What would happen if there was no natural selection?

Answer 1

A hypothetical universe in which natural selection did not occur would

- harbour no life, hence nothing for natural selection to act on, or

- be different from the reality we know to such a degree that no meaningful statements can be made about it using terms applying to this reality.

But, as an exercise of the mind, we'll consider just one possible (well, impossible, in our reality) scenario: think of an organism that replicates perfectly. It does not produce variation of any kind. Each offspring is an exact copy of the parent. Such a population, in a universe where such an organisms could exist, could grow, leading to an expanding population of exact replicas. Doesn't sound very exciting, does it?

Okay, let's consider a second scenario, just for the heck of it. Think of a population of organisms replicating with variation, but where each variant (somehow, through strange perversions of known laws of physics) has the exact same chance of obtaining food and replicating. This might result in an expanding population with much genetic diversity, but each variant would be equally represented in the population gene pool. There'd be no distinct species, just a fine gradation of morphologies spread throughout the ecology. An ecology that, as mentioned above, would have the (physically impossible) capacity of providing an unlimited amount of everything they need to each of those critters.

In other words, speculating about what life might look like without natural selection is interesting, but has no real applications, since such conditions could never occur in this universe.

Answer 2

No. What would be there to select from if there were no organisms that had traits that gave them greater survivability and reproductive success over their conspecifics?