Although some men of average height marry taller women, most shorter males who are eager to marry and start a family will seek females of the same height.
This stems from the evolutionary theory that proposes that we as humans naturally strive to be self-interested because this is what will help ensure our survival. Self-interest is a way of life for humans and it has that men preferred similar physical stature because it could signal more reproductive potential.
For example, if a man marries someone who is five inches taller than him, their offspring may be 12-14 inches taller than his.
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The same applies to women, specifically shorter females. If a short man chooses a tall woman, their children will be far smaller than the parents since they will be 6 inches taller than the parents which are not enough to warrant carrying on their genes.
In contrast, if a tall man chooses a short woman, his children will generally inherit his physical traits as he is only 1-2 inches shorter than his wife.
In general, men choose taller wives to ensure that they can have bigger families whereas women tend to prefer taller husbands so that they can be in charge of the household and provide food for their children.