When we look into the natural world, we will notice that almost all the animals we see are externally symmetrical: from insects to most fishes, from reptiles and amphibians to most birds and mammals. All of these animals exhibit symmetry in their superficial body parts. The only group of multicellular animals that does not have any symmetry belongs to the phylum Porifera (sponges). However, if we look deeper into the animal kingdom, we discover many animals with noticeable asymmetrical traits.
Why do some animals have asymmetrical traits?
While there are evolutionary advantages to animals possessing symmetry, such as enabling higher movement capabilities for survival, asymmetrical traits can also favor some. Most animals that develop asymmetrical features are the result of functional adaptation and evolution.
Asymmetrical features among animals
A famous example of asymmetrical features among animals is a male fiddler crab, known for having one outsized claw than the other. Male fiddler crabs have unequal claw sizes, which allows them to fight in combat and attract females in courtship.
Meanwhile, under the sea, flatfishes lie still on the ocean floor. Because both of its eyes are located on one side of its face, the flatfish can position themselves flat on the sand and observe the ocean above without being easily spotted by potential prey or predators. What’s more interesting is that a flatfish is symmetrical in its larva/juvenile stage and swims vertically with eyes on opposite sides of its head. But as it matures, the flatfish will undergo a phenomenal metamorphosis where one of its eyes will migrate to the other side of its skull, transforming into an asymmetric adult.
Some owl species, such as the great horned owl, have asymmetrical ears where one of its ear openings is higher than the other. As a result, sound signals will travel to the owl’s brain in two slightly different positions. Having symmetrical ears is an advantageous trait for hunting, since it enables the owl to determine the specific location of their prey from the directional information received by both ears (sound localization).
Are humans asymmetrical?
On the outside, humans are bilaterally symmetrical, meaning that if we draw an imaginary line straight down the center of a human body, we can easily divide the body into two identical halves: one left side and one right side. These two halves are mirror images of each other. However, even though our bodies are externally symmetrical, most of our internal organs are not. For instance, our heart and stomach are located slightly towards the left, and our lungs have two lobes on the left and three on the right. The reason for the asymmetrical arrangement of the inside body is that it creates more efficient packaging of internal organs into a tight cavity.
While symmetry is preferred very much by nature, often subtle asymmetrical traits remain useful in the animal kingdom.
Works Cited
Albert (2019). Types of Flatfish: the Complete Guide. [online] FishingBooker Blog. Available at: https://fishingbooker.com/blog/types-of-flatfish-complete-guide/ [Accessed 2 Feb. 2024].
Corballis, M.C. (2021). How Asymmetries Evolved: Hearts, Brains, and Molecules. Symmetry, [online] 13(6), pp.914–914. doi:https://doi.org/10.3390/sym13060914.
Discoverwildlife.com. (2023). Asymmetry: what it is and why it exists in animals. [online] Available at: https://www.discoverwildlife.com/animal-facts/asymmetry-animals [Accessed 1 Feb. 2024].
Fiddlercrab.info. (2019). Austruca variegata / Motley Fiddler Crab. [online] Available at: https://www.fiddlercrab.info/u_variegata.html [Accessed 1 Feb. 2024].
Pociask, S. (2017). Are All Life Forms Relatively Symmetrical? Forbes. [online] 1 Feb. Available at: https://www.forbes.com/sites/quora/2017/02/02/are-all-life-forms-relatively-symmetrical/?sh=33dedec022cf [Accessed 1 Feb. 2024].
ScienceDaily. (2016). Why the flounder is flat. [online] Available at: https://www.sciencedaily.com/releases/2016/12/161205110908.htm [Accessed 2 Feb. 2024].
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