The evolution of a species looks like a single thread.

But it's actually a succession of particles.

Many of those particles die out, some of which survive just long enough to bud off a new particle or two before also dying.

It's an ever-so-slight edge for those particles that persist into the future, not a point but a small streak as they persist just a little bit longer, creating a fiber that will be spun into the thread of the collective.

The species is one collective but it's composed of individuals who all die, some sooner than others.