Razib Kahn has a fascinating interview with Milford Wolpoff, one of the main scientists behind the research that argues that humans are not all part of a single family tree, descended from a single ancestor who moved out of Africa about 200,000 years ago.
This section focuses on the theory, and has a nice explanation of what mitochondrial DNA is (and why it’s important):
It gives an excellent perspective on how science works, and how scientists work (scientists are people too with all the problems that entails).
The entire thing is a bit dense, but it’s one of the better discussions I’ve seen describing the process of science in action, with little hints at all the challenges that arise from personality conflicts and competing theories.
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.
Giles Tran’s amazing rendering of glasses on the counter inspired me to check through my own POV-Ray generated library. Nothing nearly as good, but some of it is still might be useful.
Demonstrating the axial tilt of the Earth, this image shows the Earth at the northern hemisphere's summer solstice.Rotating Earth at the northern hemisphere's winter solstice.
You build 3d models in POV-Ray and then export 2d images from whichever point of view you want, so once you have the model set up you can easily change the perspective or even move objects to create animations.
POV-Ray does not have any useful sort of user interface; you’re usually creating your models with computer code. It can therefore be challenging to use, and, as with any 3d programming language, a bit of geometry, trigonometry and algebra are needed.
However, the final results can be impressive. I’m continually amazed each year by the quality of the work added to their Hall of Fame.
For much easier, quicker and not so sophisticated 3d results, I use VPython, which is also a great way to learn programming that outputs 3d images.
“On average we found that each of us carries two or three mutations that could cause one of these severe childhood diseases.”
–Stephen Kingsmore, physician, Children’s Mercy Hospital in Greenfieldboyce (2010), New Genetic Test Screens Would-Be Parents.
NPR’s All Things Considered had two related articles on last night that deal with the specific topics we’re covering this week: genetic disease and recessive alleles.
The first one is about the latest in genetic screening technology, for determining if potential parents have recessive alleles that could combine to produce children with genetic diseases. Recent research has made this much easier.
The second touches on the ethical consequences of genetic screening. It could lead to an increase in abortion rates and leads us along the slippery slope of eugenics.
What if we engineered for intelligence?
This second story would make an interesting basis for a Socratic dialogue. As would, I think, the movie Gattica, which deals with the consequences of genetic screening and genetic customizations. I see it’s PG-13 so we may be able to screen it. Similarly, I may recommend Brian Stableford’s War Games to my eight graders who might like a military science fiction book that deals with genetic optimization. Alternatively, Nancy Kress’ Beggars in Spain might offer another interesting perspective on this issue.
Wired has a brief but excellent article on the voyage of the Beagle.
Its goal was to survey the South American coastline. The captain invited along a young man named Charles Darwin, whose father thought the voyage would just be another excuse for him to slack off. The trip ended up taking five years.
This article would be a wonderful addition to our work on exploration of the Americas next time it comes around; however, it’ll also be a neat little footnote because we’ll be delving into evolution next cycle.
Wikipedia’s entry on the ship produced this wonderful cross-section. I particularly like the sketches of people and casks showing the use of of different cabins and spaces.
In the binomial classification, modern humans are Homo sapiens (Genus and species). But you’ll frequently see us described as Homo sapiens sapiens, indicating that we’re a subspecies of Homo sapiens. One of the reasons for this is the still unresolved question of the neanderthals.
Some recent research suggests that 1-4% of our genes came from neanderthals. If true, this would mean that humans interbred, successfully, with neanderthals. Since one of the key parts of the definition of a species is that its members can produce fertile offspring, neanderthals would then be a subspecies of human. Thus we would be Homo sapiens sapiens and neanderthals would be Homo sapiens neanderthalensis, as opposed to being Homo neanderthalensis, a separate species in the same genus.
Skull differences between sapiens and neanderthalensis. Image by hairymuseummatt.
Perhaps even more interesting, the same researchers who did the gene work on neanderthal bones also sequenced some bones from Siberia, and found what may well be another subspecies of humans (the original article is at Krause et al., 2010). The genes are different from what’s been found before, but are in an area, and from a time period, shared both by modern humans and neanderthals. And, modern Melanesians (from the islands north and east of Australia) may share some of the genes of the new group. So this could even be another sapiens subspecies.
There are a number of caveats to this research, which is based primarily on gene sequencing and statistics. One key assumption that I’ve always been skeptical about is that DNA mutates at a fixed rate. However, this type of science ties very closely in to our discussions of evolution and themes of what it means to be human.
There are two great novels that address these two things, but I’ll only be using one of them. The one I’ll use is The Chrysalids by John Wyndham, which I’ve mentioned before (here and here). The other is War Games by Brian Stableford (aka Optiman). While the Chrysalids deals with accelerated mutation resulting from nuclear fallout, War Games considers the effects and moral implications of intentional genetic optimization (hence the other title for the book).
Global temperature difference (anomoly) of 2000-2009 compared to 1950-1980.
NASA’s Earth Observatory is not only a great place for pictures from space, it also posts regular scientific updates, including the most recent map of the change in temperature since 1980.
The most obvious observation from the map is that the poles are warming faster than the rest of the planet, especially the North Pole. This is a pattern that has been predicted since at least the 90’s, so the temperature observations tend to show that the scientists and computer modelers who do this research may just know what they’re doing.
Blood Falls, Antarctica. Note the tent in the lower left for scale. From the U.S. Antarctic Program.
It’s also important to note that the Antarctic is not warming nearly as fast as the Arctic. The continental glaciers that would most significantly raise sea level (think 10’s of meters) are in Antarctica.
The northern hemisphere warming will likely be difficult for a number of species to deal with. Polar bears, the charismatic megafauna (I love that term) most associated with the effects of the melting Arctic sea-ice, are still in big trouble. Recent research, however, suggests that if something can be done to reduce global warming in the coming century, there will remain places with enough ice that the species may survive.
Update: Interesting article on global warming science and politics in the NY Times. It starts off talking about David Keeling, the scientist who came up with a reliable way to measure atmospheric carbon dioxide.
It starts with evidence that the mitochondria in our cells were once separate organisms and goes on to explain things like how the change from quadrupedal to bipedal, upright walking resulted in our S-shaped spine (and frequent backaches) and our unsupported intestines. It’s quite the interesting read.
