Nature: What kind of an impact does the environment
have on our health? 
Environmental conditions
Behavior
Nurture:
How much does our genetic
makeup affect our health?
Chromosomal factors
Inheritable diseases
Identical twins look similar but not identical- there are many physical differences. Identical twins have the same DNA and genetic makeup. They are natural clones of each other.
There have been many twin studies conducted on identical twins separated at birth. Why are their mannerisms, lifestyles, personalities the same? There are many coincidences (or are they merely coincidences?)