Figure 1 from Grice and Segre (2011), showing the distribution of viruses, bacteria, fungi and mites on our skin and where glands and hair follicles originate.
Our skin is an amazing organ – it keeps our guts in and intruders out. We have an average of 1.8 m2 and this area contains many distinct regions that vary in pH, temperature, moisture, exposure, etc. Your forearm is dry, your cheeks are oily and your elbow crease is considered “moist”. Hair follicles, pores, glands, nails – if we think of our bodies as planets, there are a lot of different habitats. And it turns out our habitats are home to many, many things.
Oh et al. (2014) analyzed 263 samples from 15 human beings at 18 habitats (anatomical skin sites). They were interested in the biogeography of skin – and how it varies between people and across habitats. Do all forearms look alike? Do all “dry” habitats have similar function? It was already known that there are large scale microbial diversity patterns in the skin microbiome. For example, oily sites contain relatively low taxonomic diversity, perhaps because these sites are most selective when it comes to who is able to live there. At the other end of the diversity spectrum are dry sites, which tend to have high diversity.
This week the LA Review of Books has my review of Unnatural Selection, a nifty new book in which ecological toxicologist Emily Monosson describes how living things evolve their way around the things we humans do to try and contain them.
… the introduction of the insecticide DDT rapidly led to the evolution of resistant mosquitoes, houseflies, and, yes, bedbugs. Decades of farming with the herbicide glyphosate, better known under the brand name Roundup, have led to the evolution of resistance in dozens of weed species. One after another, Monosson ticks off cases, dividing them into chapters corresponding roughly to biological classification. She goes beyond these headline examples to describe lesser-known triumphs of “resistance evolution,” such as viruses evading human immune responses and inadequate vaccination, cancer cells overcoming chemotherapy, and fish that survive water polluted by biochemical toxins.
This hits some of the same themes as that recent review about using evolutionary biology to solve major problems in the coming century, though I might have liked it if Unnatural Selection spent a bit more time discussing the cases when life doesn’t find a way—the myriad reasons we’re in the middle of the sixth mass extinction in the history of the planet. But I highly recommend the book for the folks in your life who may not realize how personal evolutionary biology can be.
Looks like this guy:
Is the cartoon version of this guy:
It walks. It breathes air. And apparently it can adapt to terrestrial life relatively “easily”.
The scientists raised groups of bichir on land for eight months to find out how they would differ from bichir raised in the water. They found that the land-raised fish lifted their heads higher, held their fins closer to their bodies, took faster steps, undulated their tails less frequently and had fins that slipped less often than bichir raised in water. The land-raised fish also underwent changes in their skeletons and musculature that probably paved the way for their changes in behavior. All in all, these alterations helped bichir move more effectively on land.
There’s a video too!
Currently there is a catastrophic outbreak of Ebola happening in West Africa. Over 1700 infections have been recorded with nearly 1000 deaths, making it the deadliest outbreak of ebola known. Infection results in a hemorrhagic fever, which starts out a bit like the influenza, but can result in bleeding from mucous membranes, organ failure, and ultimately death. But what is Ebola?
Ebola is a Filovirus. Filoviruses are a small group of viruses only known to infect mammals. They are so named because of their filamentous shape. They have tiny genomes, only ~19,000 base pairs in length, containing only seven protein coding genes and two regulatory regions. By contrast, the human genome is over 3 billion base pairs, contains around twenty thousand genes and has innumerable (by which I mean as yet unnumbered regulatory regions). Because of ebola’s simplicity, (as with all viruses), it cannot reproduce without commandeering the cellular machinery of its hosts. In the words of Cormac McCarthy, These anonymous creatures… may seem little or nothing in the world. Yet the smallest crumb can devour us.
Basically every place on our bodies is loaded with bacteria. All of these communities are important (I’ve written about some of the ways before) and more and more research seems to be finding that our microbes play an active role in fighting (or causing) disease.
So maybe it’s obvious that microbes in our swimsuit areas could be involved in sexually transmitted disease. OK, maybe not “obvious” but it may be the case with HIV and the penis microbiota. Did you know that circumcision reduces the rate of HIV transmission to men by 50 – 60%? That’s a pretty significant reduction (no pun intended). There are two major (and non-mutually exclusive) hypotheses as to how circumcision accomplishes this – morphological and bacterial. [SIDENOTE: if you are unfamiliar with the technical aspects of circumcision, I suggest Wikipedia – which has a lot of information but contains an image or two that may not be safe for work – or this Mayo Clinic site.]
** Hey y’all – it has come to my attention that the article this post is criticizing might have been more of a tongue-in-cheek textual criticism than a literal hypothesis (like I treated it). Instead of it being “this is what we think is true” opinion, I think it’s more of a “this interpretation of the Bible is more justified by the natural world”. Read at your own risk and sorry for my confusion. – S.Hird **
During his Society of Systematic Biologists presidential address at this year’s Evolution meeting, Jack Sullivan mentioned a rather…unusual…article. (Well, letter, technically.) Congenital Human Baculum Deficiency, by Scott Gilbert and Ziony Zevit was published in the American Journal of Medical Genetics in 2001; it describes their hypothesis that Genesis 2:21-23 doesn’t mean Eve came from one of Adam’s ribs, she came from his baculum.
Walruses have bacula almost 2 feet long – it is required that a picture of a walrus accompany any discussion of bacula.
What’s that, you say? Baculum is the technical term for the penis bone. Many mammals have one – presumably to aid in sexual intercourse. For mammals that mate infrequently, prolonged intercourse ups the chances that a particular male sires some babies. For mammals that must mate quickly, the baculum provides immediate rigidity. And for all mammals, keeping the urethra straight while copulating is imperative, so maybe it’s there to prevent a kink in the works, so to speak. The truth is, there are a lot of hypotheses about what bacula do but – as you might imagine – they’re kind of difficult to test. Regardless, our nearest evolutionary neighbors, the great apes, all have bacula, as do most other primates. Gilbert and Zevit cite this– the fact that our baculum is missing – as evidence for their argument. Which goes like this:
- A rib seems like an unlikely origin for Eve because male and female humans have the same number of ribs.
- Ribs also lack “intrinsic generative capacity”, which penises have “in practice, in mythology, and in the popular imagination”.
- Most mammals – and especially primates – have bacula, humans do not.
- It is therefore “probable” that Adam’s baculum was removed to make Eve, and not a rib.
The authors then continue to support their argument with alternate translations of the Hebrew word for “rib” (which they say could mean “support beam”) and claim the raphe of the human male scrotum is what Genesis 2:21 is referring to when it says “The Lord God closed up the flesh.”** I’m almost convinced!