The new movie is playing in town, so I’m hoping to see it tonight…except that I’ve been prescribed cetirizine to suppress the allergies that might be causing my tinnitus, and I’ve been known to slip into unconsciousness at odd times of the day. It’s annoying, and worst of all, it doesn’t seem to be doing anything. So, if I can keep my eyes open tonight, I’ll be going to see Godzilla, King of the Monsters.
It’s about science, don’t you know. It just got a write-up in Science magazine!
The “evolutionary biology” of Godzilla is a topic of enduring interest among devotees, with numerous fan pages and forums dedicated to the subject. If we accept Godzilla as a ceratosaurid dinosaur and Lazarus taxon—a species thought to have gone extinct, only to be rediscovered later—then it represents a sensational example of evolutionary stasis, second only to coelacanths among vertebrates. Yet, the creature’s recent morphological change has been dramatic.
Godzilla has doubled in size since 1954. This rate of increase far exceeds that of ceratosaurids during the Jurassic, which was exceptional. The rate of change rules out genetic drift as the primary cause. It is more consistent with strong natural selection.
The strength of this selective pressure can be estimated by using the breeder’s equation, where the response to selection “R” is the product of the heritability (h2) of a given trait and the strength of selection. If we assume that h2 = 0.55 for body size—a reasonable estimate according to quantitative genetic studies of lizards—then the observed increase in Godzilla’s body size would require a total strength of selection of 4.89 SD. To put this number in context, the median value of natural selection documented in a review of more than 2500 estimates in the wild was 0.16. Godzilla, it seems, has been subject to a selective pressure 30 times greater than that of typical natural systems.
One problem with this analysis: isn’t it the same Godzilla in every movie? I could be wrong, but I think this is a specific individual returning over and over again, not a member of a population of Godzillas over many generations. It would have to be a very large and prolific population to hold up under that kind of selection pressure, too. It seems more likely to me that this is an example of a long-lived individual that is undergoing continuous growth over its lifetime, and therefore this is more of a matter for the developmental biologists, and is an example of a physiological adaptation.
Even if Godzilla is multiple different members of a changing population, we have no idea of the extent of the variation present within the population. The 1954 Godzilla could have been the Peter Dinklage of Godzillas, while the 2019 Godzilla could be the Yao Ming of the group. We don’t know, but I think that trying to argue for rates of selection is premature.
I must disagree with this diagram as well.
The 1998 monster does not look anything like the others, and must be from a completely different species, so don’t try to tell me it’s a Godzilla.