The commonality among mammals, such as cats, dogs, and kangaroos, in possessing five fingers is a mystery that experts are still trying to solve. This trait is shared by various species that evolved under different conditions, including Tetrapoda, which consists of reptiles, amphibians, and birds. Even species without traditional limbs in this superclass have skeletons with five fingers, indicating a common structure across various types of animals.
The development of fingers in mammals is regulated by Hox genes, which control gene activity and determine bone type. The process involves finger buds that may continue to grow or reabsorb, leading to either the formation or elimination of fingers. Scientists have traced this evolutionary process back to a common ancestor that likely passed on the trait of five fingers to descendants.
One theory suggests that the stability of certain genes or traits over time may explain why mammals have five fingers. However, not all scientists agree with this hypothesis, and some believe that mutations like polydactyly could be an evolutionary disadvantage due to gene linkage and potential health issues. Despite ongoing research and debate among experts, the exact reason for the prevalence of five fingers in mammals remains a topic of interest and study.