What is the best explanation for how we can exhibit so many different traits from so few genes

Alleles of a gene are responsible for different traits

Explanation:

There are several variant of a gene which in pair leads to varied phenotypic characteristics or traits.

For instance, there are three alleles for blood group i.e A, B and O but there are in totality there are basic 8 blood groups including the categorization on the basis of Rh factor.  

Likewise, there are several variations of skin color; however there are majorly six genes that are responsible for skin color.  

So, basically alleles of a gene are responsible for different traits

answer: land bridge theory. land bridge theory held that shifting portions of dry land explained the finding of identical species on different continents. plate tectonic theory eventually eliminated the land bridge theory.