random scholar

Reading up on inbreeding depression and deleterious recessive alleles, I happened across a reference to a 1997 paper by W. Scheidel:

Brother-sister marriage in Roman Egypt

According to official census returns from Roman Egypt (first to third centuries CE) preserved on papyrus, 23.5% of all documented marriages in the Arsinoites district in the Fayum (n = 102) were between brothers and sisters. In the second century CE, the rates were 37% in the city of Arsinoe and 18.9% in the surrounding villages. Documented pedigrees suggest a minimum mean level of inbreeding equivalent to a coefficient of inbreeding of 0.0975 in second century CE Arsinoe. Undocumented sources of inbreeding and an estimate based on the frequency of close-kin unions (corrected downwards to 30% for Arsinoe) indicate a mean coefficient of inbreeding of F = 0.15-0.20 in Arsinoe and of F = 0.10-0.15 in the villages at the end of the second century CE. These values are several times as high as any other documented levels of inbreeding. A schematic estimate of inbreeding depression in the offspring of full sibling couples indicates that fertility in these families had to be 20-50% above average to attain reproduction at replacement level. In the absence of information on the amount of genetic load in this population, this estimate may be too high.

There is a substantial anthropological literature on the topic of brother-sister marriage in Roman Egypt, because it constitutes the most important documented exception to the incest taboo, considered a "cultural universal" in humans. There are other, more localized exceptions, but Roman-era Egyptians did not limit this kind of inbreeding to any small group (like monarchs or aristrocrats), but spread it across social classes. A 1996 paper by Seymour Parker gives a more comprehensive review. He concludes by discussing what the Roman Egypt example may contribute to our understanding of the "cultural universal":

We now approach a more difficult and murky issue: What does the present stud of brother-sister marriage tell us about the role of the incest taboo in human evolution?

Parker discusses the various complications with saying anything at all about human evolution on this basis -- most important, that the conditions under which the incest taboo may have evolved (either in hominids or earlier creatures) are not necessarily present in any recent complex societies, so the genetic or ancient cultural importance of the incest taboo may be quite removed from its present cultural importance. He concludes:

However, we can say with confidence that the Roman Egypt case shows that contrary to the implications of the various speculative theories on the functions of the incest taboo, this society existed for a few hundred years in its absence. There is not a single mention in the evidence that links sibling marriage to negative genetic effects or unhappy marriages. Finally, the very unusualness of this marital institution underlines the plasticity of human nature (Parker 1996:373-374).

Diocletian apparently ended the practice.

References:

Parker S. 1996. Full brother-sister marriage in Roman Egypt: Another look. Cultural Anthropology 11:362-376. JSTOR

Scheidel W. 1997. Brother-sister marriage in Roman Egypt. J Biosoc Sci 29:361-371. Abstract

Another one of those random Google Scholar results:

Control of scrotal colour in the vervet monkey.

J. S. Price, J. L. Burton, S. Shuster and K. Wolff

The vervet monkey has a vivid blue scrotum which pales when the animal falls in social rank. Histology and electron microscopy showed dopa-positive melanocytes in the dermis each packed with fully melanised melanosomes. By transmitted light the scrotal skin was brown on a red background: by reflected light the colour was blue. Thus the blue colour is due to Tyndall scattering over a layer of melanin. Variation of scrotal colour was not due to changes in melanocyte number or dispersion of melanosomes. Pallor was induced by injecting fluid, and blueness could be restored by removing fluid. It is concluded that the blue-to-white colour variation is modulated by the degree of dermal hydration.

I did not know that. A brown-black pigment deep in the skin gives a blue appearance due to light scattering in more superficial skin. How interesting. It's amazing the color variations that you can get from a single pigment molecule, when you throw in various scattering and iridescence effects from tissue structure.

I would never have gotten close enough to find out otherwise.

Oh, give me that disapproving look, will you? Well, would you dissect monkey scrotums?

UPDATE (6/17/2007): A reader e-mails with some updated references on blue skin coloration in mammals, letting me know that it is no longer considered to be Tyndall scattering, but instead color enhancement through phase coherence. Here's a news article from a couple of years ago that describes the research by Richard Prum:

But there is another way to create structural color, and writing in the June 15 issue of the Journal of Experimental Biology, Prum and University of Kansas mathematician Rodolfo Torres showed that the blue in mammal skin comes from "coherent scattering." The best-known examples of this process are the iridescent colors of opals, oil slicks, and soap bubbles. When light hits a layer of a certain material, some of it is immediately reflected by the outermost surface. Another portion of the light enters the material and is reflected back when it hits the bottom surface. If a particular wavelength emerges in phase with its partner in reflection, that color is enhanced; emerging out of phase results in wavelengths cancelling each other out -- and no color.

In skin, the structures that govern this phase shift are collagen fibers about four millionths of an inch in diameter. Because there's no iridescence -- the color doesn't change with the viewing angle -- and because earlier research had suggested that these fibers were arrayed in random fashion, like the molecules in air, the blue-sky explanation seemed reasonable. But using an electron microscope and a kind of mathematics called the Fourier transform, Prum and Torres showed that the collagen in mandrill and marsupial skin actually possessed what Prum dubbed "quasi-order." The fibers aren't packed together in as orderly a fashion as the molecules in a crystal, but they are orderly enough to bring the short wavelengths into phase with each other and create a brilliant blue.

That's even cooler than the light scattering story, I would say.

Now, what have we learned? Two things. First, coherent light reflection can be accomplished by biological structures in a direction-independent way.

Second, monkey scrotum researchers really defend their turf! Or at least, skin pigmentation researchers....

References:

Price JS, Burton JL, Shuster S, Wolff K. 1976. Control of scrotal colour in the vervet monkey. J Med Primatol 5:296-304. PubMed

I think I'll make this a new feature, since all kinds of interesting things pop up in my Google Scholar searches. Here's one:

Urine makes the difference : chemical communication in fighting crayfish made visible

Thomas Breithaupt and Petra Eger

In this study, they were interested in chemical communication between crayfish who were fighting with each other. So they blindfolded the crayfish, and then used fluorescent dye to see the urine. Evidently, they fan the urine toward each other using their gills or maxillipeds.

Here's part of the abstract:

Aggressive behaviour is effective in intimidating blindfolded opponents only in conjunction with urine release: receivers decrease offensive behaviour and increase defensive behaviour. Aggressive behaviour alone does not intimidate opponents. The loser of a recent fight is deterred equally well by a familiar and an unfamiliar opponent. Hence, in crayfish, individual recognition of the urine scent of a dominant individual does not appear to be significant for the maintenance of dominance hierarchies. Our results suggest that urine contains information about the fighting ability and/or aggressiveness of the signaller. The chemical signals thus far unidentified appear to be important in determining the outcome of a fight.

Smells like...victory!

References:

Breithaupt T, Eger P. 2002. Urine makes the difference : chemical communication in fighting crayfish made visible. J Exper Biol 205:1221-1231. Abstract