A peacock is displaying its colorful feathers, showcasing sexual selection.

Why Are Male Animals More Beautiful and Colorful? Sexual Selection! With Photos

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As a biologist, I find myself marveling at the amazingly complex rituals, colorful outfits, and tricky dance routines that various animals, and humans, have developed to attract a mate.  Join me as we view the world through the eyes of a biologist and look at the science of sexual selection.

Animals have evolved specific physical and behavioral attributes that increase their chances of mating and passing on their genes. Male animals are generally more colorful because they have to compete with other males to attract females. Bright colors can provide a “signal” to the females about the overall quality of a male and his genes.

It is vital for males to compete for reproduction and for females to choose between those competing males.  

Sexual selection explains why peacocks have huge tails, even though it makes them more vulnerable to predators.

Sex really does make the world go round!  Only animals that find a mate get to pass on their genes.  This explains a lot.  Suddenly the creatures and courtship rituals we see in nature begin to make more sense, with all the colorful outfits, beautiful tails, complex songs, and fancy dance steps. 

If a member of the opposite sex finds your tail, your song, or your dance moves sexy, you will have a chance to fulfill your primary biological role as a member of your species: to reproduce.  

Sexual reproduction shuffles genes to create enough differences between individuals for natural selection to take place.

Photo of a colorful male Cock-of-the-Rock
Looking sexy! Cock-of-the-Rock. Photo by G. Sranko

Sexy tails and males that can dance

The peacock’s tail is the text-book example of an adornment that really doesn’t make much sense in a dangerous world filled with predators.  Darwin was fascinated and mystified by the tail of the peacock because it seemed counter to his theory of evolution by natural selection.  Just the sight of a feather, he wrote in April 1860, “makes me sick!”  

Photo of peacock feathers
Peacock feathers. Photo by Letti Schm on Unsplash

Why would a peacock have a tail so large that its weight nearly threatens the bird’s survival?  It seems to be a completely impractical outfit that makes flight more difficult and camouflage a real challenge. 

Darwin came to understand that natural selection is the “struggle for existence,” while sexual selection is the “struggle for mates.”

Sexual selection is not a subcategory of natural selection, a point that Darwin tried to make abundantly clear.  Sexual selection arises from differences in mating success, whereas natural selection is due to variance in all other adaptations to the environment.

Natural selection arises when organisms that are better adapted to their environment have higher rates of survival than those less well equipped to do so.

Why does the blue-footed booby have such colorful feet? 

If you are trying to avoid predators, wouldn’t it make more sense to have black or brown feet that blend in a bit better?  Waving those brilliant blue feet around is like waving a blue flag in front of predators.  “Looking for a tasty bird?  Here I am!”

Check out my article about our adventures with Blue-footed Boobies and other unique animals of the Galapagos Islands.

Photo of blue-footed booby
Blue-footed booby in Galapagos. Photo by G. Sranko

Only the Best Dancers Get to Mate

Next, we’ll meet some birds in central America that just might have the most complex dance moves on the planet.  There are about 50 species of Manakin, and each species has its own set of complex dance steps.  The male Red-capped manakin does something like a moon walk up and down his favorite dancing perch.  Along with the ultra-fast fancy footwork, he also makes a snapping noise with his wings. 

Check out this short video of a male manakin doing his moonwalk:

The females gather to check out the males with their fancy moves and choose the ones they want to mate with.  If the moves are not perfect, they don’t stand a chance.  In fact, the males will cooperatively choose the best dancers among themselves, beforehand, so that at least one member of their group has a good chance of passing on his genes. 

Now that’s doing your bit for the team, fellas!!

A quick and easy guide to sexual selection

While considering the mystery of the peacock’s tail (apparently the proper term is train), Darwin proposed that it might be the result of selective pressure by females to mate with those males that displayed the greatest strength and vigor.  It appears that the females, or peahens, prefer a male with a big, colorful train because it offers proof that the male is fit and has desirable genes.

In the context of sexual selection “fitness” has a special meaning.  The phrase “survival of the fittest” is misleading; there is no such thing as the “fittest” animal and we know that the strongest don’t always prevail.  Fitness means that the animal is well-adapted to the environment it lives in.  If an animal is fit enough to survive and reproduce, that is all that is necessary to ensure their existence.  Those that are not fit will die out.

