JTW's Evolutionary Origins - Author: Buss, Leo W.
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The Evolution of Individuality
[The evolution of multicellular life] "... is characterised by an increasing sophistication of cells, tissues, and organs which perform somatic duties of value to the individual as a whole, but which require the cells composing them to limit their inherent potential for proliferation. The propensity for continued self replication has been subjugated to the interests of the whole."(Leo W. Buss, 1987, pp.53)
"In ... Drosophila, it is appropriate to view the individual as a unique, genetically homogeneous, unit. It is highly unlikely that genetic variation will arise and gain access to the gametes within a single generation. In the hydroids, however, the number of divisions of the totipotent cell line intercalated between each sexual generation is so high that it is very likely that genetic variation will both arise and be inherited."
(Buss, 1987, pp.19)
"...while the cooperative model is an appealing characterization of development in extant taxa, it is inappropriate to view the processes which gave rise to developmental programs as cooperative. The opposite is more likely the case... [The] complex interdependent processes which we refer to as development are reflections of ancient interactions between cell lineages in their quest for increased replication. Those variants which had a synergistic effect and those variants which acted to limit subsequent conflicts are seen today as patterns in metazoan cleavage, gastrulation, mosaicism, and epigenesis. Exclusively asexual, cellular-differentiating organisms are, however, known. The mode of reproduction in such forms is, without question, derived from an ancestral sexual state. The ubiquity of sex invites a simple historical interpretation: sex is common because sex is ancestral in all organisms with sexual differentiation... Sex may have been a necessary precondition for the evolution of cellular differentiation."
(Buss, 1987, pp. 125)
"...It would nonetheless produce far fewer propagules than those neighboring cells which expended no effort in producing somatic tissue. Variants which display cellular differentiation in a multicellular organism are at a severe competitive disadvantage in the somatic environment... [moreover,] back-mutations which reverse the state of differentiation... are inevitable: an organism must periodically free itself of them if it is to persist. However, asexual organisms have no mechanism for purging themselves of mutations, short of the extinction of the clone itself."
(Buss, 1987, pp. 126)
"...the receptors that ensure delivery of growth-enhancing mitogens also compel somatic function. The cytotoxic T-cell recognizes its target with the same receptor arrangement used by the macrophage to activate that cell lineage. It is compelled to attack the infected cell by the same receptor required for it to obtain mitogens from helper cells ... The immune system works by exploiting the inherent propensity of cells to further their own rate of replication."
(Buss, 1987, pp. 87)
- Buss, Leo W.
- The Evolution of Individuality
- Princeton University Press
- QH 491.B87 1987
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