WHY DID* BIRDS BEGIN TO INCUBATE? 99 
most reptiles, and to some extent by the ostrichlike 
birds (in the wild state), there is another interesting 
example of the similarity of nesting habits between 
some early birds and some reptiles. The crocodiles 
generally are known to bury their eggs in the hot sand, 
but some indicate progress by excavating deep holes 
and placing in them, with their eggs, much vegetable 
material, so that a sort of hotbed is formed, and the 
eggs are hatched by the heat generated by decay. 
Among the megapodes, or brush turkeys, of the Aus- 
tro-Malaysian regions, a similar habit prevails. Some- 
times this is varied into a surface compost heap which 
many birds, acting together, raise and use in common. 
Like the reptiles, the eggs are deposited in the night. 
But the bird out-Herods Herod in the lack of further 
paternal interest, for some of the crocodiles feed their 
young after they escape to the water, and in some 
measure they guard the place of deposit ; but the little 
brush turkey and his kin are always orphans. 
A sense, therefore, of the need of more heat or 
heat differently, or more constantly, applied may 
therefore lie at the base of incubation. Conditions 
might easily have arisen that demanded a change, for 
birds, as we have frequently seen, are easily influenced 
by changes in environment. Thus the ostrich doubt- 
less leaves its eggs to be hatched in the sand by the 
sun in some hot regions, but in others, and especially 
under domestication, it practices incubation, and it has 
in all probability changed its habits to some extent 
since the time of Job (xxxix, 14). 
With the early birds conditions quite likely arose 
