The Major Transitions in Evolution

The Major Transitions in Evolution

John Maynard Smith

Language: English

Pages: 360

ISBN: 019850294X

Format: PDF / Kindle (mobi) / ePub

Over the history of life there have been several major changes in the way genetic information is organized and transmitted from one generation to the next. These transitions include the origin of life itself, the first eukaryotic cells, reproduction by sexual means, the appearance of multicellular plants and animals, the emergence of cooperation and of animal societies, and the unique language ability of humans. This ambitious book provides the first unified discussion of the full range of these transitions. The authors highlight the similarities between different transitions--between the union of replicating molecules to form chromosomes and of cells to form multicellular organisms, for example--and show how understanding one transition sheds light on others. They trace a common theme throughout the history of evolution: after a major transition some entities lose the ability to replicate independently, becoming able to reproduce only as part of a larger whole. The authors investigate this pattern and why selection between entities at a lower level does not disrupt selection at more complex levels. Their explanation encompasses a compelling theory of the evolution of cooperation at all levels of complexity. Engagingly written and filled with numerous illustrations, this book can be read with enjoyment by anyone with an undergraduate training in biology. It is ideal for advanced discussion groups on evolution and includes accessible discussions of a wide range of topics, from molecular biology and linguistics to insect societies.



















simple derivation) that no sequence can exclude Fig. 4.6 The hypercycle. Each of the units A,B,C and D is a replicator. The rate of replication of each unit is an increasing function of the concentration unit immediately proceeding it. Thus the rate of replication of B is an increasing function of the concentration of A, and so on round the cycle. 52 Fig. 4.7 cycle. The Evolution of Templates An ecological hyper- another. The aid given by any molecule to the next one is ultimately fed back

material as well as ribozymes. It is intuitively clear that the more monomer types we have, the higher the catalytic efficiency of macromolecules can be. Metabolic efficiency of ribo-organisms, and hence their growth rate, would increase with increasing size of the genetic alphabet. This 76 Fig. 5.10 The Chicken and Egg Problem Novel base pairs (after Piccirilli et a/., 1990). What determines the size of the genetic alphabet? 77 by itself does not lead to an optimum; some other effect

regularity was referred to as the 'code within the codons' by Taylor & Coates (1989), who suggested that it originated before the tRNA/ribosome system. Consistent with this is the older conclusion (Swanson, 1984) that the first base of a codon controls amino acid size (purine and pyrimidine meaning small and large, respectively), and the middle base controls cloisteredness (purine means external, pyrimidine means internal). Why is the code redundant? Redundancy of the genetic code is apparent:

autocatalytic cycles of the pizza, is inherently autotrophic, and ions are still provided by the pyrite surface. This is the first true individuation step in the prebiotic pizza. Semicells are semi-organisms. Later, upon the development of a sufficient transport mechanism (see below), semicells became detached from the surface to form genuine protocells. This, however, required an adequate cell division (fission) mechanism. 102 Rg. 7.3 The Origin of ProtocelJs Cellularization by abstriction

reside on a circular linkage group (ULG) (Ramanis & Luck, 1986). Note, however, that molecular hybridization studies revealed that this linkage group is linear rather than circular (Hall et al., 1989). It is also discouraging that, despite previous claims, there seems to be only one The origin of centrioles and undulipodia 143 ULG chromosome per haploid genome, and there is at least one non-undulipodial gene on it (for a review, see Johnson & Rosenbaum, 1991). There is some sequence

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