Archive for January 2011
Welcome to the 6th edition of the Carnal Carnival, a blog carnival founded by Bora Zivkovic and Jason Goldman, dedicated to celebrating the traditionally gross in the animal world. Previous editions have featured poop, vomit, decay and orgasm (which is less gross, but still pretty taboo).
This month of January 2011, the carnival features BODY ODOR!
You know … when you go to the gym and there’s that one guy, shirtless and reeking of garlic, who happens to be on the treadmill next to you and you nearly pass out. Or maybe it’s your best friend and, after months of avoiding having a conversation with her about her overwhelming odor, you just buy her deodorant for her birthday. The smell of B.O. is imprinted upon each of our minds – a stench that sometimes makes us question why we have the ability to smell in the first place.
What is smell and why would we evolve this sense? What we think of as smell – sniffing odors through our noses – is just a form of chemosensing, found in bacteria, ants, dogs, and, yes, humans. We have chemoreceptors in our noses that pick up chemicals in our environment and interpret them. Bacteria use chemosensing to pick up on cues in the environment, molecules of poison or food for example, and can then move towards or away from them. Ants are well known for their pheromone trails which can alert other members of their colony to danger or to a food source.
In a similar vein, humans have retained their sense of smell to identify food and poisons. Because rotten food, such as the “smelly dead” illustrated by Viktor Poor of Stripped Science below, gives off such a rank smell and can also make us sick, we can learn to avoid poisonous food based on smell. But that’s not all this sense does. We like to think that we are far mightier than ants and that we have control over all our decisions based on mind and intellect alone. But just like the ant, we also communicate messages to each other through pheromones given off in our sweat, our body odor, that we interpret without realizing it.
The Smell of Fear
Pounding heart. Sweaty palms. Sudden inability to speak. Enhanced athletic ability. These are all human reactions to fear. When you’re scared or anxious or nervous, you feel them to your core – however, those around you might not be aware that you are so scared, much less why. Thus there is a benefit to be able to communicate this emotion to the people around you, so that they can also be aware, alert, and ready to react.
Since there is not yet evidence of telepathy, sense of smell is the obvious way for individuals to communicate with one another non-verbally.
- Does sweat produced when a person is anxious make others who smell it more likely to take risks? See this post at BPS Research Digest by Christian Jarrett
- Can the smell of sweat produced by subjects in horror (watching horror films) cause others to be more likely to see threats where there aren’t any? See Neurocritic‘s post, “I Know What You Sweated Last Summer”
B. O. is sexy?
I have a friend who doesn’t shower too frequently. Whenever his hair is looking a little greasy and he starts to smell a bit funky, someone will often joke to his girlfriend, “how do you put up with it?” He’ll then stick his armpit in her face and, with triumph, yell, “She loves my smell! She can’t get enough!” Is there any truth to this?
- Can a woman determine whether a man is aroused just by smelling his sweat? See posts at both the Neuroskeptic and Christie Wilcox, at her old site
- Can you identify your partner based on scent alone? And does this ability vary depending on how “in love” she is? See this post at Christie Wilcox’s site at Scienceblogs
- Could there be another explanation for my friend’s cocky behavior? Scicurious of Neurotopia presents an interesting study correlating the attractiveness of a man, rated by women, with his self-evaluation of his own smell
For a great overview on this topic, read Jesse Bering’s post on his Scientific American blog, “Bering in Mind,” Armpit Psychology: The Science of Body Odor Perception.
That’s just rank!
Sometimes there’s nothing else to say but that.
- How do you deal with people who have bad B.O. in public spaces? Christina Pikas writes about B.O. in public libraries
- Morning breath. We all know about this particular breed of B.O. James Byrne of Disease Prone writes about this, and the broader bad-breath diagnosis of halitosis
- People aren’t the only ones who can sense and have to deal with the stink of one another. Read about how elephants can differentiate between different human ethnic groups based on smell alone on Ed Yong’s Not Exactly Rocket Science
To learn more about the evolution of pheromones, I recommend Dr. Kara Hoover’s recent review in the American Journal of Physical Anthropology, “Smell with Inspiration: the evolutionary significance of olfaction.”
Thanks for reading, and I hope you learned a thing or two about the science of human stench.
To end, I’d like to share the greatest human-produced smell of all: The Smell of Teen Spirit
It’s that time of the month.. or rather, it was that time of the month 3 weeks ago, but I’m an idiot.
NOW ACCEPTING SUBMISSIONS FOR THE CARNAL CARNIVAL!
