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Show 112 DARWINISM CTIAP. species found in the same area. So, en.ch p:trt of the world ha its own peculiar forms of pines, firs, ~md. ccdan.;. but the closely allied. species or varieties are in a.Jmost every case inhttbita.nts of di tinct areas. Examples :u·' tlH' deodar of the Himalayas, the cedar of Lebanon, and that of North Africa, all very closely allied but confined to di stin ('! areas; and the numerous closely allied species of true pin e' (genus I inus), which almost always inhabit different coun tri <'S or occupy dill'erent stations. W c will now con. idcr sont l' other mod.es in which natural selection will act, to a<lapL organisms to changed conditions. Aclnptation to Conditions at Vm·imts Pe1·iorls of Life. It is found, that, in domestic animals and cultivated plan t::;, variations occurring at any one period of life rc;tppea.r in th<' offspring at the same period, and can be pcrp 'tua.tcd. :wei increased by selection without modifying other parts of tlw orgn.nisation. Thus, variations in the caterpillar or the cocoon of the silkworm, in the eggs of poultry, and in tho seeds or young shoots of many culinary vegetables, have he<' ll accumuhted till those parts have become greatly mo<liH ed n11d, for mttn's purposes, improved. Owing to this fa('t it is easy for organisms to become so modified. a. to avoid dan <rcrs tltat occur at any one peri d of life. Thus it is that so ma11y seeds have become ad.apted to various moclcs of clisscminal ion or protection. Some are winged, or have clown or h; tirs attached to them, so as to enable them to be canic<l lo11g distances in the rtir; others have curious hooks and prickh's, which cause them to be att:"Lched firmly to the fur of ma.1nma ls or the feather. of birds; while others are lmricd within S\\'<'<'L or juicy and brightly coloured fruits, whieh arc ·celt n11d devoured by birds, the hard smooth seeds passing throngh their bodies in a fit state for germination. In th e . trnggle for existence it must benefit a pbnt to have increasccl nt l'ans of dispersing its sec<ls, and of thus having yon11g plan ts pr(Jduced in a greater variety of soils, aspcets, and . nrJ'OntHling:-;, with a greater chance of some of them escaping their mtnt l'rons enemies and arriving at muturity. The various difl'creJH'<'S referred to would, therefore, be brought about by variation nnrl survival of the fittest, just as . urely as the length and qnali t.y v NATURAL SELECTION 113 of cotton on the seed of the cotton-plant have been increased by man's . election. . The larvre of insects have thus been wonderfully mod.tficd in order to escape the numerous enemies to whoi::ie attacks they are exposed at this period of their existence. Their colours and marking. have become marvellously ad.:tptcd to conceal them among the foliage of the pl:tnt they live upon, anll this colour often changes completely aft r the last moult, when the creature ha. to descend to the ground for its change to the pupa state, during which period. a brown.instcad ?fa green colonr is protective. Others have acqlllrcd cunous attitud.es and large ocelli, which ca.n c them to resemble the head of some reptile, or they have curion: horns or coloured cjcctilc processes which frighten away cncmic. ; while a gr?a.t number have acquired secretions whieh render them ofi'on 1vc to tho taste of their enemies, and. these arc always adorned with very conspicuous markings or brilliant colour , which serve as a sign of ineclibility and prevent their being needles ly attacked. This, however, is a portion of the very large subject of organic colonr and marking, which will be fully discussed and illustrated in a separate chapter. In this way every possible modification of an animal or plant, whether in colour, form, structure, or habits, ~hich would be serviceable to it or to it progeny at any penod of its existence, may be readily brought about. There arc ome curious organs which are u ·cd. only once in a ercaturc's life, but which arc yet essential to its existence, and thus have very much tho appearance of design by an intelligent deHigner. Such are, tho great jaws possessed by some in~ccts, u. cd exclusively for opening the cocoon, and the hard tip to the beal;: of unhatched birds used for breaking the eggshell. The increase in thickness or hardness of the cocoons or the egg: being useful for protection against enemies or to avoid accidents, it is proba.ble that the change has been very gradual, _because it would be const~ntly checked. by tho necessity for a corresponding change m the young msccts or birds enabling them to overcome the additional obstacle of a tou()'her cocoon or a harder eggshell. As we have seen, ho;evor, that every part of tho organism appears. ~o hu varying independently, at the same time, though to d.lflorcnt I |
