20 PRELIMINARY INQUIRIES. 



Still on the whole, I agree with those who think that the effect of barriers in preventing the 

 spread of species has been undervalued, and that a much slighter obstacle than is generally 

 supposed to be necessary, is sufficient to preserve neighbouring faunas from iutermixturc. 



The above are negative arguments against the peopling of oceanic islands by occasional visitants. 

 The reasons in favour of this having been effected through former continuity of land are more po- 

 sitive. One of these is the nature of the affinity which can be traced between the inhabitants of such 

 islands and of the main coast. It is not a near affinity, but faint and far off; and this is just what 

 we should expect. If the island were formerly united to the mainland, it must have started with the 

 same inhabitants as it, and under the influence of the change which must have occurred in the 

 conditions or climate of both or either through isolation, they must have gradually diverged 

 from each other by the successive development of new species. Their affinity is still indisputable, 

 although it has gradually become distant, and in the case of the island (which has had its oppor- 

 tunities of communication with the outer world very much restricted) peculiar and endemic, while 

 the mainland, not so restricted, is more expanded in its character. If, on the other hand, the island 

 had derived its inhabitants from colonization, they must necessarily be more recent than the separa- 

 tion, and the immigration must have gone on continuously through all succeeding times, so that instead 

 of our finding a homogeneous endemic fauna and flora, we shoidd have contributions of all dates, 

 and from various coimtries ; for it is to be remembered that currents and winds may, nay must, have 

 sometimes changed, in consequence of alterations on the relative distribution of land and water, in the 

 course of uncoimted ages ; and instead of having everything from the nearest land we might have a 

 morsel from one country and a morsel from another, as we certainly should have fragments of all ages 

 down to the most recent — a state of matters essentially inconsistent both with the reality, and with 

 what is understood by the term endemic. 



The richness of oceanic islands in endemic forms, therefore, seems a strong argument in favour 

 of Forbes' view and against Mr. Darwin's. It seems to be as necessary a result of isolation, as 

 restricted and confined (what may be called endemic) views used to be of the country life of the 

 untravelled Thane. When Mr. Darwin says, that had the forms of life been derived as supposed by 

 Forbes, they woidd all " have been more equally modified in accordance with the paramount import- 

 ance of the relation of organism to organism," I am not sure that I understand him. He cannot 

 mean that some paramount influence modifies the development of new species and forms into 

 certain relations with each other ? for that would be nearly equivalent to the old theory of the 

 forms of life being dependent on the physical conditions xmder which they are produced — a 

 theory which is repugnant to the whole spirit of Mr. Darwin's hypothesis ; and is repudiated 

 by himself as " a deeply-seated error." It may bo so. Still I have a strong suspicion that 

 we are in the infancy of our knowledge of physical conditions, and how they operate.* The 

 whole length which I have yet gone in ascribing effect to physical condition is to attribute 

 some influence to the mere fact of exposure to a change in condition. It stimulates or sets a 



even every species of gull, are as active tourists as the less than to the abundant exercise and unloaded mind, 



larger animals, crossing these wide straits iu all directions." that he owes the draughts of health which he drinks in 



— See Captain M'Ctintoch^s Diary in Proc. Dublin. Nat. when striding over our Highland mnirs, or pacing along 



Uist. Univ. Assoc, in N<ii. Hist. Rev. April, 185C, p. 40. our salt sea beaches. The " change of air," constantly 



* If the reader will refer to his own sensations, I think recommended by physicians, is nothing but a change of 



he will admit that, although these conditions are very physical condition : and shall we be told that this has no 



subtle, they are also very powerful. It is to them, not influence on the animal frame ? 



