Here is a picture of mine when I was a baby. I looked quite fat. I don’t why. Most babies look as fat as I was. Why?
The ARE fat. Not a lot of lean muscle yet-- the gym inside the womb is not open very often.
Because they are fat.
Googling suggests that the weight of a healthy 2-month-old infant is around 25% fat.
Since we’ve established the fact they are fat, a couple of reasons:
First, babies grow best if they have a steady source of energy. A little baby fat can help provide a cushion if the parents are having trouble scrounging up enough food. The fact that “in the wild” a baby’s nutrition comes from milk puts a second buffering factor in there. The mother’s own fat reserves can help support baby even if her food sources are unreliable.
Second, heat loss is largely a function of mass to surface area. As you get bigger, the ratio of surface area to mass gets smaller. If we’re talking cubes, a 1x1x1 cube has a surface area of 6 and a volume of only 1 (an SA:V ratio of 6:1). A 2x2x2 cube has a surface area of 12 and a volume of 8 (an SA:V ratio of only 1.5:1). A baby with the proportions of an adult would lose body heat very quickly. It makes sense to keep them a little chubby until they get big enough to regulate heat loss better.
I’ve seen this come up in articles about rescue work after disasters like earthquakes. Babies will often survive longer trapped under rubble and such than adults because they have those fat reserves. I’m sure it was very important in the past when famines were pretty common.
fat, poop and puke along with a face is what a baby is.
You left out pee, drool & snot - “A collection of uncontrolled orifices.”
But engaging, for all that.
Not only do babies have more fat than healthy fatted adults, but they have a higher percentage of brown adipose tissue, a kind of body fat that produces heat. Again, because they have such a high surface area that they need another mechanism to keep warm.
Please note that this body heat loss issue doesn’t mean you need to bundle your baby like he’s going on an Alaskan expedition when it’s a little cold out. They have these adaptations already, they don’t need all that much more help. Holding them skin to skin *or *putting just one extra layer on them is all they need to stay as warm as you are.
Babies also have shorter limbs in proportion to their body size. This makes their heads and bodies look large compared to their overall size.