Which article is better to use?

Question

When we introduce an animal in a story or or an article, should we use THE or A / AN?

Some of what I have read made use of THE while some made use of A / An.

For example, 'the giraffe' is the tallest animal. Why can't we use 'a giraffe' in this sentence?

Thanks for your help.

Answer 1

This site might help clarify it for you.

http://grammar.ccc.commnet.edu/grammar/determiners/determiners.htm

"The is required when the noun it refers to represents something in the abstract"