This month’s edition? BODY ODOR!
Submit your posts – recent or old! Dig through your archives and find your best posts that celebrate reeking stench! Even if they are not gross – I would be just as happy to celebrate those lovely pheromones and learn about how they work, when, and why.
It’s a celebration of animal smell!
It was supposed to happen tomorrow – but I will have to delay until MONDAY, JANUARY 24, 2011. Submit your posts! Submit your friends’ posts! Your mother’s posts!
Thank you and I’m looking forward to this carnival of body odor.
Last week, the selections for Open Lab, an annual collection of the best science writing on the web, were announced by this year’s editor, Jason Goldman of The Thoughtful Animal. I’m ecstatic to announce that I somehow squirmed my way onto the list with my post on cormorants overfishing in Estonia. Some of my favorite posts from the list include
- Krystal D’Costa’s essay on smell and memory in the Fulton fish market
- Jason Goldman’s telling of the must-know experiments on dog domestication in Russia
- Delene Beeland on hybridization and speciation
- Lucas Brouwers on the term “living fossil”
- Zen Faulkes on invasive Marmorkrebs crayfish
- and Christie Wilcox on her grandpa’s experience cleaning up oil spills
There are 50 total, so go check them out!
This is a pretty crazy month for me! I have only a week left at my current job, and only 2 weeks left in Philadelphia. I’ve already begun mourning leaving my apartment, my friends, and this wonderful city, trying to appreciate that moving onto new, exciting things always means a bit of loss.
Next month, I’m trying my hand at professional science journalism through a 4-month internship! So, moving to NYC and seeing what it would be like to write about science for a living. I hope I make it out alive…
Tomorrow morning I’m heading down to North Carolina for the Science Online conference! You can check out the program here: a great list of panels and workshops, including one I’m co-moderating. I’m very excited! If you want to keep up with how it’s going down, I’ll try to update my twitter (though I am old-school and don’t have a smartphone … text message tweeting ftw!) or you can follow the #scio11 twitter tag. I will be live-blogging technically, but the blog I’m writing for will not be up till after the conference – but I’ll shoot out that link when it’s up in case you want to hear my delayed in-the-moment ramblings.
“Evolutionary biology has been enriched by considering not only how adaptation happens, but also why it often does not happen,
or at least does not happen as we might naively expect.”
– Douglas Futuyma (2010)
In 2005, a group of scientists from La Trobe University in Australia investigated how species will adapt to global warming by studying a species of rainforest fly, Drosophila birchii (later published in Science). Increased temperatures may lead to drier conditions in rainforests, so the authors wanted to see how quickly this fly could adapt and develop resistance to desiccation.
As in many directed evolution experiments, they took the flies to a lab and exposed them to dry conditions, with most of the flies unable to survive the dryness. The survivors were then bred to one another. Thus generation after generation, only the most desiccation resistant flies would survive, resulting in a population that could survive dry conditions potentially induced by global warming. Right?
Well, that was the idea at least. At first, their population of flies did show a bit of increased resistance. However, in the proceeding 28 generations of selection, there was no increased resistance to desiccation, despite that previous papers had found increased resistance in 3 other Drosophila species. Drosophila birchii was unable to adapt to these conditions. What went wrong?
The assumptions of natural selection
Natural selection itself is based on three assumptions in a population. The first is that there will be variation in traits, such as multiple colors of eyes or hair. The second is that these traits be heritable through the generations, that children will inherit the traits of their parents. The third is that these variable traits have differential fitness, or that some versions of a trait might help you survive better than another. Thus certain trait variants will help its carrier organism survive better, passing that trait to its offspring which will in turn bear this trait.
In order for populations to adapt by natural selection, these three requirements must be fulfilled. When a biologist sees any population, he or she typically assumes that these they are met, and I can’t really blame them. All cellular life we know of on this planet has a hereditary mechanism, the gene, which has differential fitness depending on the variation, thus meeting requirements two and three.
But what about requirement one, genetic variation in a population? It has frequently been assumed to also exist in all populations. In his 2010 review, Douglas Futuyma quotes the famous geneticist Richard Lewontin, who concluded in his 1974 book that “genetic variation relevant to all aspects of the organism’s development and physiology exists in natural populations,” for “[t]here appears to be no character—morphogenetic, behavioral, physiological or cytological—that cannot be selected in Drosophila.”
