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[Hawkeye]

A little closer to home, humans have grown increasing their average height by about 30-40cm since the 1500's because of diet and health changes over time. The Japanese have exhibited similar growth rates in the last 100 years or so because of moving from a rice and fish diet to a higher energy western fatty diet. That is body adaptation.

I think with snakes it is a matter of the head is mainly bone and that has a slower growth rate than muscle/fat of the snakes body and hence you just get a disproportion for the period of time it takes for the head to catch up (and hence the ability for the head to catch up as Paul stated).

This is all theoretical however but seem to fit what happens.

In humans, the head is initially bigger at birth and the body catches up until the bones all fuse but if you give growth hormone the rate increases remarkably but still stops when the bones fuse (in early 20's).

Cheers Hawkeye