5 -’ 
PKOFIiSSOK K. PEAKSOX OX THE IXFLUEXCE OF XATUKAL 
Cj : C.2 : Cg 1 : -12782 : -00156, 
or, the chances of survival of an individual of the fittest tyjDe would be about eight times 
as great as those of an individual of the most frequent type after selection and about 
700 times as great as those of an individual of the most frequent type before 
selection. If r-j, v.^ be the numbers after selection in the three classes'^ of the 
fittest to survive, the most frequent after selection and the most frequent before 
selection, we find 
-00892 : 1 : -05978. 
In other words, the most numerous type before selection is still after selection about 
6-7 times as numerous as the type with the least mortality, and this latter type is 
only aljout xyj as numerous as the type to be most frequently met with after 
selection has taken place. 
Thus, although there would have been a very great evolution in cephalic index, 
due to a fairly stringent selection, the fittest to survive would always have formed 
but a small fraction of the dominant type. Even if we were to replace the selection 
here considered by a gradual evolution spread over several generations, we should 
.still reach in the main the same conclusion, i.e., that natural selection never joroceeds 
hij the survival of the fittest, or the survival of those ivith the least death-rate. These 
will always remain a small fraction of the community—they are the goal, but often 
the vei'v distant goal, to which selection tends to shift the population. 
(13.) CASE'(ii.) —Selection of Two Organs. 
In this case let the surface of survivors be : 
= c'o expt. 
(H - 
Spd - hp) 
2 Vp (v, - Hd (,r, - HA , (r. - H.P 
- hP) 
Adi-hp) 
• (c.), 
the original population : 
Z == Zq expt. — I 
4“ 
(Tpfl rjo") Hp) ^p(f ■“ HP) 
and the curve of probaljillty of survival : 
— 1 [ ~~ l\y _ -P12 ~ ^‘i) 0-2 — d) , ('p ~ hf 
T ' HO ^ l.s-Q _ u 7:- /I 2\ “f" - 2 
. (ci.). 
Since : 
(1 - Pf) (1 - Pu) 
P — dE, 
“ Pl2~)\ ' 
(cii). 
* By individuals of a type or class is meant here, as elsewhere in this section, all the group falling 
w ithin some small definite range of variation lying round a particular value of the organ {e.g., m, m + H, 
or m + /.), which defines the type or class. 
