ORGANIC DEPENDENCE AND DISEASE 
13 
On this point our present knowledge permits us to lay 
emphasis, namely, that on the whole, in the survey of the 
earth and the sum total of its multitudinous and inconceiv- 
ably variant groups of life, there lias been a strong mini- 
mum, a redeeming minority, of competent upward evolu- 
tion; and wise students of nature, in reflecting on this 
thought, have broken out into exclamations of wonder and 
amazement at the slender thread of chance by which we 
who call ourselves men have come to this estate, in a world 
where for millions of years the temptation to the easier 
way and the obstacles to independent living were con- 
stantly against us. 
Let us look at a most common illustration of the general 
fact of dependence among existing races of animal life, of 
very ancient ancestry. The oyster is early attached firmly 
to the sea bottom, to the rock or to the shell of a brother 
oyster and never stirs from its moorings for the rest of its 
life. It opens its hard valves a little way to let its servants, 
the food-bearing water currents, deliver their nutrient 
supplies and it defends itself in the struggle against en- 
emies, not by standing out in the open and meeting force 
with force but simply by closing its doors and shutting itself 
up in its calcareous caisson. To the attacks of sharp- 
toothed fishes and the relentless starfish the oyster has lit- 
tle defense. The nonresistant, flaccid, pacific creature 
within, fully equipped with the organs of special physiol- 
ogy, is essentially the same in habit as he was those millions 
of years ago when the oysters began to show themselves in 
the salt waters of the Carboniferous age. The knell of its 
progress was struck when first it settled down to a fixed 
immobile existence and, hopeless as the ox, the future holds 
for it no promise of improvement. And yet even today the 
embryo oysters have a brief period of locomotive freedom, 
proof enough in the laws of ontogeny that a free life was 
once the ancestral condition of the race. With the oyster’s 
cousin, the clam, the case is similar ; less degenerate in pliys- 
