The Dominion. SATURDAY, MAY 2, 1908. HEREDITY AND ITS LAWS.

Dominion, Volume 1, Issue 187, 2 May 1908, Page 4

The Dominion. SATURDAY, MAY 2, 1908. HEREDITY AND ITS LAWS.

/■ r ' ' I Twentt-ti-iree years ago there passed away, as one; of the great army of the average, Gregor Johann Mendei, the , venerable abbot of the monastery of .Brunn, in far-away Silesia. With a taste for, botany, he had carried out many curious. experiments with the pea.s and hawkweeds growing in the cloister gardens, and as long ago as 1865—when Darwin was writing his great books —had read papers to the local philosophical jsociety on the results of crosses made with different varieties of peas. These were duly printed, and, like most papers of the sort, put away on a few shelves, and forgotten—so completely forgotten, •indeed, that up to 1900 there was only one casual reference to them in all the intervening scientific literature. . Today, by a chance turn in the whirligig of :time, "Mendelism" is tlie last word in the study pf heredity., Had Darwin known what was being demonstrated, in that quiet monastery garden at the time lie was preparing tlie " Origin of ,

Species," it is probable that lie would have greatly modified his epoch-mak-ing theories, i • Re-discovered by. Dc Yrics some eight or -nine years ago; and; since thoroughly -tested'by experimenters in all; parts, of the. world,. Mendel's Lawis shedding new- light: on some of the darkest and most interesting problems of heredity. In -the current number of the " Fortnightly Keview,''Mr. G. Clarke Nuttall describes the' original experiments-of 1865. Taking,' for in-, stance, a tall of pea,; Mendel crossed.- it with a dwarf variety. The seeds from, this cross produced plants that were all tall, with no. dwarfs among them. Allowing these to selffertilise, he found that the issue were both tall and dwarf in quite definite proportions, namely, one 'dwarf to; three tall'. The dwarfs of, tliis generation, self-fertilised, proved ,'to be alldwarf, _ and remained so through successive generations. On the other hand, the offspring of the tall plants of, the same- generation iwere oner third pure. tall, variety withj henceforth. non,e but tall offspring; thij remaining two-thirds, impure variety,, and l producing- tall; and- dwarf; offspring,in the same proportion, of three]tall to-one dwarf;., as- the parents i Had : done. Until, quite recently hybrids were raguely described as .. ipingling: ■in modified forms the characters of father. and mother. Cut, according' to; Men-. dpi's experiments, ;no,- r<al. minglingtakes place,, and. the. hybrid will, be found 1 never to. exhibit a, characteristic oi one parent (absent in the other) in reduced form., but will simply have it or not, haye it. .However many characters are introducjed, the law, it iS; said,, still lipids, and- the offspring of hybrids, will combine )in all: possible ways, according; to. the. definite mathematical; law governing combinations. Naturally,. one asks. what. will, be the use_of the discovery .to-those who. are trying, to produce hew- varieties of plants, or improve the breed, of' animals.' 'The answer," says\,MK : ' Jfuttall,. "is that it will be of" the greatest- possible value.; _It will 1 teach the experimenter i the rationale of his work; . . For instance, supposing he - wishes to produce a. new plant hybrid,, uniting, desirable, qualities, of two varieties, he crosses, them. Now-, , the. first, generation may fas'all alike,: butnita^aU'nshat h& is, aiming at,, and in nine, cases out. of ten lie, concludes tha.t- he has failed, and proceeds no further. But. Mendelism ' -teaches him : that if he ' per-' severe? allpossible fornis that can come from the: Cross will re-appear in the second/, generation, , the - desired form among , them, and. that some, of' them, are fixed. . Which: are'. fixed can, .be unerringly determined -by keeping the. seed of each distinct, and /investigating the resulting plants.: The fixed ones will, alone'breed true;', all,-,the, others will, throw Qlf o,th,er forms in their descendants,, and- ' musti be. ignoried. The- old idea, that a new: variety could onjy be; .'fixed by workings, through, many- generations, ,-ia- quite;. . ■ . " ... In, reality, ' two generations, suffice. /to produce - and fix the new yariety, and'; one further-, generation, is': all, ~is' required-, to 'indicate fixed; individuals.'" Mendel's Law has proved to hold good, in the,,case of 1 peas, stocks, mice,, and rabbits, but to what extent it will b„e,: : found 'Ho . apply with; regard- to, human beings is- ,a,/ma,tter of, conjecture.. Detailed records over long periods of time are. necessary, to observe the laws, of human heredity,; ; and ( the problem is so complicated by the, reaction I of the environment on the inherited traits of ; each individiialthat 1 -exU'ct knowledge on the subject seems beyond' hope' of : Mendelism lends additional weight tb the theory so long Eouchti for by Weismainn, Galton, and others that characteristics acquired' by the individual are not inherited by the offspring. Ideas on the subject of heredity hare indeed rapidly 'changed during the, last, half-century. The old theory,' that '■ the reproductive cells, ivhicli may ' beponis offspring,. consist. >f samples accumulated from all parts )f the body was given; fresh •life by Herbert Spencer and Darwin, Darwin holding iii his "provisional hypothesis jf pangenisis v that' the ; reproductive jells accumulated gemmules, from all parts of the body, and that in development these gem'mules. helped to give rise to; parts like tliose ■ from which they originated. This idea is ( now generally discredited by n-ho incline with Weismann to the new that the reproductive cejls. which jive rise to the offspring are more or less . directlycontinuous \>*itli those .vhich gave rise to the parent: that is :o say, a portion of the germ-plasm ivhich forms the new individual re-, mains in a latent condition until ultimately developing in its turn into Eresh of spring. In this mode the continuity !of the gerin-plasiu from inlividual to individual is maintained. Phti theory is an • attractive one, but its value, from a sociological point of riew, is doubtful. , For even though improvement in the ehvironmentyriducational, .'sanitary, and other—may iffect only the individual, and have .no more influence on the stock' than, say, the manure which.assists the development of a plant has on the stock of that plant, the fact remains that, j though we work merely on individual j after; individual; we can, by alteration and improvement in the environment, effect and perpetuate almost as much as could be done by any process of deliberate selection in breeding.