Origin of Species Variorum

→ at least within the whole immense 1861

that from an early part of the long 1866 1869

that from an early part of the 1872

→ probably, 1861

that from the middle part of this same period the number 1866 1869 1872

→ become in any country 1861 1866

in any country becomes 1869 1872

relations of organic beings are more important; and as the number of species in

~~any~~

any

anycountry

country

goes on increasing, the organic conditions of life

must

~~will~~

will

become more and more complex. Consequently there seems at first sight

~~to be~~

to be

no limit to the amount of profitable diversification of structure, and therefore no limit to the number of species which might be produced. We do not know that even the most prolific area is fully stocked with specific forms: at the Cape of Good Hope and in Australia, which support such an astonishing number of species, many European plants have become naturalised. But geology shows us, →at least within the whole immense tertiary

period

period,

~~that~~

that

the number of species of shells,

and

and,

→probably, of mammals, has not greatly or at all increased. What then checks an indefinite increase in the number of species? The amount of life (I do not mean the number of specific forms) supported on

any

area must have a limit, depending so largely as it does on physical

conditions;

conditions:

therefore, if an area be inhabited by very many species, each or nearly each species will be represented by few individuals; and such species will be liable to extermination from accidental fluctuations in the nature of the seasons or in the number of their enemies. The process of extermination in

such

these

cases

would

will

be rapid, whereas the production of new species

must

will

always be

sloW.

slow.

Imagine the extreme case of as many species as individuals in England, and the first severe winter or very dry summer would exterminate thousands on thousands of species. Rare species, and each species will become rare if the number of species →become in any country indefinitely increased, will, on the principle often explained, present within a given period few

favorable

favourable

variations; consequently, the process of giving birth to new specific forms

would

will

thus be retarded. When any species becomes very rare, close interbreeding will