You must turn off your ad blocker to use Psych Web; however, we are taking pains to keep advertising minimal and unobtrusive (one ad at the top of each page) so interference to your reading should be minimal.

If you need instructions for turning off common ad-blocking programs, click here.

If you already know how to turn off your ad blocker, just hit the refresh icon or F5 after you do it, to see the page.

Psi man mascot

Summary: Early Comparative Psychology

Comparative psychology began shortly after Darwin published his ideas about natural selection. Darwin himself suggested in The Descent of Man (1874) that human intelligence evolved gradually. Animals might show us how intelligence looked in earlier stages.

Romanes, a friend and student of Darwin, pursued this idea in his book Animal Intelligence (1882). Romanes relied upon anecdotes (stories) for information. He assumed that animals had the same sorts of mental exper­iences as humans.

Early comparative psychologists assumed all animals learned the same way and had much the same experience. They could be arranged on a scale from least to most advanced.

This idea can be traced back to Aris­totle's "Great Scale of Nature." That idea is rejected by modern scientists, who see a tree rather than a straight line of development.

In 1894, C. Lloyd Morgan published Introduction to Comparative Psych­ology. He introduced a rule of thumb called Morgan's Canon, suggesting animal behavior should be interpreted in the simplest way possible.

However, Morgan did not follow his own advice. He believed that consciousness was necessary for even simple acts of learning, such as a chick learning to peck.

By 1900, some scientists were ready to reject the whole idea of animal con­sciousness. Jacques Loeb suggested animals were machine-like, without mental lives.

The public, on the other hand, was eager to believe stories of animal intelligence, in the early 1900s. In 1904 the public devoured stories about Clever Hans, a horse that did arithmetic, spelled words in German, and analyzed musical chords.

Hans could perform even when his trainer was absent. However, a psychologist named Oskar Pfungst showed that Hans could answer correctly only when the humans around him knew the answer to a question. Evidently Hans was responding to subtle cues from the humans.

American comparative psychologists compared different species using standardized laboratory tasks. Edward Thorndike used an apparatus which he called a puzzle box to study what would today be called escape learning.

Most comparative psychologists of the mid-20th Century assumed that laws of learning would apply to all species. Therefore they studied the most convenient species: rats, pigeons, and college sophomores.

Rat psychology faded out toward the end of the 20th Century, both in the study of learning (rat labs became less common) and in the study of comparative psychology (psychologists became interested in more species). Comparative psychology survived by merging with the European approach to studying animal psychology, called ethology.

Write to Dr. Dewey at

Don't see what you need? Psych Web has over 1,000 pages, so it may be elsewhere on the site. Do a site-specific Google search using the box below.