Why do most mammals have exactly five fingers?

If you pay attention to the paws of cats, dogs, or even koalas, you can notice that they, like humans, have five fingers. Although their arrangement may differ, the number remains unchanged. Why is this feature common to us and our smaller brothers, despite different evolutionary conditions?

In nature, nothing happens without a reason. Scientists believe that if animals have had five fingers for millions of years, there is no reason to change this number.

Mammals are vertebrate animals and belong to the superclass of tetrapods, which also includes reptiles, amphibians, birds, and humans. All representatives of this group, even those without traditional limbs, have five fingers in their skeletons, although they may be poorly defined.

However, there are exceptions: horses have only one toe on their limbs, and birds have one fused finger bone at the end of their wings. However, there is evidence that these animals, as embryos, have all five fingers, which fuse before birth. This process is largely determined by the so-called hox genes, which interact with each other in key biological pathways and control the development of organs and tissues during embryogenesis.

Why exactly five fingers?

Interestingly, animals originally had not five, but many more fingers: the first known creatures that developed fingers descended from fish about 360 million years ago and had as many as eight fingers. However, during the course of evolution, their number was reduced to five. Scientists have two theories explaining this phenomenon.

According to the first theory, the similarity in skeletal structure among most species is a result of homology, that is, descent from a common ancestor. It is suggested that this ancestor somehow evolved to have five fingers and passed this genetic code to its descendants.

The second theory asserts that each species separately developed five fingers during the process of evolution depending on habitat conditions and lifestyle.

For terrestrial vertebrates, having five fingers is important for maintaining balance and distributing body weight during movement. Many predators require this number of fingers for a reliable grip on their prey.

At the same time, in many aquatic animals, fingers are reduced or absent, as they are not needed for movement in water.

Can someone have not five, but six fingers?

Yes, in all five-fingered beings, this phenomenon is possible, but it is quite rare and usually results from a genetic mutation known as polydactyly. This condition is not always the norm for a specific species and can lead to various health problems, including mobility difficulties and joint pain.