Palaeoanthropology: Relative Neanderthal judgements
Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0308085100 (2004)
Neanderthals might have been a different species from modern humans — that is, separate from our own lineage. Or the taxonomic relationship could have been much closer. In the latest examination of this perennial issue, Katerina Harvati and colleagues come down in favour of the first possibility.
Neanderthals roamed Europe between about 200,000 and 30,000 years ago. A close relationship with modern humans would imply that ancient populations from different regions around the globe contributed to our evolution. On the other hand, finding Neanderthals to be a distinct species would strengthen the claim that modern humans arose relatively recently as a new species in Africa.
Harvati et al. have carried out a fresh assessment of the morphological differences between Neanderthals and modern humans, using variability between living primate species as a benchmark. From measurements of skulls taken from more than 1,000 specimens across 12 primate species, they show that the difference in skull morphology between Neanderthals and modern humans is similar to that between living primate species. It is also greater than the variation between populations within a species, again suggesting that Neanderthals were a distinct species.
Cryogenics: An integrated fridge
Appl. Phys. Lett. 84, 625–627 (2004)
Some measurements are best done in the cold. For high-precision photon detection in astronomical telescopes, for example, the sensors may need cooling to a few tenths of a kelvin. Existing refrigerators capable of reaching 0.1 K are costly and cumbersome; but A. M. Clark et al. now describe a microelectronic device incorporated into integrated circuitry that approaches this degree of cooling cheaply and conveniently.
The device is based on a sandwich of materials: a metal, an insulator and a superconductor. With a voltage applied to the superconductor, electrons with relatively large energies (‘hot’ electrons) are siphoned off from the metal through a thin layer of insulating oxide, cooling the metal electrode. The oxide layer is usually derived from the superconductor, because most metal oxides don't have the right properties. But by using manganese-doped aluminium as the metal electrode, Clark et al. were able to invert the conventional structure of such devices, putting the superconductor layer on top. This means that the superconductor can be thicker than usual, making it more efficient at cooling the metal. The device can thus attain lower temperatures (0.13 K) than previously possible. And it can be readily scaled up without compromising its performance.
Cell biology: Checkpoint hijack
Proc. Natl Acad. Sci. USA 101, 947–952 (2004)
Cell lines — populations of distinct cell types that divide indefinitely under laboratory conditions — are widely used in research. They are often made by inserting a cancer-causing gene into a cell. But lines immortalized with one such gene, that for the SV40 large T antigen, are often genetically unstable — that is, their genetic make-up changes. Marina Cotsiki et al. have discovered why.
When a normal cell prepares to divide, it sets up a protein spindle. Pairs of duplicated chromosomes line up along the spindle's midline. Then, if the chromosomes are perfectly aligned and attached, they separate and move to opposite sides of the cell. This process is monitored by a so-called ‘checkpoint’ protein, Bub1. If the chromosomes are misaligned or unattached, the checkpoint kicks in to halt cell division.
But when SV40 large T antigen is present, it binds to Bub1 and overrides the checkpoint. Misaligned or unattached chromosomes are allowed to separate, and the resulting daughter cells contain an abnormal mix of chromosomes — a hallmark of cancer.
Helen R. Pilcher
Climate modelling: Freshened up
Geophys. Res. Lett. doi:10.1029/2003GL018584 (2004)
As greenhouse gases accumulate in the atmosphere, their warming effect is believed to increase the amount of fresh water released into the polar oceans from increased rainfall and melting sea ice. Many climatologists have predicted that freshening of the Arctic Ocean could disrupt the large-scale thermohaline circulation in the Atlantic — a watery ‘conveyor belt’ regulated by temperature and salinity — with possibly severe effects on climate. Observations from the Nordic Seas and the North Atlantic have identified such a freshening trend since the 1960s, raising questions about whether global warming is already changing ocean circulation.
Peili Wu and colleagues have now developed a climate model for the past 150 years that agrees with observations of deep-water freshening in the Nordic Seas over the past 40 years. But their model actually predicts a short-term increase in convection in the Labrador Sea, and a more vigorous thermohaline circulation.
The authors conclude that the recently observed freshening of the deep ocean is not an early signal of climate change caused by human activities. Nevertheless, the model results are in line with the view that long-term ocean warming will result in a decline of the thermohaline circulation over the next century.
Molecular biology: Death leaves its mark
Hum. Mol. Genet. doi:10.1093/hmg/ddh065 (2004)
Many researchers analyse brain autopsy tissue in an attempt to identify genes that are working abnormally, and that might underlie psychiatric or neurological conditions. But there is an added complication: how a person dies has a profound effect on which genes were switched on in their brain.
Using a ‘chip’ carrying thousands of genes, J. Z. Li et al. compared the brains of 20 patients with depression or bipolar disorder against 20 normal controls. They found two distinct groups of active genes. Patients whose dying had been prolonged over hours or days, as a result of multi-organ failure or after coma, showed one type of gene activation profile; those who had died suddenly — from a heart attack, accident or suicide — showed another.
During prolonged illness, the brain might become starved of oxygen and essential nutrients, triggering cells to switch on ‘stress response’ genes for survival, the researchers suggest. Also, the brain tissue of these patients was more acidic than that of patients who had died suddenly, perhaps because their cells start to function without oxygen, churning out acidic by-products; this might also influence gene expression.
Evidently, then, researchers conducting gene-chip analyses on post-mortem brain tissue should take the patient's mode of death into account.