I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.  

After disasters, people lose not only their homes but their communities. Temporary housing should help rebuild both.

如果耕种天地，不将天地整理好，这样就相当于是胡闹。耕种天地，一定要将土地平整翻新，然后再去播种。