Could they also make good (and safe) priests?

Sure, women have the advantage of a larger corpus callosum and more symmetric brains. It is strange that feminists should reject evolutionary biology, when we offer so much research they could use. Women perform well in pastoral roles and tend to study and understand human behavior well. I often tell my students: «If you have been going out with your girlfriend for six months, and she does not know you better than you know yourself, you are going out with a slow woman!» [He laughs].

This interview was funded by the project MINECO Retos DER DER2016-80471-C2-2-R and the European Research Council, Grant agreement 648610 (acronym: Family Justice).

1. «Evolutionary science, family structures and human rights», held on 28 November 2017 at the Pompeu Fabra University in Barcelona (Spain). (Go back)

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ICREA researcher, co-director of the del UPF Center for Animal Ethics and president of the Great Ape Project-Spain.