Now about the giraffe. We will suppose, for the sake of illustration, two giraffes, a male and a female, whose necks are precisely five feet long. We will confine our illustration to the question of the neck alone. We will suppose this particular pair to give birth to a family of three. First comes heredity. All we ask of heredity is that the young shall be giraffes, not camels or any other species; and this heredity guarantees. Now comes variation. As this is an ideal case for the purpose of illustrating the theory, we will have one of the three shorter-necked than the parents, another the same length, while the third has a longer neck--over five feet. Now comes the struggle for existence. When this family of giraffes is fairly grown and the new-comers are approaching breeding age--mark the importance of this matter of “breeding age,” for the problem is to find out how nature determines which shall be bred from--they are obliged to forage for themselves. There is no pasture to graze; they live in what is almost a desert. There are few shrubs; scarcely anything but fairly high trees--from ten to twenty feet. If a giraffe breeder had this matter in hand and he wished to increase the length of the giraffe’s neck, the problem would be simple. He would select number three with the longest neck, pair it with the longest necked member of the opposite sex in some other family and the trick would be done. But this is in Central Africa, where there is no breeder to interfere, and the question is: can nature accomplish the same result without his help? This is what happens. First the leaves are eaten from all the lower branches as they are reached with the least effort. Then they go higher and still higher until the point is reached where number one with the shortest neck cannot reach any further and the terrible struggle for existence begins. Number two sees no danger as yet and number three has things all his own way. But with short-necked number one, a tragedy has begun. Every day now sees the food further out of his reach and even number two is obliged to reach out for his supply. The breeding time is approaching but the longer necked and therefore well-fed and vigourous females will have nothing to do with this wobbley starving creature, and the longer necked, well-fed males shun the short-necked starving females. If the starving ones mate, the mother dies before giving birth to offspring, or she cannot get nourishment enough to rear her progeny; in either case there is no effective succession. So the longer-necked are the fittest and they survive. Thus does nature “select” one by the negative process of destroying the rest, in about the same way as a man “selects” one puppy in a litter by drowning the rest. In the case of the puppies we may say “artificial selection;” in the case of the giraffe it is “natural selection.” And this theory, simple as it may seem here, revolutionized Biology.