Evidences about
biological predispositions

that difference
the innate psychology
of men
and women



We don´t propose a biological

determinism but the interaction of
biology and culture, even when
for certain phenomena one may

influence more than another.

We don´t refer to individuals

but to averages, in the same way

we can say that on average
males are taller than women.


-Sexual selection theory was

postulated by Darwin in

"On the Origin of Species"

 but found strong evidence in

studies with several animal

species and with humans in the

20th century. Trivers studied

in a famous meta-analysis dozens of

animal species in which the sex

who makes the biggest parental

investment is the most selective,

and the opposite sex competes

to be chosen. Sex differences

are based on genetic patterns that evolved from adaptations to different challenges faced by men and women. (Bateman, 1948; Trivers, 1972)

-There are few sex reversed species in which males are the ones who make the greatest parental investment and are therefore more selective in mating, which is why females are more competitive. Examples: the seahorse, some fish, frogs, birds and insects. (Trivers, 1972)

-Men on average prefer to work with things and women on average prefer to work with people. It is the result of a meta-analysis carried out with half a million individuals. The effect size (the difference) is large (d = 0.93). (Su, R. et al., 2009).

-Great differences in sex hormones between men and women, especially in prenatal, during the first six months of life and in pre-adolescence. (Alexander, 2002; Auyeung y otros, 2009; among many others). (Thornton 2009, with rhesus monkeys)

-The largest single-sample study of structural and functional sex differences in the  brain (5216 participants). Males had higher raw volumes,raw surface areas, and white matter fractional anisotropy; females,higher raw cortical thickness and higher white matter tract complexity.(Ritchie et al., 2018)

-There are small and multiple differences in the brain: measurement, density, cortical asymmetry, in the nucleus of the hypothalamus and many other parts. There is a 93% chance of knowing if a brain is female or male.(Chekroud y otros, 2016)

- There is no brain wiring entirely female or male. The brain contains different blocks of elements associated with sex. Some of them may be more linked to female traits and others to male traits. But that does not imply, as Daphna Joel (2015) and  Lucía Ciccia (2015) conclude, that there is no brain dimorphism (differences between men and women), nor does it imply maintaining that culture does not influence. Existing biological differences are significant: at the level of chromosomes and by the degree of testosterone in uterus in the eighth week of gestation, masculinizing the brain. They imply diversity of  kids' games, preferences and behaviors of all kinds. We are more similar than different, but those differences count and are not sexist biases of researchers nor are they opposed to the conquest of equal rights. (Brain Gender, Melissa Hines) For a critique of Daphna Joel's meta-analysis, that inspired many feminists, see Del Giudice et. al, 2015.

-Universality of human features: men and women are seen as different all over the world. Also around the world women are more concerned with children and men are on average more competitive.(Brown, D. E.,2004). Ellis (2011) found 65 sex differences that are apparently universal, without a single error of replication throughout ten studies.

-Many of these differences can be seen in other mammals: greater aggression in males, greater parental investment in females, greater interest in objects in males and greater interest in members of the same species in females. Between chimpanzees and humans, boys and male offspring usually spend more time away from their mothers than girls and female offspring, which could show a greater risk propensity. (Royster, P, 2005).

-Young female primates play more with baby primates than small male primates, they prefer to learn from their mothers, while males prefer to learn from their fathers, they move away from the mother more and play more violently. (Terio, K. A. et al., 2016).

-The case of the hyena is atypical, since the female has more testosterone than the male, which makes her character more aggressive. It adds evidence in favor of the effects of testosterone, shown by hundreds of studies (For example: Dloniak, S. M. et al., 2006).

