Charles Darwin was unable to explain the source of the variations he claimed were necessary for evolution This was because: such variations did not exist. variations result from magic, which he had not studied. genes had not been discovered during his lifetime. variations occur in nature and have no explanation.

The correct answer is **genes had not been discovered during his lifetime.**<br /><br />Darwin observed variations in populations and posited that natural selection acted upon these variations, driving evolution. However, he lacked a mechanism to explain *how* these variations arose and were inherited. The concept of genes as units of inheritance was developed later by Gregor Mendel and subsequently integrated into evolutionary theory, forming the modern synthesis of evolutionary biology.<br />