THE STRUGGLE FOR LIFE. 147 
diseases themselves are subject to the same laws of change of 
type, as every other creature, from the Monad up to Man, and 
evolve new species among themselves. 
Before entering on the last branch of the subject on which 
I intend to speak to-night, I must say a few words more on a 
subject already mentioned, viz.: heredity, or the tendency 
of the offspring to resemble the parent. Were it not for the 
fact that heredity retains its powers during many generations, 
races and species would be nothing like so stable as they are. 
In all species there is a tendency to throw back, that is, to be 
born with a resemblance to some more or less remote ancestor. 
There are two races or breeds of pigeons called the fantail, 
which is purely white, and the spot, which is white with a red 
tail and a red spot on the forehead. These breed remarkably 
true among themselves, but cross them, and at once coloured 
birds, with the two black bars running across the wing, of 
their common ancestor the wild rock dove, will be produced. 
Full consideration of the laws of heredity or the assumption 
of ancestral characters, is, I believe, of the greatest possible 
importance in dealing with the problems of human society. 
In every generation will be born an average percentage of 
individuals with certain physical and mental defects. For 
instance, some will be born with the nervous system unstable, 
either physically, rendering them liable to Epilepsy, Hysteria, 
and the whole train of Neurotic diseases, or mentally, lacking 
self-control, and prone to abuses of food and drink, and to 
crimes of violence and greed. Again, others are born with 
organizations which fall an easy prey to tubercle, when sub- 
jected to any unfavourable surroundings. 
Now preventive medicine, orderly government, and the laws 
of Christian kindness have by their joint efforts succeeded in 
prolonging the average duration of human life, (in this country 
by something like two years). When the nature of this in- 
crease is examined it is found to be due to the survival of a 
larger percentage to maturity, and those preserved by these 
