Posts Tagged ‘biology’

Structural Brain Differences Between Sexes Significant

Saturday, June 11th, 2011

In a research report that is more than six years old, Richard J. Haier and his research team outline how men and women achieve similar levels of intelligence in different ways.

It appears that while men and women have the same average IQ, the level of cognitive function is achieved in very different ways. Not only do women and men employ different brain regions, there is also a vast difference in the emphasis on gray and white matter.


Let’s take a look at what the researchers have done:

Here, we examine whether there are male and female differences in the correlations between IQ and GM [gray matter] or WM [white matter] volumes based on optimized voxel-based morphometry (VBM) of structural MRI data.

Not only do the researcher want to investigate if men and women use different regions to create their intelligence, they want to check if the white matter or the gray matter is “doing the heavy lifting” in the areas that are important.

If they can demonstrate these kinds deep structural differences – directly linked to functioning – in men’s and women’s brain, it will be a significant finding. Previous research has demonstrated several functional sex differences in the brain, but without the kind of unquestionable link to brain structures that the researchers are aiming for:

Functional brain imaging studies have reported a number of sex differences (Cahill et al., 2001; Gur et al., 2000; Haier and Benbow, 1995; Mansour et al., 1996; Neubauer et al., 2002; Shaywitz et al., 1995, 2001), but task-specific demands on cognitive resources with functional studies must always be considered as the task itself could affect interpretation of functional imaging results. Structural imaging correlated with off-line analyses of various cognitive performance measures and traits, on the other hand, can identify those differences in neuroanatomy which may underlie the cognitive measure of interest, irrespective of any task design constraints.

Never mind if you don’t want to grasp every technical detail; the main thing to remember here is that they are checking whether men and women use different brain regions to achieve similar intellectual functioning, and whether men and women rely on gray/white matter in the same way.

Here are the results:

These present results highlight an important dissociation of brain morphology related to intellectual functioning in normal adult brains, as the pattern of voxel types and voxel locations linked with intellectual functioning differed substantially between the sexes.

The regions employed in intellectual performance are far from the same in men and women – a somewhat startling finding perhaps. Even more shocking is that the sexes use gray and white matter in such different ways:

With respect to voxel types, men had roughly 6.5 times the number of GM [gray matter] voxels identified as related to intellectual functioning as did women, and women had roughly nine times more WM [white matter] voxels than did men.

6.5 times the number and roughly nine times more? That’s beyond significant.

These findings – as interesting as they are in their own right – also throw the next, inevitable question at us. If women and men use different neural substrates to achieve a similar general level of intelligence, are there any differences in subsets of cognitive performance?

The current results contribute to a growing body of evidence demonstrating that, although the sexes do not differ in general intellectual ability, the neural substrates of general intelligence are different. Whether similar neuroanatomical differences are associated with specific mental abilities (assessed for example by WAIS subtests) remains to be determined; our VIQ and PIQ findings need replication with larger samples.

It would be highly surprising if such marked differences in brain regions/tissue employed in cognitive functioning do not translate into different ways of processing information, integrating memory, experiencing emotion, etc.

If anyone is skeptical of the hereditary component in these gender differences – perhaps wondering if they can solely attributed to men’s and women’s different gender roles – then the researchers put that fear to rest (see the first phrase):

Although GM and WM volumes are highly hereditable in many areas (Posthuma et al., 2002; Thompson et al., 2001), there is evidence that GM volume in humans can increase with motor learning (Draganski et al., 2004) or the acquisition of a second language (Mechelli et al., 2004) and the nature of genetic determinism in general is now controversial (Silverman, 2004).

My own take on this research is that it’s amazing to see that the general level of complexity of a system (such as the brain), determines overall functioning to a higher degree than the specific components. This is why men and women have similar intelligence even though our brains are quite different.

I also feel that the research on gender specific brain differences has come far enough to once and for all let go of the belief that gender is mainly constructed, and innate factors simply a minor concern. Men and women have brains with clear differences in anatomy and physiology, and it is highly unlikely that this wouldn’t affect our conscious and unconscious brain processes. as well as our behavior in the world.

Risk aversion strongly correlated to testosterone levels

Saturday, August 29th, 2009

The evidence for substantial innate sex differences is mounting. I’ve long been a strong advocate for acknowledging this research, instead of trying to ignore it for ideological reasons, such as the postmodern feminist stance that all gender differences are culturally constructed. On the other hand, I usually take a very conservative approach, and write phrases such as “there are certain innate differences that cannot be ignored”. However, I don’t know if that conservative approach is warranted any more. As the research is progressing, it’s becoming increasingly clear that sex differences are substantial, and not limited to a few specific areas.

