Nelson and Masel
, present a theoretical argument summarized by Wagner
in his brief essay on their paper. From Wagner:
Paul Nelson and Joanna Masel present a theoretical result showing that aging in multicellular organisms is inevitable. The argument is as simple as it is powerful. Cellular senescence is a well-known consequence of the second law of thermodynamics, due to mutations, epigenetic misregulation, and protein misfolding. Molecular accidents in a cell can happen and they consequently do happen. In unicellular organisms, life is maintained because of natural selection against senescent cells and, thus, at the population level life can continue potentially indefinitely. However, in multicellular organisms, competition among cells has been killed to ensure cooperation among cells and thus the integrity of the organism. Breakdown of cooperation and unchecked competition among cells is known as cancer. Cooperation, and thus limited competition among cells, leads to the accumulation of senescent cells, while competition among cells kills the organism because of a breakdown of cooperation.
The result presented by Nelson and Masel... is a negative theoretical prediction based on very few but fundamental features of reality: senescence is a consequence of the second law of thermodynamics (molecular accidents and degradation are inevitable); senescence can be countered by natural selection; but natural selection among cells undermines cooperation among the cells of a multicellular organism. Thus, the multicellular organism is doomed either by senescence or cancer. The fact that this result is a negative prediction, like those of Gödel in mathematics, also explains why it can have a law-like certainty. It does not depend on contingent evolved properties of organisms but only on those which are intrinsic to life itself, namely that organisms are physical systems subject to the limits of thermodynamics, natural selection, and the need for cooperation among the cells in multicellular organisms.
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