Mammals, such as cats, dogs, and kangaroos, all have one thing in common with human hands: they possess five fingers. The reason for this commonality among species that evolved under different conditions is still a mystery that experts are trying to unravel.

To understand why mammals typically have five fingers, we must explore the evolution of vertebrates with four legs (Tetrapoda) that also possess five fingers. Mammals belong to the superclass Tetrapoda, which includes reptiles, amphibians, and birds. Even species without traditional limbs in this superclass have skeletons with five fingers, illustrating a common structure across various types of animals.

The development of fingers is controlled by Hox genes, which regulate gene activity and determine bone type in Tetrapoda. 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, known as “canalization,” may explain why mammals have five fingers. However, not all scientists agree with this hypothesis, and some believe that mutations like polydactyly, or having more than five fingers, could be an evolutionary disadvantage due to gene linkage and potential health issues. The exact reason for the prevalence of five fingers in mammals remains a topic of ongoing research and debate among experts.