Why are some babies always fussy and crying while others are always cheerful?

Question

I have noticed this very often. I have seen babies who are cheerful ever.
My brother in law's daughter has never (not literally though) been seen crying/fussy etc.
While as my brother's baby son is always fussy/crying.
In hospitals too I have noticed the pattern with the visitors. No, I am not talking about ill babies.

I would like to understand what causes such huge temperament differences among babies.

One thing more I have noticed is that the fussy babies are usually weak and the ever cheerful babies are mostly healthy.

Is this related to health?
Is this genetic?

Answer 1

While fussiness can indicate underlying problems, it is less a sign of weakness than a sign of sensitivity. If a baby is sensitive to noise (even a particular sound) or bright lights or certain textures, he may become fussy in those environments. It's his way of telling you he's uncomfortable. Sometimes it is difficult to figure out why he's fussing, but as you try things, you learn more about your baby. Children may outgrow some of their sensitivities as they age, but some will stay with them.

There is a body of psychology dealing with highly sensitive persons. You can read a little about it in this article from Psychology Today: The Highly Sensitive Child by Maureen Healy or on this website: The Highly Sensitive Person written by Elaine Aron, a researcher in the field of Sensory-Processing Sensitivity (SPS).

Answer 2

Short answer (and apologies to MetaFilter): babies are weird. Personality is something that starts developing from day one, and it is influenced by both genetic and environmental components. My daughter's a more apprehensive person than my son, and while generally happy as a baby, wasn't of the super-bubbly-isn't-life-grand outlook on life and could be VERY fussy (and at nearly 5, is better but still doesn't look at new situations with positive anticipation). My son was a "Gerber baby" in the parlance of our families; super cheerful, loved surprises and new things, would happily be held by anyone. He never went through the bad separation anxiety that she did, and is generally a more relaxed individual when it comes to new situations.

They're both super-healthy squirts, and get personality traits from both sides of the family. The daughter, while unhappy with changes to her schedule and routine, also has never met a stranger, which is TOTALLY like my father and TOTALLY unlike me and my husband. My son is rather unflappable, just like me, but can flip out when he's frustrated, just like his father. It's fun to see the different personality traits show up and realize just how individual each child is.