XXIX. THE ORGANIC SCIENCES

BIOLOGICAL EVOLUTION

HENRY E. CRAMPTON

tion between blended and alternative cause the male or the female condior Mendelian inheritance, and rightly insists that the essential thing is the segregation of parental characters in later generations. Pearl" has a very significant paper on the effect of the personal coefficient in work on Mendelian inheritance.

tion can be positively referred to specific chromosomes as their physical bases, which is of far greater importance than the reference of all heritable characters to the germplasm. Wilson adds some impor

62

tant observations on the sex-chromoHeredity and the Genotype Con- somes in hemiptera, and offers a ception. The analysis of heredity valuable critical discussion 02 03 of made by Johannsen has become more the whole subject, including the widely known through its discussion newer knowledge relating to sexat the meeting of the American So- limited characters, i. e., those which ciety of Naturalists. Johannsen re- appear in only one sex but which are states his principles, defines his so coupled with the differential chroterms and concepts, specifies the role mosome that they may disappear in of selection, and insists that inheri- the first hybrids, only to become evitance should be understood as mean- dent in the next generation. Moring the appearance in parent and off- gan" also gives some valuable data spring of similar character due to and discussions of this topic, and identical "genes," and not a trans- cites examples from his own results mission of personal peculiarities with Drosophila. Sturtevant and from parent to offspring. A "genotype" is practically an elementary species, existing within, so to speak, the specific type; selection simply sorts out the genotypes of a species, and falsely appears to exert an effect upon heritable characteristics. Shull, East, and Jennings support the views of Johannsen, on the basis of their own observations, while Harris 22 insists that the full biometric proof is not as yet at hand.

10

50

Mutation.-The origin of new forms in experimental material of Drosophila by mutation, and forms that breed true to their new characteristics, is announced by Mor

gan 38 39 and Loeb and Bancrofts;

some of these are apparently spontaneous, while others are initiated by treatment with higher temperatures, radium emanations, and Röntgen rays.

Davis and Gates1 give very interesting discussions of experimental evidence relating to Oenothera lamarckiana, the classic plant of De Vries's studies, and contend that this type has really originated by the hybridization of O. biennis and O. grandiflora. If so, the mutations observed by De Vries must be subjected to renewed scrutiny.

Heredity and Sex.-At present, this subject is focal in the entire area of investigation, not only because cytological results are becoming progressively coördinated with experimental findings, but also be

Goodale15 16 add their concrete observations to those already at hand. Tennent and Pinney" have discovered a differential chromosome in echinoderms, while Stevens53 54 observes them in the guinea-pig and in mosquitoes, but in the latter case there seems to be no relation to sex determination, she contends. Gerould" has published an interesting paper on the inheritance of polymorphism in the cabbage butterfly, and finds also that the determination of sex depends, as in Abraxas, upon the heterogametic character of the female parent, not the male. Guyer's discusses the relative values of nucleus and cytoplasm in heredity, upon the basis of enzymatic interaction between the two, which does not of course affect the validity of the established facts of sex determination.

Miss King 29 31 attacks the contention of those upholding the ancient view that germ cells from the organ of one side of an animal produce female offspring, while the germ cells of the other side become individuals of the opposite sex. By experimental evidence obtained with rats and amphibia, she shows that this view is not supported. A further result is very significant, namely, that the relative amount of water in the egg seems to have some influence in determining sex, a result which appears in the contrasted sex ratios of normally developing eggs and of

others with reduced relative volumes of water. Ordinarily males always exceed the females in number, as Miss King shows for rats,30 and Moenkhaus for flies, although the expected numbers of each should be equal if there was no interference with the sex determinants identified as specific chromosomes. Why the excess of males should appear, remains for investigation.

34

gametic constitution into the body of white animals, also of known gametic types, after excising the original organs. In one such experiment, six offspring of the white mother, mated with a black male, were black; no influence of the maternal soma manifested itself. The facts are unquestioned, and the results speak for themselves; their importance cannot be overemphasized or overstated. Guthrie" contends that in his similar experiments with fowls he has succeeded in demonstrating an effect by the maternal soma, but his own account, like that of Davenport, shows that regeneration of the partly extirpated original gonad took place, so that eggs produced subsequent to the operation were by no means necessarily formed by the engrafted organ. Castle discusses the facts and interpretations in the case, in reply to criticisms by Guthrie of his and Phillips' work.

In a larger way, Shelford"7 48 49 gives some exceedingly interesting facts as to the relations of organisms to their environmental situations.

Heredity and Environment.-The purely negative or eliminative effects of environment conditions stand unquestioned and unquestionable; on the other hand, the efficiency of external circumstances as originative and positive factors is doubted by all, saving only a few of the so-called neo-Lamarckian school. The sphere of activity of external agents has been greatly restricted by the results in the field discussed above, but direct examination is also essential. MacDougal, in his presidential address delivered at Ithaca, gives an admirable statement of the recently established cases of alterations in somatic form induced by environmental agencies. He contends that such He shows that the fishes of streams agencies have exerted direct effects upon the germ cells of the altered individuals and that no proof has been brought forward to show that a purely somatic character has subsequently been introduced into the series of germ-plasmic characteristics. Sumner restates his interpretation of his results with mice, reported last year. Payne has bred the fruit-fly for 69 generations in the dark, and when the light reactions of the last born flies were tested, they proved to be substantially the same as in the original stock-a negative result of much interest in connection with the problems of cave faunas. Shull gives an extensive and excellent account of his experiments on the rotifer Hydatina, to determine the part played by external factors in the change from the parthenogenetic to the sexual modes of reproduction. He finds that changed temperature conditions do act, but not directly as such.

