A silver fox. Image by Zefram via Wikimedia Commons.
Evan Ratliff has an excellent article that ties well into our discussions of evolution. It’s on the breeding of foxes to make them want human companionship, much the same way wolves were domesticated.
… researchers … gathered up 130 foxes from fur farms. They then began breeding them with the goal of re-creating the evolution of wolves into dogs, a transformation that began more than 15,000 years ago.
Wild boar (top) versus a domesticated pig (bottom). Note the floppier ears, a trait common to domesticated animals. Figure from Darwin (1968).
It worked remarkably well, and not just with foxes, but with rats and mink as well.
The scientist in charge, Dmitry Belyaev, was looking into something that Darwin observed in 1868: domesticated animals are smaller, with floppier ears and curlier tails, than their untamed ancestors.
In terms that we’ve studied, domesticated animals all have similar physical characteristics (phenotype) and Belyaev wanted to find the genotype. His theory is that there is:
… a collection of genes that conferred a propensity to tameness—a genotype that the foxes perhaps shared with any species that could be domesticated.
Well, it’s really kilobucks and economic systems, but that does not have the same rhythm for a title. We’re reprising the market versus socialist economies simulation game, my student came up with last year for his IRP.
I though I’d also include a little lesson on the metric system as a subtext. Hence the creation of the kilobuck. I’ll also talk about the centidollar, decidollar, decadollar and hectadollar.
One kilobuck, the official currency of the market versus socialist economy simulation game.
NPR reports on the discovery of a 11,500 year old house in Alaska that probably belonged to some of the first people to migrate to the Americas over the Bearing Land Bridge during the last Ice Age. Just 500 years later the Land Bridge was submerged by rising sea levels.
It’s a good article to go to for our discussion of human migration patterns. It also has the added poignancy of the fact that, at the end, the home was turned into a burial crypt for a young member of the family.
Color 'fingerprints', with four color standards labeled Y (yellow), R (red), G (green), and B (blue).Gene sequences extracted from sediment in Buzzards Bay, MA, and separated using gel electrophoresis (Image from Ford et al., 1998)
One of the more basic techniques in the microbiologist’s toolkit is gel electrophoresis. It’s used to separate long molecules, like proteins, RNA and DNA from one another. Different organisms have different DNA sequences, so electrophoresis can be used to identify organisms and for DNA fingerprinting. Chromatography is also used to separate different molecules, usually pigments. Therefore, using some filter paper, food coloring, and popsicle sticks I created a nice little chromatographic fingerprinting lab exercise using chromatography as an analogue for electrophoresis.
Food colors and test tubes.
Using a standard set of four food colors (red, blue, green and yellow), I grabbed each students individually and had them add three drops of the colors of their choice to a test tube with 1 ml of water in it. One students went with three straight blue drops, but most picked some mixture of colors. I kept track of the color combinations they used, and labeled their test tube with a unique, random number.
When they’d all created their own “color fingerprint” in the test tubes, I handed them back out randomly, and gave them the key of names and color combinations (but no numbers). They had to find out whose test tube they had.
Diffusion of a drop of dye mixture through filter paper. At least three different colors are visible. The colors at the outer edge are the most difficult to distinguish.
I was kind enough to give them a few little demonstrations of chromatography I’d been experimenting with over the last day or so. The easiest technique is simply to place a couple drops of the sample on a filter paper (we used coffee filters “requisitioned” from the teachers lounge), and chase it with a couple drops of water to help the dye spread out. This method works, but since the sample spreads out in a circle, the inverse square law means that the separation of colors can be hard to see.
While the drop method worked well for most students, one who was a bit more analytically-minded, interested in the project, and had a particularly difficult sample, tried doing it using a filter paper column. Since I wanted to show them the proper way of conducting experiments, particularly about the importance of using standards, and I wanted to check if they were able to interpret their results correctly, I also did the full set of samples myself as columns. The standards are essential, because the green food color is actually a mixture of green and blue dyes.
Our color chromatography setup is as you see at the top of this post. We used popsicle sticks to keep the filter paper strips away from the glass surface.
