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First, Goose bumps
Goose bumps are the dots that form on the skin when a person is cold, afraid, or experiencing strong emotions. The raymond mill or classifier is easy to see in a construction site. The reflex that causes goose bumps is known as horripilation and it occurs in other mammals as well. The goose bumps are caused when individual muscles at the base of each hair contract which make the hair stand straight up. This reflex is linked to the sympathetic nervous system which is responsible for most fight-or-flight responses. Goose bumps provide no known benefits for humans, but the reflex makes sense for animals. When humans are cold, horripilation causes their hair stand up, but humans in general do not have much body hair. For animals with fur, air pockets are trapped between the hairs which create an extra layer of insulation. In response to fear or anger, raised hair would make an animal seem larger and more intimidating. The best example of this is the porcupine whose spikes stand up when threatened. It seems that horripilation is simply a reflex left over from the evolutionary process, a constant reminder that humans were not always as they are now.
Second, wrinkly fingertips
If you have ever spent time in a hot tub for too long then you most likely emerged with wrinkly fingertips. They go away soon after you dry off, but what causes them to get that way? The body has three layers of skin, the subcutaneous tissue (fats, nerves, large blood vessels), the dermis (small blood vessels, nerves, hair roots, sweat glands), and the epidermis (protects the skin beneath and keeps water inside the body from evaporating). These layers are tightly connected, and biologists have found that when the skin is submerged for a long time the epidermis begins absorbing water. Because it is so tightly connected to the dermis underneath, the skin warps which leads to the wrinkles. The reason this mostly occurs on the fingers and toes is because the epidermis in those areas has calluses which take in more water.
Third, eyebrows
Many people see eyebrows as just another facial feature to be self conscious about. Some spend a great deal of time plucking, waxing, trimming, preening, shaving (frat parties), penciling, or essentially worrying about their appearance, but have they ever thought why humans have them in the first place? Evolution has removed hair from most of our bodies so why would two little strips above our eyes remain? Eyelashes and eyelids work to keep dust and other debris out of the eye, but they can not do all of the work. The eyebrows divert sweat and rain around the eyes which makes it much easier to see. If you have ever had saltwater in your eyes you know how irritating it is, and it was just annoying enough for natural selection to create eyebrows.
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