They have to exist or not in their own right. I mean, with kids, you don't say, 'Which is your favourite,' or 'Which did you enjoy bringing up the best?'
What greater thing is there for two human souls than to feel that they are joined - to strengthen each other - to be at one with each other in silent unspeakable memories.
Sometime during the many millions of years that have elapsed since mammalian faunas came into existence, some sort of island crossed from West Africa to South America.