The plot to the left shows the distribution of heights of American women, ages 20 to 29, according to the 2007/2008 census. Data here. I couldn’t find data on UK heights, but it should be similar. Data for the heights of men are similar but shifted up a bit. The circles are the data and the line is fit of a Gaussian function to this data. The most probable heights are around 165 to 170 cm (5 ft 4 in to 5 ft 6 in). The width (standard deviation) of the Gaussian fit is 7 cm.
All organisms, from us to bacteria, need to adapt to survive. As I start to write this post, I have just had lunch and so I guess my blood sugar is probably peaking nicely. Some of this sugar will need to stored for later consumption, and doing this will involve flipping switches in my biochemistry to go from my pre-lunch state of burning food reserves to storing excess calories from my lunch.
In a post on Surrey’s blog I boasted that I was twice as good as a hamster, according to one common metric for measuring the achievements of an academic scientist. However, I am sadly not superior to all furry mammals, a cat beats me, by that same metric. I average out at about 28 citations per paper I have published. F.D.C Willard*, who was a cat, averages out at 34.
This Friday I am teaching an introductory lecture on genetic switches, so I had a look around on the web for topical examples. My favourite is recent work by Guenther, Kingsley and others in Stanford on work on the genetics of blond hair. Of course we know what blond hair must be determined by our genes, blond parents tend to have blond children. But we are still working out what are the genes involved. Amongst our twenty-odd thousand genes is KITLG, which like a a lot of our genes is involved in a lot of different things, including how our bodies make blood, and whether we have blond hair.
In the biological physics course I am teaching, I talked a lot about the fact that on lengths greater than around a tenth of millimetre, diffusion of molecules is too slow to supply the needs of living organisms. To get round this they had to evolve pumps, propellers and cargo transport infrastructures. The time to diffuse a distances increases as the square of the distance travelled and so diffusion is slow on all lengths large enough to be visible to the human eye.
This shows a flock, also called a murmuration, of starlings at sunset. The hundreds or thousands of starlings are moving almost as if they are a single body, and mostly there is a pretty clear edge to the flock. It is pretty obvious where the flock ends and the rest of the sky begins. As the flock is a three-dimensional object, this should mean that the flock has a well defined surface, which separates the volume of sky occupied by the starling flock, from the surrounding sky where there are no starlings.
I don’t think I am particularly good at reading social situations, but I get by. But I would guess that I am better at reading social situations than a dead salmon. A few years ago, Bennett and coworkers used the latest hi-tech method to study brain activity, functional magnetic resonance imaging (fMRI), to study the brain of dead salmon. While they were using the brain imaging technique on the brain of the deceased salmon, they showed it pictures of groups of people in different social situations.
In The Wizard of Oz, the Tin Man is seeking a heart. Lacking a heart is taken to mean that you cannot love. This is poor science of course, our emotions are felt by our brain, and our heart is a pump. Without a heart, our blood would not be pumped around our body, our tissues would be starved of oxygen and food, and we would rapidly die.
In Friday’s lecture on biological physics I covered why we and all animals bigger than roughly a few millimetres need hearts, why we need pumps to pump fluid round our bodies. The reason is some simple physics: We need pumps as without the flow pumps produce, molecules such as oxygen would only diffuse around our bodies. I am about 1.85 m tall. Diffusion is agonisingly slow over distances like that. Oxygen takes decades to diffuse over a metre. This is far far too slow to support life. Hence the need for a pump.
This week I have mostly been doing 11 contact hours of teaching plus prep for that, and a little reading of James Le Fanu’s interesting if a bit depressing book The Rise and Fall of Modern Medicine. The 11 contact hours included six on Friday in which rather ridiculously I introduced the beautiful symmetry of the cowpea mosaic virus to two entirely different audiences on the same day — one at 11:00 am and the other at 2:00 pm. I was doing my best at 2pm but it was a long week, so I had probably had a bit more enthusiasm in the morning.
Over the last two days, six physicists have won Nobel Prizes, but just like last year, and the year before, etc, I missed out. Ah well, it could have been worse, at least actual biologists won the Nobel in Physiology or Medicine. Yesterday, three physicists changed the light bulb, forever, and were awarded the Nobel Prize in Physics. Today, three physicists saw smaller things than they should have been able to, and picked up the Nobel Prize in Chemistry. They won it for developing techniques for imaging with light, objects that are smaller than the wavelength of the light. The effect is illustrated in the figure up top of this post, on the left is a living cell imaged using a conventional microscopy — details are blurred by the size of light photons we are using to image the cell. On the right is the cell imaged using one of the techniques that got the prize. There you can see individual spots in the image, these spots are the locations of individual protein molecules .