Answer 3:

When we look to the individuals of the same variety or subvariety of our older cultivated plants and animals, one of the first points which strikes us is that they generally differ much more from each other than do the individuals of any one species or variety in a state of nature.

When we reflect on the vast diversity of the plants and animals which have been cultivated and which have varied during all ages under the most different climates and treatment, I think we are driven to conclude that this greater variability is simply due to our domestic productions having been raised under conditions of life not so uniform as and somewhat different from those to which the parent species have been exposed under nature.

There is also I think some probability in the view propounded by Andrew Knight that this variability may be partly connected with excess of food.