ZOOLOGY

Nelson Evening Mail, Volume LXI, 11 June 1927, Page 7

ZOOLOGY

NEO-LAMARCKISM HESLOP. HARRISON'S EXPERIMENTS IN INDUCED. MELANISM : Dr'. Ti'ilyard was followed with, the closest' tilterosfc in dealing with NeoJjsn9a.rpUis.ru,i{i the course of his lecture at the Schoobof Music last evening. Dr. J. \V. Hcslop-Harrison, lecturer in .Genetics a;t Armstrong University, N'owcastle-on-Tync, he said, lias recently made a brilliant study ,of this subject, lie noted that, in tho industrial area around Newcastle,' as also around Esison in Germany, Pittsburg in U.S.A., ano* certain other similar centres, one species of. moth after another during the last fifty years'has been replaced by a black variety, called scientifically a iljeliihii; form. These melanics were not known before the industrial era, and the supposition 1 arose in his mind that it bad been tho change of cnviroiimcht'duc to industrialism that had caused the organisms to .go black like their .surroundings. Slimy other 'men have had this idea, but always'thc anti-Lamarck-iau complex of the present-day had rc•sfraincd'them from (lie-rf.sk of losing their reputations by following it out.

ELEGANT EXPERIMENTS

Harrison, however. . was made of tougher material, lie did not care a fig for his reputation: Ho would pursue tho subject to tho bittor cud and find out the'truth. To this end, he devised some very' elegant' experiments, which I propose .to tell you.about in part in this lecture. One-of the moths which had, gone black .at Newcastle was the I'arly thorn moth, Sblenia bilu'naria, a doublorbroodcd species which feeds, on hawthorn.and is,easy to war. Assisted •by a. friend in. Sussex, Dr. Garrett,.Harmon, now. tried the following tests: — (1) The ordinary pale, buff type of this moth was brought from Sussex, where no black form had ever been found, and was reared on hawthorn from a hedgo right in the industrial area around Newcastle. In the third generation some black forms appeared, and these immediately behaved, on crossing, as iruo Mendelian reccssives. As a rosult, a permanent black form was soon obtained' wjiich, bred true and is now established as a definite subspecies. (2) Further Sussex specimens were reared, in Sussex, on Sussex hawthorn twigs .which were kept in water in which a small quantity of lead nitrate had been dissolved, tests being made to show that the lead salt was drawn_ right to the topmost leaf of each twig before the caterpillars were fed on it. The same results exactly were obtained as in the previous experiments. . (3) A third similar set of experiments was made with manganese sulphate substituted for lead nitrate. Again, similar results were obtained. Harrison's conclusions from these experiments are quite definite and cannot be explained away by anybody, howcvor hostile ho may be (0 Lamarckian doctrines. Tho onsot of melanism was undoubtedly caused'in each case by a change in tho food-plant, which had been contaminated, firstly by .growing in an industrial area whose air and soil were soaked in various chemicals, secondly by tho addition of lead nitrate in minute doses, to tho food, a.ud thirdly by tho addition of manganeso sulphate. These aro changes.in the environment. Hcnco tho experiments aro a definite proof of the broad truth of the Lamarckian position.

"BACK TO DARWIN"

In order to understand how much this means ■to-biologyi'-sve must qo back to Darwin and tho origin of species, and recall how.he succeeded in carrying the conviction of the truth of evolution to the human mind, through his advocacy of natural selection, whereas Lamarck, much earlier, had failed when he tried to explain evolutiou as taking place through the action of the environment. Darwin, of course, really believed to some extent in the influence of environment, but his later followers, known as Noo-Darwinians, took a much more rigid position. Their protagonist was Weissmann, who advanced ;tno theory that the germ-plasm was separated quite early in the embryo from .the .body-plasm or soma, anil that therefore the environment could only affect'the latter, not tho former, so that tho; Lamarckian hypothesis of inheritance of acquired characters was an impossibility.

THE GREAT MENDELIAN SCHOOL

.Tho Weissmannian hypothesis is tho orihodox view-about heredity held by tho.great"Mendelian schp6l of the present day,as well, as by tho Neo-Da-rwin-iins. Tho Mcudclians; explain; all their results by the action'of what arc called "factors ; but. nobody has yet been able to explain what a Meiidelian factor really is. .Morgan -and his school profess to find all the characters of the adult organism represented, by what aro called "genes" in the chromosomes, but the essential point in this, doctrine, that crossiug-ovor of genes occurs when sponn and ovum unite, has never been demonstrated and is puro theory. Heslop Harrison's results come as a bombshell, moro particularly to the Mcndelians, because his mclariic forms bohave exactly like Mendelian recessives; in fact, his, experiments proclaim tho unity of Mendelian phenomena with sbmombtkctii of. inheritance of acquired 6haracters—-a very| nasty position for orthodox Noo-Darwinians to wriggle out of. •

\ '''v/ : THE; ; NEW ; ;SCIIOOL

Tho now school known as iuductiouists arc attempting to solvo tho pro jjlcm along intermediate lines by means of one or, other of tho new theories knownias parallel and somatic induction, which-are more' acceptable to the modern mind than either Weismarin's hypothesis on thej one hand or Lahiarok's on the ■. other. In these, the getm-plasni .and the body-plasm are not considered as absolutely separated, hut the latter is t.ho immediate environment of tho former, .'lii somatic induction, the change in the environment supposed'to affect'the body-plasm directly, and this induces a secondary change in the germ-plasm, which then becomes hereditable. In.parallel induction, it is supposed that the change in tlie environment; produces parallel changes, in both germ-plasm and bodyplasm, the former being hereditable and the latter only affecting the individual. Both theories are really specialisations from Lamarck's- general, theory 1 of the inheritance of acquired ' characters. It is quite'clear that Harrison's results must be classified under one or other of tho induction theories. In his earlier papers Harrison himself claims that his results prove parallel induction, and that the" distinction between this, .and genuine Lamarckism is purely academic. In later papers, he claims to havo discovered a .now principle operating 'for the origin, of. sbecies by means of a change in the chemical constitution of .the food of the parents. But even so. fodd' is a part of our environment, and certainly ta'niarck claimed- that-any animal that continually ate soft, food would in the cud into a. race Without teeth, "instancing the slotba as an example. Tho whole problem is of immense impor.taileo both to science as a whole arid more particularly to humanity in. its social problems, for ftis intimately bound up with the ques"tion of recent deterioration of physique in over-civilised races of mankind. If the effects of slum conditions, wft food,

lack of exercise of tho limbs due to motoring, etc. is once definitely proved to bo hoioditable, then the white races must change their ways or prepare to go out in due time and give way to a mure primitive and robust race.

INSECT WORLD Harrison's experiments also open up a way to the explanation <;if the immense mass of closely related species in the insect world. "Most of these forms are plant-feeding; generally speaking, those insects which will eat any kind of plant food are primitive, those confined to one or two plants only are specialised. Thus we can imagine a single primitive polyphagous species giving rise to many de-

rived specie's each'feeding on one species or plant only. . A-studyof such groups would give us clearer ideas as to which species- wer* safo to bo ut>ud in such now economic work as that which- we are now undertaking a* th* Gawthr&n Institute, viz. coiltro) of noxious *wteeits by insects, and thus again tho 'dose"can nection between pure .arid applied-science is clearly demonstrated. '; ■'■■•'• • ■ u