First introduced with Nidoran in Generation I, and later expanded to other Pokémon in Generation IV, gender differences have greatly enriched the playing experience of both casual and hardcore players alike. Of The 720 Pokémon currently in existence, 109 exhibit some form of variation between the sexes, ranging from subtle differences in design such as female Pikachu’s heart-shaped tail, to more obvious differences like male and female Meowstic of the current generation.
The inclusion of such differences is a nod to the real-life phenomenon of sexual dimorphism, which describes the differences in appearance between males and females of the same species. These differences can include color, shape, size, secondary sex characteristics, and even certain behaviors.
Perhaps the most well-known example of sexual dimorphism is of the peacock and peahen. Male peacocks exhibit spectacular coloration and ornamentation with their elaborate tails and colorful plumage, while female peahens are rather plain and inconspicuous. However, the astute biologist (or PokéBiologist) will point out an important detail, that while the male’s tail may be great for attracting a mate, from an evolutionary perspective, it appears to be of great hindrance, not only inhibiting its ability for flight but also making it a clear target for predators. So the question is, how did such a trait arise if it puts the male at a disadvantage and how does it remain fixated in the current gene pool?
The answer, my friend, is sexual selection, the primary cause for sexual dimorphism. In a way, sexual dimorphism itself is a byproduct of these sexually selective pressures, which favor certain traits over others in the mating process. In his book The Red Queen: Sex and the Evolution of Human Nature, Matt Ridley remarks that, “Sexual selection theory suggests that much of the behavior and some of the appearance of an animal is adapted not to help it survive but to help it acquire the best or most mates.”
For birds and mammals, the burden of reproduction usually falls more heavily on the female than the male. For a female, reproducing comes with many upfront costs such as expending time and energy guarding an egg or carrying a developing organism for an entire gestation, in addition to the care that said offspring requires after birth/hatching. Males on the other hand, typically are not as involved and can indiscriminately disperse their seed without worry. Thus, females must be more selective with whom they mate with, resulting in a dynamic where it is often the males that are colorful and ornamented while the females remain plain, as this pressure does not apply to them.
Returning back to the example of the peacock, while the tail may not aid in its survival, it does have the major benefit of attracting a mate. A male that wasn’t as flamboyant may be able to evade predators more easily, but it ultimately means nothing if they can’t reproduce. Ridley likens this to a student with testing anxiety, stating, “If a student is brilliant but terrible in examinations – if, say, she simply collapses with nervousness at the very thought of an exam – then her brilliance will count for nothing in a course that is tested by a single examination at the end of the term.”
But not all forms of sexual dimorphism follow these “traditional” gender norms. Females can often be larger than their male counterparts. This often pairs nicely with sexual cannibalism, common in arachnids such as spiders, in which the female eats her mate following copulation.
One particularly extreme example of this size disparity can be found in the anglerfish. For the longest time, scientist doubted the very existence of a male angler fish until it was discovered that the males they were looking for were most likely right in front of them the whole time. You see, male anglerfish are much smaller than their female counterparts. These little lads are destined to become no more than a sperm-filled wart on the side of a larger female angler fish, as they bite down on a prospective mate and gradually merge circulatory systems giving up all sense of bodily autonomy in the process.
In the Pokémon World, most cases are nowhere near as extreme as the angler fish. In fact, most seem to be on the subtler side, at least in regards to the earlier generations of Pokémon. The later generations however, appear to show more obvious dimorphism than previous ones. Unfezant, much like the real-life pheasant it was based on, displays clear dimorphism from sexual selection, with the male bearing a pink mask and bright green plumage, while the female is simpler and has plain brown plumage instead. Pyroar also takes a hint from our world, copying the dimorphism displayed between male and female lions.
However, the Pokémon that displays the most differences is hands-down Meowstic, not only having different physical features but also learning different moves. In a reversal of traditional gender norms, the female is mainly for offensive purposes, learning more attack-based moves, while the male plays a more supportive role. This dimorphism even extends to their Hidden Abilities; females have the Competitive ability while males have the Prankster ability.
The complexity of the Pokémon World never ceases to amaze me, and this added feature makes the biology of this fictional world seem all the more real. With a new generation of Pokémon on its way, there’s no telling what types of sexual dimorphism will be presented to us next.
What’s your favorite Pokémon that displays sexual dimorphism? Leave it in the comments, and if you’re interested in learning more about sexual selection and evolution in general, I highly recommend checking out Matt Ridley’s book The Red Queen: Sex and the Evolution of Human Nature. It’s a great read if you’re a biology nerd like me, and even if you’re not it still has some fascinating insight on the evolution of human sexuality, and who doesn’t like sex?