The greatest weakness in Darwin’s theory was his failure to explain

The greatest weakness in Darwin’s theory was his failure to explain variations. He had explained variations but was not able to tell anything about their source or how variations arise in a species. He told that there are differences among species which help them to adapt to the environment in a better way but he was not able to explain how these variations arise in species. He did not hold and any evidence for explaining this.

He had very nicely explained the concept of overproduction using examples that every species has the ability to produce a large number of animals but since due to large number of organisms and limited resources, there is a struggle of existence between members of same species. He also explained that only that organism survives who by competing to gete adaptd to the environment and is fit for their environment and therefore survives.

Since, Darwin was failed to explain the sources of variations, correct option is (d) variations.