This question is from a friend (as the result of a very weird conversation). She believes that it would be natural for boys to always end up taller than their mother. I’m not so sure so I want to see what the teeming many can come up with.
Males on average grow taller than females. Therefore, sons are normally going to be taller than their mothers, or most other women for that matter.
Especially women from the previous generation, because humans get taller and taller.
I’ve been told that a good way of predicting a child’s height is the following:
Let the father’s height be x and the mother’s height be y (in inches).
For a boy, the most likely height is (x + y + 5)/2.
For a girl, the most likely height is (x + y - 5)/2.
This is because adult men are about five inches taller than adult women (and some other facts about the inheritance of height which I won’t go into).
You can see then that the most likely height for a son is (x + y)/2 + 5/2. Since the average difference between the mother’s and the father’s height is that the father is five inches taller, this means that on average the son will be taller than the mother. Of course, this doesn’t mean that sons will always be taller than their mothers, just that on average they will. Indeed, there are (somewhat unlikely) circumstances where you can even predict that the son will probably be shorter than their mother. Suppose the mother is nine inches taller than the father (so x = y - 9). Then the formula predicts that the most likely height for the son is ((y - 9) + y + 5)/2, which equals (2y - 4)/2, which equals y - 2. So if the mother is considerably taller than the father, the son will probably be shorter than his mother. But, once again, this is only the most likely height, not what it will always be.
As Der Trihs says, most male children grow up to be taller than most women. If you pick any random woman and any random male newborn, the child will grow taller than the woman in most cases. So of course most male children grow up to be taller than their mothers.
The other point to bearing mind in regression towards the mean. Basically any child will have the average of their parent’s traits. So any child will have the average genetic growth potential of mother and father. Note however that this is genetic potential. There are also a very strong hormonal effects on growth, and males will grow taller than females. As a result males will on average be ~3 inches taller than the mean height of their parents, 3 inches being about the addition that being male adds to genetic potential.
There are only two times you are likely to get an exception. First is if the mother is genetically *much *taller than the father, at least 4 inches taller. In that case case the male growth advantage may not be sufficient to counter the regression to the mean. The second is if the child is physically prevented from growing due to disease, illness or stress. In those circumstances taller women may very well produce sons shorter than they are.
Or in simpler form, males will on average be ~3 inches taller than the average height of their parents. 
Well, two and a half, but you get the point.
And the formula doesn’t imply that there’s any specific height gain from having a tall mother or father.
I think the formula may be a good baseline, but not 100% accurate. My brother and I are both between 6’0" and 6’1", and our dad’s 6’3" and mom’s 4’11", so by the formula, we should both be 5’9" and a half-inch.
Also, according to the formula, my son ought to be 6’3" and a half-inch- our heights average to 6’1". I don’t know if that’s the case- she’s freaky tall for her side of the family (dwarfs all but the tallest men, including her grandparents, parents and sibling), while I’m tall for my mother’s side, but about average for my father’s side.
I suspect he’ll end up at least my height, and probably closer to hers, but I don’t know if he’ll end up an inch and a half taller than her, and 3 inches taller than me.
Of course it’s not 100 percent accurate. It’s based on averages. I’m almost exactly the average of my parents’ heights- if the formula were 100% accurate, I’d be about two inches taller.
There’s probably more recent data by now, but this 2002 CDC report [PDF warning] says the average adult U.S. male is 5’9.6" and the average woman is 5’4.2." (They did stop collecting data when the subjects were 19.) That makes it pretty obvious most guys are going to be taller than their mothers. If you apply the formula posted upthread and assume two average-height people have one child of each gender who is also average-height, you get a son who will be 5’9.2" and a daughter who is 5’4.4." That is, you’d have a son who is a little shorter than his father but much taller than his mother and sister, and a daughter who is much shorter than her father and her brother and just a little taller than her mother.
I’m wondering why anyone would doubt this. It’s not like it’s any great secret that men in general tend to be significantly taller than women.
I am .5 inches taller than both parents -
well, I was a decade ago- now they are shrinking…
They were both 5’10" and I am 5’10 1/2"
I also understand that a child is approximately half its adult height when its aged two years. Assuming of course that it hasn’t any growth retarding illness at that time.
Does this match any parent’s observation?
I’m taller than my father, but not my mother. My brother (who has a different father) is taller than her.
Basically the differential in male and female heights is genetically determined, assuming proper nutrition to all concerned. Height genetically seems to be a trait that is due to several sets of genes that work together to determine height. Some genes make you taller than others. When you get genes from parents, on the average you get some talls and some shorts…but you may get only shorts from Mom and from Dad, or only talls from Mom and Dad…such are the benefits of sexual reproduction.
Males with identical height genes as females will grow taller. This appears to be the case when tall genes are in the presence of testosterone.
Of course, due to many factors such as nutrition and the genes present in populations (think pygmies and Masai), some females are taller than some males, but in all human populations, Males tend to be taller on average than females. There are many exceptions of course.
My daughter is exactly my wife’s height. My son is exactly my height.
Both are pissed off about it - my daughter would love to be taller (my wife is not tall), and my son doesn’t like being the tallest person around.
My father and mother are both 5’6" , give or take a 1/4 inch. I’m 6’ 2" . How did THAT happen?
Strictly unscientific, but for whatever reason based on the informal observations I’ve made re parent/child pairs I’ve seen in my life, it always seemed to me that if the mother being tall had more impact on the son being tall.
Put another way i almost never saw tall mothers with short sons, but did see tall mothers with short daughters.
This may be a general average but individual children vary widely in height and so relying on this will give you some very gimpy results. It would predict my daughter to end up at 6’3" or so, which seems very unlikely.
My mother was the same height I am (5’4"). I don’t know how tall my father was.
My step-father was 5’2". My first half brother is 6’1", next is 5’8" half sister is 4’10" last half brother 5’2"
One must look beyond just the pervious generation.
My dad’s 5’10", my mom’s 5’8", so I should be just under 6’ by the formula. I’m 6’3".
My sister is 5’7", but she had knee surgery in sixth grade and had to have her growth plate closed before surgery. According to those tests they do when you are a kid, she was supposed to be 6’. (And it predicted me at 6’2", which is pretty good.)