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* The heart of a woman is, on an average, smaller than that of Men.

* A smaller heart implies a smaller pumping intensity.

* Just as there is a cap on the height of a tree due to limitations imposed by work against gravity,

  a smaller heart in the case of a woman, supports a smaller frame (height and weight), due to the smaller pumping

  intensity.

 

How did this variation come about in the human genome ?  :vava:

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I think you’re confusing correlation – that women are on average less tall and massive than me, and that their hearts are on average less massive than men’s – with causation – that women are on average smaller than men because their hearts are smaller. Note that this is only an on-average correlation – there are many healthy, small-bodied women with hearts larger than many healthy large-bodied men.

 

Like all organs and the entire body, the heart grows in response to many factors. What causes the human body to eventually stop growing is not that it reaches the limit of what the body’s heart can pump blood throughout, but due to a complicated system of genes, signaling chemicals and regulatory hormones present in various organs, known collectively as the endocrine system. Along with other factors such as diet and exercise, this system ultimately controls the size of all of the organs, including the heart.

 

How did this variation come about in the human genome ? :vava:

Because heart mass correlates strongly to non-obese body mass, I think what you’re asking is actually why, on average, are women smaller than men?

 

The high-level answer for that the differences between men and women’s endocrine system that result in differing amounts of hormones that produce men and women’s reproductive organs and secondary sexual characteristics are usually also accompanied by differences in growth-regulating hormones. This doesn’t always happen – some women are taller than their male siblings, because of differences in their similar but slightly different genes, or differences in their gestation, births, or diet.

 

An exact explanation of why in humans – and in all our cousin species in our biological family, the great apes – males are on average bigger than women is something of a mystery. The simple answer is, as with all evolutionary biology, that populations where women were on average smaller than men had an evolutionary advantage over ones where they were not, so had more descendants, so that now most populations are that way. Why this is where the mystery and scientific speculation enters into the question. Most anthropologists, I think, speculate, based in large part on observing our great ape cousin species’ behavior, that it is because males physically fight one another to decide who mates, while females do not, so evolution has selected for males who are good at this kind of fighting, and thus large and strong, but not selected this way for females.

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