WCP2089

[1] [p. 23]

SIR C. LYELL TO A. R. WALLACE

73 Harley Street. May 2, 1867.

My dear Sir, — I forgot to ask you last night about an ornithological point which I have been discussing with the Duke of Argyll¹. In Chapter V. of his "Reign of Law" (which I should be happy to lend you, if you have time to look at it immediately) he treats of humming-birds, saying that Gould² has made out about 400 species, every one of them very distinct from the other, and only one instance, in Ecuador, of a species which varies in its tail-feathers in such a way as to make it doubtful whether it ought to rank as a species, an opinion to which Gould inclines, or only as a variety or incipient species, as the Duke thinks. For the Duke is willing to go so far towards the transmutation theory as to allow that different humming-birds may have had a common ancestral stock, provided it be admitted that a new and marked variety appears at once with the full distinctness of sex so remarkable in that genus.

According to his notion, the new male variety and the female must both appear at once, and this new race or species must be regarded as an "extraordinary birth." My reason for troubling you is merely to learn, since you have studied the birds of South America, and I hope collected some humming-birds, whether Gould is right in saying that there are so many hundred very distinct species without instances of marked varieties and transitional forms. If this be the case, would it not present us with an exception to the rule laid down by Darwin³ and Hooker⁴ that when a genus is largely represented in a continuous tract of land the species of that genus tend to vary?

[2] [p. 24] I have inquired of Sclater⁵ and he tells me that he has a considerable distrust of Gould's information on this point, but that he has not himself studied humming-birds.

In regard to shells, I have always found that dealers have a positive prejudice against intermediate forms, and one of the most philosophical of them, now no more, once confessed to me that it was very much against his trade interest to give an honest opinion that certain varieties were not real species, or that certain forms, made distinct genera by some conchologists, ought not so to rank. Nine-tenths of his customers, if told that it was not a good genus or good species, would say, "Then I need not buy it." What they wanted was names, not things. Of course there are genera in which the species are much better defined than in others, but you would explain this, as Darwin and Hooker do, by the greater length of time during which they have existed, or the greater activity of changes, organic and inorganic, which

have taken place in the region inhabited by the generic or family type in question. The manufactory of new species has ceased, or nearly so, and in that case I suppose a variety is more likely to be one of the transitional links which has not yet been extinguished than the first step towards a new permanent race or allied species....

Your last letter will be of great use to me. I had cited the case of beetles recovering from immersion of hours in alcohol from my own experience, but am glad it strikes you in the same light. McAndrew⁶ told me last night that the littoral shells of the Azores being European, or rather African, is in favour of a former continental extension, but I suspect that the floating of seaweed containing their eggs may dispense with the hypothesis of the submersion of 1,200 miles of land once intervening. I want naturalists carefully to examine floating seaweed and pumice met with at sea. Tell your correspondents to look out. There should be a [3] microscopic examination of both these means of transport. —

Believe me ever truly yours, | CHA. LYELL.

[1] [p. 413]

Extract of Letter to A. WALLACE, Esq.

May 2, 1867.

I forgot to ask you last night about an ornithological point which I have been discussing with the Duke of Argyll¹. In Chapter V. of his 'Reign of Law' he treats of hummingbirds, saying that Gould² has made out about four hundred species, every one of them very distinct from the other, and only one instance, in Ecuador, of a species which varies in its tail-feathers in such a way as to make it doubtful whether it ought to rank as a species — an opinion to which Gould inclines — or only as a variety or incipient species, as the Duke thinks. For the Duke is willing to go so far towards the transmutation theory as to allow that different hummingbirds may have had a common ancestral stock, provided it be admitted that a new and marked variety appears at once with the full distinctness of sex so remarkable in that genus. According to his notion the new male variety and the female must both appear at once, and this new race or species must be regarded as an 'extraordinary birth.' My reason for troubling you is merely to learn, since you have studied the birds of South America, and I hope collected some hummingbirds, whether Gould is right in saying that there are so many hundred very distinct species without instances of marked varieties and transitional forms. If this be the case, would it not present us with an exception to the rule laid down by Darwin³ and Hooker⁴, that when a genus is largely represented in a continuous tract of land, the species of that genus tend to vary? In regard to shells I have always found that dealers have a positive prejudice against intermediate forms, and one of the most philosophical of them — now no more — once confessed to me, that it was very much against his trade interest to give any honest opinion that certain varieties were not real species, or that certain forms, made distinct genera by some conchologists, ought not so to rank. Nine-tenths of his customers, if told that it was not a good genus or good species, would say what they wanted was names, not things. Of course there are genera in which the species are much better defined than in others, but you would explain this, as Darwin and Hooker do, by the greater [2] [p. 414] length of time during which they have existed, or the greater activity of changes, organic or inorganic, which have taken place in the region inhabited by the generic or family type in question. The manufactory of new species has ceased or nearly so, and in that case I suppose a variety is more likely to be one of the transitional links which has not yet been extinguished than the first step towards a new permanent race or allied species. Sclater⁵ gave me Euplocamus melanotis and E. lineatus as an example of two distinct species — Tenasserim⁶ and Pegu [Bago] which pass through every intermediate variety in the intervening country of Arracan; but when I asked if it was proved that the two extremes of the series would not intercross and produce fertile hybrids, he said the experiment had not been fairly tried. I suppose we have a good deal to do before we get all the facts which we shall one day probably have in confirmation of the theory of transmutation, or of such a divergence as will be accompanied by the sterility of hybrids. It may require several hundred thousand years. M'Andrew⁷ told me last night that the littoral shells of the Azores being European, or rather African, is in favour of a former continental extension; but I suspect that the floating of sea-weed containing their eggs may dispense with the hypothesis of the submersion of 1,200 miles of land once intervening. I want naturalists carefully to examine floating sea-weed and pumice met with at sea. There should be a microscopic examination of both these means of transport.

CHARLES LYELL.