The Color Blue Is Surprisingly Rare in Animals and Plants. There’s a Good Reason for It

Blue pigments are scarce in nature. However, evolution has led to other strategies.

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Pablo Martínez-Juarez

Blue is considered a primary color. Two of its shades, blue and indigo, are distinguished in the rainbow, while two other shades appear in the two main color models: additive RGB (blue) and subtractive CMYK (cyan).

Earth is often referred to as the “Blue Planet.” However, the color of the sky and seas is more the exception than the rule among animals and plants.

Why? This is due to a combination of evolutionary and chemical reasons.

First, let’s review some basic notions of color science. Colors are simply our brain’s interpretation of a fragment of the electromagnetic spectrum, that of visible light. Each frequency in this segment is associated with a color, from the lowest frequencies that we interpret as red to the highest frequencies, blue.

The color of objects depends on the frequency or frequencies at which they emit or reflect light. In the case of animals and plants, the color is a result of the reflection of light, except for some bioluminescent exceptions. For instance, if we see something blue, it’s because it absorbs light in other ranges of the spectrum and reflects the higher frequencies.

Due to resource optimization, green is the dominant color in the plant world. This color is attributed to chlorophyll, which is essential for photosynthesis. A blue plant would be less efficient in photosynthesis because it’d be returning the most energetic frequencies of light, which are needed for the process.

However, the absence of blue in plants not only affects leaves. It also affects flowers, with only about 10% of them having blue pigmentation. As researcher Kai Kupferschmidt told Live Science, the molecules that absorb the red side of the spectrum and reflect the blue are typically very large, making them difficult for the plant to synthesize.

Despite this challenge, some plants still produce blue flowers. Some scientists believe this rarity could give these plants an evolutionary advantage by helping them stand out among pollinators and differentiate themselves from other plants.

And What About Animals?

Many animals embody the saying “We are what we eat” through the color of their skin, which is partly influenced by their diet.

For instance, flamingos acquire their pink color from carotenoids found in the algae they consume, along with crustaceans that also feed on the same algae. Carotenoids are the pigments responsible for the vibrant colors in carrots and other vegetables, and they transfer through the food chain to give flamingos their distinctive hues.

In fact, excessive consumption of carotenoids can even affect the color of human skin. When our bodies are unable to convert an abundance of carotenoids into vitamin A, they can be stored in various areas of our body, potentially affecting our skin color.

However, no carotenoids produce the color blue, so it’s rare to find animals with a blue hue due to pigments. That said, some animals do have a blue color, but they achieve it through other means.

The trick here is nanostructures. This coloring method relies on iridescence. Nanostructures reflect light in a way that cancels out most wavelengths, allowing the blue wavelengths to “escape” to the outside.

For instance, the nanostructures on the scales of Morpho butterflies’ wings lead to this phenomenon. This feature is also present in the feathers of birds like the blue jay (Cyanocitta cristata), the skin of venomous blue-ringed octopus (genus Hapalochlaena), and the scales of fish like the royal blue tang (Paracanthurus hepatus), as well as in mammals such as the golden snub-nosed monkey (Rhinopithecus roxellana).

Just like in everything else, there are exceptions. In the animal kingdom, the rare blue-colored exception is another butterfly: those of the genus Nessaea. These butterflies are the only known animals that produce blue pigments instead of relying on microscopic structures.

Some people believe that the scarcity of blue animals and plants may have influenced the development of color-related language. It’s thought that early humans didn’t initially differentiate between all colors but gradually added new categories to their color palette. They probably first distinguished between light and dark and then went on to identify colors like red, green, and yellow.

Interestingly, it seems that blue, as a primary color, was one of the last to be recognized in the development of our color terminology. And this is even though blue is very visible in the sky or ocean. However, it’s not so easy to spot on land, which could explain why our ancestors didn’t feel the need to differentiate the color blue specifically.

Image | Chait Goli

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