How did hair and feathers appear? Many scientists desperately seek answer to this question, and Russian biologists from Severtsov Institute of Ecology and Evolution seem to find it. Researchers conducted a long-term research of hair, feathers and scales, and are sure that all three structures appeared independently and were never related.
Frankly speaking, a hypothesis about hair and feathers having the same origin is at least strange. Hairy ancestors of mammals and flying dinosaurs with feathers appeared about 200 million years ago. However, birds originated from sauropsids, which had water resistant, horny and scaly skin without any glands. As for pre-mammals, their skin was soft and possibly had many different glands. This fact may be the reason why feather follicle lacks glands, and hair follicles usually have one or several gland ducts inside.
Keratin skin appendages, scales, feathers and hairs owe their origin to interaction of two skin layers: external ectoderm and underlying mesoderm. Same genes are responsible for their generation – scientists know bout ten at the moment. Feather and hair follicles have much in common. Well, genes can interact in different combinations due to environmental conditions, for example, or due to different signals from an organism, and evolution made same genes and tissues generate hairs and feathers independently. Architectonics of feather and hair are similar, follicle structure of hair has much in common with feather follicle, but still essential differences exist. For instance, even mechanisms of moving out of follicle are different for feathers and hairs.
Here a question appears – if scales, feathers and hairs are independent products of evolution, then why they have so much in common? Because structures made of the same tissues and having same functions can’t help being similar.
All this makes sense – both feathers and hairs appeared to protect an organism from cold and freeze and have similar patterns of warming a body. Hair stems and various parts of a feather have cavities, which form protective air space in multilayer feather or hair coat. However, external covers always have several functions, that is why both feathers and hairs have minors tasks, which, however, never harm the main function of warming. Feather has changed a lot and serves for aerodynamic operations, but feather evolution went separately from evolution of birds. We should not forget that not all creatures that have feathers, are birds – just remember feathered dinosaurs, which weren’t able to fly.
We cannot say that the problem of feathers and hairs is completely solved. Researchers are going to analyze data on biochemical processes of keratinization, which take place in external covers of birds and mammals, and to find whether the hypothesis about primal function of feathers and hairs being extraction of excessive sulfur from an organism is true.
Source: Science News