28 April 2010

A lesson from the salamanders

I've recently finished reading The Ancestor's Tale by Richard Dawkins, which contains an abundance of fascinating insights into evolutionary biology. One of the more interesting ones concerns the salamanders of California's Central Valley.

Salamander habitat consistes of the mountains around the valley, not the valley floor itself. That is, the area where salamanders are found is an elongated ring of uplands, surrounding an internal area of non-salamander-habitable territory (the valley floor).

If you look just at the southern end of the ring, you will find that there are two distinct varieties of salamander which can easily be distinguished on sight. To the east are salamanders whose hides are patterned with irregular patches of black and yellow, while those to the west are an even brown in color. The salamanders themselves are well aware of the difference -- there is a small area where their ranges overlap, but they do not interbreed with each other. By this criterion, they would normally be considered two separate species.

The interesting part comes when you head north along the two separated sides of the valley. Let's take the eastern side. There, as expected, you see only salamanders of the black-and-yellow patchy type. But as you head further north along the eastern foothills, the black-and-yellow patches get less and less distinct. By the time you get to the north end of the valley, there has been a smooth transition to salamanders with mostly-brown skin and indistinct lighter patches. Then, as you head down the western foothills of the valley -- the other side of the "ring" -- you find salamanders with fainter and fainter light patches as you go south. By the time you're back at the southern end of the valley where you started, they are the plain brown western salamanders you originally saw.

In the south, there are two distinct species. But around the "ring" of the valley, the one type gradually becomes the other, with no noticeable discontinuity at any point.

Dawkins uses this to illustrate how the division of our successive proto-human ancestors such as the Neanderthals, Homo ergaster, the australopithecines, etc. into successive species is misleading. If you were to meet a living Homo ergaster, you would certainly classify it as a separate species from yourself, and you'd be right. But if you had a complete record of all the hundred thousand or so generations of intermediate descendants of that creature which lead forward in time to yourself, you would see only gradual change, no sudden discontinuity. Anthropologists sometimes argue vociferously about where exactly the line between two such successor species should be drawn, but it's actually a meaningless question. Cases like the California salamanders, where we see a gradual transition between two distinct species which live at the same time, are rare -- but between two species separated in time, where one is the ancestor of the other, it's the norm.

It occurs to me that the salamander has a lesson for us in another area: human races. Of course, no serious anthropologist would argue that human racial differences are analogous to differences between species. Humans populations from different parts of the world can, and routinely do, interbreed when they come into prolonged contact -- despite efforts, in some cases, to prevent it by law and custom. All humans are the same species; genetically speaking the racial differences are superficial, and they are likely of recent origin (how they arose is a fascinating question which, unfortunately, I don't have space for here). Nevertheless, those differences are very noticeable, and throughout history many humans have attached importance to them, to the disastrous misfortune of humanity as a whole.

We all know, for example, of the horrors which have happened in our own country because so many people thought there were significant innate differences between light-skinned humans of European descent and dark-skinned humans of African descent. But the United States is like the southern end of the Central Valley. If you were to start out in, say, Scandinavia, and travel through western Russia, the Balkans, Turkey, the Fertile Crescent, Egypt, the Sudan, the Horn of Africa, and finally Central Africa, you would find that the human populations around you changed only gradually in skin color and facial features, with very little in the way of discontinuities. The same would be the case if you set out from Europe and traveled across Russia and Central Asia to China.

Even aside from the hundreds of millions of "mixed-race" people born in regions where migration has brought previously-distinct populations together, human racial variation has always been a matter of gradual gradation over geographical distance, not sharply-bounded categories. If more people had been aware of this throughout history, humanity might have avoided a great deal of nonsense and cruelty.

9 Comments:

Anonymous rita said...

This makes me think about how difficult it's been in human history past for people to comprehend the scope of the "big picture". You certainly can't see it when your education & POV is constricted to what you know about your immediate surroundings.

We live in an exciting time in human history to have so much information & knowledge at our fingertips. Just to be able to glimpse the scope of our evolutionary biology is mind changing.

28 April, 2010 06:49  
Blogger Shaw Kenawe said...

Great post, Infidel. Especially since I've just finished reading Chapter 5, "BEFORE OUR VERY EYES," in Dawkins' newest book, "The Greatest Show on Earth, the Evidence for Evolution."

This chapter deals with the variations that evolved in Podarcis sicula [a common Mediterranean lizard] in two islets off the Croatian coast--the changes occurred over a very, very, very short time--from 1971, when 5 pairs of Podarcis sicula from one islet, Pod Kopiste, were transported to its neighboring islet, Pod Mrcaru, which was Podarcis sicula-less--to the present.

Because of the difference in the food supply for the newly transported lizards, over a mere
37 years, the descendants of the tranported lizards had evolved larger heads because of the nearly vegetarian only diet they were forced to eat on the second islet. [The lizards needed stronger jaws to process the mainly cellulose-based diet found on the second islet, as opposed to the lizards on the first islet, where there was more abundant insect food supply.]

In the same chapter he discusses the changes over time in guppies in an experiment by Dr. John Endler.

Fascinating reading. But unfortunately, those who refuse to educate themselves on Evolution will never accept this evidence.

28 April, 2010 07:07  
Blogger Infidel753 said...

Rita: Certainly for most of the time humanity has existed, most people knew nothing about the world beyond their immediate environment. Even now a lot of people are rather hazy about foreign countries.

What's really striking to me is how strong the commonalities among all life on Earth are.

Shaw: Great book, isn't it? It was that, as well as The God Delusion that inspired me to read some of his earlier books.

I remember those Croatian lizards. Obviously some people will never accept evolution no matter what evidence there is, but if people are reachable at all, that book should do it.

28 April, 2010 08:42  
Blogger boomer bob said...

Fascinating read, Infidel.

I wonder if they're wrestling with immigration laws in salamander valley :-)

28 April, 2010 09:33  
Blogger Tim said...

Since we seem to be unable to see past our collective nose, I dream of a day when there is but one color of people, that would be brown.
But of course even at that,eye color or hair color will be what we War about. Religion hopefully will be a distant memory so at least well have better things to Kill for.

28 April, 2010 09:38  
Blogger Infidel753 said...

Boom: At least salamanders don't have religion. That's got to work in their favor.

Tim: This is a whole other issue, but I think by a few decades from now personal appearance will be modifiable at will, which should make an end to this racial nonsense once and for all.

28 April, 2010 09:54  
Blogger tnlib said...

Most interesting. Did you know the Smoky Mountains have 30 species of salamanders, making it the s. capitol of the world? Wonder if any of them cross-breed.

I've always maintained that horses and even dogs discriminate to a certain degree. For instance, a black horse often does not like a white or spotted horse. My black lab mix has a fluff complex. No joke. Of course these guys cross-breed like crazy if they have the right equipment.

Their own bodily comforts are just food.

28 April, 2010 16:45  
Blogger Ranch Chimp said...

Good Morning Mr.Infidel!

Actually I read this yesterday, but was interrupted from when I got to comment. Thought it was a really interesting posting. Of course I expect that the Dr.Dawkins book is really good as well.

29 April, 2010 06:34  
Blogger Infidel753 said...

TNLib: Wow, there are racist horses?:-) I had no idea.

If those salamanders are different species, they can't interbreed -- that's how biologists define a species. If they could interbreed, you'd regularly see intermediate types.

RC: It's a very interesting book that starts with modern humans and takes you backward through the evolutionary process right to the beginning, discussing all the common ancestors we have with the other types of life on Earth. Really gives you a good sense of the relationships among living things.

29 April, 2010 07:20  

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