Well, it's the egg.
All beings come from unicellular beings and what's an egg? a developing unicellular form of life.
Actually every embryonary evolution stage is a fast-forward copy of actual life evolution. For example, very early-staged human embryos look are one cell, then a handful cells, then they look like simple fish, several weeks later they get arms and legs, after a couple of months the tail shrinks and nearly disappears. Well, this is exactly our evolution branch. Hereafter, the first egg was a bacterium.
/ –