-Congenital hyperplasia: supply of testosterone to unborn female babies: then they show preferences for toys and male game patterns (competitive vs cooperative), occupational preferences, and slightly more homosexuality and bisexuality than the average. (Brown, Hines et al., 2002)

-Boys raised as girls play aggressively and prefer objects to people. (Colapinto, 2000)

-Twenty-five baby boys born without a penis-cloacal exstrophy-were castrated and educated as girls but had male behavior patterns: rough and tumble play and male interests. More than half said they were boys when they were 5 years old. (Reiner, 2000)

(Reiner, 2004)

-In early childhood differences between boys and girls were evidenced by studies done all over the world: levels of aggression and competition, choice of toys. Girls play mother games and boys tend to turn anything into a vehicle or a weapon. According to a meta-analysis of 1788 papers, the choice of toys would be a mixture of innate and acquired predispositions, but that difference would be decreasing in recent years. (Todd, B. K. et al., 2017)

-Higher prenatal testosterone correlates with less eye contact at 12 months, reduced vocabulary at 18 months, less social skills at 48 months, higher mental turnover at school age. (Baron-Cohen, 2004)

-Male students in the Sciences on average had a stronger drive to systemize than to empathize in comparison to females in the Sciences. Students in the sciences on average had a stronger drive to systemize more than to empathize, irrespective of their sex. The reverse is true for students in the Humanities. These results strongly replicate earlier findings. (Baron-Cohen et al.,2018).

-Skills in mathematics and science for men and women: there are no differences in average but in the distribution tails there are more men (more in the upper and lower end of ability). Biological and environmental factors influence. (Halpern et al, 2018)

-Differences in visual-spatial skills (mental rotation) consistent in 10 European countries, Ghana, Turkey and China. (Geary & De Soto, 2001)

-Differences in personality (Meta-analysis of Feingold, 1993). Janet Hyde (2014) found moderate to large sex differences in spatial rotation, kindness, search for sensations, interests in things versus interests in people, physical aggression, masturbation, pornography and attitudes about casual sex, among others.

-Contemporary mate preferences can provide important clues about human reproductive history. Five predictions were made about sex differences in human mating preferences based on Darwin's sexual selection theory, parental investment theory (Trivers,1972), which adds evidence for the first, human reproductive capacity and sexual  asymmetries  regarding certainty  of paternity  versus maternity. Females were found  to value cues to resource acquisition in potential mates more highly than males. Signs of reproductive capacity (youth and physical attractiveness) were valued more by men. These differences may reflect different evolutionary selection pressures in men and women and provide powerful intercultural evidence of current sexual differences in reproductive strategies. The predictions were based on data from 37 samples taken from 33 countries located on six continents and five islands (with 10,047 study participants). (Buss, 1988).

-Women show greater social interest and better tools to relate socially from very young age, but since socialization could reinforce that role, its origin would not be completely clear. In this study, it was observed whether these differences arise in 48 primates that grew in a controlled environment. Compared with males, females of 2-3 weeks of life look more to the face (d = 65), specifically to the eyes (d = 1.09) and between 4-5 weeks of life  establish more contact with known and unknown caregivers (d = 064). (Simpson et al., 2016)

-The greater the prosperity and gender equality in a country, the more personality differences exist between men and women. Study carried out in 55 nations with 17,637 people. (Schmitt, D. P., 2015).

-The greater the prosperity and gender equality in a country, the fewer women study STEM careers, focused on objects and systems (mathematics, physics, engineering, computer science), and more women study traditionally female careers as nursing, careers focused on people and living beings (medicine, psychology, languages, veterinary, biology). Data collected among almost half a million people. (Stoet, G., & Geary, D. C., 2018)

-Resistance to change in communities that tried to nullify sexual differences like the kibbutzim (collective farms) of Israel (Aviezer, O. et al., 1994).

-In Turner Syndrome, a genetic disorder that affects women who are missing all or part of an X chromosome, it is common for girls to have problems in math and with tasks that require spatial skills such as reading maps or visual organization. (Murphy & Mazzocco, 2008)

-For a couple of generations life priorities and women´s iterests changed very little. (Feingold 1994)


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