We must not be misled by such a case as that of the multiplication of rabbits in Australia. Apart from such circumstances as human interference, the earth is already crammed with life of a kind, not the highest life nor the most intense life, but at any rate fully extended life. Man alone multiplies persistently, irresistibly, and has done so from the very first, so that, arising locally, he is now diffused over the whole surface of the earth. To quote from Professor Lankester again: “Man is Nature's rebel. Where Nature says Die! Man says I will live! According to the law previously in universal operation man should have been limited in geographical area, killed by extremes of cold or of heat, subject to starvation if one kind of diet were unobtainable, and should have been unable to increase and multiply, just as are his animal relatives, without losing his specific structure.... But man's wits and his will have enabled him ... to ‘increase and multiply,’ as no other animal, without change of form.” Not only has man made himself the only animal which constantly increases in numbers, but this increase, as Professor Lankester points out in another part of his lecture, already threatening certain difficulties, will be much more rapid than at present, assuming the birth-rate to remain where it is, when disease is controlled. It is within our power, as Pasteur declared long ago, to abolish all parasitic, infectious or epidemic disease. This must be and will be done--within a century, I have little doubt. The problem of the increase of human population will become more pressing than ever. Professor Lankester suggests that in one or five centuries the difficulty raised by our multiplication “would, if let alone, force itself upon a desperate humanity, brutalised by over-crowding and the struggle for food. A return to Nature's terrible selection of the fittest may, it is conceivable, be in this way in store for us. But it is more probable that humanity will submit to a restriction by the community in respect of the right to multiply.” The lecturer added that we must therefore perfect our knowledge of heredity in man, as to which “there is absolutely no provision in any civilised community, and no conception among the people or their leaders, that it is a matter which concerns anyone but farmers.” =The secret of multiplication.=--Professor Lankester, however, omits to point out the astonishing paradox involved in the fact that--as I pointed out at the Royal Institution in 1907--man, the only ceaselessly multiplying animal, has the lowest birth-rate of any living creature.[19] From the purely arithmetical point of view, what does it mean? We may defer at present any deeper interpretation.