Imagine something happened in space, some force reaction, that changes the way we know Earth. So everything starts to go in the opposite direction, Earth spinning, moon activities, sun, bunch of climate changes, etc... then would the human race (regarding human body/form) exist in the way we know it? And hoping it could be preserved, what do you think new life will look like? May the Force be with you all :)
closed as too broad by Zxyrra, SRM, Alexander von Wernherr, Mołot, Burki Feb 9 '17 at 10:11
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As stated by other posters, gravity is related to the Earth's mass, not the spin. However, if the earth was spinning in one direction and something caused it to spin in the other direction, you would have a period of massive changes.
Randall Munroe addressed what would occur if the Earth suddenly stopped spinning here. If this was part of your story's timeline, you might address this cataclysm and how some people survived.
Gravity is not caused by the Earth's spin. If you're near the equator, the spin of the Earth does counteract the force of gravity a little bit, but only by about 0.3%. So gravitationally, nothing would really be affected by the Earth spinning in the opposite direction.
If the Earth starting orbiting the sun in the opposite direction, the biggest change would be that the seasons would go in the opposite order: Winter to Fall to Summer to Spring. Of course, if you're in the middle of Winter or Summer when this happens, you're not going to notice anything. If you're in Spring or Fall when this happens, you'll definitely notice when Spring changes back into Winter or Fall changes back into Summer.
As for the global climate, here's an article that explores that a little bit. The short version is that the directions of trade winds would change, causing different effects in different areas. So places that are now habitable would become less and less habitable, while other areas would become more habitable.
Gravity may still exist. But the sudden change in direction would kill most living things on earth.