Sexual reproduction because in that the genes combine in an almost random process unless it is affected by natural selection, this causes an increase in the gene pool of the population making. This results in evolution and as the population of one place can change so much it can become another species.
Biodiversity plays an important role inecological health as much as it does for human health. ... Ecosystem engineers aredefined as: "...organisms that directly or indirectly modulate the availability
If you look at Cosmos episode 1, I'm sure you find an answer there.
Then maybe we would die because sometimes we people eat fish and also the ecosystem of the ocean like the animals that eat fish such as sharks.