THE EELATION OF BINARY FISSION TO 
VARIATION. 
By J. Y. SIMPSON, D.Sc. 
It has hitherto been commonly assumed that binary fission as a method of 
reproduction amongst unicelkilar organisms is mere duplication, and that the 
daughter-products of the process are exactly alike. The generalisation was pro- 
bably in the first instance botanical ; thence it spread to zoology, and from lack 
of investigation has been accepted within the most recent times*. Its use in 
theory is obvious. In binary fission we do not look for variation ; accordingly 
we are left with an excellent rationale of conjugation, and so, finally, of sexual 
reproduction, viz. a means to produce variation in the interests of evolution. 
As the result of certain considerations I have been led to the view that binary 
fission is not mere duplication, and that the products of such division are more 
or less unlike. A similar conclusion has been already reached by Ernest Warren 
in his studies on Parthenogenesis. Thus in a paper entitled " An Observation 
on Inheritance in Parthenogenesis "f he states: "From twenty-three Daphnia, 
themselves originating from Parthenogenesis, broods were produced consisting of 
three to six individuals. The parents were measured, and the offspring were 
allowed to grow up. On measuring the offspring it was at once obvious that 
the children of the same brood exhibited very considerable variability." 
Perhaps it should be stated here that the contention is not that there is 
ahvays variation in binary fission. Of this I have very little doubt, but it 
would be exceedingly difficult, perhaps impossible, to prove ; for where the varia- 
tion was not quantitative it might be qualitative. Indeed there were many 
instances where the products of binary fission did appear to be singularly alike, 
and they might well have been called duplicates so far as their qualities were 
revealed by a magnification of 625, but these instances were by no means the 
majority. On the other hand there were also numerous instances where even 
with a magnification of 105 it was evident on careful examination that there 
was considerable dissimilarity between the daughter forms. 
* Adam Sedgwick's Presidential Address, Section D, Report of British Association for 1899, 
pp. 759, 760. 
t Proceedings of the Royal Society, Vol. lxv. p. 155. 
