In my opinion we should refer to genetics. One thing is the genotype - the characteristics given to a person by his gene heritage. The other thing is the phenotype - which is basically the genotype modified by evolution in life.
Let me explain it in a very simple way (I will refer only to the physical part, but this is available also to the intellect): genotype means that if you are born from average hight parents, your gene heritage should make you have an average hight too. But if you practice a sport like basket or volley, you'll have a hight over the average ... this is the influence of the environment ... this is the phenotype.
Now back to the topic. I think it is very likely to have people with the similar genotype (or at least the part of the DNA related to the face) and also some people with similar phenotype. But the probability for each person to have a "twin" phenotype (in their lifetime) is not very big.
Name: Melanie
Comments: Perhaps the doppelganger person is rather our own more high evolved [..] self interacting with us on our plane for a specific teaching purpose, perhaps we are indeed a hologram living all the facets of our existence and because of loneliness, selfishness or some other reason the two facets unite at a certain point in time and space. I often see people or mannerisms that I recognize as me while understanding that the instance is for some spiritual teaching purpose, something my soul is learning.
This is really interesting. How come there hasn't been more public informatin on this?