Species Versus Variety

Many years ago I compared the birds from the separate islands of the Galapagos Archipelago with those from the American mainland.

I was struck how vague and arbitrary was the distinction between species and varieties.

On the islets of the little Madeira group there are many insects which are characterized as varieties in Mr. Wollaston’s admirable work, but which it cannot be doubted would be ranked as distinct species by many entomologists.

Ireland has a few animals regarded as varieties, but have been ranked as species by some zoologists.

Our experienced ornithologists consider our British red grouse only as a strongly-marked race of a Norwegian species.

• Whereas most rank it as an undoubted species peculiar to Great Britain.

A wide distance between the homes of 2 doubtful forms leads many naturalists to rank both as distinct species. But what distance 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?

Many forms are as varieties. They have so perfectly the character of species that they are ranked by other highly-competent judges as true species.

But to discuss whether they are rightly called species or varieties, before any definition of these terms has been generally accepted, is vainly to beat the air.

Many of the cases of strongly-marked varieties or doubtful species well deserve consideration; for several interesting lines of argument, from geographical distribution, analogical variation, hybridism, &c., have been brought to bear on the attempt to determine their rank.

An example is the primrose and cowslip, or Primula veris and elatior.

These plants:

• differ considerably in appearance.

• have a different flavour

• emit a different odour

• flower at slightly different periods

• grow in different stations

• ascend mountains to different heights

• have different geographical ranges

• can be crossed only with much difficulty.

  • This was done by Gartner’s numerous experiments

On the other hand, they are united by many intermediate links that are not hybrids.

An overwhelming amount of experimental evidence shows that they descend from common parents. Consequently, they must be ranked as varieties.

Close investigation is the basis of how to rank doubtful forms.

We find the most forms of doubtful value in the best-known countries.

If any wild organism is highly useful or attractive to man, varieties of it will be found recorded as species.

The common oak has studied closely. Yet a German author makes more than a dozen species out of forms, which are generally considered as varieties.

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 some variation.

But if he confine his attention to one class within one country, he will soon make up his mind how to rank most of the doubtful forms.

His general tendency will be to make many species, for he will become impressed, just like the pigeon or poultry-fancier before alluded to, with the amount of difference in the forms which he is continually studying.

He does not know the analogical variation in other groups and in other countries to correct his first impressions.

As he extends the range of his observations, he will meet with more cases of difficulty when he encounters more closely-allied forms.

But if his observations are extended, he will make up his own mind on which are varieties and which species.

No clear line of demarcation has yet been drawn between:

• species and sub-species.
  • Sub-species are forms which come very near to, but are not quite, species.
• sub-species and well-marked varieties
• lesser varieties and individual differences.

These differences blend into each other in an insensible series.

• A series impresses the mind with the idea of an actual passage.

Individual differences are the first step towards such slight varieties that are barely worth recording.

• Then I look at varieties which are more distinct and permanent.
• This leads to more strongly marked and permanent varieties.

The permannent varieties lead to sub-species, and then to species.

The passage from one stage of difference to another higher stage might be due merely to different physical conditions in 2 different regions in the long term.

But I have not much faith in this view.*

The passage of a variety is caused by natural selection accumulating differences of structure in certain definite directions.

Hence I believe a well-marked variety may be justly called an incipient species;

Not all varieties or incipient species necessarily attain the rank of species.

While in this incipient state, they may become extinct.

Or they may endure as varieties for a long time.

• This has been shown by Mr. Wollaston with the varieties of certain fossil land-shells in Madeira.

If a variety were to flourish so as to exceed in numbers the parent species, it would then rank as the species, and the species as the variety.

Or it might supplant and exterminate the parent species.

Or both might co-exist and rank as independent species.

The term ‘species’ is arbitrarily given for the sake of convenience to a set of individuals closely resembling each other.

It does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms.

The term variety, again, in comparison with mere individual differences, is also applied arbitrarily, and for mere convenience sake.

I thought of tabulating all the varieties in several well-worked floras.

At first this seemed a simple task.

But the following convinced me that this would be difficult:

• Mr. H. C. Watson
• Dr. Hooker

This whole subject is rather perplexing.