If a healthy human is at a certain muscle state and then experiences muscular atrophy solely due to disuse/lack of exercise, is it easier to gain that muscle back than if the human had never reached that certain muscle state. If so, is there a name for this effect. The reason I'm wondering is because it seems like muscle mass was definitely periodic in ancient times when food would become scarce during the winter, and that an increased ability to put back on muscle might have developed evolutionary-wise. I thought that this would fit best in biology, let me know if this isn't the case.
Muscle memory specifically in the effects of hypertrophy. There is also muscle memory for skills which shares some factors but mostly differs.
When muscle hypertrophies or "gets bigger" extra nuclei are recruited to make more sarcomeres or proteins involved in muscle action. Once these nuclei have been recruited and essentially activated once, they're much more easily activated again.
Above is an answer based on my knowledge, but you can wait for Atl LED if you need references.
Disuse and lack of exercise are actually exceedingly new problems when considered on an evolutionary scale. The bigger evolutionary pressure for the last few million years has been not starving to death, therefore not maintaining expensive muscle fibers unless they were absolutely necessary.
I haven't found any evidence of previous musculature effecting growth, but I'm going to look into it more (only some quick pubmed searches), and edit this answer. If someone else knows more immediately, please feel free to answer.