This doesn’t mean that we forget about culture, or the plasticity of the human brain that allows us to adapt to a range of situations–regardless of our gender. But it does mean that we need to start acknowledging that the very organ that filters our experience of life, and the “software” that runs that organ, are substantially different between an average man and an average woman. This also means that the inner experience of being a man is different from the inner experience of being a woman.

Recently I was sent a very interesting link about new research that has been carried out to map the relationship between gender, testosterone and risk aversion (Gender differences in financial risk aversion and career choices are affected by testosterone. Paola Sapienzaa, Luigi Zingalesb and Dario Maestripieri, 2009). The strength of this research is that it connects a well known gender specific variable (testosterone) to a specific behavior (risk aversion). It is one thing to prove that there are innate biological differences between men and women, but it is far more convincing when a biological variable can be shown to directly affect behavior.

Let’s see what they say about the experiment:

Prior research has shown that testosterone enhances competitiveness and dominance, reduces fear, and is associated with risky behaviors like gambling and alcohol use. However, until now, the impact of testosterone on gender differences in financial risk-taking has not been explored.

The researchers, using an economic-based measure of risk aversion, found that higher levels of testosterone were associated with a greater appetite for risk in women, but not among men. However, in men and women with similar levels of testosterone, the gender difference in risk aversion disappeared. Additionally, the researchers reported that the link between risk aversion and testosterone predicted career choices after graduation: individuals who were high in testosterone and low in risk aversion chose riskier careers in finance.

In other words, the levels of testosterone that men routinely have, lead to increased risk taking, compared to the levels of testosterone that women usually have. Women who have higher than normal levels of testosterone, approach the risk taking behavior of men, simply by having increased levels of this hormone.

This is not to say that there aren’t a range  of other factors that can increase or decrease risk taking, but those factors in no way detract from the result of the researchers.

Additionally, the study demonstrated that prenatal levels of testosterone, which are much higher in boys, have an impact on risk aversion later in life:

A similar relationship between risk aversion and testosterone was also found using markers of prenatal testosterone exposure.

At this point in time, it is irresponsible to maintain the claim that sex differences are completely, or for the most part, socially constructed.

The updated list of the different research methods that support innate sex difference is thus:

  1. Mapping brain structure and function using new imaging techniques such as PET (positron emission tomography) and fMRI (functional magnetic resonance imaging)
  2. Studying the behavior of newborns or infants
  3. Studies from the field of evolutionary psychology
  4. Cross-cultural studies
  5. Research that connects innate biological differences to specific behaviors

Cross-cultural personality traits

Friday, August 14th, 2009

A friend of mine passed on a very interesting research report to me the other day. It’s called Why Can’t a Man Be More Like a Woman?  Sex Differences in Big Five Personality Traits Across 55 cultures (Schmitt, Voracek, Realo, Allik, 2008). The full report isn’t available online, unless you are a student or a researcher yourself, but I’ll be quoting some relevant passages.

As you may know, I’m interested in the emerging research that investigates the innate differences  between men and women. Even though innate sex differences shouldn’t be overexaggerated, it is a breath of fresh air that we are actually studying these differences, instead of pretending that they don’t exist. The whole gender discourse needs to be infused with solid research — be it biological, sociological or cross-cultural.

Innate sex difference can be studied in a few different ways:

  1. Mapping brain structure and function using new imaging techniques such as PET (positron emission tomography) and fMRI (functional magnetic resonance imaging)
  2. Studying the behavior of newborns or infants
  3. Studying evolutionary psychology
  4. Doing cross-cultural studies

Number 2 and 4 are perhaps the two most reliable sources, since differences between newborns are innate by definition, and traits that persist across cultures can hardly be said to be culturally constructed. The article that my friend gave to me, is an excellent example of a cross-cultural study. Let’s see what the authors have to say about personality traits in different cultures:

In many studies, including several meta-analytic investigations, it has been found that men tend to be more assertive and risk taking than women, whereas women are generally higher than men in anxiety and tender-mindedness (Brody & Hall, 2000; Byrnes, Miller, & Schafer, 1999; Feingold, 1994; Kring & Gordon, 1998; Lynn & Martin, 1997; Maccoby & Jacklin, 1974). These sex differences in personality traits can be detected in early childhood (Else-Quest, Hyde, Goldsmith, & Van Hulle, 2006; Wilgenbusch & Merrell, 1999) and remain fairly constant across adulthood (Feingold, 1994; McCrae & Costa, 1984). The effects of these sex differences lead to predictable differences in men’s and women’s leisure behaviors, occupational preferences, and health-related outcomes (Browne, 1998; Collaer & Hines, 1995; Lippa, 2005).