Experiment with filter paper taped to the glass.
The experiments worked well, and for best results, let the it dry because the colors show up better. One focus with my students was on note-taking and recording results; after a few iterations that worked out well too. Another nice aspect of using the series of columns is that it looks a lot like the electrophoresis bands.
I did try some other variants of the chromatography: top down, bottom up and even taped down. The last version, where I taped the filter paper to the glass to create a restricted column, worked very well.
Variants of the experimental setup are shown in the three columns from left: taped down where the filter paper is taped to the glass; bottom up, where movement of the water and die is driven by capillary action; and top down, where the sample droplet is placed at the top of the column.
NYU scientists have traced the evolution of tomcod fish that’s been driven by pollution in the Hudson River. The NPR article is nice because it really breaks down how fish with the right genes preferentially survived the PCBs and dioxins in the river, and passed their genes on.
It also turns out that the fish “selected” for pollution tolerance end up being more sensitive to other things, like high water temperatures. It really puts, “survival of the fittest” in context. The fish are “fit” for polluted rivers, but not “fit” for warmer water.
You should be able to see three heartbeats on the bottom line (labled Z), though the Z obscures part of one of the waves.
We were working on plate tectonics last week, and the conversation went from earthquakes to heartbeats.
I think it started with the question of, “How do we know what the inside of the Earth is like if no one’s been down to see it?”
I agreed that we’ve not even been down to the bottom of the crust because the heat and pressure would collapse any hole we tried to drill. I did not mention that terrible movie, “The Core”, because beyond maybe the first ten minutes where there is some actual speculative science fiction, it’s really not worth seeing.
But beneath the crust, how do we know how thick the mantle is? How do we know that the inner core is solid metal (mostly iron) while the outer core is liquid metal?
Not wanting to go into too much detail I tried to explain about seismic waves. Different types can go through different materials and if you monitor their reflections off different parts of the Earth’s interior you can puzzle out the layering and composition. I just gave the simplest demonstration: if you tap a piece of wood with you knuckle, could you tell that it was wood and not metal? What if you tapped a bucket, could you tell if it was full of water or not? Well seismic tomography work in much the same way, except that you’re usually picking up the reverberations from the earthquake rather than making it yourself by hitting the bucket. There’s also a bit more math involved.
But tapping the bucket gives a quick easy feel (pun intended) for the process. My students at least seemed satisfied.
So then I pointed out that you could use an app called iSeismo, to detect seismic waves. Both the iPhone (and its variants) and the iPad have accelerometers that can be used to pick up motion in all three dimensions. My students from last year remembered it, and at least one already had it loaded on his phone.
A quick test showed that the phone’s pretty sensitive. You can pick up two people jumping together all the way across the room. This part of the demo is nice because it helps prove that seismic waves from earthquakes can go very far. You can also see the little squiggles as the waves are picked up.
I did not try it this time, and I’ll need to confirm if it will work, but since the time on the phones should be well synchronized over the network, and iSeismo can output the actual data, we should be able to use three iPhones to triangulate the location of the jumpers. This might work in nicely with geometry now that I think about it.
Checking for a heartbeat using iSeismo.
Anyway, finally, a student asked if the phone might be able to pick up his heartbeat if he lay on his back.
We tried it. Lying on his back on the floor while holding his breath, we could see his heartbeat quite clearly.
NPR’s Brian Reed has an excellent two-part series on the small island nation of Kiribati‘s preparations to adapt to global warming.
Kiribati. (Map from the U.S. Congress via Wikimedia Commons).
Small island nations are the most sensitive to the effects of global warming. Rising sea levels will substantially affect places where the land is just a few meters above sea level. But small islands also have limited capacity to adapt to significant changes.
These articles tie in to our questions of modern migration, which we discussed last cycle (C3) and environmental change.
[googleMap name=”Tarawa Island, Kiribati” description=”Tarawa is the capital of the Kiribati Islands” width=”480″ height=”480″ mapzoom=”10″ mousewheel=”false” directions_to=”false”]Tarawa Island, Kiribati[/googleMap]
