Seed of humanity

They live a few years, and reproduce. But they came to a halt when they realised they can't reproduce.. 1 man 2 women? His children can't reproduce with the other wife's children because they have alot of genes in common from their dad, resulting in birth defects. Humanity will die off if it keeps on going relying on babies with birth defects.

Achievement gained: A faulty tree
End Of Story