Re: Earthworm have both male and female parts but cannot fertilize themselves.

Hi Judy

Earthworms are members of the 'oligochaetes' (means 'short bristles') 
which is a Class of segmented worms or Annelids (means 'little rings'). 
All oligochaetes are hermaphrodites (they have male and female 
reproductive organs) and most (except a few isolated cases) are unable to 
self-fertilise.

This means that they have to reproduce by finding a mate and therefore 
provides an opportunity to maintain genetic diversity and avoid 
inbreeding. Any basic biology/genetic textbook should tell you about the 
advantages of genetic diversity and a larger 'gene pool'.

Also, as they are hermaphrodite, when they mate, both individuals can be 
fertilised, so twice as many young may be produced, all of which share 
genes from two separate individuals - so, given their particular ecology 
and body plan, this IS advantageous to earthworms, and their well-
developed reproductive system is seen as being highly evolved and 
specialised.

I hope that answers your question,

Dr David Hubble, UK