By far the most significant results are given by Castle and Phillips.2 The authors transplanted the ovaries from black guinea pigs with known

are arranged in definite orders, from mouths to sources, and that the series of a small stream is like that of the upper part of a larger stream. It is more surprising to learn that in ponds, there is, so to speak, a stratified arrangement of species, and that the strata of newer-formed ponds are duplicates of some of the series found in an older body of water. These papers point two definite morals: that a great deal remains to be discovered in the field of general natural history in the best sense of the phrase, and that too little attention is directed to field studies in natural history.

The time-honored discussion of the value of color and coloration is enlivened by the strong attack made by Roosevelt upon the teachings of Thayer. The latter author 61 restates his position in two papers of the year.

Pearl" gives some results bearing on the problem as to the relative concealing merits of barred and self-colored plumage in fowls exposed to the attacks of natural enemies, and finds, in opposition to Davenport's contention, that no definite advan

tage accrues to either type of coloration. Sumner has secured some remarkably interesting results with flat fishes, finding that these forms tend to simulate the texture of the substrata upon which they are placed. This is true for black and white patterned surfaces.

Heredity and Genetics.-As definite knowledge of the laws of biological inheritance increases, it will become progressively available for the betterment of organic breeds serving human interests, and for the betterment of the human species itself. Already one essential principle has been established, namely that nature is more important than nurture-that heredity provides the characters which are then subjected to environmental influences and modifications, if such can be produced.

"Euthenics and Eugenics."
Science Monthly, Vol.

(Popular
LXXVIII, No. 1.)

9. DAVIS, B. M.-"Genetical Studies on
Oenothera." (American Naturalist,

Vol. XLV, No. 532.)
Kellicott has present-

ed the case for genetics in compact
and readable form, in a volume based
upon a series of general addresses.
Davenport, Stevens and Marshall
also point out how known biological
laws can be employed socially and
agriculturally. A special paper by
Rosanoff cites additional evidence
that human phenomena are in essen-
tial accord with other zoological
facts, in so far as insanity seems to
be inherited in Mendelian ways.

Finally, mention may be made of two volumes of a general nature,

11.

10. EAST, E. M.-"The Genotype Hypo-
thesis and Hybridization." (Ameri-
can Naturalist, Vol. XLV, No. 531.)
H. K.-"Inheri-
tance in Maize." (Report of the Con-
necticut Agricultural Experiment
Station, 191 r.)

-and HAYES,

12. EMERSON.-"Inheritance in Maize." (Report of the Nebraska Agricultural Experiment Station, 1911.)

13. GATES, R. R.-"Mutation in Oenothera." (American Naturalist, Vol. XLV, No. 538.)

14. GEROULD, J. H.-"The

Inheritance

of Polymorphism and Sex in Colias philodice." (American Naturalist, Vol. XLV, No. 533.)

Castle has published a book which 15. GOODALE, H. D.-"Studies on Hy

gives an excellent outline of the whole subject of heredity as it stands to-day; it is particularly welcome as

a

basis for further investigation, especially with reference to the determination of sex. Crampton has presented an outline of the field of evolution in general, and of human evolution in particular; and he endeavors to show that evolution as an all-inclusive process is continuous,

16.

brid Ducks." (Journal of Experimental Zoology, Vol. 10, No. 3.)

"Sex Limited Inheritance and Sexual Dimorphism in Poultry." (Science, Vol. XXXIII, No. 859.) 17. GUTHRIE, C. C.-"On Evidence of Soma Influence on Offspring from Engrafted Ovarian Tissue." (Science, Vol. XXXIII, No. 856.)

18. GUYER, M. F.-"Nucleus and Cytoplasm in Heredity." (American Naturalist, Vol. XLV, No. 533.)

inasmuch as mental, social, and ethi-19. HARRIS, J. A.-"The Measurement

cal phenomena follow the same course of historic development as the structures of organic forms.

20.

21.

22.

of Natural Selection." (Popular Sci-
ence Monthly, Vol. LXXVIII, No. 6.)
"On the Correlation between
Somatic Characters and Fertility: Il-
lustrations from the Involucral Whorl
of Hibiscus." (Biometrika,
VIII, Parts 1 and 2.)

Vol.

"The Distribution of Pure Line Means." (American Naturalist, Vol. XLV, No. 539.)

"The Biometric Proof of the Pure Line Theory." (American Naturalist, Vol. XLV, No. 534.)

23. HATAI, S.-"The Mendelian Ratio and Blended Inheritance." (American Naturalist, Vol. XLV, No. 530.) 24. JENNINGS, H. S.-"Assortative Mating, Variability and Inheritance in Size in the conjugation of Paramoecium." (Journal of Experimental 44. PINNEY, E.-"A Study of the ChroZoology, Vol. 11, No. 1.)