How can we absorb all that excess carbon dioxide that is being released into the atmosphere by the burning of fossil fuels? Preserving Earth’s forests and planting more trees might help, but it won’t be sufficient. One idea is to use carbon-scrubbing machines that would pull the carbon dioxide out of the air. The recovered carbon dioxide could then be used in such products as high-carbon cement, dry ice, or synthetic gasoline. Or it could be stored deep underground again.
Current technology would need to be improved before carbon-scrubbing is economically feasible. But the basic techniques are in place already – they’ve been used in submarines for decades.
Reference: Lackner, Klaus S. Washing Carbon Out of the Air. Scientific American pp. 66-71, June 2010.
Sunday, May 30, 2010
Wednesday, May 12, 2010
Did Neanderthals Mate With Modern Humans?
When modern humans (Homo sapiens) migrated out of Africa around 140,000 to 100,000 years ago, it is likely that they ran into their more primitive cousins the Neanderthals (Homo neanderthalensis), who were already living in Europe. Both species probably evolved separately from the same ancestor, Homo erectus.
Did the two groups mate when they met? All we really know is that the Neanderthals disappeared about 28,000 years ago. Some scientists hypothesize that they were attacked or simply out-competed by modern humans; others claim that the two groups interbred, causing Neanderthal features to be absorbed into a larger population of modern humans.
Now there is new evidence that perhaps they did interbreed. Using modern DNA analysis techniques, scientists have determined that the Neanderthals have more genetic variations in common with present-day humans in Europe and Asia than with modern humans in Africa. These data suggest that interbreeding may have occurred if/when the two species met in Europe, before modern humans migrated out of Europe to Asia.
Did the two groups mate when they met? All we really know is that the Neanderthals disappeared about 28,000 years ago. Some scientists hypothesize that they were attacked or simply out-competed by modern humans; others claim that the two groups interbred, causing Neanderthal features to be absorbed into a larger population of modern humans.
Now there is new evidence that perhaps they did interbreed. Using modern DNA analysis techniques, scientists have determined that the Neanderthals have more genetic variations in common with present-day humans in Europe and Asia than with modern humans in Africa. These data suggest that interbreeding may have occurred if/when the two species met in Europe, before modern humans migrated out of Europe to Asia.
Thursday, May 6, 2010
How Safe is Live Kidney Donation?
It’s been about 60 years since the first live kidney donor operation. There have been scattered reports that kidney donation is safe, but most published studies have been limited in scope and used inappropriate control groups against which to compare mortality statistics.
A recent report strengthens the hypothesis that live kidney donation is relatively safe. The report compares mortality data for essentially all 80,347 live kidney donors in the United States between 1994 and 2009 to a carefully matched control group of people who were eligible to donate but were not asked to do so. Mortality statistics were followed in both groups for up to 12 years (median 6.3 years) after donation by the live kidney donor group.
The results indicate that there is a small risk of death from the surgical procedure itself, as would be expected of any similar major surgical procedure. Early post-surgical (three-month) mortality was 3.1 per 10,000 kidney donors, compared to 0.4 deaths in the control group over a similar three-month period. After that, however, there were no differences in survival between the donor and control groups out to 12 years.
The results support the hypothesis that there is no long-term mortality risk associated with live kidney donation except for the usual risks of surgery. Presumably a follow-up study will be done in years ahead to extend the definition of “long-term” to beyond 12 years.
A recent report strengthens the hypothesis that live kidney donation is relatively safe. The report compares mortality data for essentially all 80,347 live kidney donors in the United States between 1994 and 2009 to a carefully matched control group of people who were eligible to donate but were not asked to do so. Mortality statistics were followed in both groups for up to 12 years (median 6.3 years) after donation by the live kidney donor group.
The results indicate that there is a small risk of death from the surgical procedure itself, as would be expected of any similar major surgical procedure. Early post-surgical (three-month) mortality was 3.1 per 10,000 kidney donors, compared to 0.4 deaths in the control group over a similar three-month period. After that, however, there were no differences in survival between the donor and control groups out to 12 years.
The results support the hypothesis that there is no long-term mortality risk associated with live kidney donation except for the usual risks of surgery. Presumably a follow-up study will be done in years ahead to extend the definition of “long-term” to beyond 12 years.
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