Man is related to the apes not alone in the structure of his body and brain, but also in the blood stream that courses through his veins. This has been conclusively proved by the remarkable series of blood tests conducted by Professor G. H. F. Nuttall at Cambridge University. By these tests, it was shown that man and the chimpanzee are blood relations; that the gorilla is a more distant relative, and the orang a relative more distant still. Below the anthropoids, the blood relationship is represented with diminishing force in the baboons and monkeys. These blood tests confirm the conclusions of zoology and prove the truth of evolution. Fig. 44 is a picture of Haeckel’s genealogical tree of humanity. It enables us to visualize in its main outline the history of the evolution of life. At the bottom of the tree are the monera and the amœbæ—tiny creatures consisting of a single cell. As growing life assumes diverse forms, the foremost creatures are represented by higher and higher positions on the trunk of the tree, or by diverging branches in the ascending order. Life is seen to progress from the simple to the complex, past the sponges, the molluscs and the fishes, through the amphibians, the reptiles, the marsupials, rising higher and higher in the scale of being, through lemurs, apes and anthropoids, until, at the topmost summit of the tree appears man. And what has been the secret, the driving force back of this process of evolution? To understand the causes of evolution, it is necessary to understand the four fundamental laws of life. First, that while creatures resemble their parents through heredity, they nevertheless differ more or less from their parents—this is the law of variation. Secondly, that more creatures are born than can survive—this is the law of surplus population. Thirdly, that among living creatures, and owing largely to over-population, there is continually going on a struggle for existence—this is the law of struggle. And fourthly, that out of this struggle there results the survival of the fittest. Variation, surplus population, struggle, spell the survival of the fittest. In the struggle for existence, those creatures possessing the best bodies and the keenest minds, those that could best protect themselves from their enemies and obtain their food—in a word, those that were best adapted to their environment—survived, while the others perished. Those whose variations were unfavorable, the weak, the inferior, died. But those whose variations were an advantage, the strong, the superior, survived. In consequence of the survival of the fittest, Nature, throughout the unfolding ages, kept breeding from the best. And this practice could have but one result—the gradual improvement of every race of creatures.