This sequence of dominant functions,[A] of physiological dynasties, would seem therefore to be a fact.  And our series of forms described in the second, third, and fourth chapters is merely a concrete illustration showing how this sequence may have been evolved.  The substitution of other terms in the anatomical series there described—­amoeba, volvox, etc.—­would not affect this result.  By a change in the form of our history we have eliminated to a large extent the sources of uncertainty and error.  And the dominant function of a group throws no little light on the details of its anatomy.

  [Footnote A:  See condensed Chart of Development, etc., p. 309.]

If we can be satisfied that ever higher functions have risen to dominance in the successive stages of animal and human development, if we can further be convinced that the sequence is irreversible, we shall be convinced that future man will be more and more completely controlled by the very highest powers or aims to which this sequence points.  Otherwise we must disbelieve the continuity of history.  But the germs of the future are always concealed in the history of the present.  Hence—­pardon the reiteration—­if we can once trace this sequence of dominant functions, whose evolution has filled past ages, we can safely foretell something at least of man’s future development.

The argument and method is therefore purely historical.  Here and there we will try to find why and how things had to be so.  But all such digressions are of small account compared with the fact that things were or are thus and so.  And a mistaken explanation will not invalidate the facts of history.

The subject of our history is the development, not of a single human race nor of the movements of a century, but the development of animal life through ages.  And even if our attempts to decipher a few pages here and there in the volumes of this vast biological history are not as successful as we could hope, we must not allow ourselves to be discouraged from future efforts.  Even if our translation is here and there at fault, we must never forget the existence of the history.  Some of the worst errors of biologists are due to their having forgotten that in the lower stages the germs of the higher must be present, even though invisible to any microscope.  Our study of the worm is inadequate and likely to mislead us, unless we remember that a worm was the ancestor of man.  And a biologist who can tell us nothing about man is neglecting his fairest field.

Conversely history and social science will rest on a firmer basis when their students recognize that many human laws and institutions are heirlooms, the attainments, or direct results of attainments, of animals far below man.  We are just beginning to recognize that the study of zooelogy is an essential prerequisite to, and firm foundation for, that of history, social science, philosophy, and theology, just as really as for medicine.  An adequate knowledge of any history demands more than the study of its last page.  The zooelogist has been remiss in not claiming his birthright, and in this respect has sadly failed to follow the path pointed out by Mr. Darwin.