But if tusks increase the chances of survival (through fighting off predators or spearing food), it would have evolved via natural selection in both male and female narwhals. However, a small proportion of females have tusks. The male with the largest tusk is the most dominant and has the most mating opportunities. The males use the tusk to attract females and warn off male rivals. The narwhal, or unicorn of the sea, is an Arctic whale that has a long spiral tusk, up to three meters in length. The brown color of the females' feathers evolved through natural selection where the fittest survive in this case, the ones that are camouflaged from predators. These differences in appearance of the sexes evolved through a process called sexual selection.Ī good example of this is the mallard, one of the most common ducks in the world. Consequently, it is in the interest of females to be more picky about their mating partners. This is known as anisogamy and usually causes males to compete for females through the evolution of weapons such as antlers in deer, or adornments such as the beautiful tail of the peacock. Throughout most of the animal kingdom, females have a finite number of eggs, whereas males have an infinite number of sperm. To understand why some species evolved special traits or appearances you need to know why the males and females of many species evolved to look so different to one another. Yet research is revealing more about animals that defy expectations when it comes to sex norms. Most people know that male seahorses become pregnant and give birth.

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