Only the best will survive

Just came back from a field trip at Smith Lake, a nation park locates 320km north from Sydney. We did quite a lot of sampling and experiment to study how to detect human impacts on ecosystem and environment.
One of the experiments is to set small mammal traps to trace the biodiversity within the region. A primitive marsupial little mouse, antechinus, was caught. According to my professor, this Australian native animal produce 10 to 12 babies each time and these tiny young will attach babies attach themselves to the mother's teats for about 25 days to a month after their birth. However, the mother antechinus only has 6 to 8 teats which imply that competition starts once they come to our world. It sounds cruel but it just the way of evolution. That is what Darwin said that only the best will survival.
By the way, competition seems start even before life begins as only one of the millions sperm can win the game.

Caption: Babies in the pouch of an antichiuns.