Bering strait closure caused the end of last Ice Age in the long run

A very interesting new climate theory the one mentioned today at Science Daily: while the cooling of Earth was caused by orbit perturbations, leading to the closure of Bering Strait and the formation of the Beringia isthmus, this last caused such perturbation in global oceanic currents that in the long run sentenced the Ice Age to its end.

The Atlantic Ocean is saltier than the Pacific, what leads to water flowing from this latter to the former. This circulation can only go through the south or via the Arctic Ocean. With Bering Strait closed, Atlantic salinity grew and the North Atlantic Conveyor (Gulf Stream) was enhanced leading to a gradual meltdown of the North Atlantic Ice sheets (in North America and Northern Europe), which in turn lead to higher sea levels and eventually to the reopening of the Bering Strait and the stabilization of climate in the Holocene.

It took many many thousand years though.

Genes, brains and fractals (various brief notes)

I'm feeling intellectually saturated right now and don't feel like writing or even reading too much at the moment. However there are some interesting news I think I should mention. Therefore I'll just make a quick reference here... by the moment.


Genes:

Some of these news come from the new PLoS ONE issue:

D. López Herráez et al. have found several evolutionary markers that seem to define short height in Pygmies (as an adaptative response to low iodine diet) and cartilaginous tissue that may correlate with "racial" differences as shown in facial traits (facial features are largely defined by cartilages).

G. Resink et al. explore the parallels and differences between genetic structure in Sahul and language families. This report is also discussed at Dienekes' blog.

Also I have been reading Subramanian's paper on Penguin DNA and molecular clock (thanks to German again) but, sadly, it is not as clarifying as the press release would suggest. I need to re-read it in order to make up my mind.


Brains:

At Science Daily we are informed of the fact that larger brains are not necessarily correlated with greater cognitive power, that bees and dogs can essentially understand the same things about their surroundings.

Also at SD, it is mentioned that IBM has managed to recreate with supercomputers the wiring complexity of a cat-like brain.


Chaos:

For those interested in Chaos theory and fractal geometries (I love it but also beats me), New Scientist deals with the three dimensionalization of the classical Mandelbrot Set, gallery included.
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Inefficient selection behind complexity

In the pure Darwinian scenario of draconian selection that can exist for instance among microorganisms, which are numerous enough for drift and randomness not to be a factor, and among whom competence is maximized like in the ideal free market of liberal economists, all accidental extra copies of genes (paralogs) are eventually erased because they are inefficient.

But among a much smaller population, like humans, Darwinian evolution works inefficiently and these troublesome extra copies of genes do in fact persist. In principle paralogs are problematic and can cause degenerative diseases like Alzheimer because they produce less efficient proteins. But what Ariel Fernández and Jianping Chen of the University of Texas have found is that these paralogs also drive complexity, that it is the accumulation of these errors by drift what in fact generates complexity, that complexity can only arise when selective evolution becomes weak and drift (chaos) rules instead.

After all every order is just a subset of pure Chaos, right?

Source: Science Daily.
Original paper: Human capacitance to dosage imbalance: Coping with inefficient selection. Genome Research 2009 (paywall).
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Complexity is simple: proteins auto-assemble just naturally

Researchers from the United States have discovered that bacterial proteins self-assemble stochastically (that is: randomly) and not directed by any centralized force of any sort. This random system is probably also found in eukaryotic cells like ours.

In spite of this randomness, patterns emerge and the system just works fine, as Alan Turing had predicted for a different context some 60 years ago.

According to co-researcher Jan Liphardt:

Random lateral protein diffusion and protein-protein interactions are probably sufficient to generate the observed complex, ordered patterns. This simple stochastic self-assembly mechanism, which can create and maintain periodic structures in biological membranes without direct cytoskeletal involvement or active transport, may prove to be widespread in both prokaryotic and eukaryotic cells.

Source: Science Daily

Research paper (open access): Greenfield D, McEvoy AL, Shroff H, Crooks GE, Wingreen NS, et al. (2009) Self-Organization of the Escherichia coli Chemotaxis Network Imaged with Super-Resolution Light Microscopy. PLoS Biol 7(6): e1000137. doi:10.1371/journal.pbio.1000137

Author Summary:

Cells arrange their components—proteins, lipids, and nucleic acids—in organized and reproducible ways to optimize the activities of these components and, therefore, to improve cell efficiency and survival. Eukaryotic cells have a complex arrangement of subcellular structures such as membrane-bound organelles and cytoskeletal transport systems. However, subcellular organization is also important in prokaryotic cells, including rod-shaped bacteria such as E. coli, most of which lack such well-developed systems of organelles and motor proteins for transporting cellular cargoes. In fact, it has remained somewhat mysterious how bacteria are able to organize and spatially segregate their interiors. The E. coli chemotaxis network, a system important for the bacterial response to environmental cues, is one of the best-understood biological signal transduction pathways and serves as a useful model for studying bacterial spatial organization because its components display a nonrandom, periodic distribution in mature cells. Chemotaxis receptors aggregate and cluster into large sensory complexes that localize to the poles of bacteria. To understand how these clusters form and what controls their size and density, we use ultrahigh-resolution light microscopy, called photoactivated localization microscopy (PALM), to visualize individual chemoreceptors in single E. coli cells. From these high-resolution images, we determined that receptors are not actively distributed or attached to specific locations in cells. Instead, we show that random receptor diffusion and receptor–receptor interactions are sufficient to generate the observed complex, ordered pattern. This simple mechanism, termed stochastic self-assembly, may prove to be widespread in both prokaryotic and eukaryotic cells.
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