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From Groups to Individuals: Evolution and Emerging Individuality QUOTES

From Groups to Individuals: Evolution and Emerging Individuality QUOTES

1 " Thus, it appears that unicellulars are biological individuals whose cohesiveness presupposes the constant action of an immune system. According to the view defended in the previous sections, it means that they are true 'organisms'. If this is correct, it means that the reflection offered about the emergence and maintenance of individuality in multicellular organisms through the activity of an immune system needs in fact to be raised at the level of the much more ancient transition from independent replicators to the first prokaryotic cell. Because this transition is not very well known, and because basically nothing is known of the possible role of the immune system in this transition, I will leave this discussion for now, pending more experimental evidence in the near future. I think, though, that it raises the fascinating hypothesis that immunity has been a key element in both the evolutionary transition to multicellularity and the very ancient evolutionary transition to the first cell - often conceived of as the first 'true' biological individual. It also suggests that each cell in multicellular organisms like us may have its own immune system. RNA silencing has been convincingly described as the 'genome's immune system'. Within this perspective, one can conceive a hierarchy of immunological individuals, or 'organisms': a multicellular living thing like us is an organism insofar as it possesses an immune system, and in addition it comprises billions of cells, which themselves are organisms insofar as they each possess their own immune system. It is an attractive hypothesis, though it probably needs to be complemented by an analysis of the way in which the whole organism regulates immune responses at the level of each cell. "

― , From Groups to Individuals: Evolution and Emerging Individuality

2 " William Hamilton once referred to the 'gavotte of chromosomes' seen in the process of cell division and in sex. This is a good image - a courtly dance, tuned by evolution, of joining and separating. We can seen some of the same thing on a larger scale, in - to adopt Julian Huxley's phrase - 'the movement of individuality.' The process at this larger scale is not itself an adaptation, a to-and-fro tuned by evolutionary design. Instead it is the recurring upshot of masses of separate evolutionary events. But there is some of the same rhythm of sealing off and opening up, of consolidating and reaching out, in the dynamic linking organisms and Darwinian individuals. "

― , From Groups to Individuals: Evolution and Emerging Individuality

3 " Hamilton's original contribution was to realize that indirect fitness effects impact upon the purpose of adaptation. The basic condition for natural selection to favor any trait is that the individuals who carry genes for this trait are, on average, fitter than those who do not. However, the adaptations that subsequently evolve are not designed for maximizing the individual's personal fitness, but rather her inclusive fitness, i.e., the sum of all the fitness effects that she has on all of her genetic relatives, each increment or decrement being weighted by the corresponding coefficient of genetic relatedness (Hamilton 1964). In other words, the adaptive agent remains the same as in the traditional Darwinian view (i.e., the individual organism), but the adaptive agenda is changed. This idea has subsequently been formalized by Grafen (2006), who has shown the mathematical connection between the dynamics of natural selection and an optimization program in whih the individual strives to maximize her inclusive fitness, for a wide class of models, including those that allow for social interaction between relatives.
Grafen A. 2006. Optimization of inclusive fitness. J Theor Biol 238: 541-563.
Hamilton WD. 1964. The genetical evolution of social behaviour I & II. J Theor Biol 7: 1-52. "

― , From Groups to Individuals: Evolution and Emerging Individuality