Getter Robo is full of things that defy the laws of physics, but it’s not really the physics that we’ll be looking into today. It’s the implications the title robot’s power source has for biology that concerns us.
Getter Rays are called the energy of evolution. (As is Spiral Power from Gurren Lagann, in direct homage to Getter.) They are said to be what originally wiped out the dinosaurs on the surface, and are still harmful to the reptilians of the Dinosaur Empire. Most of the other things they do don’t really have anything to do with evolution at all.
Now, I realize that the Cretaceous mass extinction is one of the real-life events with the most fictional explanations (right up there with how the Sphinx lost its nose and the identity of Jack the Ripper), but even before the evidence for an asteroid impact around that time started to pile up, it’s generally been thought that it had a specific cause. Getter Robo’s explanation seems to be essentially that it was just particularly fast evolution, but in reality evolving more quickly is what makes a creature less likely to become extinct.
And what’s this “energy of evolution” anyway? Evolution isn’t really a force; it’s (as John Green would put it) a side effect of dying. Natural selection, the fact that some traits make organisms more likely to survive and/or to reproduce, is a common sense fact, and combined with the way heredity works it means any population of individuals that reproduce and die will change over time. Of course evolution happens faster when there are more mutations, so maybe what the Getter Rays do is increase the rate of mutation in mammals, while simply being lethal to reptiles?
I wonder what an ad for Getter Rays would look like. “Are you under attack by dinosaurs? Demons? Aliens? Ask your mad scientist if Getter Rays are right for you. Side effects include headaches, nausea, epic sideburns, memory loss, death, cancer, megalomania, and being absorbed by your mecha. Do not use Getter Rays if you are pregnant, as they may increase the risk of birth defects. Do not exceed the recommended dosage, as this may cause the Getter Emperor to exist.”