426 



NATURE 



[March 6, 1902 



Now, as a matter of fact, the spectroscope shows us that stars 

 in all these stages actually exist at the present day in the 

 heavens. In some the temperature is increasing, in others it is 

 decre;ising, and, although small stars must run through their 

 development quicker than large ones, this is quite insuOicient to 

 account for all the present differences. l'"rom which it follows 

 that some of the stars are much older than others. The sun was 

 amongst the earliest of formed stars. When it was born, the 

 sky must have presented an almost uniform blackness. There 

 was no Milky- Way ; no Orion or Southern Cross ; no Pleiades 

 or Dog Star. All these, and many others, have been added 

 since : not altogether, but one after the other, through the long 

 ages during which the sun was undergoing development. Judg- 

 ing by the relative ages of the .stars, it seems probable that the 

 process of concentration of the original cosmic dust commenced 

 near the solar system and spread outwards to the Milky- Way. 

 But, however this may be, the process is not yet over. JIany 

 nebula' have not yet condensed into stars. Swarms of meteorites 

 still traverse .space, and, even in the neighbourhood of the 

 solar system, they are so abundant that the earth alone is esti- 

 mated to collect more than twenty millions each day. 



However, slow as the process of conden.sation is, it is not 

 endless. In time all the meteorilic dust will be collected into 

 stars or planets, and in time the law of dissipation of energy 

 will bring all these bodies to a uniform temperature. So at 

 last the movements due to the original unequal distribution of 

 matter will cease and the life of the universe will come to an 

 end. We know of no process of rejuvenescence by means of 

 which dissipation of energy, and the force of gravitation, might 

 be counteracted. Several attempts have been made to refute 

 the theory of dissipation of energy, but all have failed. The 

 ether which pervades space is the only part of the universe which 

 shows no sign of evolution. It alone remains unchanged. 



A casual glance at the stars gives us the impression of immu- 

 tability. We still speak of the fixed stars in much the same 

 way as our forefathers used to speak of the everlasting hills. 

 But we know that they are not fixed. W'e know that the 

 nearer stars, including the sun itself, are in swift movement ; 

 and we infer that all are so. But we can see no connection be- 

 tween their movements. Single stars, or small groups of stars, 

 are rushing through space in various directions, and we cannot 

 detect any common centre of gravity which holds them in con- 

 trol. The stars have not yet attained the regularity of move- 

 ment that gravitation must bring about in a very ancient system, 

 and this idea of the comparative youth of the universe is 

 strengthened when we remember that large numbers of the 

 primitive meteorites are still wandering in space uncondensed 

 into stars. If it be true that the sun is one of the oldest stars 

 in the universe, and if, as geologists think, the earth is not more 

 than a hundred millions of years old, then it may very well be 

 that the creation of the cosmic dust out of which the stellar 

 universe has been formed took place less than two hundred 

 millions of years ago. But although it may be possible to place 

 a limit to the age of the universe, we can fix no time for its 

 duration. It is impossible to form an estimate of the hundreds 

 of millions of years that will pass before the end approaches. 

 Still, a time must come when .ill energy will be equilibrated, 

 and when, possibly, the visible universe may resolve itself into 

 invisible, motionless ether. 



In the solar system we can study the development of a 

 meteoritic swarm in greater detail. Here we find that the 

 whole of the meteorites did not collect into a single mass, but 

 that several planets, as well as the sun, svere formed simul- 

 taneously. It has been shown by Prof. G. H. Uarwin that the 

 effect of many collisions among a swarm of meteorites would be 

 gradually to eliminate orbits ol great eccentricity until, in time, 

 a regular system would be developed, when the whole of the 

 meteorites would travel nearly in the mean plane of their aggre- 

 gate motions. The larger of the meteorites would tend to 

 settle towards the centre, while other aggregations might easily 

 occur at ditTerent distances from the centre. And of these the 

 outer planets would be larger than the inner ones, because in 

 the more distant regions, where the attraction of the central sun 

 was less, the movements of the meteorites would be slower, and 

 there would be a greater tendency to agglomeration than where 

 the movements were more rapid. As meteorites contain but 

 little oxygen, hydrogen, carbon, silicon and alkalis — sub- 

 stances which are all abundant on the surface of the earth — 

 large numbers must have been fused together to form the earth, 

 andthe lighter substances must have collected near the surface. 



