Many mammals, including humans, dogs, and cats, have five fingers on their front limbs.
Source: Fun Science Website of the United States
Most mammals have five fingers, but why is that? According to a report from the Fun Science Website of the United States on May 7th, the scientific community has various explanations for this.
Mammals belong to the tetrapod superclass, which also includes reptiles, amphibians, and birds. Even members lacking traditional limbs, such as whales, seals, and sea lions, still retain traces of five toes in their skeletal structure. While there are exceptions, like horses having only one toe and birds having a fused bone at the end of their wings, scientists have found that these animals had up to five fingers or toes in their embryonic stage, some of which disappeared during development.
Researchers at Pennsylvania State University in the United States stated that this process is largely controlled by Hox genes. The proteins encoded by Hox genes help regulate the activity of other genes. During the embryonic development of animals, these genes ensure that different body parts end up in the correct positions. Therefore, they play a role in determining the skeletal pattern of tetrapods and help achieve this by aiding in controlling the proteins created by sonic hedgehog genes.
Subsequently, fingers start to grow like buds on plants. In different animal species, some fingers can continue to grow, while others are reabsorbed by the body.
It is still unknown when mammals began following the "five-finger rule." The first known animals to develop fingers evolved from fish approximately 360 million years ago, with up to eight digits at that time. However, the presence of five fingers in most existing tetrapods suggests that this feature is likely "homologous." This means that these organisms have a common ancestor and share certain genes or structures. The common ancestor of all existing tetrapods likely evolved five fingers at some point and passed on this pattern to their descendants.
Another theory is the canalization phenomenon, where over time, a gene or trait becomes more stable, reducing the likelihood of mutations. According to this theory, if a feature has existed for millions of years, there is no reason to change it.
However, not all researchers agree with this explanation. Some scientists point out that polydactyly (having more than five fingers) is a mutation in many mammals, including humans. But polydactyl species are not common, possibly because polydactyly is a disadvantage in evolution.
