But which vertebrate is heir to the future?  It would have been a hard choice between reptile and bird.  I feel sure that I, for one, should not have selected the mammal, a small, feeble being, hiding in holes and ledges, and continually hard put to it to escape becoming a mouthful for some huge reptile.  And yet the persecution, the impossibility of contending by brute strength, may have forced the mammal into the line of brain-building and placental development.  The early development of mammals appears to have been slow.  Palaeontology proves that they were long surpassed by reptiles and birds.  But the little mammal had the future.  The battle was to go against the strong.

Once again.  The arboreal life of higher mammals would seem to be most easily explained by the view that they were driven to it by stronger carnivorous mammals having possession of the ground.  Brain was good, for it planned escape from enemies.  But it did not give its possessor immediate victory over muscle, tooth, and claw in the tiger.  That was to come far later with the invention of traps and guns.  Brain gave its possessor a sure hold of the future, and just enough of the present to enable it to survive by a hard struggle.  And the same appears to have been true of primitive man.

Thus all man’s ancestors have had to lead a life of continual struggle against overwhelming odds and of seeming defeat.  It was a life of hardship, if not of positive suffering.  The organ which was to give them future supremacy, whether it was backbone, placenta, or brain, could in its earlier stages aid them only to a hardly won survival.  The present apparently, and really as far as freedom from discomfort and danger is concerned, always belongs to forms hopelessly doomed to degeneration or stagnation.  Crabs, not primitive vertebrates, were masters of the good things of the sea; and, in later times, reptiles, not mammals, of those of the land.  Any progressive form has to choose between the present and the future.  It cannot grasp both.  I am not propounding to you any metaphysical theories, but plain, dry, hard facts of palaeontology; explain them as you will.

And here we must add our last word about conformity to environment; and it is a most important consideration.  Conformity to environment is not such an adaptation as will confer upon an animal the greatest immunity from discomfort or danger, or will enable it to gain the greatest amount of food and place, and produce the largest number of offspring.  Indeed, if you will add one element to those mentioned above, namely, that all these shall be attained with the least amount of effort, they insure degeneration beyond a doubt.  This is the conformity of the bivalve mollusk.  The clam has abundance of food, enormous powers of reproduction, almost perfect protection against enemies, and lives a life of almost absolute freedom from discomfort, and the clam is really lower than most worms.