The smallest unit capable of evolution is...?

Question

species

group

individual

population

clone

Answer 1

Actually, the correct answer is a gene.  It can change over time through mutation, and its phenotypic effects are seen in individuals and in collections of individuals.  A mutated gene's frequency will probably rise in a population if that mutated gene provides a selective advantage to the organisms that have it.

Answer 2

population

The allele frequency change in a population over time is evolution.

Answer 3

It is the population that is the smallest unit capable of evolution.  Natural selection acts on the individual, they are able to survive or just have more viable offspring.   To better explain it pretend there is a drought, and in this drought seeds develop a thicker shell.  The birds that eat these seed need to break them open, however only birds with thick beaks can eat the seeds.  No genetic change is made on these birds at this time, just selective pressures favoring thick beaks.  If the drought persists for several years the thickness of the beaks may remain.  The population has now changed, evolved, to having a thick beak.  Over an extended period of time, thousands of years, thick beaks along with other traits may define this population as a new species.