Each theory contains important truth.  Naegeli’s view of the importance of initial tendencies, inherent in the original living substance, is too often undervalued.  My own conviction, at least, is steadily strengthening that, without some such original tendency or aim, evolution would never have reached its present culmination in man.  His error lies in emphasizing this factor too exclusively.  The fundamental proposition of Weismann’s theory, that heredity is due to continuity of germ-plasm, seems to contain important truth.  But we need not therefore accept his theory of a germ-plasm so isolated and independent as to be beyond control or influence by the habits of the body.  The importance of use and disuse, and the transmissibility of their effects, would seem to supply a factor essential to evolution.  Weismann has done good service in emphasizing the stability of the germ-plasm.  Evolution is always slow, and, for that very reason, sure.

If these conclusions are correct, they have an important practical bearing.  Struggle and effort are essential to progress.  Not inborn talent alone, but the use which one makes of it, counts in evolution.  The effects of use and disuse are cumulative.  The hard-fought battle of past generations becomes an easy victory in the present, just because of the strength acquired and handed down from the past struggle.  Persistent variation toward evil is in time weeded out by natural selection.  And, while evil remains in the world, we are to lay up stores of strength for ourselves and our descendants by sturdily fighting it.  But the effects of right living through a hundred generations are not overcome by the criminal life of one or two.  Evil surroundings weigh more in producing criminals than heredity, and their children are not irreclaimable.

The struggles and victories of each one of us encourage the rest.  There is, to borrow Mr. Huxley’s language, not only a survival of the fittest, but a fitting of as many as possible to survive.  And in the midst of the hardest struggle there is the peace which comes from the assurance of a glorious triumph.

                Condensed Chart of Development of the Main Line
                    of the Animal Kingdom leading to Man.

|                            | ORGANS        | MOST RAPIDLY
PHYLOGENETIC |                            | APPROACHING   | ADVANCING
SERIES.      | NEW ATTAINMENTS.           | CULMINATION.  | ORGANS.
-------------+----------------------------+---------------+-

-------------
Amoeba.      | Cell.                      |               |
-------------+----------------------------+---------------+-

-------------
Volvox.      | Somatic and reproductive   |               | Reproductive.
| cells                      |               |
-------------+----------------------------+---------------+-

-------------
Hydra.       | Simple reproductive organs.|               | Reproductive.
| Gastro vascular cavity.    |               |