The ‘Y’ of it all...

The ‘Y’ chromosome is unique in that every male in a family line will have an identical copy of the same chromosome for all time (plus any mutations over time). Females, on the other hand, will have one ‘X’ chromosome from the father and one from the mother. A daughter will always have one ‘X’ from her father, but her daughter (grand daughter to the mother) may not, which means the effect of any individual ‘X’ chromosome is diffused into the general population and not confined to a single line as is the ‘Y’. Thus, within a family line, this means the daughters may not have ANY of the original male parent’s DNA after a couple of generations, but sons will always have at least the genes on the ‘Y’ chromosome.

Genetic studies have demonstrated that about 10% of the males in Central Asia (and 0.5% of the world’s population) are direct descendants of Gengis Khan – which is quite the genetic legacy. Similarly, the Kohenim, the hereditary tribe of Jewish ritual priests (not rabbis) generally have the same ‘Y’ chromosome. So, we have a unique piece of genetic information that is reliably transmitted for generations, but what does that mean and what characteristics does it influence?

‘Y’ it is special

Genes on chromosomes are usually paired, with one partner providing ‘his’ copy of a particular gene and the other providing ‘her’ copy. This means that the effect of the gene will be the ‘average’ of the two, one copy may be suppressed, or they may act in concert. This is highly beneficial in that a single bad copy does not necessarily mean disaster for the organism, and in fact, a single ‘bad’ copy can be beneficial in some circumstances. For example, populations in the malaria belt may have modified copies of a gene for hemoglobin, which when paired with a normal gene gives the recipient some resistance to malaria and improves their chance of survival. The down side to this is that if both parents have the same modification, there is a 1 in 4 chance a child will be born with a severe ‘genetic’ disease (sickle cell anemia, etc) and not survive to adulthood.

This demonstrates the importance of having paired genes in most chromosomes, but this is not the case with the ‘X’ and ‘Y’ chromosomes, which are not paired. This lack of pairing means that a defect in a gene on the ‘X’ chromosome can’t be overridden by a paired ‘good’ gene on the ‘Y’ chromosome. Diseases caused by this are referred to as ‘sex-linked’, or ‘X-linked’, such as hemophilia. Such diseases can only affect the males of a line, but daughters (who can have both a good and bad gene copy) have a 50% chance of ‘transmitting’ the disease to their daughters. Since there are many clear examples of specific genetic diseases relating to the mismatch between the ‘X’ and ‘Y’ chromosome, there must be other factors which are influenced as well.

Both smarter and dumber

One important factor is IQ, which, depending upon the metric used, is up to 80% inherited. In a given population, the average IQ of men and women is identical within the precision of any IQ test. However, the distributions of IQ are different for men and women; the distribution in men is wider than that for women, which means the smartest fraction of men will always be smarter than the smartest fraction of women. In other words, there are more ‘very smart’ (and also very dumb) men than women, and there are many historical examples of high talent being transmitted in the male line. NOTE that this does NOT mean intelligence is determined by just the father’s DNA, only that the ‘Y’ chromosome creates higher variability, for good or ill.

Boys will be boys...

Other ‘Y’-localized factors seem to be related to behavioral patterns; boys and girls differ in temperament and preferences from the earliest ages and continue to diverge throughout development. Twin and other genetic studies show that much behavior, perhaps even complicated behaviors, preferences, drives and other factors which make up a personality are strongly inherited, with perhaps less than 20% coming from shared environmental factors (family, upbringing, etc). It is clear that there are many other loci common to both sexes which affect intelligence and behavior, but at least some factors which make up sex-associated differences must be present on the ‘Y’ chromosome for this behavioral divergence to manifest. This also means, as with IQ, the variability of behavioral traits are likely to be greater in the male than in the female. So - what does this mean in evolutionary terms?

Anyone for a hook-up?

A woman can almost always find some male to impregnate her, regardless of her status, wealth, looks, etc. However, (except in the case of rape) men have to have qualities which make a woman receptive to them, and those who cannot find a willing mate will not have male children to carry their ‘Y’ chromosome. Because of the singular nature of the ‘Y’, sexual selection will concentrate its effects there and those effects will be carried by the male line. In addition to behaviors which affect mate selection, there are also factors which have an effect on the survival of offspring.

Gotta feed the kids

Historically, children from low-status families and those in mother-only households had a greatly reduced chance of survival. Thus, a father too stupid to make a good living or so violent that he got himself killed was less likely to pass along those attributes to his male (or any other) heirs. Since mankind is a quintessentially social animal, behavior will also affect how a person fits into a culture. Behavior outside whatever is accepted by a culture will reduce a society’s cooperation with him and likewise reduce his chances of successfully siring and maintaining heirs. Over a period of time in a culture with few outside influences (as was the world until quite recently), there will a tendency toward physical and behavioral homogeneity, particularly in males. In other words, people and cultures tend to co-evolve, and the bulk of the cultural molding is carried through the male line on the ‘Y’ chromosome because of its unique persistence. One can see this anecdotally in stereotypes of cultures: “The Irish are…, Russians are always…, Swedes can’t…, Germans tend to...”, etc. These stereotypes stem from the observed behavior of the ‘average’, or prototypical member of that culture and are often somewhat accurate. This intra-cultural homogenization seems to be expressed most highly in relatively isolated cultures, some examples being the Japanese, Koreans, Icelanders and Pacific Islanders. This says nothing about which behaviors are better or worse, only that those behavioral characteristics worked best in that culture and so enhanced the chances of survival of the gene set which promoted it.

Yup – we run the place!

In conclusion, yes Virginia, there is a patriarchy, and there will always be one because of the peculiarity of inheritance carried by the ‘Y’ chromosome. Strong cultural mixing will disrupt traditional behavioral patterns for a time, but history shows that civilizations are fleeting at best, and eventually relative cultural isolation will again become the norm, starting another round of cultural/genetic co-evolution, dominated by males. Sorry...