150 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”of salmon. Salmon spawn in rivers high up in the mountains and subse-
quently migrate to the sea. When mature and ready to mate, they swim
upstream to their birthplace. It was demonstrated that the cue for homing
is the odor of the water of their birthplace imprinted on the young fish.
7.6.5 Trial and error versus reasoning
Higher vertebrates are capable of learning from experience. Figure 7.14
shows a raccoon trying to reach a food by random trial. After several
unsuccessful attempts, it learns from experience that it must first move
away from the food source in order to get it. Figure 7.15 shows a chim-
panzee solving the problem of getting a banana that is hung from the
ceiling without resorting to trial and error; it reasons that the banana can
be reached by stacking boxes on top of one another.
It is worth mentioning that birds of the corvid family, which
includes ravens, crows, jays, magpies, and nutcrackers, have high intel-
ligence and good reasoning power. They can fashion tools or carry out
Fig. 7.14. A raccoon that is unable to reach a bait, not knowing that it must first move
away from the food and turn around the hitch to get it. The attempt is successful after
trial and error. [See Note 37; courtesy Dover Publications.]