Observed sex differences in personality traits such as assertiveness and anxiety also appear to be culturally pervasive (Costa, Terracciano, & McCrae, 2001; Lynn & Martin, 1997). Feingold (1994) found that women in Canada, China, Finland, Germany, Poland, and Russia tended to score higher than men on scales related to the personality traits of neuroticism, agreeableness, and conscientiousness. Men, in contrast, scored higher in the extraversion related trait of assertiveness across cultures. In a much larger study, self-report responses to the Revised NEO Personality Inventory (NEO-PI-R) across 36 cultures revealed that women in most countries are higher in several traits related to neuroticism, agreeableness, warmth, and openness to feelings, whereas men score higher on scales measuring assertiveness and openness to ideas (Costa et al., 2001; McCrae, 2002).

In other words: important sex differences in personality traits persist across cultures to an extent that would be highly unlikely if these traits weren’t inborn. This is of course what evolutionary psychologists have been claiming all along, but here we have a wealth of actual research backing up those claims.

However, the study itself was not only about validating these sex difference in personality traits across cultures (though it did that too), it was also about comparing the magnitude of these sex differences in traditional and modern societies. Many of us probably believe that sex differences become smaller in post-traditional societies, due to gender equality and women entering the work force. But this research presents some counter-intuitive results:

Sex differences in most personality traits, however, are not uniform in magnitude across all samples. At times, sex differences can be much larger in some cultures than in others (Fischer & Manstead, 2000; Guimond et al., 2007; Schwartz & Rubel, 2005). One unexpected finding has been that sex differences in personality traits are often larger in prosperous, healthy, and egalitarian cultures in which women have more opportunities equal with men (Costa et al., 2001; McCrae, 2002). Both in self-report and in other-report data, Asian and African cultures generally show the smallest sex differences, whereas European and American cultures—in which living standard and gender equity indexes are generally higher—show the largest differences (McCrae et al., 2005). With improved national wealth and equality of the sexes, it seems differences between men and women in personality traits do not diminish. On the contrary, the differences become conspicuously larger.

This study provides strong support for the claim that with greater human development and with greater opportunities for gender equality, the personalities of men and women do not become more similar (see also Costa et al., 2001; McCrae, 2002; McCrae et al., 2005). To the contrary, in more prosperous and egalitarian societies the personality profiles of men and women become decidedly less similar. Moreover, these changes appear to result from men’s cross-cultural personality variation. In more traditional and less developed cultures a man is, indeed, more like a woman, at least in terms of self-reported personality traits.

These are interesting findings indeed. The explanation that the authors offer is that in traditional societies, people are restrained by the lack of resources, making individual differences smaller. For example, if everyone is starving, then everyone will be short, but if everyone gets enough food then individual height differences will be more prominent. Similarly, when men and women have ample resources and the freedom to choose their own lifestyles, innate differences will be more prominent than in a traditional society where everyone needs to sacrifice individual needs to help secure food and safety.

Ironically, the more egalitarian we become, the more we can expect men and women to display different personality traits. This may not be what some feminists intended, but it appears to be an unavoidable consequence of “releasing” the innate differences into action.

Brain Gender in Tweens

Wednesday, July 22nd, 2009

About a week ago, featured an interesting article about how the brains of tween girls and boys react to potential social interaction. First of all, it’s interesting to note that the journalist is still trying to be politically correct, and tiptoeing around the facts:

Only in the past few years have scientists been able to use imaging technology to look inside men’s and women’s heads to investigate whether those stereotypical gender differences have roots in the brain. No concrete results have emerged from these studies yet

I suppose you could say that no concrete results have emerged, if you’re expecting a complete brain manual for both sexes and all individuals. However, if by concrete results you mean results that clearly demonstrate that men and women have brains that function differently, and that are structured differently, then yes – concrete results have emerged.

Interestingly enough, after firing off that politically correct introduction, the author proceeds with an almost biologically deterministic statement about the research report on tweens and social interactions:

a new functional magnetic resonance imaging (fMRI) study of children offers at least one explanation for some common tween social behaviors: girls are hardwired to care about one-on-one relationships with their BFFs (best friends forever), while the brains of boys are more attuned to group dynamics and competition with other boys.

