The human brain and its associated mental capacities evolved to assist self-preservation.
Conclusion (So)
An individual's aesthetic judgments must be evaluated in terms of how much they promote that individual's survival.
Intermediate Conclusion (Thus)
The capacity to make aesthetic judgments is an adaptation to past environments in which humans lived.
Evidence
The brain and its mental capacities evolved to assist self-preservation.
Evaluate
There two conclusions drawn, so technically the answer could deal with either reasoning move, but the first reasoning move from claim 1 to claim 2 seems pretty solid (and is already a less likely target, given that it's an intermediate conclusion).
It's essentially assuming that . That's pretty boilerplate natural selection thinking, so the answer probably won't focus there.
The move from Intermediate to Main Conclusion is based on two different claims about aesthetic judgments:
Since they "evolved to" assist self-preservation they assist self-preservation.
Goal
On a first pass, be picky about finding normative language in the answer that relates to our conclusion, which is about "how we should evaluate something".
It'll probably sound something like,