Two routes to knowledge

Today I had a frivolous discussion with one of my junior colleagues on whether 'explanations' should start from cause or from the effect. To illustrate, if one asks you why have men evolved into two eared creatures, you may answer

1. for biaural hearing
2. to put on glasses

This is teleology. The answers are not really a cause at all, but effects of having two ears. The real reason of having two ears is that's how evolution has shaped them.
I would like to hear from anybody interested.