the term watch out behind you will be obselete
There would be less genetic variation in humans
They are present because if the face was solid bone, the anterior portion of the head would weigh more than the posterior part of the head, making it off balance. The air-filled bones weigh less than solid bone, so the head stays balanced on the neck.
Having just now looked at some humans, I am unable to detect any curly thing in the back of their head. Perhaps if you clarified what you mean? == == If I get what you're referring to, it's called a "whorl" and is that point where your hair pattern goes in sort of a whirlpool-like pattern. You'd see it more clearly in people who's hair is quite short. Not everyone has a very obvious one, and some have whorl that goes clockwise while others go counterclockwise.
it creates more cells
if you are upside down then more blood will be rushed to your head due to gravity
Head
there will be more animals alive !
All living animals, creatures, plants and humans
Humans seem to use their eyes as pointers to show fellow humans where to look. Apes tend to rely more on where the head is facing. More in the Related Link below.
humans cannot survive without food for more than a week
It is more a matter of possibility. No one has breached over 20 mph.
it will go back and deliver more messages
Yes some time this can happen.
There would be more CO2 then Oxygen. Humans would either adapt to it or slowly start dying.
We'll run out of fossil fuels eventually.
humans and bears. There's many more, but that's what came at the top of my head.
As you can sence in the back of your head 6 more will die