Why a person doesn't evolve in one lifetime
...mutant cells that don't do their specialized job so well tend to replicate more quickly than non-mutants, and so gain a competitive advantage, freeloading off the others. In such a case, our wonderfully wrought bodies could grind to a halt...
To renew themselves, epithelial tissues retain a population of undifferentiated stem cells, like the unformed cells present in embryos, that have the ability to grow into different types of cells. When replacements are needed, some of these stem cells divide to make transient amplifying cells (TACs). The TACs then divide several times, and Pepper and his co-workers think that each division produces cells that are a little more developed into mature tissue cells.
All this costs a lot of metabolic energy, so it is not very efficient. But, the researchers say, it means that the functions of self-replication and proliferation are divided between separate groups of cells. The stem cells replicate, but only a little, and so there's not much chance for mutations to arise or for selective pressure to fix them in place. The proliferating TACS may mutate, but they aren't simply copying themselves, so there isn't any direct competition between the cells to create an evolutionary pressure. As a result, evolution can't get started.
Mixing the oceans proposed to reduce global warming
In a letter to the editor published in Nature this week1, James Lovelock and Chris Rapley suggest that this deus ex machina could be an "emergency treatment for the pathology of global warming". Large vertical pipes could, they say, be used to mix nutrient-rich waters from hundreds of metres down with the more barren waters at the surface. This could cause algal blooms at the surface, which would consume carbon dioxide (CO2) through photosynthesis. When the algae die, some of this carbon could sink into deep waters. The algae may also produce chemicals that spur cloud formation, further cooling the planet.
2 comments:
We have at least two cell-based mechanisms by which we do indeed evolve profoundly within our lifetime: 1) Immunity and 2) memory, learning and other forms of mental adaptation. Our ancestors evolved the ability to evolve within an individual lifetime--and to transmit advantageous behaviors to offspring by teaching and culture. We've adaptively outpaced our non-cultural competitors that way--i.e. along with destroying the habitats of everything else. Still, if all knowledge disappeared, it's not obvious that surviving humans would organize and innovate enough in time to avoid being wiped out.
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