9 of the Most Dramatic Examples of Sexual Dimorphism

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.

Here are nine incredible examples of sexual dimorphism in the animal kingdom.

1. Mandrills

The mandrill is widely considered to be the most sexually dimorphic mammal species. Looking at the differences between males and females, one of the first things you'll notice is that males exhibit a more vibrant coloration on their faces and behinds. There's even a noticeable difference between males in the same group, with the dominant adult male exhibiting the brightest red.

Another striking contrast between mandrill sexes, though, is their size. While the average female weighs about 27 pounds, some males can weigh up to 82 pounds.

2. Triplewart Seadevil Anglerfish

Living as deep as 6,600 feet below the ocean's surface—hidden away from the human eye—the triplewart seadevil anglerfish is arguably the world's most extreme and downright bizarre manifestation of sexual dimorphism. The females of this species measure about a foot in length, while males barely reach half an inch. This dramatic disparity in size is largely due to the species' parasitic mating practices in which males attach themselves to females and become permanently fused to them through tissue and interconnected circulatory systems.

3. Pheasants

In addition to their larger size, male pheasants differ from females in their colorful, decorative plumage and extra-long tails. Female pheasants, in contrast, are quite minimal in their appearance. This makes it easier for hunters to distinguish between species, as only roosters (males) are allowed to be hunted throughout the U.S.

Depending on the species of pheasant—of which there are about 50—males might also exhibit neck rings, ornamental wattles, and spurs.

4. Elephant Seals

These pinnipeds are named for the males' large proboscises (noses) that elongate during puberty and wind up looking like stunted elephant trunks. Their proboscises help them emit incredibly loud roars as they congregate on the U.S. West Coast during the mating season, from December to March.

The rhythmic clicks they make with their notorious snouts help identify them as individuals. Studies show that they could be the only nonhuman mammals to use rhythm to recognize other members of their kind.

Besides their proboscises, males can also weigh up to 10 times more than females. The size difference is more prominent in southern species.

5. Orange Tip Butterflies

Like elephant seals, these butterflies are also named in honor of the sexual dimorphism they exhibit. The bold orange tips found on the forewings of the males makes them unmistakable. Females, all-white with black wingtips, are less colorful, though both sexes exhibit a similar mottled green appearance with wings closed. This helps trick predators into thinking they're just fallen leaves.

Because orange isn't a common color of butterfly wings, the Natural History Museum of London says the wingtip coloration is another defense tactic: They want to fool predators into thinking they're poisonous, and with the peptide toxin glacontryphan-M lingering on their wings, they would not be lying.

6. African Lions

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.

Lions are the only cats that exhibit sexual dimorphism. While it was once believed that males' manes evolved to protect their necks in fights with other males, further research contradicted that theory; when lions fight each other, they mostly target the back and hips. It's now thought to be nothing but a symbol of male fitness. Male lions are also larger and sometimes twice as heavy as lionesses.

7. Mandarin Ducks

While both sexes of the Mandarin duck possess beautiful plumage, males are especially striking with their red bills, pronounced crests, and array of colorful feathers. The males have "whiskers" that flank their bills and two parallel white lines adorning their purple chests. Also unique is the orange "sail" on their backsides.

With any luck, their colorful plumage lands them a mate for life. Because of their monogamy, they're known now as symbols of love and fidelity throughout Asia, where they hail from.

8. Orangutans

As they reach sexual maturity, male orangutans begin to develop enlarged cheek flaps and throat sacs 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. In maturity, they'll use their large throat sacs to make their signature guttural barks.

Besides this distinguishing face morphology, male orangutans are generally twice to 2/3 the size of females, the Orangutan Conservancy says. And they look even bigger, with hair longer and bushier than their female counterparts'.

9. Peafowls

Peafowl are arguably the ultimate example of sexual dimorphism. While males (peacocks) sport a flamboyant and iridescent "train" of tail feathers they can open up in a grand display, females (peahens) are primarily brown, gray, and cream with white bellies. When the males are ready to mate, they'll fan out their feathers and give them a shake before rushing at their objects of affection.

The majestic plumage of the peacock is impressive to humans and peahens alike, but it does not always advantage them in the wild. With their subdued coloration, peahens are more capable of blending in and hiding from predators.

Are All Animals Sexually Dimorphic?

Sexual dimorphism is common among most animals, including humans, but not all—and many species exhibit more dimorphism than others. Humans, for example, exhibit only about 15% whereas orangutans exhibit more than 50%. Sexual dimorphism displays in different ways depending on the species—either through colorful plumage or size or hair—and can by psychological in addition to or instead of physical.

In general, vertebrates tend to be more sexually dimorphic than invertebrates. In the case of insects exhibiting dimorphic traits, females tend to have larger bodies than males—called "reverse dimorphism"—which is thought to be an advantage for carrying eggs.