Evolution of colour vision facts for kids

The way animals see light and colour has changed a lot over millions of years. This is called the evolution of colour vision. It helps animals see the world based on the different wavelengths of light. This is super helpful for many reasons, especially for finding food!

For example, many plant-eating animals, called herbivores, use their colour vision to spot yummy fruit or fresh leaves that are good to eat. Hummingbirds, for instance, often recognize their favourite flowers by their bright colours. Even predators use colour vision to help them find their prey.

However, this mostly applies to animals active during the day. Animals that are active at night have much weaker colour vision. Their eyes are better at collecting light in the dark. This is because their retinas have more rods, which are special cells that help them see in low light. Colour differences are much harder to see when it's dark anyway.

Who Has Colour Vision?

Arthropods

Besides animals with backbones (called vertebrates), the only other land animals that have colour vision are arthropods. This group includes insects, spiders, and crustaceans. Even aquatic arthropods, like crustacea, can see colours.

The way they see colours is a bit different from vertebrates. But the tiny molecules that actually do the work, called opsins, are very similar. These opsins are like the sensors that pick up different colours of light.

Vertebrates

Many vertebrates, like teleost fish, reptiles, and birds, have four different types of opsins. This means they can see a wide range of colours, even more than humans! Scientists think that the very first ancestors of land animals and egg-laying animals (like reptiles and birds), which lived about 360 million years ago, also had this amazing four-colour vision.

Mammals and Colour Vision

Interestingly, most mammals lost a lot of their colour vision over time. This happened during a long period in Earth's history (the Mesozoic Era) when early mammals mostly lived as nighttime animals. Seeing colours wasn't as important in the dark.

Today, most mammals only have two types of opsins. This means they are bichromatic, seeing fewer colours than animals with more opsins. Think of it like seeing the world in mostly blues and yellows, without much red or green.

However, some primates, like Old World monkeys, have developed three-colour vision again. This means they can see reds, greens, and blues, just like humans. Our ancestors, the anthropoid apes and humans, came from this group of monkeys. That's why most monkeys and humans have good colour vision, while many other mammals do not.

Seeing Ultraviolet Light

Did you know that some animals can see light that humans can't? This is called Ultraviolet (UV) light. UV light plays a big part in how many animals, especially insects, see colours.

Many arthropods can see UV light. This is a special trait that helps them in their environment.

Birds, turtles, lizards, many fish, and some rodents also have special UV sensors in their eyes. This means they can see UV patterns on flowers and other wildlife that are completely invisible to us! It's like they have a secret world of colours we can't even imagine.