Essays of a Biologist

by Julian Huxley

Meanwhile, let it be remembered, the simplest forms have survived side by side with the more complex, the less specialized with the more specialized. Even when we can trace a causal relation between the rise of one group and the decay of another, as with the mammals and birds on the one hand, and the reptiles on the other, even then numbers of the defeated group continue to exist. Thus, in broad terms, evolution is not a transformation, be it progressive or no, of the whole of living matter, but of a part of it.

I will endeavour to sum up, in brief, what seem to me the salient points of that process, a sketch of which, inevitably hasty and inadequate, I have just tried to give.

During the time of life’s existence on this planet, there has been an increase, both in the average and far more in the upper level, of certain attributes of living things.

In the first place there has been an increase in their size, brought about by two methods, first by the increase of size of the units of life themselves (cells, metazoan individuals, communities), secondly by their aggregation; and this has been accompanied by a (very roughly) parallel increase in the duration of life.

Next, there has been an increase in their complexity; and this in its turn depends upon the fact that a division of labour has been brought about between the parts of organisms, each part becoming specialized for greater efficiency in the performance of some particular function. In the fewest words, the separate bits of machinery of which organisms are composed have become more efficient.

In the third place, there has been an increase in the harmony of these parts, and consequently in the unity of the whole. Delicate mechanisms for co-ordination have been developed, and arrangements whereby one portion becomes dominant over the rest, and so a material basis for unification is given.

In the fourth place, there has been an increase of self-regulation. The outer environment changes from month to month, from hour to hour. The more complex products of evolution are in high degree exempt from the consequences of these changes, through being the possessors of a constant internal environment which, beyond the narrowest limits, it is most difficult to alter.

Fifthly, there has been an increase in the possibility of bringing past experience to bear on present problems. At the base is the power of modifying normal reactions with repetition; then come some simple degrees of memory; then associative memory, as in birds and mammals, for whom most reactions are not given in the inherited constitution, but must be learnt; then rational memory, in which the power of generalization liberates life from blind dependence upon the local and the accidental; and finally tradition, whereby the amount of experience available to the developing race is not constituted merely by the isolated and limited experiences of its members, but by their sum. More and more of the past becomes directly operative in the present; further and further into the future can the aim of the present extend.

Finally we can conclude with a high degree of certainty that the psychical faculties—of knowing, feeling, and willing—have increased in intensity, and also in their relative importance for the life of the individual organism.

We have condensed our summary into these six general statements; if we wish to reach a still more general form, the most general form possible, we can redistil it thus: During the course of evolution in time, there has been an increase in the control exerted by organisms over their environment, and in their independence with regard to it; there has been an increase in the harmony of the parts of organisms; and there has been an increase in the psychical powers of organisms, an increase of willing, of feeling, and of knowing.