WCP2960

[1]¹

29 Friar's Stile R[oa]d.

Richmond.

Surrey.

July 22 1909.

Dear Dr. Wallace,

Your extremely interesting letter has just reached me. What a dreadful business with all those lotions &c &c[.] If you are able to have us after our return from Switzerland, must it necessarily be a week end? We may find it very difficult to fit it in, owing to promised visits to relatives, but if we could spend a day with you during some week, there would probably be no difficulty.

Your new book sounds most interesting, and will I think deal with many matters which I have more or less investigated. If American data are of any value I can send you a lot when [2] I get home; and I will of course see what can be obtained in Switzerland.

It has always seemed to me that the very large number of tropical species may in a considerable degree be connected with the fact that tropical conditions have persisted, with little changes for enormous periods; permitting very many minute adaptive adjustments, and causing relatively little extinction. In accordance with this, in many groups I think tropical species are better defined than those of temperate regions².

In the north temperate region for various reasons, there have been many more or less catastrophic occurrences thus during the later Tertiary in North America[.] There was first the invasion of Old World species via Bering Straits, then an incursion of S. American forms via Panama, & then the Glacial Period at the end², [3]³ crowding & destroying the fauna & flora. Consequently our Florissant beds⁴ (late Miocene⁵ apparently) show numerous genera now extinct, or extinct in N. America, & no doubt the total number of genera today is less than during the middle tertiary. Since the glacial period, in N. America there has been room for expansion⁶ — & hence the very numerous very closely allied species of Argynnis⁷, Colias⁸ &c among butterflies, Aster⁹, Solidago¹⁰, Senecio¹¹, &c &c among plants¹². These are most of them not at all on the same footing as the old tropical species, & should not be treated so statistically.*¹³

*Francis Darwin¹⁴ generously gave me a page of Charles Darwin's¹⁵ MS, in which he discusses N. America and brings out substantially the same point. This was written apparently prior to 1859¹⁶.

Did you ever examine the writings of Perkins¹⁷ & others on the insects of the Hawaiian Is. [?] The aculeate Hymenoptera of the Hawaiian Is. for example include only very few genera, which are supposed to [4] represent about half-a-dozen insects originally [3 words illeg. struck through] arriving from elsewhere. These few have given rise to a simply marvellous multitude of species, closely allied, & mostly with different habitats¹⁸. It is quite the same with microlepidoptera¹⁹, which have been beautifully figured by Lord Walsingham²⁰. Now here we seem to see what a single type can do in the way of species when it has a free field²¹. It is an unpruned tree of nature²². On continental areas, such "trees" are lopped in every direction, leaving us remnants which do not show the possibilities inherent in the race²³. Of course we find in America as I presum[e]d elsewhere, a succession of flowering periods ^{of different plants} throughout the season, each accompanied by special insects. Consequently the longer the season, the greater [the] room for different species of both plants and insects. In insects I have noted cases in which a species would emerge early in the season in the south, [5]²⁴ and later & later as it went north, until finally there came a point at the northern limit of its range, when it only just had time to get out & reproduce before the cold weather. A little further north it would naturally fail entirely. It must be the same with various plants.

One difficulty in getting up the statistics that you desire will be in obtaining data from more or less uniform areas. Thus we have on cards a catalogue of the flora of Boulder County, Colorado²⁵. This is a very small area on the map, & you might be astonished at the number of species, did you not know it to include about five different life zones, each with a largely distinct flora. Now this has nothing to do with the favorableness [sic] of the conditions at any particular spot, for as a matter of fact the flora of any single [6]²⁶ uniform area in Colorado is not especially rich.

Forgive me for all this talk, which I fear will weary you!

Yours very sincerely, | Theo. D. A. Cockerell²⁷. [signature]

We will certainly bring some fossils if we get any!