The idea here is that at any point in a healthy population, there will be many variants of genes in the population, which are replenished infrequently by new mutations. Thus, when selective pressures come around, there is a full stock of variants to differentially survive and lead to new adaptations. This is why small populations and inbreeding are considered such problems: the small gene pool means fewer gene variants and an increased inability to adapt to new conditions.
But why should this have to be true? Is a lab-bred stock of Drosophila really enough to show that there is variation in natural populations, when the lab has a completely different set of selective pressures?
Selection bias in evolutionary studies
When the researchers studying the rainforest Drosophila birchii analyzed the genetic diversity of their collected populations, they found very low variation in the desiccation gene group compared to other genes in the population such as wing size. This lack of variation prevented the flies from adapting to new conditions – though the researchers weren’t sure why. Perhaps these dessication genes had (relatively) recently been under selective pressure, and had not had time to reconstitute the genetic diversity in the population.
Unfortunately, there are very few studies of this kind so it’s hard to draw any conclusions. After all, people studying evolution usually want to study EVOLUTION IN ACTION and not evolution when it doesn’t happen. I suspect that past experiments that have found low genetic diversity have been tossed simply because it seems less interesting evolutionarily – when maybe it is in fact more interesting.
This would be a form of selection bias: the choice of study populations or species unconsciously (or consciously) swayed by the desired outcome of EVOLUTION IN ACTION. In his 1991 Croonian Lecture at the at the Royal Society, Anthony Bradshaw gave a compelling example of this sort of selection bias in evolutionary studies (published here).
In Prescot, Merseyside, a copper refinery opened up next to a meadow that had many species of grasses and wildflowers. Over time, the soil was contaminated by copper, killing off many of the plants. However, after 70 years, there were 5 species that were still able to thrive in these meadows! They had adapted and developed a resistance to copper.
Even now I’m thinking to myself, “oh! cool! How did they adapt that way? How did that mechanism work? How quickly did the resistance gene spread?” etc. But what I’m forgetting is that, while five species did adapt, twenty-one species failed to adapt. If there really was massive diversity at all genes in each population, you would think that at least one would confer some benefit to survive the copper. But this did not happen: twenty-one species went locally extinct.
Just as interesting a question as “How did these 5 adapt?” is “Why did these 21 fail to adapt?” But it’s a question that’s only begun to be reconsidered. Death and extinction are far more powerful forces in shaping the whole of biodiversity on our planet than successful adaptation, but these evolutionary failures that occur all around us are little studied. Especially as we anticipate global climate change causing unknown impacts on species worldwide, we should be studying non-evolution to get a better sense of what natural genetic variation actually looks like and what we may be facing in the future.
Bradshaw, A. (1991). The Croonian Lecture, 1991: Genostasis and the Limits to Evolution Philosophical Transactions of the Royal Society B: Biological Sciences, 333 (1267), 289-305 DOI: 10.1098/rstb.1991.0079
Futuyma, D. (2010). EVOLUTIONARY CONSTRAINT AND ECOLOGICAL CONSEQUENCES Evolution, 64 (7), 1865-1884 DOI: 10.1111/j.1558-5646.2010.00960.x
Hoffmann, A. (2003). Low Potential for Climatic Stress Adaptation in a Rainforest Drosophila Species Science, 301 (5629), 100-102 DOI: 10.1126/science.1084296
As long as we’re considering human nature in terms of how we treat one another this new year, we may as well consider how we treat other species. That is, conservation.
Once you start thinking about Homo sapiens as just another organism competing for resources, traditional views about conservation start to crumble. We’re raised, once again in anthropocentrism, believing that it is our job to take care of the planet. But if we’re competing, who really cares what we destroy along the way? Is it not just part of evolution, of natural selection and survival of the fittest?
I have a lot of thoughts on this matter, but I’d like to point you all to a post by Andrew Thaler of Southern Fried Science. As a biologist studying hydrothermal vents, he often wrestles with the question of, “who cares? Why should we save hydrothermal vents?” In his post, he really gets down to the thick of it, the point that gets to me every time: we evolved behavior to care about the environment.
What makes us truly unique is not our ability to destroy, but our ability to conserve. No other species in the history of the planet has recognized the inherent value in another species, not as a resource, food source, or substrate, but simply as another living organism. No other species has expended its own resources, its own precious energy, to protect another, simply for the sake of the other species existence. No other species has ever planned and implemented an initiative to bring a species back from the brink of extinction. As certain as humanity’s ability to destroy has driven countless species to extinction, it is our unique and, frankly, unnatural desire to preserve and protect species and ecosystems for purely altruistic reasons that defines us.
Read the full post here.