Different but becoming similar
For a species to survive, it must be able to adapt to its environment and reproduce. Many species specialise in a particular habitat. They find their own niche in nature. This is called evolution or development. When unrelated species develop similar behaviours and appearance, it is called convergent evolution. The different species live in the same climate and environment – but in different parts of the world. What animals can you think of that are similar but not related?
The Siberian flying squirrel lives from the eastern parts of Finland all the way through the Asian taiga to Korea and Japan. It lives in the forest, and uses its skin flaps to glide up to 50 meters between treetops and branches.
The flying phalangers such as the sugar glider, are marsupials that resemble flying squirrels both in apperence and way of living. But they are not closely related. The sugar glider lives in Australia, and has developed the ability to glide completely separate from the flying squirrels.
Photo: David-Cook-CC-BY-NC
Wings has evolved many times through history, in different groups of species unrelated to eachother. Bats, birds and insects all have wings, that have evolved independantly.
Gliders and flying squirrels
The sugar glider, Petaurus breviceps, is a marsupial native to Australia, that can glide thanks to extendable skin flaps between its front and back legs. It is very similar to the flying squirrel, a placental mammal that lives in other parts of the world. The species have a similar appearance and flying ability, but are not closely related. They have adapted to a similar environment and have almost the same appearance.
The oldest shark finds are about 420 million years old. Sharks are well adapted to swimming quickly and silently through the water, with their streamlined bodies.
Photo: Kakidai-CC-BY-SA
The ancient relatives of dolphins became water-living arond 40 million years ago - meaning they have existed much shorter than sharks. Dolphins are mammals, that have gotten a similar body and way of living as the sharks - without being related.
Photo: sheilapic76-CC-BY
Dolphins are mammals and sharks are fish
Dolphins and sharks are also examples of convergent evolution. The dolphin is a mammal whose predecessor lived on land. Over time, it adapted to life in the water. The dolphin developed a long, streamlined body. It has a powerful tail fin and fins on the sides and top of its body that allow it to move quickly and smoothly through the water. Sharks have a similar body shape but are a cartilaginous fish. The body is held up by cartilage, and the shark breathes with gills beneath the water. Dolphins have a skeleton of bones, and breathe air at the surface. Despite these differences, they are very similar, and share the same niche in nature.
The boa constrictor squeezes its prey to death and swallows it whole. Boas live in South America and give birth to live young, but apart from that, they are very similar to pythons living in Asia. The similarities in appearance and ways of living have developed independant of eachother.
The royal python lives in Africa, and many other pythons live in Asia. They have a similar way of living and appearance as boas, but they lay eggs which they incubate. The similarities between boas and pythons are examples of convergent evolution.
The emerald boa is a boa living in the tropical parts of South America. It is very similar to the green tree python.
Photo: Joseph-Bylund-CC-BY-SA
The green tree python lives in Southeast Asia and New Guinea. It has many similarities with the emerald boa, but the species are not closely related.
Photo: Jesper-Flygare-Malmö-Museer
The fossa is predator living in Madagascar. Its body and way of living is similar to cats, but they are not closely related.
Photo: Rod-Waddington-CC-BY-SA
The jaguarundin is a small wild cat, that resembles the madagascan predator fossa, without being closely related.
Photo: Rod-Waddington-CC-BY-SA
Boas and pythons – similar but different
The boa and the python are also examples of convergent evolution. They shared a common ancestor more than 60 million years ago, and are not closely related. Nevertheless, they are very similar. They have lived in the same natural niche for a long time, adapting to the climate and environment.
The fossa that looks like a cat
The predator known as the fossa, which lives in Madagascar, resembles a cat in appearance. The fossa has flexible ankles and is a good tree climber and can jump just as well as a cat. But they are not closely related. The fossa belongs to a unique family of predators – only found in Madagascar.
The trilobites were among the first animals on Earth with good eyesight. The eyes evolved about half a billion years ago! The trilobites' eyes are similar to those of today's crustaceans and insects.
The cephalopods, such as octopuses, belong to the molluscs. Cephalopods have advanced eyes, with retina, cornea and lens - just like vertebrates have. However, the eyes have evolved through convergent evolution - completely independently of each other.
Photo: Laszlo-Ilyes-CC-BY
Vertebrates' eyes developed from brain cells, while the molluscs' eyes developed from skin cells. Yet, they have gotten very similar shapes and functions.
Photo: Pathogenhk-CC-BY-SA
The eye has evolved many times
Another example of convergent evolution is the evolution of the eye in different species. Scientists believe that the eye has evolved many independent times since life first appeared on Earth. The earliest examples of eye evolution date back more than 500 million years to the trilobites that lived in the oceans. Many species alive today have eyes that function in a similar way. Mammals, cephalopods (such octopuses) and fish have eyes with a retina, lens and cornea.