Once outside of the water, these animals gradually adapted themselves more and more to life on land. Some became reptiles (creatures who crawl like lizards) and they shared the silence of the forests with the insects. That they might move faster through the soft soil, they improved upon their legs and their size increased until the world was populated with gigantic forms (which the hand-books of biology list under the names of Ichthyosaurus and Megalosaurus and Brontosaurus) who grew to be thirty to forty feet long and who could have played with elephants as a full grown cat plays with her kittens.
Some of the members of this reptilian family began to live in the tops of the trees, which were then often more than a hundred feet high. They no longer needed their legs for the purpose of walking, but it was necessary for them to move quickly from branch to branch. And so they changed a part of their skin into a sort of parachute, which stretched between the sides of their bodies and the small toes of their fore-feet, and gradually they covered this skinny parachute with feathers and made their tails into a steering gear and flew from tree to tree and developed into true birds.
Then a strange thing happened. All the gigantic reptiles died within a short time. We do not know the reason. Perhaps it was due to a sudden change in climate. Perhaps they had grown so large that they could neither swim nor walk nor crawl, and they starved to death within sight but not within reach of the big ferns and trees. Whatever the cause, the million year old world-empire of the big reptiles was over.
The world now began to be occupied by very different creatures. They were the descendants of the reptiles but they were quite unlike these because they fed their young from the "mammae" or the breasts of the mother. Wherefore modern science calls these animals "mammals." They had shed the scales of the fish. They did not adopt the feathers of the bird, but they covered their bodies with hair. The mammals however developed other habits which gave their race a great advantage over the other animals. The female of the species carried the eggs of the young inside her body until they were hatched and while all other living beings, up to that time, had left their children exposed to the dangers of cold and heat, and the attacks of wild beasts, the mammals kept their young with them for a long time and sheltered them while they were still too weak to fight their enemies. In this way the young mammals were given a much better chance to survive, because they learned many things from their mothers, as you will know if you have ever watched a cat teaching her kittens to take care of themselves and how to wash their faces and how to catch mice.
But of these mammals I need not tell you much for you know them well. They surround you on all sides. They are your daily companions in the streets and in your home, and you can see your less familiar cousins behind the bars of the zoological garden.
And now we come to the parting of the ways when man suddenly leaves the endless procession of dumbly living and dying creatures and begins to use his reason to shape the destiny of his race.
One mammal in particular seemed to surpass all others in its ability to find food and shelter. It had learned to use its fore-feet for the purpose of holding its prey, and by dint of practice it had developed a hand-like claw. After innumerable attempts it had learned how to balance the whole of the body upon the hind legs. (This is a difficult act, which every child has to learn anew although the human race has been doing it for over a million years.)
This creature, half ape and half monkey but superior to both, became the most successful hunter and could make a living in every clime. For greater safety, it usually moved about in groups. It learned how to make strange grunts to warn its young of approaching danger and after many hundreds of thousands of years it began to use these throaty noises for the purpose of talking.
This creature, though you may hardly believe it, was your first "man-like" ancestor.
