If now we trace the history of life up to man, we find in him--as we have seen--the lowest birth-rate of any animal and the longest ante-natal period in proportion to his body weight, the longest period of maternal feeding, and by far the lowest infant mortality and general death-rate. A chief fact of progress has been, in a word, the supersession of the quantitative by the qualitative criterion of survival-value. Immeasurably vast vital economy and efficiency have thus been effected. The tendency of progress, in short--a tendency coincident with the evolution of ever higher and higher species--is to pass from the horrible Gargantuan wastefulness of the older methods towards the evident but yet lamentably unrealised ideal--that every child born shall reach maturity. This great historical tendency, which will ultimately involve the restriction of parenthood to the fit, fine and relatively few, has occurred under the impartial rule of natural selection simply and solely because it has endowed with survival-value the successive species in which it has been demonstrated. =The rise of parenthood.=--Consistently with this fact and with the argument of the previous chapter is the tendency towards the lengthening of infancy, a very characteristic condition of the evolution of the higher forms of life. This lengthening and accentuation of infancy makes for variety of development, and, as we have seen, is supremely instanced in man, where it depends upon, and makes possible, the transmutation of fixed instincts into the plastic thing we call intelligence. Thus, to quote the words of Dr. Parsons,[44] “we find that as infancy is prolonged in the progress of species, the care given to offspring by parents is increased. It extends over a longer period and it is directed more and more towards the total welfare of offspring. The need of a potentially many-sided and enduring kind of parental care is filled through the social group we call the family.” Apart from those immensely significant creatures, the social insects, we find well-marked though primitive signs of motherhood amongst the fishes, and in a few cases, such as the stickleback, the beginnings of fatherhood. But it is not until we reach the mammals, and especially the monkeys and apes, that we find a great development of motherhood, far more prolonged and far more important than the more frequently extolled parental care found amongst the birds.