Mandrills are one of nature's most extreme examples of sexual dimorphism.
Mandrills are one of nature's most extreme examples of sexual dimorphism. (Photo: Curioso/Edwin Butter/Shutterstock)

Ever wonder why males and females of the same species can sometimes look radically different from each other? It's all thanks to a condition known as sexual dimorphism, which is generally triggered by the process of sexual selection through competitive mating. Sexual dimorphism can manifest in many fascinating ways — size, coloration, behavior and the presence of secondary sex characteristics like tail feathers, breasts or antlers.

One of the best examples of this is the mandrill, which is widely considered to be the most sexually dimorphic mammal species. When you examine the images of the male and female mandrills above, one of the first things you'll notice is that males exhibit a more vibrant coloration on their faces and behinds. However, if you were to encounter one of these majestic primates up-close, you'd quickly realize that the most dramatic difference between their sexes is their size. While the average female mandrill weighs about 27 pounds, some male mandrills can weigh up to 82 pounds!

Mandrills have nothing on the triplewart seadevil, though. Living as deep as 6,600 feet below the ocean's surface, these creepy-looking anglerfish are arguably the world's most extreme and downright bizarre manifestations of sexual dimorphism. As exhibited in the diagram below, the females of this species measure about a foot in length, while males barely reach half an inch.

Triplewort seadevil (Cryptopsaras couesii)
(Photo: Commons sibi/Wikimedia)

This dramatic disparity in size is largely due to the species' parasitic mating practices. (That's right, it's love at first bite!)

As MNN's Bryan Nelson explains, "The evolution of the male anglerfish has left them highly reduced. In some species, the males are not even capable of feeding themselves. Instead, they must quickly find a female to attach themselves to, or die. After attaching, their circulatory systems merge and she provides him with sustenance, while he provides her with sperm."

Continue below to learn about more animals that exhibit striking instances of sexual dimorphism.

Pheasants

Ringneck Pheasant (Phasianus colchicus)
(Photo: Piotr Krzeslak/Szczepan Klejbuk/Shutterstock)

In addition to their larger size, male pheasants are characterized by their colorful, decorative plumage, ornamental wattles and extra long tails. Female pheasants, in contrast, are quite minimal in their appearance.

Elephant seals

Elephant seal (Mirounga leonina)
(Photo: David Osborn/jo Crebbin/Shutterstock)

These pinnipeds are named for the males' large proboscises that slightly resemble an elephant's trunk. The reason they've developed this bulbous schnoz has less to do with their appearance and more to do with proboscis' ability to emit incredibly loud roars during mating season.

Orange tip butterflies

Orange tip (Anthocharis cardamines)
(Photo: Matthijs Wetterauw/anderMeertinsPhotography/Shutterstock)

These butterflies are named in honor of the specific sexual dimorphism they exhibit: the orange tips found on the forewings of the males.

African lions

African lions
(Photo: Jason Prince/Maggy Meyer/Shutterstock)

The iconic bushy manes of African lions are highly linked to the process of sexual selection, and studies have shown that lionesses are more likely to pick a mate that boasts a dark, thick mane.

Mandarin ducks

Mandarin ducks (Aix galericulata)
(Photo: Panu Ruangjan/Super Prin/Shutterstock)

While both sexes of the Mandarin duck possess beautiful plumage, the males of this species are especially striking with their red bills, pronounced crests and array of colorful feathers.

Orangutans

Orangutans (Pongo pygmaeus)
(Photo: Sergey Uryadnikov/GUDKOV ANDREY/Shutterstock)

As they reach sexual maturity, male orangutans begin to develop enlarged cheek flaps that are meant to exhibit their dominance. When there is more than one male within a family, the more dominant male will exhibit more exaggerated cheek flaps.

Peafowls

Peafowls (Pavo cristatus)
(Photo: Brigida Soriano/igor.stevanovic/Shutterstock)

Peafowl are among the most well-known and gorgeous examples of sexual dimorphism. While males (peacocks) sport a flamboyant and iridescent "train" of tail feathers that can open up in a grand display, females (peahens) possess a significantly more subdued appearance.