Short answers, pulled from the story.
The human finger structure traces its roots back to lobe-finned fish millions of years before the first human walked upright. This five-digit plan known as pentadactyly is shared by almost all land vertebrates and remains homologous to the bones within the wings of birds and bats.
The human hand contains fourteen digital bones called phalanges with two located in the thumb and three in each of the other four digits. These bones form the skeletal architecture that allows for manipulation and sensation while connecting to muscles deep within the forearm and palm.
The furrows on fingertips are caused by blood vessels constricting due to signaling by the sympathetic nervous system rather than simple skin swelling. This physiological response supports the rain tread hypothesis which posits that the wrinkles evolved to help fingers grip things when wet.
Fingertips can regrow in less than 8 weeks if torn off during childhood provided the tear occurs above the nail. No healing occurs if the tear happens below the nail because the distal phalanges are regenerative in youth and stem cells in the nails create new tissue that ends up as the fingertip.
The ratio of lengths between the index and ring finger has been linked to higher levels of testosterone and to various physical and behavioral traits. This connection includes penis length and the risk for development of alcohol dependence or video game addiction.
The brain maintains an orderly somatotopic representation of the hand on the cerebral cortex specifically in the somatosensory cortex area 3b. This map is so precise that surgeons at the Institute of Reconstructive Plastic Surgery in New York were able to use MRI brain scans to observe how the cortical maps of a 32-year-old man with fused fingers separated and took the layout of a normal hand after surgical division.