# The How and Why Library/Life/Animals-Section XV
#### XV. Water Babies and Other Babies that Drink Milk

As we have seen all the way through—and will see a great deal more, the more we look carefully at the picture in Nature's wonder book, the higher forms of life keep summing up the lives below, and foretelling higher lives to come.
The earthworm, with his joint-ringed body, foretells the crawfish, with his jointed shell; the crawfish foretells the fish, with his tail set the other way, and the shell made into scales. The bird is a fish with true scales only on his legs, and the other scales changed to feathers and feather quills, the fins changed to wings and the tail turned back fiat, like the lobster's.
You know, when you are listening to a story, if you happen to get to listening to something else for a few moments, how the rest of the story gets all mixed up? Then you ask mama to tell part of it over again.
Mother Nature seems to want to be so sure that we will not miss the smallest part of her story—the story of lower lives growing into higher all the time. So she keeps going back and telling it over and over again, whether we ask her to or not.
The higher the form of life, the more features of all forms of life it has in it. The crawfish, for example, couldn't show us what wings looked like because his people and their near relations didn't have any wings. Nor Mr. Fish couldn't show us what feathers are because he never was a bird. But the bird can show us the fins of the fish in his wings, the fish's scales on his legs, the jointed rings of the earthworm in his backbone, the whole earthworm in his intestines.
Not only because they are made of the same stuff, and because they have similar habits, are animals that look so different supposed to belong to the same great family, but there are many "connecting links" between different animals, like the fish that fly. Go far enough down the tree of life and you will find where one branch of the family is connected with some other branch that seems as different as can be.
Fish and birds, the owl and the pussy cat, all belong to one great family—the back-boned family. But among the back-boned family those that suckle their young, as the cat does, are higher than thosethat do not. Animals and people learn and go up higher in life, in proportion as they are sociable. A mother and her babies are sociable with one another. They love each other and they teach each other. The mama cat learns to be shrewd and careful because she has other little mouths to feed and lives to protect, beside her own. It is just as true in the insect world. For example, the ants and spiders are both very bright. They know how to do many wonderful things, and these wonderful things are most of them done in taking care of their eggs, and the babies that are hatched out of these eggs.
And do you know about how these ants keep other insects for cows? These "cow" insects are the little green lice that you find on plants. They are not good for the plants but they make good "cows." They give down a kind of honey dew, just as the old cow gives milk for her babies. Don't you wonder if this honey dew is meant for the babies of the aphis or plant lice? If it is true that they do give this sweet milk for their babies, they are really mammals, too, and when the higher animals feed their young in this way they are simply repeating something that is done away down in the insect world.
Another odd thing about these aphides is that sometimes they lay eggs, and sometimes they bring forth their babies alive, already hatched. It is when they have wings that they lay eggs but have no milk, and in the state that they bring forth their young alive, they have this milk. So the more we think about it the more it seems as if these little bugs are mammals, too.
But whether the aphis is one kind of a "bird" that suckles its young and so seems to want to remind us still more of the relation between birds and mammals, it is certain that there are egg-laying animals that suckle their young. One of these is the spiney ant-eater. Another is the duck mole. You can see from his name that he must be something like a duck and something like a mole. He burrows in the ground and suckles his young like a mole and he has a bill and lays eggs like a duck.
Then there are fish that suckle their young. They might be called fish because they live in the water, and swim like fish; or they might be called sea-lions because they have sharp teeth and eat meat like dogs or lions, and suckle their young as the lioness does her cubs.
As we find some mammals laying eggs—most of them seem to have dropped their egg-laying habits with their wings—so we findsome mammals that have wings but that do not lay eggs. Thus the great families of nature seem to be held together on both sides; just as you keep yourself in a tree by holding on to two different limbs, one with the left hand and one with the right. Bats have wings, as you know, much like the wings of a bird, and much like the fins of a fish, with great spiney ribs running through them. But bats suckle their young just as Mama Dog does her puppies.
Notice how, in still another way, Nature seems to want to make sure that we see that we are all relations and should be kind to one another and find joy in studying each other's lives and in making these lives as happy and helpful as possible.
As we have seen that the lowest forms of life, both animal and vegetable, begin in the water so, in each new class of animals, there is this same grading up. Each begins as a water kind, goes up to land kinds, and then to tree kinds. Among the birds there is the duck that lives most of the time in the water. He swims more than he flies. Then there are the long-legged, long-billed birds that live most of the time on the edge of the water. There are other birds that build their nests in bushes or low trees near the water, and get their food from the seeds that grow on water plants or by catching fish or other water animals. Higher up are other birds that build their nests on the dry land in the meadow far away from the water. Others build in the bushes, higher up; others in low trees; still others in the tallest trees, You know how much brighter a crow in a pine tree is than a goose on a pond.
So with the frogs—water frog, toad, a kind of land frog, and a tree toad; and even a flying frog. Notice the same thing among the rodents; the animals with sharp front teeth, like the two that first appear in baby's mouth. The beaver is a water rodent; the ground squirrel, rat and mouse are ground rodents. Then there is the tree squirrel and the flying tree-squirrel.
Water insects, moist-place insects, dry-land insects, bush insects, tree insects. Water mammals—the whale; "whales" that climb on rocks and get themselves called seals, "sea-lions" or sea-dogs; then our own home dogs. And some of these love water, like the water spaniel and Newfoundland dogs. Some are land dogs, like the fox, the wolf and greyhound. Others of this great dog-toothed, flesh-eating family—the "carnivora"—like the bears, can climb trees. They really do climb trees to get the food that a little insect brother, the bee, gathers and makes over in its own body to feed itsyoung just as mama bear gives milk out of her own body to feed her cubs.
How did animals and plants come to be so much like other animals and plants; and plants and animals so much like each other in shape, in their way of growing, moving and feeding and reproducing? Why does the growth of every tree keep showing us how many different kinds of things each little seed can grow into—root, bark, leaf, blossom, fruit? One answer is that all things are related to one another, branched out from the same beginning, just as great families grow into brothers and sisters, uncles and aunts; cousins and second cousins—differing more and more, as a rule, as they are more distantly related.
Another idea is that all the great families of animals—as bees and bears, birds and fish, horses and elephants—were made different in the first place, but yet made to resemble each other in these many unexpected ways to teach us how much we can learn from one another, and do for each other.
Anyhow we can all agree that living things are much more alike than we might suppose, when we know little about them, whether we agree as to just how they got to be so much alike or not.
And we can all agree, also, that it is much better to see where we are like other people in the things we believe, instead of quarrelling over the things in which we differ from them; and that, whatever else we believe, we can be sure that we are the happiest and most useful in proportion as we live to help every other body and every other thing—if we know and feel that all living things are little brothers in the water, the earth and the air.