Variation Under Nature

‘Variety’ means the community of descent though it can rarely be proved.

Monstrosity is some considerable deviation of structure in one part, either injurious or not useful to the species, and not generally propagated.

Monstrosities graduate into varieties.

Some authors use the term:

• ‘variation’ to imply a modification directly due to the physical conditions of life
• ‘variations’ as modifications that are not inherited

We have many slight differences which may be called individual differences. Examples are those in the offspring from the same parents.

This is observed in the individuals of the same species inhabiting the same confined locality.

These individual differences afford materials for natural selection to accumulate, in the same manner as man can accumulate individual differences in his domesticated productions.

These individual differences generally affect what naturalists consider as unimportant parts.

The most experienced naturalist would be surprised at the number of the cases of variability even in important parts of structure which he could collect on good authority, as I have over the years.

Systematists are not pleased to find variability in important characters. Few men will laboriously:

• examine internal and important organs
• compare them in many specimens of the same species

An example is the branching of the main nerves close to the great central ganglion of an insect being variable in the same species.

I would have expected that such changes could happen slowly.

Mr. Lubbock is a philosophical naturalist.

He has shown quite recently:

• a degree of variability in these main nerves in Coccus
  • These may be compared to the irregular branching of a tree stem.
• that the muscles in the larvae of certain insects are not uniform

Authors sometimes argue in a circle when they state that important organs never vary.

These same authors practically rank that character as important (as some few naturalists have honestly confessed) which does not vary.

Under this point of view, no instance of any important part varying will ever be found: but under any other point of view many instances assuredly can be given.

Polymorphic Genera

In terms of individual differences, I am extremely perplexed by ‘protean’ or ‘polymorphic’ genera wherein the species present an inordinate amount of variation.

In most polymorphic genera some of the species have fixed and definite characters.

With a few exceptions, polymorphic genera in one country are polymorphic in other countries and at former periods of time.

• This is proven by Brachiopod shells

These facts are very perplexing because they show that this kind of variability is independent of the conditions of life.

I suspect that these polymorphic genera variations are in points of structure which:

• are of no service or disservice to the species
• have not been seized on and rendered definite by natural selection, as hereafter will be explained.

Some forms have the character of species but are so similar to some other forms or are so closely linked to them by intermediate gradations.

• Naturalists do not rank them as distinct species. But these are most important for us.

Many of these doubtful and closely-allied forms have permanently retained their characters in their own country for a long time just as good and true species have.

When a naturalist unites 2 forms with others having intermediate characters, he treats the one as a variety of the other.

How should we decide if something is a variety or a species?

In many cases, a variety is a variety because the observer assumes that their species exists elsewhere or in the past.

• It is not because the intermediate links have actually been found

There are so many varieties that might not be actually varieties.

• Some botanists have classified a form as a species, while other classed it as a mere variety.

Mr. H. C. Watson has marked for me 182 British plants which are considered as varieties, but have all been ranked by botanists as species.

In making this list, he has omitted many trifling varieties, but which nevertheless have been ranked by some botanists as species. He has entirely omitted several highly polymorphic genera.

Under genera, including the most polymorphic forms, Mr. Babington gives 251 species. Whereas Mr. Bentham gives only 112, a difference of 139 doubtful forms!

Amongst animals which unite for each birth, and which are highly locomotive, doubtful forms, ranked by one zoologist as a species and by another as a variety, can rarely be found within the same country, but are common in separated areas.

How many of those birds and insects in North America and Europe, which differ very slightly from each other, have been ranked by one eminent naturalist as undoubted species, and by another as varieties, or, as they are often called, as geographical races!