All the adaptations brought along the long and difficult road to colonise the earth produced species that were increasingly better equipped to face the challenges of survival. But all of these achievements, over millions of years, were only possible because each and every one of these living beings was capable of producing descendents.
Perpetuating the species, continuing the process of life is a risky, dangerous mission. You have to find a mate, competing against other candidates, find the right place to bring your children into the world, build a home, defend them from enemies and feed them until they become independent. An exhausting task, simply to pass on your genes to future generations.