Like father, like son: What is special about being male?

We never bought gender-specific toys for our son until he started asking for cars. At 19 months he discovered his grandfather’s car (we don’t own one) and he was fascinated. He is two now and he’s in love with things that have wheels; cars, diggers, motorbikes, trucks, trains etc., but he never wanted to play with the dolls I have at home.  He is a two-year-old boy in love with cars and football, just like his father. What is special about being male that they prefer cars over dolls?

Well, there is all the psychology and sociology behind this question but as you can guess, I will address the biology: Males have the Y chromosome.

Our DNA is folded into thread-like structures called ‘chromosomes’ so that it fits into our tiny cells. Male or female, we all have the ‘autosomal’ chromosomes in pairs numbered from 1 to 22 with plenty of genes and other stuff on them. Then, we have the two gender chromosomes X and Y. Females have a pair of the X chromosome, males have an X and a Y. And it’s the few genes on this single Y chromosome that establish the male gender. Activation of one gene named SRY (Sex-determining region Y) initiates a series of events that eventually lead to the release of male hormones and, therefore, development of a baby boy. (see ‘Mum, why do I have blue eyes?’ for basic information on DNA and genes)

The Y chromosome is also unusual in the way it is inherited from father to son. While all other chromosomes undergo some sort of shuffling during development, the Y chromosome escapes this. It only undergoes rare single letter changes on its DNA. This makes the Y chromosome an excellent and relatively simple source for looking into our evolutionary history. For example, analysis of changes on the Y chromosomes locates the first ancient human male populations to Africa.

Now, there are no studies that link Y chromosome directly to the behavioural preferences of boys, but there are clues elsewhere. A study that measured babies’ visual attention in cars or dolls found that baby boys were more interested in cars than dolls while baby girls were more interested in dolls than cars*. This means we have some degree of an innate (most likely hormonal) choice for the kind of toys we would like to play with. Since hormones in boys are triggered by genes on the Y chromosome, we could assume there is some genetic background to boys’ love for cars, but more research needs to be done to verify that.

And guess what? Vervet monkeys also showed similar preferences**, suggesting there is an evolutionary force that awakens inside us as babies, telling us what to play with. Why? There is no definite answer to this, but possibly because of the tasks that men and women have undertaken as adults in our evolutionary history.

We will encourage our son to care for baby dolls and play with kitchenware because we believe such toys could introduce him to important future skills such as fatherhood and cooking. You reckon that’s going against the forces of the Y chromosome and evolution?

Betul

Here is some more information about the Y chromosome and also related genetic abnormalities:

 

References:

Eggers, S. and Sinclair, A. (2012). Mammalian sex determination – insights from human and mice. Chromosome Research 20, pp.215-238.    Pubmed: 22290220

Jobling, M.A. and Tyler-Smith, C. (2003). The human Y chromosome: an evolutionary marker comes of age. Nature Reviews Genetics, 4, pp.598-612.   Pubmed: 12897772

*Alexander G.M., Wilcox, T. and Woods, R. (2009). Sex differences in infants’ visual interest in toys. Arch Sex Behav., 38, pp.427-433.   Pubmed: 19016318

**Alexander, G.M. and Hines, M. (2002). Sex differences in response to children’s toys in nonhuman primates (Cercopithecus aethiops sabaeus). Evolution and Human Behavior, 23, pp.467-479.

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