6 ideas
Organisms must constantly evolve just to maintain their current fitness, because their parasites, predators, and competitors are evolving against them in real time. Like the Red Queen telling Alice she must run to stay in the same place, survival requires perpetual change with no permanent advantage.
Sexual reproduction is costly and inefficient compared to cloning, yet it persists because shuffling genes each generation lets hosts produce offspring with novel resistance combinations parasites haven't adapted to. Genetic variety is a defense mechanism against fast-mutating pathogens, not a way to spread good genes faster.
Human desires, preferences, and emotions are best understood not by what they consciously aim at but by how they historically improved reproductive success. Jealousy, status-seeking, and mate preferences are explained as solutions to ancestral problems of passing on genes, regardless of present-day intentions.
Traits that hurt survival, like the peacock's tail, evolve because the opposite sex prefers them, and that preference itself becomes self-reinforcing through runaway selection. Females choosing showy mates produce showy sons and choosy daughters, locking the costly ornament into the population.
Because females invest far more in each offspring (pregnancy, lactation) than males, the two sexes evolve different optimal strategies: females are choosier and seek quality, males compete for quantity of access. This asymmetry, not culture alone, predicts widespread differences in courtship and promiscuity.
Human intelligence, language, and creativity may have ballooned not because they aided survival but because they served as sexually selected advertisements of fitness, like the peacock's tail made of mind. The brain becomes a courtship organ whose extravagance signals genetic quality to potential mates.