New Rule for Science Journalism...

Agreed!



[Hat tip to PZ Myers]

Happy Turkey Day!

There's a Turkey in my fridge waiting to be cooked, but I couldn't resist writing a quick post full of links on today's official bird. Enjoy!

On this blog

• Mid-week Reptilian #8: Wild Turkey
• A Dinosaur on the Christmas Table

External Links

• From Dinosaur to Turkey  | NatGeo (Jump to Video, Facts)
• Your Holiday Dinosaur | Berkeley's UC Museum of Paleontology
• Turkey Day Science: What Do Gobblers Gobble? | USGS Western Ecological Research Center Blog
• This Thanksgiving, Make a Wish on a Dinosaur | Smithosonian Blog

 

Sex, Life, Death and the Scientific Method

Why do women live longer than men? That question caught my eye when it popped up in my twitter feed, so I followed the link over to a podcast on the Scientific American website.  Before I could even listen to the podcast I noticed that someone posted the following in the comments section:

"I have a possible explanation of why women live longer than men. Men have an XY sex chromosome while women have an XX sex chromosome. This results in both the greater potential for genetic (chromosomal) variation in men that successfully adapts to the environment (and passes the same to succeeding generations) and genetic mutation which results in both chromosomal deleterious deterioration and maladaptation that results in early cell and male human death (and which, therefore, is less likely to pass the deleterious chromosomal variation to succeeding generations). Thus, men, in general, live shorter lives than women because their environmental success has a significantly more profound influence on how appropriate their genetic make up is to adapting to the same. At the same time, men's genetic make up (XY vs XY) is much more susceptible to deleterious genetic aberrations and maladaptations. Of course, the aforementioned is simply theory."

Viewed through the lens of science, this suggestion makes a great hypothesis, so I thought I'd mention it here (total avoidance behavior, by the way - I've got a thesis to write!!). So why is it a good hypothesis? Because a good hypothesis is (among other things) one that suggests practical ways to challenge it's own validity. Using claims that logically follow from the original hypothesis, we can test those claims with experimental or observational data. In this case, our hypothesis is:

XY individuals lead shorter lives (on average) than do XX individuals because (on average) mutations in either the X or Y chromosome have the potential to result in greater phenotypic change.

So what statements or predictions follow from this claim that we can test empirically? How can we try and falsify this idea? In this case, we need to look beyond humans for the answer to that questions...

Now, before we get all myopic and try and pretend all gender differences in all species boil down to this single hypothesis, we should be mindful of the myriad other differences between males and females that contribute to longevity.  For example, in humans...

But hey, nothing in science would ever get done if we didn't take things one step at a time, so lets take a closer look at the hypothesis at hand.

I just so happens that here are other mechanisms of sex determination than the XX/XY system found in humans and other mammals. Many reptiles and birds, for example, have a ZW/ZZ system where unlike the mammalian system, ZZ=male and ZW=female. So putting this fact together with our summary statement above, we've come up with a quick prediction: that in birds and reptiles with ZW/ZZ sex determination, the females should be the shorter-lived sex.

So what's the story in birds?  A quick web search (sorry - I need to get back to work!) revealed that people have actually considered this hypothesis before and done some of the leg work for us already.  For example, in Austad 2006 (reference below) the author writes:

Another way to investigate the hypothesis that the sex possessing the heterogametic chromosomes is going to be longer-lived is to consider birds, because the sex-chromosome situation is reversed compared with mammals. In birds, it is the female that has 1 short and I long sex chromosome, and therefore does not have the backup of the 2 long sex chromosomes (the Z chromosomes) that the male has. The prediction is that if heterogametic sex is a key factor, then male birds should be longer-lived. In fact, in 3 species of birds,  including budgerigars, zebra finches, and Japanese quail, males outlive females, at least in captivity. For every bird species that I have been able to find in which there is good captive data, males outlive the females. Certainly, this is provocative evidence that would seem to favor the heterogametic sex hypothesis. It is of concern, however, that in some avian species, the female has been reported to outlive the male, but all of these reports were from field studies and are thus difficult to interpret for the reasons discussed previously.

I like the heterogametic sex hypothesis because it is biologically interesting. Unfortunately, that does not mean it is true.  There are some problems with this hypothesis that can be illustrated with Brandt's bat, a small bat that weighs about 7 grams and is a third to a quarter the size of a mouse... [author cites a study that found males appeared to be longer lived.]  We just don't know the answers to these questions because we do not know what the underlying physiology is and whether behavioral differences or physiological differences are responsible for this remarkable observation in a Siberian cave.

