Fingers and other skin areas, such as toes, become wrinkly when kept in water due to a biological response that enhances grip. This phenomenon, often observed when hands and feet are submerged in water for extended periods, is primarily caused by the autonomic nervous system, which controls involuntary body functions.

Here’s a detailed explanation of the process:

1. Water Absorption in the Skin: When the skin is submerged in water, it absorbs water. The outer layer of the skin, known as the stratum corneum, is made up of dead skin cells that contain keratin, which can absorb water and swell. However, this swelling alone doesn’t fully explain the wrinkling pattern.
2. Autonomic Nervous System Response: Research suggests that the wrinkling is an active process controlled by the autonomic nervous system. The nerves constrict blood vessels beneath the skin, which reduces the volume of the fingertips. This causes the skin to pull inward, creating wrinkles.
3. Functional Advantage: The wrinkling of the skin in response to prolonged water exposure is believed to provide a functional advantage. The wrinkled skin increases friction, which helps improve grip on wet or submerged objects. This evolutionary adaptation would have been beneficial for our ancestors who needed to handle objects or navigate through wet environments.
4. Research Findings: Studies have shown that individuals with nerve damage (such as those with certain types of neuropathy) do not exhibit the wrinkling response, reinforcing the idea that this is a neurologically controlled process rather than a passive swelling.

In summary, the wrinkling of fingers and toes in water is a result of an active physiological response that enhances our ability to grip objects in wet conditions. This adaptive trait likely provided evolutionary advantages in terms of handling objects and mobility in aquatic or wet environments.