Beginners' zoology . ions live longer and leave more offspring, and becauseof heredity transmit the desirable qualities tosome of their young. Variations which are dis-advantageous for getting food, defence, etc., causeshorter life and fewer offspring. Thus the fittestsurvive, the unfit perish; an automatic naturalselection occurs. Darwin taught that variations are infinitesimaland gradual. Recent experiments and observa-tions seem to show that many variations are bysudden jumps, somewhat resembling so-called freaks of nature. As to whether these sports,or individuals with new peculiarities, s
Beginners' zoology . ions live longer and leave more offspring, and becauseof heredity transmit the desirable qualities tosome of their young. Variations which are dis-advantageous for getting food, defence, etc., causeshorter life and fewer offspring. Thus the fittestsurvive, the unfit perish; an automatic naturalselection occurs. Darwin taught that variations are infinitesimaland gradual. Recent experiments and observa-tions seem to show that many variations are bysudden jumps, somewhat resembling so-called freaks of nature. As to whether these sports,or individuals with new peculiarities, survive,depends upon their fitness for their environ-ment. Survival of the fittest results from thisnatural selection, but the selection occurs be-tween animals of marked, not infinitesimal, dif-ferences, as Darwin taught. Darwins theory isprobably true for species in the usual state of nature; the newtheory (of De Vries) is probably true for animals and plants underdomestication and during rapid geographical Fig. 282. — Em- BRYO OF A Turtle, show-ing four gill slits.(Challenger Re-port.) REP TILT A 149 Table for Review (for notebooks or blackboards). Fish Tadpole Frog Turtle Lizard Limbs, kind andnumber Are claws present ?How many ? Covering of body Teeth, kind of, ifpresent Which bones foundinman are lacking? Chambers of heart Respiration Movements
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1921
