All birds have wings, feathers and a beak. In addition, all lay eggs. But that was almost it with the similarities. All you have to do is compare a tiny hummingbird to an ostrich to see how different the appearance of birds is, even though they all belong to the same class of animals. The different appearance is by no means accidental, but has developed in the course of evolution because the animals have adapted to certain habitats and ways of life. The long tongue of the hummingbird, for example, is perfect for sucking nectar from flowers and the long legs of the African ostrich enable the ratite to go on long hikes in times when food is scarce.
But do the special adaptations go so far that, conversely, it is also possible to infer a bird's appearance from its lifestyle, its habitat and perhaps even its function in the ecosystem? A team led by biodiversity researcher Alex Pigot from University College in London investigated this question and measured almost 10,000 birds from museums around the world (Nature Ecology and Evolution). The scientists compared nine physical characteristics, including the beak, the tail, the wings and the legs, and related them, among other things, to what the birds eat and how they get their food. For example, they further divided insectivores into birds that catch their prey in flight, search on the ground or find them under water. It turned out that the appearance can be used to tell very well where and how an animal lives. Some of these relationships were obvious, such as the above-average wings of species that spend most of their lives in the air. However, the biologists found that the combination of all nine body characteristics made surprisingly precise statements about the way of life possible.
The penguin is not related to the alk. Nevertheless, the two look alike
Their method is much more precise than corresponding predictions based on family relationships, they write in their study. In these, it is assumed that closely related species also have more similarities in their lifestyle than species that separated early in the course of evolution. This is often true, but not always, as the comparison between penguins and alkene birds shows, for example. The relationship between these two animals is basically exhausted from the fact that both are birds. From a purely spatial point of view, these animals never came into contact with each other: penguins only live in the southern hemisphere. Alkene birds, which include puffins and guillemots, occur only in the northern hemisphere. Nonetheless, penguins and alken birds are similar in appearance: both have beaks, bodies and wings with which they can swim well and quickly and hunt fish under water.
Biologists speak of convergence. The current study is also evidence of this basic principle of evolution, in which the same physical characteristics develop independently several times, simply because of the environmental influences that affect a living being from outside. "Evolution is a predictable process," says Alex Pigot. If it started again under the same conditions, living things would appear that would look very similar to those that exist on Earth today.
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