In asexual reproduction, the reproducing cells produce a copy of their $DNA$ through some chemical reactions. However, this copying of $DNA$ is not accurate and therefore, the newly formed $DNA$ has some variations.

It can be easily observed in the above figure that in asexual reproduction, very few variations are allowed. Therefore, if a trait is present in only $10\%$ of the population, it is more likely that the trait has arisen recently. Hence, it can be concluded that trait $B$ that exists in $60\%$ of the same population has arisen earlier than trait $A$.