Trial and error

In Behavior of the Lower Organisms (1906), Jennings named three significant features of behavior. The second was reaction by varied or overproduced movements, with selection from the conditions those movements produce.¹ He called it, in brief, reaction by selection of overproduced movements. He held that this and the law of the readier resolution of physiological states supply the mainsprings for the development of behavior. The second he called constructive and the third conservative.² He added that the effectiveness of the method depends on how well the movements fit to relieve the organism from unfavorable conditions. He noted that the rapid movements of Paramecium are more likely to save it from a diffusing chemical than the slow motion of Amoeba.³

Driesch (1908) said he would avoid Jennings's term. He found its psychological aspect out of place, and he thought the word "trial" implied some sort of experience.⁴ In simple random movement, he wrote, nothing of that sort is known. He did accept the term for an experiment described by Yerkes, where a series of trials becomes an immediate reaction when the stimulus returns. Elsewhere he thought it unjustified, since there is no objectified experience and no criterion for a "liked" state in lower animals.⁵ He judged Jennings's resolution of physiological states to say about what his own "historical basis of reaction" says.⁵

Loeb (1916) argued against explaining orientation to light by will or by Jennings's method. He described a machine that turns toward a lantern when light falls unevenly on it. He concluded that neither fondness for light, will-power nor trial and error makes the machine follow the light.⁶ Child (1924) contrasted the two reaction patterns. In his reading, trial and error depends on the absence of mechanisms giving direct orientation. The tropism theory postulates such mechanisms in all reacting organisms.⁷ He therefore held that the tropism mechanisms imply more evolutionary standardization, or adaptation, than trial and error does, although Loeb denied that the tropism itself is regulatory or useful.⁷

Other authors in the held texts use the phrase more loosely. Lotka (1925) wrote that the artificial adjuncts to our correlation apparatus evolve by selection, by trial and error. He said David Hume had clearly recognized this.⁸ Thompson, in On Growth and Form, uses the phrase for a drawing method. The investigator draws cross-sections and the coordinate systems that seem best to correspond, by observation and by trial and error.⁹ In these cases the phrase names a procedure of trying and keeping, without a claim about experience or mind.