Why are Siblings different?

Question

I have noticed that the Second Child of a muliple child family is usually bigger than the first.

So, does the original fetus become a template for next? And does the next grow larger because the womans body already understands the hormonal changes? Programmed?

Have a look around,...2nd borns are usually larger than 1st borns and this even spans gender separation within families.

Answer 1

The difference would be a function of the nurture not nature.

Answer 2

In my expeience that's not necessarily true. I'm not bigger than my brother and he's two years older. My best friend is smaller than her sister who is three years older. If I stopped to think about it.....and had the time to honestly! I think I would find that it is maybe a fifty fifty split between the second born being bigger or not. Siblings simply differ because of the way the genetics of the parents combine in each situation. And, of course the diet of the mother during pregnancy and the diet and situation while children are growing up can have an effect as well.

Answer 3

Mmmm. No. My dad's younger brother is the same size as him. The children in my mother's family are all about the same size. My bf is smaller than his sister. (I have no sibs).

Any reason for a child's size at birth and during fetal development is largely genetic. What the mother eats usually plays no part in the baby's size, just hers. A woman's body is "programmed" for child birth the minute she is born. Any reason for a child to be bigger as it grows is a result of both genetics and nurture, not its placement in the line of siblings.

Answer 4

There has been some research on this topic. There are a lot of variables here. You need to look at same sex siblings. Obviously you cannot validly compare girls with boys. You need to ask whether you are looking at birth weight, which would be affected by nutrition in the womb, or adult weight and height which would be affected primarily by what you eat.

There is some relationship between birth order and birth weight -- second and third babies tends to be larger.

Answer 5

well, everything's a mixture of genes and the environment..it depends on which genes the 2nd baby gets from his/her parents.. and of course, most of the time, the mother knows better the second time around... :)

Answer 6

Good observation, but I don't know why that is.

Maybe the mother's body is used to pregnancy so she eats more with less vomiting?

Answer 7

i think it's more of genes distribution... it's not always the same...