Courage, intelligence, adaptability, prowess, bodily vigor, speed,
alertness, ability to hide, ability to build structures which will
protect the young while they are helpless, fecundity--all, and many
more like them, have their several places; and behind all these
visible causes there are at work other and often more potent causes of
which as yet science can say nothing. Some species owe much to a given
attribute which may be wholly lacking in influence on other species;
and every one of the attributes above enumerated is a survival factor
in some species, while in others it has no survival value whatever,
and in yet others, although of benefit, it is not of sufficient
benefit to offset the benefit conferred on foes or rivals by totally
different attributes. Intelligence, for instance, is of course a
survival factor; but to-day there exist multitudes of animals with
very little intelligence which have persisted through immense periods
of geologic time either unchanged or else without any change in the
direction of increased intelligence; and during their species-life
they have witnessed the death of countless other species of far
greater intelligence but in other ways less adapted to succeed in the
environmental complex. The same statement can be made of all the many,
many other known factors in development, from fecundity to concealing
coloration; and behind them lie forces as to which we veil our
ignorance by the use of high-sounding nomenclature--as when we use
such a convenient but far from satisfactory term as orthogenesis.



II. UP THE PARAGUAY

On the afternoon of December 9 we left the attractive and picturesque
city of Asuncion to ascend the Paraguay. With generous courtesy the