The Foundations of Ethology
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Pp. xvii, 380, 33 text-figs. Cloth, DJ, 8vo.
and in the preceding section, the growth of the genealogical tree—evolution—would be a near cer tainty on the basis of comparison alone, even without the additional tes timony of fossils. 4. Documentation Through Fossils If our interpretation of the distribution of older and of more recent char acteristics is correct, the more widely distributed characteristics should appear first, in the lower, that is, in the older strata of our planet's crust. 82 IV. The Comparative Method The more
perceptible. Erich von Holst demonstrated that the difference in the forms which a fixed motor pattern takes at different intensities is to be explained in the following manner. The automatic cells generate the impulses which are coordinated by central coordination, as will be described in Section 13 of this chapter. These impulses activate motor cells in the anterior horn of the spinal cord, and these cells respond with slightly different thresholds to the same quality of excitation. At a low
only in quantity. To the naive observer, it would seem obvious that the latter were true, but this intuitive assumption must be supported by rational confirma tion. The first verification consists of the absolute predictability of the subsequent stage of intensity—once the preceding stage has been gone through. When Seitz demonstrated cichlid fighting to our students in Konigsberg, he accompanied the actions of the fish with a running com mentary, in much the same way a radio announcer would do
is strongly stimulated by the sight of a nar row cleft and by the touch of soft edges offering only limited resistance to being widened. Tame starlings seem to enjoy it enormously if one per mits them to thrust their bill between two fingers that offer only a little resistance to being pried apart. Also, the starling quickly learns to rec ognize objects soft enough to be torn by prying, such as a newspaper lying on a soft support. The frequency of prying is increased only to a small degree by
object seemed promising. On the other hand, they show very clearly that the phyletic information is not given to the organism in the form of a unitary, if simplified, image of the object, but by a number of mutually independent responses to very simple config urations—to key stimuli—whose effects add up in accordance with Seitz's law. 1. The Innate Releasing M echanism (IRM) 161 Although the sum of the key stimuli to which an IRM responds does not, by any means, represent a unitary complex