As a biologist, I will affirm the message of the first graphic - that the variations we see among human populations are variations in the expression of the genes that we all share. For example, we all have the same number of melanocytes, the pigment producing cells, and the variation we see in skin pigmentation is due to which type of melanin is being produced, how fast it is being produced and how quickly it is being broken down. Many folks have direct experience with changes in melanin production - for example the induction of more melanin production by exposure to sunlight [tanning]; or skin darkening during pregnancy; or age spots :-) Also, this post is not at all intended to be a detailed discussion of the topic - you can find many, many books on the origin of race - but rather this is intended as a simplified introduction to the topic [in response to a classroom discussion!!]
However, a natural question is how did humans get from this
to this?
One thing to consider is the map below, from Jared Diamond. It shows human origins in Africa, and then the migration of humans throughout the world. An important concept here is to think of these populations as simply divergent groups, isolated from one another, and therefore any genetic changes related to appearance could become distinctive for that group.
The following graph of genetic analysis of different groups demonstrates both the divergence of different groups as well as the nearness of relationships [genetic distance] within groups. Notice the concordance of the genetic data and the migration graph [the migration graph is based partially on genetic data as well as on archaeological and anthropological data]. Sorry - you will have to turn your head sideways to read the names of the different human populations.
Perhaps a helpful analogy would be the derivation of different breeds of dogs - a common ancestor that through selective breeding [genetics] has given rise to dozens of different 'races' of dogs. The are all the same species, with variations on a theme, and the variation can be due to the differential expression of a single gene as has been shown for the differences in dog sizes. The take-home message for humans is that a complex of genes control the size and shape of facial features and other morphological [body] characteristics, and that heterogeneity among those genes give rise to folks who look different, and likewise homogeneity would produce similar traits.
When one considers how much variation can be generated in the dog species over a relatively short period of time, it is rather amazing that there has not been greater diversity among human populations given the long periods of time. Given the 'shrinking' globe, it is not hard to conceive that the future will see a diminution of human variability, with physical differences becoming less and less prominent.
Hahaa. Thank Dr. S!
ReplyDeleteI understand the dog analogy better now. I guess I just don't understand how certain races have certain characteristics. I understand humans change because of the environment, but what about facial features? Nose? Eyes? Lips?
Good question - and it's really complex :-) But, all of the features that you mention are controlled by a set of genes that control their size and shape. Look at caucasians and you will see a variety of lip features from slender to full. If a group of full lipped folks went off somewhere and only married amongst themselves, after a while, the whole population would have full lips.
ReplyDeleteAnother unfortunate example of facial characteristics is trisomy 21, which fortunately has dropped the racist connotations of Down syndrome - Down coined the term "mongolian idiocy." As you know, many trisomy 21 individuals have very similar facial characteristics, and this is all because of a genetic defect on the 21st chromosome. This tells us that chromosome 21 is very important in determining facial characteristics even though we don't know much about exactly what is going on.
Does that help??
Any thoughts on Mitochondrial Eve, our common mother who existed about 200,000 years ago?
ReplyDeleteI don't see humankind evolving into light browned creatures who conduct rocket science by day and dunk basketballs by night. I see us becoming increasingly tribal, with all the ensuing rivalries and conflicts.
ReplyDeleteS3 - I guess that's the difference between an optimist and a pessimist!! However, you make a good point about tribalism, the worst kind of which centers around religions who claim that any non-adherent is an apostate worthy of death.
ReplyDeleteBB - ME and the male equivalent Y-Adam have been the object of much study and much is known about these pieces of DNA that all folks today seem to share. The choice of Eve and Adam was in retrospect unfortunate, because of the implication of a single ancestor. This is not the case, but rather it indicates a common ancestor that lived among many contemporaries at the time. Besides the wiki entry on ME, you might want to also read this somewhat dated discussion of ME:
ReplyDeletehttp://www.talkorigins.org/faqs/homs/mitoeve.html
Also BB - if you want to put on your scientist hat, have a look at this good analysis and critique on ME: http://www.evolutionpages.com/Mitochondrial%20Eve.htm
ReplyDeleteThanks for the references, Dr. S. All this biological complexity can be tiring, however. Thinks I'll relax with a good book, say Genesis 1.
ReplyDeleteNot quite on topic, but I have always believed in the logic of intelligent design. However, I never believed for one minute ID advocates would change the thinking of evolutionists for the simple reason that we are not conducting reasonable debate based on science and logic, but arguing opposing religious beliefs, and we all know that leads nowhere.
ReplyDeleteThat's a good choice Bizzy 'cause Genesis sure ain't biology!!
ReplyDeleteAva G - you are correct - ID is just another form of creationism. Properly understood, evolution is purely science and is therefore non-theistic, i.e. has nothing to say theologically. It's beyond the realm of science to make claims about a creator of any sort from Yahweh to the intelligent designer to the flying spaghetti monster.
ReplyDeleteGuess I don't "properly understand" evolution then because I still think it takes a mighty heap o' faith to get from rocks to DNA. I scoured the internet for a scientific explanation and didn't find nothin'.
ReplyDeleteAva - you, like many others, confuse evolution with the origin of life. Neither Darwin nor current evolutionary biologists study the origin of life. Evolution is about changes within species and the origin of new species. Life from non-life is called abiogenesis, and that's where you should search for research in this topic. Of course rocks did not spring forth bacteria, but rather 'life' likely arose in the 'primordial soup' of the oceans.
ReplyDeleteThanks for pointing out the distinction. Read Wickipedia's take on abiogenesis. Lots of could have, could be, might have, may have, suggests that, possible that, may be able, most likely, etc. terminology. Favorite theory is that precursors to life on earth came from outer space.
ReplyDeleteWell, Ava, one way or another, we are all aliens, and at the minimum, 'we are stardust' :-)
ReplyDelete