I am trying to write a paper on Sexual Selection. Any advice on where to look for research!

Depending on what you already know and what kind of paper you want to write (I assume it is something like a term paper?) you may want to first check textbooks and maybe wikipedia to get a general idea.

 

Then check Pubmed for instance and pick out reviews of specific cool examples to make your paper stand out. Homosexual rape and sexual selection in worms ´, for instance.

However helpful Wikipedia may be, and however factual most of the content is on it, your teacher/professor will most likely not recognize it as a credible source. I agree that textbooks would be a good place to start, though be wary of books not published in the last five to ten years or so.

That's why they invented a scroll wheel. To scroll down to the end of a wikipage to read and click on the sources and references.