Why We Have Five Fingers
Scientists have believed for years that our arms and legs gradually evolved from fins as our habitat changed from water to land. In a recent study, researchers discovered two genes responsible for fingers in humans and fin rays in fish—establishing the first proven molecular link between the two types of appendage.
A research team in Montreal set out to determine how the evolution to five fingers occurred—as fossil records indicate our human ancestors were polydactyl—had more than five fingers. They discovered that, in humans, as well as mice, certain genes are activated in separate domains of the developing limbs to produce five digits. In fish, the same genes are activated in overlapping domains of developing fins, producing more fin rays.
When scientists reproduced the fish-type gene regulation in mice, the animals developed seven digits per paw. Findings of this study show that malformations of the fingers during fetal development may result from mutations in DNA sequences that are responsible for regulating certain genes.