For ethnicity/race, we have a thread for that: http://talk.collegeconfidential.com/college-admissions/1843141-race-in-college-applications-faq-discussion-12.html#latest.
Very few non-religious men want to attend colleges where the student population is almost all male. That’s partly why there are only four secular all male colleges left in the US. To a lesser extent, I assume most women don’t want to go to a college where the sex ratio is too lopsided either, although more all women’s colleges have survived into the 21st century.