Chapter 12 – Geographical Distribution – continued

What is Darwin’s point in chapter 12?

In chapter 12 is just a continuation of chapter 11 and discusses about life being distributed around the planet.

This is summarized in the following paragraph (and it’s perhaps one of the longest sentences in the entire book).

“The relations just discussed, namely, low and slowly-changing organisms ranging more widely than the high, some of the species of widely-ranging genera themselves ranging widely, such facts, as alpine, lacustrine, and marsh productions being related (with the exceptions before specified) to those on the surrounding low lands and dry lands, though these stations are so different the very close relation of the distinct species which inhabit the islets of the same archipelago, and especially the striking relation of the inhabitants of each whole archipelago or island to those of the nearest mainland, are, I think, utterly inexplicable on the ordinary view of the independent creation of each species, but are explicable on the view of colonisation from the nearest and readiest source, together with the subsequent modification and better adaptation of the colonists to their new homes.”

As in preceding chapters, it seems like the prevailing view of the origin of life is that each specific life was created at each location. Animals and plants that exist on islands were individually created and placed there. Though perhaps it was the prevailing view at the time, again, it would be incompatible with the Biblical view of creation.

I would agree with Darwin with his “view of colonisation from the nearest and readiest source, together with the subsequent modification and better adaptation of the colonists to their new homes.” However, it could still be compatible with “single centres of creation” where species were created at one particular point and migration caused their dispersal and low scale changes occurred over time.

There are several interesting facts that Darwin points out in the chapter.

In the beginning of the chapter he notes the adaptablity of fish to fresh and salt water.

“salt-water fish can with care be slowly accustomed to live in fresh water; and, according to Valenciennes, there is hardly a single group of fishes confined exclusively to fresh water, so that we may imagine that a marine member of a fresh-water group might travel far along the shores of the sea, and subsequently become modified and adapted to the fresh waters of a distant land.”

He also mentions that several amphibians are not found on islands.

“Batrachians (frogs, toads, newts) have never been found on any of the many islands with which the great oceans are studded.”

Also, only certain types of mammals are found on islands.

“as yet I have not found a single instance, free from doubt, of a terrestrial mammal (excluding domesticated animals kept by the natives) inhabiting an island situated above 300 miles from a continent or great continental island;”

“Though terrestrial mammals do not occur on oceanic islands, aerial mammals do occur on almost every island. ”

Cathar1950 wrote: How is that different then a creature evolving in a center of evolution that migrated and changed at every stage of evolution and enough distance that they evolve separately?

I don’t see much of a difference. The only difference is the organism arising from either a “center of creation” or a “center of evolution”.