What did darwin believe was the primary cause of evolution?

→ Darwin believed that the need to adapt, in similar words, the changes occruing in the environment caused evolution.

The main cause of evolution, according to Darwin, was natural selection. Natural selection is a process in which a group of organisms with certain characteristics survive and thrive, in comparison to other organisms with different characteristics. This idea basically means that having some characteristics makes you suited for an environment.

And how would that ↑ explain Evolution?

Well, evolution is the change in species that occurs during time. But for you to change, there must be a cause for that change, which is none other than the need to survive, reproduce, etc.

→ As mentioned before, not all characteristics are enough to surive, and hopefully the image pasted below will help you.

Hope it helped,

BioTeacher101

answer; i believe that the correct answer is(d) nondisjunction during meiosis;