Gunpreet, Subject Matter Expert at Edumarz
Answer: Trait B is likely to have arisen earlier.
We know that reproduction gives rise to new individuals that are biologically and genetically similar, but still different because of variations that arise as a result of mutations. Some of these variations survive and get inherited to the next generation while all the variations do not have equal chances of survival.
In this case, the population of the species has reproduced asexually. In asexual reproduction, cell division results in the creation of similar cells with identical copies of DNA. Though chances of variations are more in sexually reproducing organisms, some amount of variation occurs even during asexual reproduction. Therefore, in this species, a trait may come into existence in some members due to sudden mutation by environmental factors. This trait is then inherited by the next generation on replication and then generation after generation gets accumulated. As trait B has been accumulated in 60% of the population, it means it is being accumulated in the population for a long time in comparison to trait A which is present in only 10% of the population. Thus higher the proportion of a trait or character in a population means it has arisen earlier in that population.