Identifier: hormonesheredity00cunn (find matches)
Title: Hormones and heredity; a discussion of the evolution of adaptations and the evolution of species;
Year: 1921 (1920s)
Authors: Cunningham, Joseph Thomas, 1859-
Subjects: Hormones Mendel's law Heredity Hormones
Publisher: London, Constable
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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e,and this is only overcome after long exposure to thelight. On the other hand, if the disappearance of thepigment were due to a mutation, were gametogenicand entirely independent of external conditions,there would be no development of pigment afterthe longest exposure. To prove that an inheritedcharacter is an acquired character is quite as goodevidence as to show that an acquired character isinherited. The latter kind of evidence is very dif-ficult to get, for the effect of conditions in a singlelifetime is but slight, and is not likely to show aperceptible inherited effect. The theory that adap-tations are due to the heredity of the effects of PLATE III. PIGMENTATION OF THE LOWER SIDE OF AFLOUNDER (PLEURONECTES FLESUS) WHICHWAS EXPOSED TO DAYLIGHT REFLECTEDFROM A MIRROR, FROM SEPT. 189O TONOV. 1891. THE SPECIMEN WAS ABOUT SIXMONTHS OLD AT THE BEGINNING OF THEEXPERIMENT, AND THEN HAD NO PIGMENTON THE LOWER SIDE. REPRODUCED BY PERMISSION OF THE ROYAL SOCIETY FROMPHIL. TRANS. 1893. B.
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RECAPITULATION 213 stimulation assumes that the same stimulus has beenacting for many generations. It is necessary, however, to consider how far theconclusions drawn from these experiments are con-tradicted by the mutations occurring in nature, someof which have already been mentioned. We willconsider first ambicolorate specimens. If theabsence of pigment from the lower side in normalFlat-fishes is due to the absence of light, how is itthat the pigmentation persists on the lower side ofambicolorate specimens, which is no more exposed tolight than in normal specimens ? The answer is thatin the mutants the determinants for pigmentationare united with the determinants for the lower sideof the fish. My view is that the differentiation ofthese determinants for the two sides was due in thecourse of evolution to the different exposure to light,was of somatic origin, but once the congenitalfactors or determinants were in existence they wereliable to mutation, and thus in the ambicoloratespeci

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