The peacock’s tail represents a bunch of sexually selected traits involving color, size, shape, etc.  In this case, the tail provides a “signal” to females regarding the overall fitness of the male.  Signals in this context are attributes and behaviors that are not easy to acquire.  They must be “costly” to ensure that only the best individuals can present the right signals, whether exaggerated sexual ornaments or complex behaviors.

Photo of peacock
Peacock. Photo by Viktor Shimin on Unsplash. 

With time, these traits can evolve to become more and more pronounced until they actually limit the individual’s fitness.  The peacock’s tail could get so big and cumbersome that they have no chance of escaping predators.  Such a peacock would not be “fit” and would have no chance of passing along its genes.

 For a close-up look at the Blue-footed booby see my article about the unique animals of the Galapagos Islands. 

How can the bird produce such an intense blue pigment in its feet?  Boobies pick up carotenoid pigments through their diet which becomes concentrated in their feet.  Higher concentrations of blue pigment make the color in their feet more intense.  Carotenoids also play a role in the bird’s immune system, and pigments deposited in their feet means that less is available for an immune response which could prove harmful to the bird’s health.  

Intense blue pigments are therefore costly to the bird, and only healthy individuals with brightly colored feet have a good chance of attracting a mate.  Both males and females have blue feet so, in this case, both genders are assessing their potential mate’s suitability or fitness using foot color as one signal.  There are lots of signals to consider, of course, including the ability to pull off intricate dance moves, to make the correct vocalizations at the right time, to angle the head and neck in just the perfect pose, etc.  

There’s a lot to consider before you put all your eggs in one basket by hooking up with the right (or wrong) mate!

Did you think that colorful outfits were restricted to birds? Guess again! Lots of male animals have evolved fancy displays to help attract females… even spiders! Check out one of the amazing Peacock spiders of Western Australia, Maratus splendens, showing off his best dance moves!

Types of sexual selection

The difficult task of attracting a member of the opposite sex usually involves two distinct mechanisms: 

1. mate choice or intersexual selection; where members of one sex (usually females) choose members of the opposite sex, and

2. intrasexual competition or competition between members of the same sex (usually males) for access to mates.

Females are typically choosier and males typically more competitive (while acknowledging the reverse can also be true).   Given that males usually have limited access to females, females tend to choose while males tend to compete.  

This begins to explain all the fancy outfits and all the tricky moves that males must use to attract a female.  And it explains why males in general are so competitive, even to the extreme of fighting one another to the death.  Another example of intrasexual selection is the dominance hierarchies that form in many species (such as lion prides and wolf packs), providing the highest-ranked individuals with preferential access to mates.

Everything boils down to evolutionary advantage and survival of the species

Without reproduction any given species would cease to exist.  But how important is sexual selection?  Turns out that it plays a key role in giving species an evolutionary advantage by maintaining the fitness of individuals within a changing environment.

 A study published in 2015 found that it is vital for males to compete for reproduction and females to choose between those competing males. Sexual selection through the existence of two sexes maintains population health and protection against extinction.

When you look at it this way, the dance of the manakin, the intensely blue feet of the booby, and the intricacy of the peacock’s tail all begin to make complete sense.

One of the best examples of sexual selection and mate choice is the group of birds living in the jungles of New Guinea; the fascinating Birds of Paradise.  See my 4 min presentation on Sexual Selection. (The colorful bird below is a male Cock-of-the-Rock from South America, not a Bird of Paradise — look at the video and you’ll see Western Parotia Birds of Paradise mating!!)

Lions Are Sexy Too!… Why and Why Not!

Lions provide a couple of great examples of sexual selection. Ever wonder why male lions have manes and why they have such an amazing roar that can carry for several miles? Find out – read my in-depth articles Why Lions Have Manes and How Lions Communicate and why the Lion King Roars.

Image of article about lion manes
Image for webpage titled "How do lions communicate? Why do lion roar?"

References

Sexual Selection by Patricia Brennan (2010). Nature Education Knowledge 3(10):79
https://www.nature.com/scitable/knowledge/library/sexual-selection-13255240

Sexual selection protects against extinction.  Lumley, A., Michalczyk, Ł., Kitson, J. et al.  Nature 522, 470–473 (2015). https://doi.org/10.1038/nature14419

Sexual selection by David J. Hosken and Clarissa M. House,
Current Biology, Volume 21, Issue 2, Pr62-R65, January 25, 2011.
Open Archive DOI: https://doi.org/10.1016/j.cub.2010.11.053

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