I believe that biology is a very real factor in creating gender differences, but it’s important to remember that behaviors are usually a combination of biology, culture and free will. Claiming that biology only is responsible is usually a premature claim, in a world where we still need to work out the details around how biology, culture and free will affect gendered behavior – not to mention how these three factors continously interact.

This caveat aside, the research report becomes yet another piece in the puzzle of the emerging knowledge base around biological brain differences between the sexes:

The results suggest that as girls progress from early puberty to late adolescence, certain regions of their brains become more active when they face a potential social interaction. Specifically, when an older girl anticipates meeting someone new — someone she believes will be interested in her — her nucleus accumbens (which is associated with reward and motivation), hypothalamus (associated with hormone secretion), hippocampus (associated with social learning) and insula (associated with subjective feelings) all become more active. By contrast, boys in the same situation show no such increase in activity in these areas. In fact, the activity in their insula actually declines.

Finally, the author even offers us a potential explanation that is grounded in evolutionary psychology:

Perhaps it’s evidence that evolution has programmed boys to compete within large groups, so they can learn to eliminate rivals for women — and that girls have been programmed to judge, one-on-one, who would be the most protective father for offspring.

As always, it’s good to remember that evolutionary psychology is still speculatory in many ways, especially when it’s used in the context of explaining a research report that wasn’t in itself explicitly examining the validity of an evolutionary psychology claim.

Principles of Evolutionary Psychology

Wednesday, July 8th, 2009

What is evolutionary psychology and why is it interesting in a discourse about gender issues? Marriam Webster defines evolutionary psychology as the study of human cognition and behavior with respect to their evolutionary origins. In other words, the way we think and behave nowadays, may well be adaptations to solve recurrent problems in human ancestral environments.

A simplified way of putting it is that if a behavior or way of thinking was advantageous for thousands of years (for example during the stone age), then it may well have been hardwired into the human brain. We are not born as blank slates, and it makes sense that the programming that we are born with be useful for our survival and reproduction. However, what was useful in the past, may not be useful nowadays, even though the programming remains in our brains.

Evolutionary psychology can be a controversial field. Its proponents want to explain all human behavior using this theory, while its detractors emphasize the importance of human flexibility and continuous biological adaptation to the current cultural climate. In my opinion, the truth is somewhere in between those two polarities, and I leave it up to you to determine what importance you want to allot to each stance.

Let’s have a look at some of the basic principles of evolutionary biology and how they relate to gender issues:

  • Since women are the ones who get pregnant (since times immemorial…), women have always been forced to choose a man carefully. A woman can only carry one child at a time, and a pregnancy takes nine months, which means that she’d better choose a man with good genes, because she won’t get very many chances to pass on her own genes. She also needs a man around who’s willing to protect and provide for the child, be it the father or a man who thinks he is the father. This means that the emotional connection to the man is crucial for a women, because the emotional connection is a good indicator of whether he’ll stick around or if he’s only interested in sex.
  • The principle above changed with the introduction of the female birth control pill, which enabled women to have sex without risking pregnancy. However, the old dynamics are still part of female nature, competing with the new dynamics that the pill introduced. This means that to some extent women are still looking for a confident man who can be a good protector, and preferably a man who can provide for the child – even if she’s only interested in a sexual relationship, and not in having children.
  • Men, however, do not get pregnant and therefore don’t need to choose their sexual partners as carefully. Fathering a bastard child could potentially be done at a very low cost, if you don’t have to assume the role of father for that child. However, being a committed father has always been a very good option for men, since in past eras the survival rate of your children was much higher if you stuck around.
  • Since men can father a child at a very low cost while women cannot, women end up being the sexual selectors more often than men.
  • Men are attracted to beautiful women. Beauty in this case is not some kind of esoteric concept, it is simply another word for proportional and symmetric facial features. Since women instinctively know that their looks are important when attracting a man, we have a whole cosmetic and plastic surgery industry catering to the needs of women. Evolutionary speaking, men are attracted to female beauty, due to symmetric facial features being a predictor of good health in the past, and good health is crucial if a woman is to survive a pregnancy, and pass on the man’s genes.
  • Gay men generally care more about their looks than straight men, and know more about grooming and skin care. The reason for this is simple: gay men are looking to attract other men, and even if those other men are also gay, they are still 100 percent men – and therefore attracted to good looks. Lesbian women, on the other hand, are often more relaxed about their looks, since they are attempting to attract other women, and women care less about good looks (even though good looks are still far from unimportant).