Monthly Archives: January 2003

Mysteries of the Brain Part – 6


This post was published on  Thu, 23 Jan 2003.

One of the most important parts of our identity is our sex. One of the first things you notice when you meet someone is to note if the person is a male or a female. We all know that there are fundamental differences in the behaviour of the two sexes. How deep is this difference? Are our brains different? Are our brains different at birth or are the differences developed later due to environment? We study these topics in today’s VERITAS.


We know that male children play more of rough games while female children play more of social games. By a very young age the sex of the individual has started defining him/her. And yet there is NO difference between the brains of males and females in the beginning!!! The difference is caused by the sex harmones that start affecting the brain from a very early age.


The default behaviour to to produce the female nature. So if androgens(male sex harmones) are prevented from acting on the brain the individual acquires female tendencies. This effect happens only in the early period of brain development. Later variations in sex harmones do not change the basic makeup. It is not that females lack testosterone (the main male harmone). Females lack this harmone during the brain development. Thus female is the basic inner sex.
Males and females excel in different intelluctual tasks. For example females do better at verbal skills than males. Males are more expert at mathematical reasoning. Several other differences also exist.
How much sex harmones we produce affect us throughout our lives. A female with high levels of the male sex harmone(testosterone) would
do better at mathematical reasoning than a female with lower amount of this harmone. So you would think that higher testosterone would
similarly affect males. Not really. We must remember that testosterone is a harmone that also causes aggressive behavoiur. And we know that
most hyper aggressive males are not the best mathematicians. The reason? There is a optimal level of this harmone that is most effective. Males
with this low optimal level do well at mathematical skills. A higher level of this harmone rapidly decreases mathematical reasoning powers
The action of the sex harmones not only changes the way we behave. These sex harmones create structural differences in the brain as well. The male brain and female brain starts looking different after a few years of development. For example the corpus collosum ( the connection between the left and right brain hemishphere) is larger in famales than males. This suggests that females tend to use both hemispheres more equally.  This effect has been verified experimentally as well. In a set of mice the right hemisphere was damaged. Spatial abilities (such as navigational skills) were severly reduced in male mice. Female mice however had a lesser reduction in this ability. Males usually solely use their right hemisphere for spatial skills. Females use the hemispheres more equally.
Even for speech males and females use different parts of their brain. Females usually use the front of their brains. Males rely more on the back of the brain.
It has become fashionable to attribute the differences in male and female behaviour to the society and how our ancestors lived. However experiments show that there is not much Science in such talk. Male mice tend to use the geometry of the surroundings to find their way. Female mice tended to use landmarks to find the way. Male and female humans behave exactly the same way….The differences are fundamental
and go beyond our how our ancestors lived.


We must remember that the environment has a huge effect on how the natural tendencies are enhanced/decreased. Differences within a sex sometimes are greater than differences between the two sexes.


Most of the material for this VERITAS has been taken from the article “Sex differences in the brain” by Doreen Kimura (Scientific American 2002)


More Reading :






Go, wondrous creature! mount where Science guides:
Go, measure earth, weigh air, and state the tides:
Instruct the planets in what orbs to run,
Correct old time and regulate the Sun;



      Our Sun is a part of the galaxy named Milky Way. THe sun is a medium size star in one of the arms of the spiral Milky Way galaxy. This arm is called the Orion arm. There are about a million stars in the Orion arm of the Milky way. The Milky way galaxy contains about 300 billion stars.

      Galaxies do not occur as independent islands in the universe. They do not float as lonely objects in the other wise empty universe. They usually occur as a cluster or colony. So a set of galaxies usually occurs together. We are a part of a cluster named “The Local Group”. THis cluster has about 30 Galaxies. Three of these galaxies are large and the rest quite small.

      The largest galaxy in the Local Group is Andromeda. Though this galaxy is our neighbour, light takes 2 million years to reach us from there!

      Our Milky Way is the second largest galaxy in the Local Group. The third largest is the Triangulum galaxy which contains about 50 billion stars.

      Our Local Group is near another cluster called the Virgo Cluster. The Virgo Cluster is HUGE. It contains about 150 major galaxies and about a thousand smaller ones. This cluster is about 100 million light years from the Local Group.

      The Local Group along with our neighbouring clusters like Sculptor Group(5 large Galaxies) , Maffei Group(16 galaxies), Leo I Group , Virgo Group( 150 large Galaxies ) and several others form what is known as the Virgo SuperCluster. THis is our intergalactic area of space. THis is our home ground 🙂

      The universe has millions of such Superclusters.

      The gravitational pull of the Virgo Cluster is so huge that it is pulling our Local Group towards itself. One day our Local Group would no longer exist as an independent cluster of galaxies. We will become a part of the Virgo Cluster.

      See the attached pictures:


Pic 1) The Virgo SUpercluster: This is a “map” of our local neighbourhood. See how large the Virgo Cluster is compared to the LOcal Group.

Pic 2) The Andromeda Galaxy: THis is our immediate neighbour. It is about 2 million light years from us and is the largest galaxy in the LOcal Group.


Enjoy your smallness,




  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                 

  Instruct the planets in what orbs to run,                          

  Correct old time and regulate the Sun;