Reproduction creates competition. Many organisms don’t survive to maturity, and the ones that do compete with each other to maximise the prevalence of their own genes in the next generation of offspring.

This kind of competition between genes is reflected in fierce competition between individuals of a species, which forms the second fundamental framework around which ecosystems are based.

[Two stories of sexual selection in species]

[Perhaps tell the story of how plants developed flowers as a means of accelerating fertilisation]