One design; common descent.
This is called Occam's razor. The simplest hypothesis is assumed to be the correct one.
The reason the simplest hypothesis is assumed to be the correct one is that more complicated hypotheses have more opportunity to run into a mode of failure. In a Rube Goldberg contraption, what happens if the cat wakes up before the spoon taps it?
Life only has to begin, and find a niche where it can survive. Then it will go forth and replenish the land.
You still need a Creator, but you don't have to stick Him in a sweat-shop cranking out almost-duplicates for eons.
He can push the button and take the rest of the day off.
He didn't. He created them capable of reproducing.
He can push the button and take the rest of the day off.
He did. The seventh.