EPILOGUE 
125 
found, as we have already stated, that this law was 
approximately fulfilled by some small forms of life 
developing in restricted regions. 
We have already indicated that any attempt to 
prognosticate the future numbers of Man, by extra- 
polating the curve of his growth in the past, must fail, 
not merely because we have no exact numerical record 
of his past, but also because the factors which determine 
his numbers are numerous, and are liable to momentous 
changes. And even had we a numerical measure of 
all the factors, and numbers sufficiently accurate to 
permit of an analysis disclosing the part played by 
each, accurate prediction would still be impossible, 
for we are not aware what governs the rising of life- 
forms inimical to, or beneficial to, Man. In the past, 
plague, cholera and yellow fever have at times played 
havoc with the human race. What we regard as 
utterly insignificant and useless forms of life often 
thrive at our expense. We disappear while they de- 
velop in countless numbers. Plagues of caterpillars, of 
“locusts,” of the * boll weevil,” of mice, etc., reveal 
how relatively helpless we are, when Nature develops 
life on lines that oppose our well-being. Entomologists 
have expressed a fear that Man may actually be over- 
whelmed by the insect world. However much we 
may discount. their terrors on the ground that possibly 
they magnify their office, the dangers, it is easy to 
see, may become formidable. It oftens happens that 
Man reaches results, through better (1) agricultural 
technique, that are most hopeful; only to learn a 
little later that his improved varieties of plants are 
very liable to be attacked by disease or by insect pests. 
At present we have no knowledge what it is causes the 
various evils, that harass mankind, suddenly to take on 
a serious form, and it is by no means certain that 
increased scientific knowledge will enable Man to 
cope with his enemies. We do not know what Nature’s