
1899] THe SCOPE OF NATURAL SELECTION 195 
because it is suited to its environment; (2) because it can repro- 
duce similar organisms in sufficient number to maintain or increase 
its relative position in its environment. The more perfect the 
organism the less its chance of elimination, consequently so long as 
its reproductive power is successfully maintained it is to its advantage 
if it can reduce to a minimum the loss incurred by the organism in 
successful reproduction ; it will follow, therefore, that the cells which 
throw off least reproductive material from the adult structure will 
require less nutriment, and therefore the collective organism will, 
other conditions equal, survive under competitive conditions. For this 
reason protoplasmic growth will be reduced as far as possible when 
beyond the needs of the organism, and the reproductive buds or units 
from each cell will tend to be reduced both in size and number. For 
these reasons it would obviously be of advantage if merely the mor- 
phological elements were extruded from the different cells,’ and these 
when collected in the reproductive centre would form the material for 
the new individual. 
6. As differentiation of reproductive function continued run- 
ning a parallel course with other specialisations of structure, natural 
selection continuing to favour the best-formed individual and _ off- 
spring that environments could allow, two tendencies would become 
manifest: (1) a tendency to reproductive economy, by which every 
unnecessary development would be eliminated so as to make reproduc- 
tion a less and less expensive process to the organism; (2) owing to 
increased complexity, specialisation, and evolution of structure, repro- 
duction would become a more and more delicate process, and would 
constantly have to be conducted with increasing care, and the stages 
of development of the organism would therefore become increasingly 
prolonged. The development of the individual, and the capacity of 
that individual when developed for competition with other individuals, 
would form two partly competing and partly complementary elements 
of race progress, and the resultant of the two would correspond 
to the line of progressive adaptation and development. With the 
increasing length of the period of development differentiation of sex 
becomes first an advantage and then a necessity. 
7. A progressively specialised method of food supply will be 
required to keep pace with the other specialisations. 
In applying these conceptions to the interpretation of phenomena, 
certain points must be specially emphasized :— 
(a) Every important specialisation of structure must be represented. 
(b) As, however, one of the causes of evolution of structure 
is quantitative complexity, it follows that every quantita- 
tive element need not be represented, but only the right 
’ In the extrusion of the polar bodies from the ovwn, we may possibly have an instance 
of what on a smaller scale is universal among multicellular organisms. 
