Abstract
IT was nearly one hundred years ago that Charles Darwin began his scientific studies in the University of Edinburgh. No more fitting subject, I think, could be found for an address than certain problems relating to his doctrine of evolution. Perhaps the best way of treating these general subjects is by trying to answer some definite questions. For instance, we may ask: “Why are some characters inherited and others not? ” By characters we mean all those qualities and properties possessed by the organism, and by the enumeration of which we describe it: its weight, size, shape, colour, its structure, composition, and activities. Next, what do we mean by “inherited ”? It is most important, if possible, clearly to define this term, since much of the controversy in writings on evolution is due to its use by various authors with a very different significance—sometimes as mere reappearance, at other times as actual transmission or transference from one generation to the next. Now, I propose to use the word inheritance merely to signify the reappearance in the offspring of a character possessed by the ancestor—a fact which may be observed and described, regardless of any theory as to its cause. Gur question, then, is: “Why do some characters reappear in the offspring and others not? ”
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Abridged from the presidential address delivered to Section D (Zoology) of the British Association at Edinburgh on September 8.
We purposely set aside complications due to hybridisation and Mendelian segregation, which do not directly bear on the questions at issue.
In a letter to NATURE Sir Ray Lankester long ago directed attention to the importance of this consideration when discussing inheritance. He a so pointed out that Lamarck's first law, that a new stimulus alters the characters of an organism, contradicts his second law, that the effects of previous-stimuli are fixed by inheritance. (NATURE, vol. 51, 1894.)
In other words, all characters are "acquired during the lifetime of the individual," and "inherited" in the sense here defined has just the same meaning. Much the same view was advocated by Prof. A. Sedgwick in his address to this Section at Dover in 1899, and it has also been developed by Sir Archdall Reid and others.
The name "mutation" might be given to the alteration in the factors instead of the variation due to it. The latter might then be termed a muta-tional variation and would be opposed to a modificational variation. At present the term "mutation" is applied to three different things: the actorial change, the variation or difference, and the new product, respon se for character.
We might perhaps distinguish the two cases by calling them constant and inconstant characters, or "natural" and "acquired," as is commonly done when describing immunity. It should be meant thereby that one is acquired usually (under normal conditions), the other occasionally (when infection occurs). Error creeps in when the term "acquired" is opposed to "non-acquired" or to "inherited."
Herbert Spencer's "physiological units," Darwin's "pangens," Weismann's "determinants," are all terms denoting factors, but with somewhat different meanings. More recently Prof. W. Johannsen ("Elemente der exakten Erblichkeitslehre," 1909) has proposed the term "gene" fora factor, " genotype" for the whole assemblage of factors transmitted by a pecies, and "phenotype" for the characters developed from them. This clear system of nomenclature, although much used in America, has not been generally adopted in this country.
American Naturalist, vol. 55, 1921; Jour. of Exper. Zoology, vol. 31, 1920.
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GOODRICH, E. Some Problems in Evolution1. Nature 108, 404–409 (1921). https://doi.org/10.1038/108404a0
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DOI: https://doi.org/10.1038/108404a0