natural selection

to cull out, weed out

a culling out, weeding out / (especially in biology) a selection

weakness

weak, powerless, vulnerable, vincible, delicate / weak, inept, incompetent / low tolerance

nature / spontaneity

world / border

boundary / a bounded area or region / a bounded group of people, a society, a world as a social grouping, such as business, celebrities, or finance / the border edge of a thing

border, boundary, limits

natural / spontaneous