Thursday, March 09, 2006

Re-thinking planets

Michelle Thaller at the CS Monitor has a very nice article about rethinking the rules for formation of planets around stars. Our solar system is organized with rocky planets inside and gas giants outward (plus Pluto and planet X), and I remember being taught that the pressure of solar radiation tears the bulk of gasses off of planets whose orbits fall inside a certain radius. (Another idea I remember is that Jupiter formed at the orbital distance corresponding to the condensation point of water in the primordial dust cloud.) But the Spitzer telescope and other search methods are finding lots of examples of big gas giant-like planets very close to their star, along with planets orbiting brown dwarfs and a fair number of systems which likely resemble ours.

What I love about this is that the science is getting outside of an n=1 (our own system) and really sampling what is available in nature's palette. The next decade or so should be very interesting.

Yeast and ethanol production

The February Trends in Genetics has a nice write-up of the evolution of alcohol production by yeast. Modern fermentation relies on the yeast metabolizing 6-carbon sugars but choosing to halt at the 2-carbon stage (like ethanol) rather than completing the process by going all the way to carbon dioxide. This is a loss of potential energy for the yeast-- even though it's a happy outcome for humans!-- so it's interesting to understand the natural selection events which favored this stopping short behavior.

Ethanol is metabolically a dead-end molecule, but it's a single enzymatic step away from the more central 2-carbon relative, acetaldehyde. The enzyme involved, alcohol dehydrogenase (ADH), can shuttle 2-carbon molecules back and forth between these two configurations, so it could have emerged during evolution either to gather in ethanol as a fuel source, or as a way to make ethanol from acetylaldehyde (think of a deserted railroad track where you're not quite sure which direction the trains run).

Evolutionary analysis suggests that ADH was initially used to make ethanol, suggesting that ethanol itself is useful to the cell. The current theory is that ethanol helps keep competitors away. Ethanol is toxic to other competing microbes, so-- as long as it's not needed for fuel-- the yeast can make enough ethanol to poison the waters for competitors. Later, when sugars run out, it can reel the ethanol back in and use it as a secondary fuel.

There's also a suggestion from molecular clock data that this ability to accumulate ethanol was favored soon after the emergence (50-100 million years ago) of fruiting trees. The six-carbon sugars which are the basis for modern fermentation became widely available then, so several yeasts jumped on the opportunity and evolved new ways of controlling their metabolism to generate this useful by-product.


Kate Wong at Scientific American has a nice writeup of the continuing back-and-forth about the "hobbit" skeletal remains found in Indonesia. The two theories are either that the bones belonged to a Homo Sapiens suffering from secondary microcephaly, or belonged to a previously unknown hominin (for example, possibly a remnant Homo Erectus?). If the second were true, the recent age of the bones suggested that we humans have had close relative species up to nearly the dawn of history. Kate seems to be weighing on the side of "abnormal human" rather than non-human.

Take a look at the comments, too- Kate has a great readership.

Wednesday, March 08, 2006

"Nessie" = "Dumbo?"

The BBC is reporting a new theory of the Loch Ness Monster . With most of the sightings chalked up to too much time at the distillery, the remaining two-bumps-and- a-tube sightings are --wait for it-- circus elephants.
Here's your proof:
Loch ness monster as an elephant

I'm going to have to place this somewhere between Monty Python and Calvin and Hobbes.

Tuesday, March 07, 2006

Friday, March 03, 2006


Norm Bleichman has modest proposal for generating a *really* secure password.

Life outside of kids III: Things fall apart

This is the third post, with maybe one more to come, to look at the "grandmother effect," in which human grandmas who are past their childbearing years can nevertheless contribute to the propagation of their genes indirectly by taking care of grandkids. The first post is here and the second post is here . This post is much more speculative.

What interested me when I first read about the grandmother effect was the possibility that human evolution had taken us (via the disposable soma ) out of the birth-reproduction-death treadmill and instead we as a species (or at least the females among us) were "programmed" for an extended, extragenetic-- probably social and cultural-- contribution to the species. This is probably true anyway, but more specifically, I was looking for some hint that humans would be capable of extreme longevity. I'm interested in long-lived cognitive function, and I have to emphasize that the rest is outside my expertise. With that said, I think the idea of greatly extended lifespans looks unlikely.

Among the killers of humans today are cancer, cardiovascular disease and dementia. These all start as failures of a specific system. One possible way to extend the average lifespan would be to plug holes-- to attack these diseases as they emerge, so that a major disease is delayed or the faulty part replaced, ab infinitum. An enthusiastic proponent of this approach (combined with other strategies) is Dr. Aubrey de Grey who pops up in the major media every now and then talking about lifespans on the order of centuries. De Grey's idea is that a mixture of delaying disease and replacing diseased tissue might allow great extensions. He was recently on the receiving end of a major smackdown for claiming that excessive pessimism on life extension by other gerontologists was costing lives .

So far, so comic. I guess what has me pessimistic about life extension by plugging holes is some very recent evidence that healthy tissue in elderly primates just gets worn out. A study in this week's Science shows that elderly captive baboons living develop sensescent cells in healthy tissues , suggesting that, well, they're getting old all over. Senescent cells were seen in vitro in skin and connective tissue cells, and were measured using three different measures. Moreover, the percentage of senescence went way up in cells from older animals. With a bit of extrapolation, you would guess that baboons of around 30 years of age are going to wear out in multiple places. Illnesses arising from this kind of senescent failure could not be fixed piecewise, and that makes me think that the lifespan of these animals is pretty near maxed out.

UPDATE: Aubrey De Grey is also written up in the Economist from last week.

Thursday, March 02, 2006

Wednesday, March 01, 2006

Operate on a beating heart

The New Scientist describes a robotic system which can compensate for the motions of the heart, allowing surgery to continue while the heart beats (gently). The surgeon wears eyepieces which track his gaze. He first scans over the heart; then tracks the beating motion of a single region; and the machine calculates the topography of the heart and its motion from that point forward. This means that the surgical tools stay stationary with respect to the heart.