Why do we have milk teeth?

[Eels]

Why do mammals have milk teeth? Is it simply because it allows for the rapid erosion caused by a milk diet in the early years of life? How did it come about in evolutionary terms?

[Ethel]

Milk teeth are much smaller than permanent teeth, and I think most mammals would be unable to accommodate a full set of permanent teeth in their small baby mouths.

The milk teeth are already present in the gums at birth - they don't have long to develop. The permanent teeth are much harder, as well as being bigger.