(2) The second great fact is that among all the young born to a pair of parents, no two are exactly alike, nor are any exactly like their parents; nor are any two taken from all produced by all parents of that species exactly alike. They all resemble their parents at the corresponding age, in a general way and even very closely; but the resemblance is far from amounting to identity. This is called “variation.” It is familiar to us all in the case of the organism which we know best, and observe most closely, namely, man. It is also a matter of common observation in the case of dogs, cats, horses, and other domesticated animals. Many of these “variations” are exhibited in points of size, proportion, and colour, which are easily noted at once by the eye. But “variation” is really a deep-seated thing, and depends on causes which lie below the surface. We know that the offspring of men and of animals and of plants, give evidence of variations in what we call constitution, tendency, temperament, aptitude, strength, and that the colour, and even size of this or that part, are really only indications of a deep-seated difference in the living chemistry, the forces of nutrition and growth which reside in the living substance. The fact that many thousands of a species may be born and only a few survive, means therefore that many thousand varieties, often varieties not readily measured by the eye, are produced in each generation, from which a few individuals are in some way “selected” for survival. (3) The third great fact is that though there is variation, amongst all the offspring in each generation, there is also a continual and definite inheritance by offspring of the qualities and structure of their parents to a degree which altogether preponderates over the variations. To put it in another way, we all know that every parental organism transmits to its young not only the qualities and structure of the species, or of the race, or of the family, but also transmits its own peculiarities or variations in which it departed from its parents, and from its brothers and sisters. This is best illustrated by our daily experience of human families.