Comparative Psychology before World War I 69associates. Although he tried to be careful in selecting these,
some of them are rather far-fetched and have led to a vilifica-
tion of Romanes and his methods. His reputation was fur-
ther tarnished because, in his efforts to establish continuity,
he tended to anthropomorphize (i.e., attribute human proper-
ties to animals). Romanes’s many contributions are often
neglected.
A more conservative approach to animal behavior was
taken by another Englishman, C. Lloyd Morgan, in his book
An Introduction to Comparative Psychology(1894). Al-
though this was a multifaceted work, Morgan is best remem-
bered for one sentence, which has come to be known as
Lloyd Morgan’s Canon:
In no case may we interpret an action as the outcome of the ex-
ercise of a higher psychical faculty, if it can be interpreted as the
outcome of the exercise of one which stands lower in the psy-
chological scale. (p. 53)Morgan clearly believed in a hierarchy of psychological
processes, with some processes being higher, or more com-
plex, than others. He suggested that we can only invoke the
higher processes when behavior cannot be explained in terms
of lower, or simpler, psychological processes. This principle
is often confused with a related dictum, the law of parsimony
(Dewsbury, 1984; Newbury, 1954). The terms “law of parsi-
mony” and “Occam’s razor” can be used interchangeably for
most purposes. These terms refer to the assumptions made in
providing an explanation rather than to the complexity of the
psychological processes that are invoked. Thus, other things
being equal, we should strive for explanations that do not
multiply explanatory principles and that are simple explana-
tions in that sense. Morgan (1894), by contrast, noted that
“the simplicity of an explanation is no necessary criterion of
its truth” (p. 54). It would be possible to construct an inter-
pretation based on lower psychological processes but that
introduces numerous additional assumptions and is thus con-
sistent with Morgan’s Canon but inconsistent with the law of
parsimony or one that is parsimonious but in violation of the
canon. The canon implies, for example, that we should be
very careful in attributing consciousness to animals. By no
means did Morgan wish to suggest that animals lack con-
sciousness; rather, he meant that we could invoke such a
process only when necessary to explain observations that
could not be explained with psychologically lower complex
processes.
Other investigations in the growing field of animal
behavior studies were conducted by such Britishers as
Douglas A. Spalding, Sir John Lubbock, and L. T. Hobhouse
and Americans such as Lewis Henry Morgan, T. Wesley
Mills, George W. Peckham, and Elizabeth Peckham. Espe-
cially notable was the work of Charles H. Turner on the com-
parative psychology of crayfish, ants, spiders, bees, and other
invertebrates. Turner was an African American scientist of
the time who published significant research in major journals
(see Cadwallader, 1984).COMPARATIVE PSYCHOLOGY BEFORE
WORLD WAR IBuilding on these foundations, comparative psychology
emerged as a significant, visible discipline during the late
nineteenth and early twentieth centuries in the universities of
the United States (see Dewsbury, 1992). Hall had been called
to the presidency of Clark University and brought with him
Edmund C. Sanford, who ran the laboratory. They taught
courses and attracted students to comparative psychology.
The laboratory course included work on microscopic ani-
mals, ants, fish, chicks, white rats, and kittens. Graduate stu-
dent Linus Kline (1899), who did some of the teaching,
suggested that “a careful study of the instincts, dominant
traits and habits of an animal as expressed in its free life—in
brief its natural history should precede as far as possible any
experimental study” (p. 399). The best known of the early
Clark studies were those on maze learning published by
Willard S. Small (1901). Kline mentioned to Sanford that he
had observed runways built by feral rats under the porch of
his father’s cabin in Virginia, and Sanford suggested the use
of a Hampton Court maze as an analog of the learning re-
quired of rats in nature (Miles, 1930). Small and Kline con-
structed the mazes and other devices in which to study the
learning process in rats. Thus, the early studies were designed
to mimic situations the subjects faced under natural condi-
tions. The Clark program was not limited to such studies.
Under the influence of Hall, there was a strong developmen-
tal focus, as in Small’s (1899) study of the development of
behavior in rats and in Conradi’s (1905) study of the devel-
opment of song in English sparrows. James P. Porter (1906)
analyzed the naturally occurring behavioral patterns of two
genera of spiders.
Robert M. Yerkes, under the influence of William James
and Hugo Münsterberg, was a mainstay of comparative
psychology during this period at Harvard. He studied the be-
havior of a wide variety of invertebrates such as crayfish
(Yerkes & Huggins, 1903) and published one of the early
classics of the field, The Dancing Mouse(Yerkes, 1907), a
comprehensive study of a mutant mouse strain. Yerkes and
his students also studied a variety of behavioral patterns and
species, including sensory function, such as Cole’s (1910)