WHY DO ANIMALS BECOME EXTINCT? 235 
example of the dependence of plants on ani- 
mals, for their existence hangs on that of a 
small moth whose peculiar structure and hab- 
its bring about the fertilization of the flower. 
The two. probably developed side by side until 
their present state of inter-dependence was 
reached, when the extinction of the one would 
probably bring about that of the other. 
It is this inter-dependence of living things 
that makes the outcome of any direct inter- 
ference with the natural order of things more 
or less problematical, and sometimes brings 
about results quite different from what were 
expected or intended. 
The gamekeepers on the grouse moors of 
Scotland systematically killed off all birds of 
prey because they caught some of the grouse, 
but this is believed to have caused far more 
harm than good through permitting weak and 
sickly birds, that would otherwise have fallen 
a prey to hawks, to live and disseminate the 
grouse distemper. 
The destruction of sheep hy coyotes led the 
State of California to place a bounty on the 
heads of these animals, with the result that in 
