Question

the distribution of skin pigmentation from the poles to the equator forms a
o cline
o chwartz
o kepllin
o koan

Explanation:

A cline is a gradual change in a phenotypic or genetic characteristic of a population across a geographical gradient. Skin pigmentation shows a gradual change from the poles to the equator due to differences in UV - radiation exposure, fitting the definition of a cline. The other terms (chwartz, kepllin, koan) are not relevant in this context.

Answer:

A. cline