Even though asexual reproduction seems like a simple solution to continuing a species, many monerans and protists also undergo sexual reproduction. While asexual reproduction expands a population, it does not make it possible for the population to change in any way. All of the organisms created in asexual reproduction are clones, so they have the same genetic information and the same characteristics as the parent organism. As long as environmental conditions remain steady, asexual reproduction maintains a healthy population; however, if anything in the environment changes, the population may suddenly be at risk. Because all the individuals are alike, any problem that may befall one cell will probably visit them all, possibly resulting in the loss of the entire population.
In organisms that reproduce sexually, all of the offspring are different. Each one contains a unique set of genetic information, half of it inherited from one parent and half from the other. Since individuals in the population vary, it is unlikely that a change in the environment would create problems for everyone. In fact, a change that reduces the survival rate of some might improve the survival rate of others.