NO. 1688, VOL. 65] 



Consequently, the collisions between the.se meteorites must have 

 occurred with sufficient rapidity to melt the whole mass. Kor 

 after a solid crust had been formed, all the meteorites which fell 

 on the earth would remain on the surface as they do now. 



As with the solar system, so, also, in the carlh itself we can 

 trace distinctly a physical evolution. The discovery of tidal 

 friction gave an independent proof that the earth had had a be- 

 ginning not infinitely remote, for if that had been the case, the 

 tidal friction would have reduced the time of the earth's rotation 

 on its axis to that of the moon. Also we have sufficient geo- 

 logical evidence to .show that not more than one hundred millions 

 of years ago the earth was in a molten condition, and, probably, 

 shone with its own light. As cooling went on, the silicates 

 crystallised out, forming a solid crust over the still molten, me- 

 tallic interior, the earth then becoming a dark body. At that 

 time all the water above the crust was in a state of vapour which, 

 subsequently, fell as hot rain, forming a boiling ocean. With 

 this rain the denudation of the primitive crystalline rocks com- 

 menced, and their debris was deposited on the bed of the ocean 

 as sedimentary rocks. Gradually the continents were formed, 

 the new ranges of mountains following each other in orderly suc- 

 cession, the great oceans becoming narrower and deeper as well 

 as more and more salt. These processes are still going on, but, 

 as the eaith is cooling, the internal energy which uplifts the 

 mountains must be diminishing, and in time it will be in- 

 sufficient to counteract the denudation. Then the whole of the 

 land will be swept into the sea, and the waves of the ocean 

 will roll over the surface of the earth unopposed ; unless, 

 indeed, before that time arrives the ocean should have been 

 frozen into a mass of ice, or should have sunk slowly into the 

 ground. All these things are approaching, but which of them 

 will come first it is impossible to say. 



Organic Evoliilion. 

 When, during the course of physical evolution, the ocean had 

 become sufficiently cool for the existence of protoplasm, minute 

 living organisms appeared on its surface. These increased in 

 size, varied in many directions, and, in time, discovered the 

 bottom of the sea, on which they established themselves, chang- 

 ing from swimming to crawling creatures. Gradually these 

 organisms managed to live in safety among the rough waters of 

 the sea coast, and then they spread over the land, first the 

 plants and then the animals, which came to feed on the plants. 

 Once established on land and breathing air, improvements in 

 the circulatory system of the higher animals became possible. 

 The purified blood was kept separate from the impure blood, 

 and increased rapidity of physiological processes heated the 

 body, so that, in the birds and mammals, a stream of pure, 

 warm blood was poured upt)n the brain. Thus stimulated, the 

 brain developed rapidly, and the psychological evolution, thus 

 inaugurated, has reached such a height in man as to place him 

 mentally apart from the rest of the animal kingdom. 



Biological evolution differs from physical evolution in being 

 brought about by the transmission of bodily variations from one 

 generation to another. And in psychological evolution, mind is 

 transmitted from parent to offspring, as well as the organ in 

 which it is to be manifested. InteUigence, however, depends, 

 not only on the structure of this organ, but on e.arly associa- 

 tions and education, by which means the wisdom of one 

 generation is handed down to the next. 



Psychological evolution consists of two parts. The first is 

 intellectual, and is found in all the higher animals as well as in 

 man. The second is ethical, and is exclusively human. 



Intellectual evolution, like biological evolution, is due to 

 competition between different individuals and the action of 

 selection. We probably see the first germs of ethical evolution 

 in parental affection, which, among gregarious animals of 

 suflicient intelligence, widened into social symp.ithy, and this, in 

 man, gave rise to the social or civic virtues. 



This advance also appears to have been, or, at any rate, may 

 have been, due to selection, and the result w.as the emergence 

 of what is called utilitarian morality. Morality, in the strict 

 sense of the term— that is, formal morality— also appears to have 

 arisen from sympathy, but not by means of selection. The 

 long and constant use by man of formal morality has made it 

 instinctive, and has thus given rise to the conscience. 

 Secondary Causes. 

 When we think of the whole work that has been .accomplished 

 by evolution we are overwhelmed by its vastness. The results 

 of organic evolution, particularly, are so marvellous that, to our 



