Groundbreaking even today.

Although many have tried to look at Parasyte as an Alien Invasion manga (and it is a fresh one at that if not slightly relying on a successful shonen coming of age formula) what none of the reviewers have alluded to is how much realistic Parasyte is towards explaining the role of parasites in the ecosystem.

Albeit the manga doesn't scientifically "verify" the role of parasites, many of what you see in this manga happen to coincide with real parasites all over the world.

If parasites' existence were easy to explain this manga would only be slightly noteworthy but the things from how parasites need additional food to how they have a close symbiotic almost mutualistic relationship with their host separate this from your average invasion manga.

What makes this especially noteworthy is that, by accident or by purpose, reading this manga allows you to separate the complexity of why parasites exist in reality maybe even more so than a biology text book.

The thing that makes this happen is because parasites are sort of easy to define but to comprehend the theory behind their existence like how they outnumber several top species or how they break the food chain theory of humans being on top or how certain parasites complement and extend the host's instinct (like our desire to procreate) it's really hard to fill all this in if you know little about parasites. Especially as you go deeper into the rarer parasites that act like the parasites in this manga where they insert and change the inner anatomy of their host as well as their instincts.

By sort of turning parasites into living weapons with a catch and a virtual pet hunger meter, it transcends most of the explanation needed for the basic necessity of parasites and as you dig deeper into the manga and as the parasites' objective match closer to that of the humans - it becomes a sort of bridge as to how parasites seem to harm their host while at another extent seem to be useless outside of harming their host for self-preservation. Seeing parasites depicted like this in the manga helps bridge one closer to the interpretation that maybe just maybe parasites harm their host because they adapt slower to their host's habits and mentality and yet they stick very close to what makes their host survive and the combination in turn becomes very chaotic like the events shown in your typical fantasy war or battle or coming of age series but sort of alien.