May 2, 1887.] 



♦ KNOWLEDGK ♦ 



145 



' ^ ^LUSTR ATED MAGAZINE^ ^ 

 N€E,LITERATURE,& 



LONDON: MAY 2, 1887. 



THE STORY OF CREATION. 



A ri.AIX ACCOUNT OF EVULUTIOX. 



Br Edward Clodd. 

 PA3T n. 



CHAPIER V. - XllE ORIGIX OF Sl'B.ClES—e<mtiuited. 



VI. Natural selection tends to maintain the balance be- 

 tween living thim/s and their surroundings. These sur- 

 roundings change ; there/ore living things must adapt them- 

 selves tli-:r^to, or perish. 



^ treating of the obsciu-ity which liangs around 

 the ultimate causes of variation of living 

 things, stress has been laid on the ceaseless 

 and elusivelv complex interplay between them 

 and the medium which surrounds, quickens, 

 and nourishes them. As Gegenbaur remarks, 

 the energies which cause changes in the 

 urganiism either lie without the organism or for the most 

 part are to be sought for without it.* An important dis- 

 tinction has to be made at the outset between plants and 

 animals in the feebler response of the plant to its surround- 

 ings through the early secretion of cellulose which walls it 

 in, and in its greater subjection to those surroundings by 

 virtue of its fixed place. While the animal can wander, 

 within cert.iin limits, in search of food, the plant is com- 

 pelled to take what comes to it, and, moreover, is powerless 

 to escape the effects of altered temperature and climate. 

 Hence its range of variation is limited compared to that of 

 the animal. And however numerous the species of plants 

 may be, the differences between them do not lie in the 

 modes of nutrition, but in the modes of reproduction, 

 whereas in animals, in addition to the variation in their 

 modes of locomotion, we find them divided into three 

 groups: 1, simple forms without body cavity; 2, higher 

 forms with body cavity ; 3, highest forms with digestive 

 cavity separate from bodj' cavity. Bat for this early 

 " parting of the ways " life would probably have remained 

 vegetal. 



That the foudi of the medium was the first quickener of 

 variation is shown in the rise of the earliest a]iproicli to 

 unlikeness at the surface, as in the membranous lilm which 

 envelopes the lowest life-forms, and, among the higher 

 animals, in the gradual specialisation of lines of communica- 

 tion — the nervous system and sense organs — with the outer 

 world from infoldings of the skin. The diffused sensitive- 

 ness to smell, light, and sound became localised, the sense of 

 touch remaining general over the body-surface, except where 

 horny skin is secreted. Obviou.-ly, therefore, the tendency 

 to vary which inheres in living things being stimulated by 



* " Comparative Anatomy," p. 57 (Eng. ed.). 



interaction between them and their surroundings, the 

 degree in which variatioas ai-e useful to living things — 

 i.e., in enabling them to win in the univei-sal struggle 

 for food and place — determines, under the action of natural 

 selection, their siu-vival. 



The slow but ceaseless changes in things without have 

 involved adaptive changes in all organisms except the 

 lowest. Seemingly, all things remain as they were from the 

 beginning. The ninge of our experience is too narrow, the 

 time since scientific observation of nature began is compara- 

 tively so recent, the changes in living things so beyond 

 direct detection, that we cannot wonder at people's reluc- 

 tance to accept the theorv that the countless species of 

 plants and animals which have succeeded one another have 

 a common descent, through infinite modifiaxtion, from 

 structureless germs. And, in fact, not only is life vastly 

 older than any record of it, but the fossil-yielding rocks 

 supply no key to the origin of the leading groups, whose 

 representative types of to-day are so little altered that every 

 fossil as yet found can be put into existing classes. Huxley 

 remarks that " the whole lapse of geological time ha.s thus 

 far yielded not a single new ordinal tx^pe of vegetable 

 structure," and although "the po.sitive change in |)assing 

 from the recent to the ancient animal world is gi-eater, it is 

 still singularly small." * The variation in ordinal type of 

 animal structure is only about ten per cent, of the whole. 



Yet we know that nothing is rigid : the earth records the 

 gradual ascent of life-forms in structure and the changes in 

 its crust, in a scripture that cannot be broken. The agencies 

 within, and the fer more potent agencies without, that have 

 wrought those changes, pursue without pause their slow and 

 sometimes sudden working. The great globe itself, on 

 which a mere fraction of the sun's energy suflices to sus- 

 tain life, speeds through space ; careens and brings the 

 seasons in their sureness ; spins and gives, unfailing, the glory 

 of sunrises and sunsets; and, in periodic changes of its 

 orbit, crowns at one epoch its poles with vines and oaks and 

 water-lilies, and at another epoch covers them with im- 

 pa.«sable snow. 



Changes of climate and level, with the alterations in soil 

 which they bring about, profoundly affect food and the 

 power to obtain it. And the necessitj- for food being a 

 strong — perhaps the strongest — stimulus to motion, the 

 organism which the more readily adapts itself to the changed 

 conditions, or is better equipped to resist them, wins in the 

 struggle. The new functions to be discharged involve 

 changes in structure, because the organs exist for the work 

 which they have to do, not the work for the organs, iloreover, 

 changes which arise in the structure are not limited to one 

 part, the whole organisation being, in Darwin's words, " so 

 tied together during its gi-owth and development that when 

 slight variations in any one part occur, and are accumulated 

 through natural selection, other paits become modified." 

 Take, for example, the growth of the deer's antlei-s, which 

 in some species attain a weight of seventy pounds in a few 

 weeks. 'The increased supply of blood which this involves 

 necessitates readjustment of circulation, and the increased 

 . weight which the skull has to bear necessitates more power- 

 ful muscles and ligaments, with increased .strength of the 

 \ bones to which they are attached. More food is needed to 

 supply the energy thus expended, involving more active 

 digestion, and therefore modification of the digestive organs. 



So far as the individual is concerned, there are the changes 

 wrought in it by use and disuse — in the one case leading to 

 the development of organs, in the other case to their decline. 

 " Thus I find," Darwin remarks, "in the domestic duck that 

 the bonea of the wing weigh less and the bones of the leg 



♦ " Lay Sermons,' p. 216. 



