Survival of the fittest: Raw competition? Intense cooperation? Both are essential. Interactions between and within species are among the most powerful evolutionary forces on Earth, and understanding them may be a key to our own survival. In evolutionary terms, sex is more important than life itself. Sex fuels evolutionary change by adding variation to the gene pool. The powerful urge to pass our genes on to the next generation has likely changed the face of human culture in ways we're only beginning to understand. .