OCR Text |
Show 50 DOUBTFUL SPECIES. [CnAP. II. as a variety, can rarely be found within the same country, but are common in separate areas. How many of those birds and insects in North America and E~rope, which differ very slightly fr01n each other, have been ranked by one eminent n~turalist as undoubted species, and by another as varieties, or, as they are often called, as geographical races! Many years ago, when comparing, and seeing others oompare, the birds from the separate islands of the Galapagos Archipelago, both one with another, and with those from the American mainland, I was much struck how entirely vague and arbitrary is the distinction between species apd varieties. On the islets of the little Madeira group there are many insects which are characterised as varieties in Mr. Wollaston's admirable work, but which it cannot be doubted would be ranked as distinct species by many entomologists. Even Ireland has a fevv animals, now generally regarded as varieties, but 'vhich have been ranked as species by some zoologists. Several most experienced ornithologists consider our British red grouse as only a strongly-marked race of a Norwegian species, whereas the greater number rank it as an undoubted species peeuliar to Great Britain. A wide distance between the homes of two doubtful forms leads many naturalists to rank both as distinct species ; but what distance, it has been well asked, will suffice? if that between America and Europe is ample, will that between the Continent and the Azores, or Madeira, or the Canaries, or Ireland, be sufficient? It must be admitted that mal?-y _forms, considered by highly competent judges as varieties, have so perfectly the character of species that they are ranked by other highly competent judges as good and true species. But tq discuss whether they are rightly called species or varieties, before any definition of these t~rms has been generally accepted, is vainly to beat the a1r. Many of the cas~s of strongly-marked varieties or doubtful species well deserve consideration ; for several interesti:pg lines of ~rgument, from geographical distribution, an~logical vn;ri~tion, hypridism, &c., have been brought to bear qn th(3 attempt to determine their rank. CIIAP. II.] DOUBTFUL SPECIES. 51 I will here give only a single instance,-the well-known one of the primrose and cowslip, or Primula veris and elatior. These plants differ considerably in appearance ; they have a different flavour and emit a different odour; they flower at slightly different periods; they grow in somewhat different stations; they ascend mountains to different heights; they have different geographical ranges; and lastly, according to very numerous experiments made during several years by that most careful observer Gartner, they can be cross~d only 'vith much difficulty. vV e could hardly- wish for better evidence of the two for1ns being specifically distinct. On the other hand, they are united by many intermediate links, and it is very doubtful whether these links arc hybrids; and there is, as it seems to me, an overwhelming a1nount of experimental evidence, sho,ving that they descend from common parents, and consequently must be ranked as varieties. Close investigation, in most cases, will bring naturalists to an agreement how to rank doubtful forms. Yet it must be confessed, that jt is in the best-known countries that 've find the greatest number of forms of doubtful value. 1 have been struck with the fact, that if any animal or plant in a state of nature be highly useful to man, or from any cause closely attract his attention, varieties of it will almost universally be found recorded. These varieties, moreover, will be often ranked by some authors as species. Look at the common oak, how closely it has been studied; yet a German author makes more than a dozen species out of forms, w·hich are very generally considered as varieties; and in this country the highest botanical authorities and practical men can be quoted to show that the sessile and pedunculated oaks are either good and distinct species or mere varieties. When a young naturalist commences the study of a group of organisms quite unknown to him, he is at first much perplexed to determine what differences to consider as specific, and what as varieties; for he knows nothing of the amount and kind of variation to which the group is subject; and this shows, at least, how very generally there is smne variation. But if he confine his attention |