Question: Which has the greater impact on allele frequencies, genetic drift or natural selection. Explain your answer and include some date as evidence.   Edit

Answer: None of them can act in isolation; both of them play important role in allele frequency. However, the effect of them on allele frequency varies depending on the size of population in question. In small population the effect of drift is greater than natural selection and vice versa. The drift can also subdue selection when the frequency is very small - even in case of large population. For instance, when unfavourable mutations are typically removed quickly in larger populations, new helpful mutations are as vulnerable to loss through drift as are neutral mutations. Not till the frequency for the helpful mutation reaches a particular point will drift have no significant effect.  Edit