Because they do not evolve in the sense of inherited traits, which can deal with the evolution of a organism for survival. Acquired traits are learned traits.
Here is how to do it! if you have any questions feel free to ask in the comments :)
“3rd eyelid” that covers the eyes, but is transparent -- J. Watch for obstacles and prey while still protecting the eyes
<span>Long eyelashes -- E. Keep desert sand out of eyes
</span>
Eyes set on the side of the head -- I. Watch for predators approaching from the side or behind
Eyes set in front -- G. “binocular” 3D vision to better hunt prey
<span>Large amounts of body fat -- H. keep warm in an icy habitat
</span>
<span>Staying under rocks at midday -- B. keep cool in a hot habitat
</span>
Bright, colorful markings -- A. warn predators away by appearing toxic
<span>Drab, brown coloration -- D. camouflage from predators in the dirt
</span>Singing a loud, complicated song -- F. attracting more mates than others
<span>Remaining so still that breathing is not detectable -- C. prey will come right up to be captured</span>
I am afraid there is no specific answer to your question becuase there is not only one fell good chemical, there are 4:
Endorphin, Serotonin, Oxytocin and Dopamine.
Hope it helped,
Happy homework/ study/ exam!