We are also aware of some mammals in which the males are significantly longer-lived than the females; we have very good captive data for 2 of these species, the guinea pig and the golden hamster. In both species, the males live substantially longer than the females, thereby contradicting the heterogametic sex and estrogenic hypotheses. Again, this is a problem in a general biological sense; it may very well be that one of these hypotheses is absolutely valid for humans but is just not generalizable to the rest of mammals. I would like a general explanation, and that is something we currently do not have.

So strictly speaking, this hypothesis is toast. Plenty of evidence to the contrary is floating around out there, so we can rule it out as an accurate summary of reality. But does that mean we just throw it out? Heck no!  Instead of viewing hypotheses as a black and white question of "true vs. false," we instead seek to refine the statement (if possible) and make a new hypothesis consistent with this new information.

For example, we may include the caveat that other processes might matter more in some species than accumulated deleterious effects, thus restricting the kinds of organisms we can apply our hypothesis to.  Also, better experimental investigations could better challenge the core idea behind our hypothesis: genetic changes in the sex chromosomes and their resulting phenotypic changes.  As you can see, all this hypothesizing and testing can snowball into an entire career of work fairly quickly.

As much as I'd love to continue probing the world of longevity and gender genetics, I'm afraid I've got work to do (thesis work!). If I've piqued your interest and you turn up any other interesting studies on the subject, feel free to share in the comments below.

References

• Austad, Steven N. 2006 "Why women live longer than men: Sex differences in longevity." Gender Medicine 3(2). doi:10.1016/S1550-8579(06)80198-1

U.S. Math & Science Students Need Our Help

The U.S. ranks very low in math and science compared to other nations -- 35th in Math and 29th in Science. That's embarrassingly low, a threat to the future of our nation's economy, and most importantly it's a problem we can solve. So why are we so far behind?

While digging through TIMMS results can be thought provoking, you must, must, must watch this video which provides a sobering comparison between US student attitudes towards math and science with those of their counterparts from some of the top ranked countries. So click here if you can spare 3 minutes -- it's worth it! The video was produced as part of the Connect A Million Minds (CAMM) campaign, "Time Warner Cable’s philanthropic commitment to connect youth to ideas, people and opportunities that will inspire them to become the problem solvers of tomorrow."

You can see more CAMM videos here.  For more information, look here, here, here and here.

[Hat tip to DNLee]

Do Reptiles Hibernate or Brumate?

Nearly everyone knows what hibernation means, but when speaking of reptiles the term brumation seems to reign supreme.  Why? Is one term more correct than the other?  To try make sense of these competing terms, I recently did some digging into the history of the word brumation which brought me to the following conclusions:

1. The term brumation is (mostly) unnecessary jargon.
2. Both hibernation and brumation should be acceptable terms to use in most (if not all) situations, however hibernation is the better term to use in a public forum.

As for why I've arrived at these conclusions, we need to look back a few decades to see where this word "brumation" came from, what we knew about hibernation way back then, and what we've learned about since.

Fascism, Communism and Socialism and Other Awesome Signs

There are some great signs from the Rally to Restore Sanity up on HuffPo. Here are a few of the 800+ of them available for your browsing pleasure.

If you aren't already in that club...

Fascism a political philosophy or movement "that exalts nation and often race above the individual and that stands for a centralized autocratic government headed by a dictatorial leader, severe economic and social regimentation, and forcible suppression of opposition."

Communism is a social structure advocating elimination of private property.

Socialism includes any of "various economic and political theories advocating collective or governmental ownership and administration of the means of production and distribution of goods."

Moving on...

and the oh-so-appropriate...

Consider Humanism

The American Humanist Association has launched a huge ad campaign today, which "will include a spot on NBC Dateline on Friday, November 12, as well as other television ads." Fund raising for the campaign is ongoing, and is up to $200K as of today.

The Stiefel Freethought Foundation was the primary sponsor of the Consider Humanism campaign with a $150,000 donation. Another $50,000 was raised from supporters of the American Humanist Association for the launch of this campaign, bringing the total ad buy to $200,000 so far.

You can read more in the press release, watch the AHA's videos on vimeo, by visiting http://www.considerhumanism.org and by clicking the images below for higher resolution PDFs.

Using Reptiles For Public Education, Outreach

Melissa Kaplan has a great website regarding reptiles in captivity, and included among her writing is some great advice for using animals in public outreach and education. Though geared towards reptiles, the comments I think apply broadly -- check it out!

The Power of Data Visualization & Comparison

David McCandless: The beauty of data visualization (TED Talk)

Computational statistics and computer programming abilities are -- and will continue to be -- valuable skills in the job market (and in the sciences).  If I could offer any career advice to students, it is to work hard to learn these two things well!

Why Not Vote Republican?

While some of those claims need fact checking, there are excellent lines in there! Feel free to quote any favorites in the comments below.