Dozens of genes found in humans today have been traced to Neanderthals and Denisovans. They made their way into the human species when some of our direct ancestors mated with ancient lineages that are now extinct.
Interbreeding like this happened in Africa and in Eurasia, producing many human hybrids – you can read more about them here. Recent genetic decoding has revealed that it partly accounts for differences in our physical appearance – things like skin and hair colour – and affects our health.
Some of this “undead” DNA even helped us survive in places we were otherwise ill-equipped for. Here are four examples.