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“Humans adapted to their environment using reason, adaptation is why they survived, humans have the capability of reason”

This is a non-sequitur, and a misstatement. Reason isn’t an all-or-none proposition. There is a wide spectrum of reasoning ability.

It’s not circular if you don’t try to force it to fit your conclusion:

At some point in the development of life on earth, due to a combination of factors, some creatures had a greater ability to reason reliably (for a very primitive definition of reason). They were more successful/prolific as a result of this ability (better able to evade predators, better able to find food), and the increased ability to “reason” became more common over time.

Fast forward to early hominids, where the ones who can figure out cause-and-effect and so on are more likely to live long enough to produce offspring (or produce more offspring). The ability to reason has by now grown to the point where truly-complex thought is now possible. More, or higher-quality, food means more fuel for the growth and functioning of the brain. Plus, those who have the genetic factors that would permit a larger brain *if enough food were available*, and it becomes a synergistic loop. Bigger brains are better able to reason out how to obtain food, and more food means the brain works even better. Those individuals who were able to realize their genetic potential for large brains capable of complex thought then pass that genetic potential to their offspring.

This (eventually) brings us down to today. Were it not for the success our more primitive ancestors had in being able to reliably reason and thus improve their own lot (and energy intake), we would not be the reasoning beings we are today. All the way down the years, if reasoning could not be trusted, and thus not able to contribute to a creature’s ability to thrive and out-compete its rivals, it would not have persisted.

The above is meant to demonstrate that it is entirely possible for evolution to result in a reliable ability to reason. In other words, we can trust the reasoning ability our brains, even if that ability arose as a product of evolution, because unreliable reason demonstrably would not have benefited life at any point, while reliable reasoning would.

This is a non-sequitur
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Nope. It relates directly to your argument. A non-sequitur would be something like “Reason is a fish. We evolved from fish, so reason evolved.’

https://en.wikipedia.org/wiki/Non_sequitur_(logic)

To more sharply define your circular argument, it is “begging the question”, where you include the very thing you’re trying to prove (that we survived because reason evolved) in the proof itself (because of reason evolving, we survived).

http://www.nizkor.org/features/fallacies/begging-the-question.html