No theory in science has received the public abuse of evolution theory. Evolution is the descent of organisms from ancestors, where most features remain constant, but gradual changes do accrue across generations to give rise to forms that are fundamentally different from ancestral forms. Individuals differ from each other. These differences lead to different probabilities of survival and reproduction.
Differences are partially inheritable.
These differences accumulate over many generations to provide new species. Trees produce about 0.5 to 10 million seeds in an average lifetime. Blending genotypes gives greater diversity in the potential of the progeny, and a better chance that some of the progeny will make it. Clonal plantations of Eucalyptus in Brazil grow better than stands with similar genotypes developed from seeds. Uniform sizes among stems allows for more efficient use of resources at the stand level.