THE INDUCTIONS OF BIOLOGY. 



equal force no force which can set up a new evolution 

 among the units of any other. 



And so we reach the remarkable conclusion, that the life ul 

 a species, like the life of an individual, is maintained by the 

 unequal and ever- varying actions of incident forces on its 

 different parts. An individual homogeneous throughout, and 

 having its substance everywhere continuously subject to like 

 actions, could undergo none of those changes which life con- 

 sists of; and similarly, an absolutely-uniform species, having all 

 its members exposed to identical influences, would be deprived 

 of that initiator of change which maintains its existence as 

 a species. Just as, in each organism, incident forces constantly 

 produce divergences from the mean state in various directions, 

 which are constantly balanced by opposite divergences indi- 

 rectly produced by other incident forces ; and just as the 

 combination of rhythmical functions thus maintained, consti- 

 tutes the life of the organism ; so, in a species, there is, through 

 gamogenesis, a perpetual neutralization of those contrary de- 

 viations from the mean state, which are caused in its different 

 parts by different sets of incident forces ; and it is similarly 

 by the rhythmical production and compensation of these con- 

 trary deviations, that the species continues to live. The 

 moving equilibrium in a species, like the moving equilibrium 

 in an individual, would rapidly end in complete equilibration, 

 or death, were not its continually- dissipated forces continually 

 re-supplied from without. Besides owing to the external 

 world, those energies which, from moment to moment, keep 

 up the lives of its individual members ; every species owes 

 to certain more indirect actions of the external world, those 

 energies which enable it to perpetuate itself in successive 

 generations. 



97. What evidence still remains, may be conveniently 

 woven up along with a recapitulation of the argument pursued 

 through the last three chapters. Let us contemplate the facts 

 in their synthetic order. 



