Fear of the body of any switch from the status quo. The body has no knowledge of hospitals or medical help. Any injury can prevent producing progeny and thus logically should be avoided. Any unknown range of movement for example belongs in this unknown and if we made it to this day without it, it is not a must.
Fear of the unknown as a risk that cannot be estimated. What is behind door number two? What lies beneath me in the dark?
Fear of the imagined unknown. How will the limb coming my way augment chances of me eating solid foots in the near future and so on. This usually results in us acting on those imagined futures and missing out on what is happening now.
Fear that comes from our genes: fear of loud noises and heights and mothers in law if you are of Polish decent. Trying to overcome it instead of accepting it will result in ulcers cancer and the like. Listening to these fears openly and honestly will result in being a reasonable person who can put them in the right place when needed.
Fear of the mind from any switch from the social status quo. The human animal survives in groups and must therefore abide by the laws of the group. Any chance of ostracizing by the group may result in death and lack of progeny.
The Martial Art of Walking 