Because skin falls off, or are you talking bout why don't people stick together? 
        
             
        
        
        
Answer:
All
Explanation:
You would need carbon dioxide to be able to sustain life forms such as plants, warm enough temperatures to allow the development of animals, (because they cannot be frozen), they would, of course, need oxygen to allow anyone to breathe, and finally liquid water to sustain healthy life, because we must hydrate that is necessary for survival. 
 
        
             
        
        
        
The mother and father will have intercourse, and run the chance of the sperm reaching the egg.
The mother will go through a period of around 9 months (The time varies with each person), but at least 8 months. There are three trimesters of pregnancy and they all about 13 weeks long each.
By around week 5, the baby is already developing rapidly, and by week 16, the weight of the baby will skyrocket, nearly doubling its size and weight. Week 20 and your baby will begin to move a lot more than usual and has already developed to the point where it can make expressions and move its arms and legs by week 40, your baby is almost completely developed, has started practicing breathing, and the mother will be suffering through mood swings, cravings, and cramps. 
Labor consists of three stages. There is no real starting point for labor, but you will know when it starts at the beginning of contractions, and your cervix starts to dilate. That is Early Labor.
Active Labor is more painful, and the dilation of your cervix is more rapid, this is around the end of the first stage and the beginning of the second stage, or the pushing phase. You will begin to push the baby out. This phase ends with the delivery of the baby. The final stage, the third stage, is the delivery of the placenta. After that, you are done. 
Something to keep in mind: Your water "breaking" is the rupture of your <span>fluid-filled amniotic sac. It may rupture before labor and will give you a warning of the start of your labor, OR you are so far underway into labor, that you don't feel it break.</span>
        
                    
             
        
        
        
40,000/180,000 = .222222
.22222 x 100 = 22.22222
Answer: 22.2%