In the attack on my theory many facts were brought forward which show that in the animal and vegetable kingdoms the individual is always sacrificed to the advantage of the race. There is no doubt as to this, and in the course of this book I have given exact facts bearing on it. I instanced plants such as the Agave and some Cryptogams which die as soon as they have reproduced; I have also spoken of the small female round worms (_Nematoda_) which are brutally torn in pieces and devoured by their progeny. It would be difficult to find better cases of the sacrifice of the individual to the species. The rule, however, does not apply to man, who, in this respect, stands in a special position. Since the arrival of man, several species of animals have disappeared from the earth. Man has played a large part in the destruction of the Moa (_Aepyornis_) of Madagascar, the largest member of the class of birds. He destroyed the Dodo of the Island of Mauritius and Steller’s sea cow (_Rhytina stelleri_), a harmless relative of the Manatee, from the shores of the Aleutian Archipelago. Man is about to cause the extinction of several species of harmful carnivorous animals, such as the wolf and the bear, and possibly it will not be long before automobiles have replaced the horse, which would then become extremely rare. However, although he has destroyed so many other species, man has taken good care of himself. The progress already made by civilisation has considerably reduced our mortality. Every year, a large number of young infants are kept alive by the aid of hygiene and medicine. The decrease of war and of assassination has also played a part in maintaining the race. The position which man has acquired in the world makes it more likely that what we have to fear is too great an increase of population, and although the theory of Malthus has not been verified in all its details, it is still true that man could multiply on the face of the earth too abundantly. It is already clear that almost in the proportion that humanity stops the effusion of its blood in war, it tends to limit the propagation of the race. As the future of the species seems to be safe, it is natural to consider in the first place that of the individual. In this respect the facts of general biology are of special interest. Man is not the only social animal on the earth. Long before his appearance other living beings existed in organised societies. The splendid colonies of Siphonophora float on the surface of the seas, whilst in the ocean depths there are societies of corals of extraordinary variability, whilst again, on land, many kinds of insects live in highly organised societies. This social life has been developed without external assistance, and without any code to regulate the conduct of the individuals united for a common purpose.