WCP4873

[1]

9, St. Mark’s Cresent N.W.

July 6th. [1867]¹

My dear Sir Charles

I think the fact that the only placental land mammals in Australia (truly indigenous) are the smallest of all mammals, is a very suggestive fact as to how they got there. Mice would not only be carried by canoes but they would also be carried ^transported occasionally by floating trees carried down by floods. I think myself however, that it is most likely they were carried by the earliest canoes of prehistoric man, and that they are an example of rapid change of specific form, owing to the ancestral species having been [2] subjected to a great change of conditions both as regards climate and food, and having had an immense area of new country to roam over and multiply in, the very first of which it would be subjected to different conditions.

These considerations I think fully meet the facts, and there ought to be no large rodents found in the caves of Australia and no other rodents of very distinct type from those now living. When any such are found it will be time enough [3] to consider how to account for them. It is as you say a most important fact, that in three such distinct localities as New Zealand, Australia and the Mauritius, no bones of extinct carnivora or other mammalia should be found along with the wingless birds and marsupials; while abundance of remains of these groups are found. We may I think fairly claim this as a proof that such placental mammals did not exist in these countries, — and the fact that the only exceptions in the existing Australian fauna are [4] mice indicates very clearly that they are a recent introduction.

When all the known facts are in our favour, I do not think we need trouble ourselves & to answer objections and overcome difficulties that have not yet arisen and probably never will.

Believe me | Yours very truly | Alfred R. Wallace [signature]

Sir Charles Lyell