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On average, men are about 13 centimeters (5 inches) taller than women. This is something that is pretty easy to see just by looking around in a crowd of people, but that does not mean that it is easy to figure out why it is the case.
In fact, this height difference has stumped scientists for quite a long time.
It has long been known that the gender hormones likely had an impact on this, but researchers could not find the genetic mechanisms that caused it to take place. They long assumed that the genes that caused men to get taller would be found on the Y chromosome, which only men have.
This is a very reasonable assumption, but if the new study published in the Journal of Human Genetics proves to be correct, that assumption would be wrong.
The paper cites other studies that look closely at a gene known as SHOX, which is on both the X and Y chromosomes, so it is processed by both men and woman. The fact that it is on both types of chromosomes meant it was often ignored when studying height, given that scientists thought the cause for the height difference would be found only on the Y.
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One particularly useful study they referenced had height and genome data from nearly a million people. Out of that million, 1225 had chromosomal aneuploidy, which is a condition where the individual processes an atypical number of one or the other of the chromosomes.
When the individual had a higher-than-normal number of Y chromosomes, they had an average of 3.1 centimeters (1.2 inches) of extra height compared to those who had extra X chromosomes. In the study, the authors wrote:
“This finding is consistent with the hypothesis that reduced SHOX expression in females results in a net difference in height between the (***).”
While the evidence is very strong that the SHOX gene is largely responsible for this expression of dimorphism in humans, it is likely not the only factor. Height can be influenced by many things including nutrition, so differences in cultural diets for men and women may also contribute.
In the end, while this study may not answer all the questions regarding height, it does help explain the differences and will help future researchers expand their knowledge in this area even further.