WCP4049

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The Dell, Grays, Essex

May 26th. 1875

Dear Newton¹

I send you the List of Genera of Palaearctic region though I can hardly think it will be of any use to you; as it is very imperfect & unequal & I intend wholly to reverse it when I get your list of genera &c. of Europe.

I am sorry you are so disturbed about distinctness of Nearctic & Neotrop. regions. Your statistics do not in the slightest degree affect my conviction that they sh^d. be kept absolutely distinct. When you compare the richest ^{and most isolated} region in birds, with the poorest ^{& least isolated} it is not at all surprising that the [2] latter sh^d. have less peculiar genera than the subdivisions of the former. But we cannot form Regions on numerical statistics of one class of animals, and of one kind — the number of peculiar genera. If you carried this system out, you would have a curious & most unnatural set of regions. I think the number of characteristic forms absent from a district must also be taken into account, as well as the number of forms present which are not found in the region ^{in question, even if they are common to another region,} and in both these kinds of statistics the Nearctic region will stand out as strongly distinguished from either of the Neotrop. subregions. [3] But the most radical question is, what are our zoological regions to be? or rather, are we to have any at all, or are we to have ornithological regions, Reptilian regions, Mammalian regions, Piscian regions — Molluscan regions;- & if these why not Coleopterous and Lepidopterous regions;- why not even Passerine and Picarian Psittacine, and Columbine regions? These will all differ widely; but I hold, & I think you will agree with me, that they would be confusing & almost worse than useless. What we want are not mere Zoological regions but Biological, for I believe that plants & animals must be radically affected by the series of geographical changes which our "Regions" are intended [4] to summarize,- though affected in different ways,- just as insects are affected by them differently from most vertebrates. Now Mammalia both living & extinct show the Nearctic Reg. to be quite distinct from the Neot, and so much more allied to the Palaearctic that it has been proposed to unite them. For Lepidoptera the same union has been proposed. In Reptiles & fishes,— it is sufficiently distinct from both. The proper plan seems to me to be, to point out the scarcity of peculiar forms in birds & account for them, by the powers of dispersal & habits of migration in this class,- the successive unions & separations of the Nearct & Neot regions,- the forced interminglings of the two by the Glacial Epoch pushing the Nearct. fauna southward &c. &c.

Again I believe that all north of Nicaragua was once part of the Nearctic region. There the great oceanic separation [5] (2) of the two regions once existed, and all north of this has been peopled by immigration of Neotrop. forms w owing to favourable climatal conditions, comparatively recently. No form that does not pass S. of Nicaragua sh^d. be considered Neotropical. — Thus Meleagridae will be wholly nearctic. & several other genera will have to be added to the list of peculiar Nearctic genera.

Please let me have the list of European & Pal. genera as soon as you can.

Yours very truly | Alfred R. Wallace [signature]

This is written in great haste;- the subject wants developing, but you will see my meaning.

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