Why is there sex—or, more precisely, sexual reproduction? If you're an evolutionary biologist, the answer isn't obvious. Sexual reproduction is biologically costly, requiring not only competition for mates but also the creation of entire populations in which only half the individuals can give birt h. That reality has led scientists to wonder why it arose in the first place. After all, in asexual reproduction—as occurs when bacteria divide—not only can you skip the wooing and its costs, but every individual is a potential mother. ...read more read less