Skip to main content
main-content

Über dieses Buch

This book gathers together much of the author’s work – both old and new - to explore a number of the key increases in complexity seen in the natural world, seeking to explain each of them purely in terms of the features of fitness landscapes. In a very straightforward manner, the book introduces basic concepts to help readers follow the main ideas. By using variations of the NK model and including the concept of the Baldwin effect, the author presents new abstract models that are able to explain why sources of evolutionary innovation (genomes, symbiosis, sex, chromosomes, multicellularity) have been selected for and hence how complexity has increased over time in some lineages.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
Life on earth emerged around 4 billion years ago and its complexity has been increasing ever since. This book seeks to explore the conditions under which natural selection [3] would favour some of the key mechanisms by which those increases in complexity have come about, using simple models of evolution on abstract fitness landscapes. Wright [11] was perhaps the first to view natural evolution as a process of adaptation through a multidimensional space of fitness peaks and troughs (Fig. 1.1, top). Turing [10] would later highlight the potential universality of that view when considering ways to design intelligent computers: evolution as a general search process. Whilst no simple correlation between the amount of DNA in a given organism and its perceived complexity exists—lilies have more DNA than humans, for example—it is clear that the two are interrelated. Five ways in which an increase in the amount of DNA may occur are explored here.
Larry Bull

Chapter 2. Genomes

Abstract
Genome length is one of the degrees of freedom exploited by evolution in the variation of organism complexity and this can be seen to have increased over time in some lineages. Metazoan morphological complexity is known to be correlated with genome length, for example [3]. This chapter explores the effects of fitness landscape ruggedness upon the evolution of genome length in asexual haploid organisms. Hence cells/organisms with genomes of linked DNA are assumed to have already emerged (e.g., see [8]).
Larry Bull

Chapter 3. Symbiosis

Abstract
Symbiosis represents evolution bringing together the genomes of different species and it is well-established that the phenomenon has been of great significance (e.g., see [11]). When the relationship between the symbionts evolves in the direction of increasing dependency, “a new formation at the level of the organism arises—a complex form having the attributes of an integrated morphophysiological entity” [9, p. 5]. This chapter explores the effects of fitness landscape ruggedness and connectedness upon the evolution of symbiotic organisms which live in close association.
Larry Bull

Chapter 4. Sex

Abstract
Whilst a number of explanations for various aspects of the evolution and maintenance of eukaryotic sex have been presented, none gives a unifying view of the wide variations in the process seen in nature. Sex is here defined as successive rounds of syngamy and meiosis in a haploid-diploid lifecycle. This chapter suggests that the emergence of a haploid-diploid cycle enabled the exploitation of a rudimentary form of the Baldwin effect (e.g., see [20] for an overview) and that this provides an underpinning explanation for all the observed forms of sex [5].
Larry Bull

Chapter 5. Chromosomes

Abstract
Chromosome size, number and types are some of the degrees of freedom exploited by evolution in the variation of eukaryotic organism complexity and this can be seen to have increased over time in some lineages. This chapter explores the effects of fitness landscape ruggedness upon various aspects of chromosomes drawing upon the results in Chap. 4: the effects of varying the number of chromosomes in a sexual diploid are explored using versions of the NK model. Results suggest that landscape ruggedness, chromosome length, and the initial function of the chromosome copy, can all affect evolution. The effects of sex determination chromosomes and hence mating types is also explored within the model, with the XY (ZW) and X0 (Z0) systems shown to be beneficial under certain conditions due to the ruggedness of the fitness landscape.
Larry Bull

Chapter 6. Multicellularity

Abstract
Approximately 550 million years ago the Cambrian explosion brought forth all the major phyla of multicellular animals. Multicellularity is thought to have evolved up to 200 million years before that and has occurred at least three times—in fungi, plants and animals (see [9] for an overview). This chapter explores the effects of fitness landscape ruggedness upon the evolution of multicellularity in eukaryotic organisms.
Larry Bull

Chapter 7. Conclusion

Abstract
Whilst there is no clear correlation, complex organisms typically contain more DNA than simple organisms—whether it is in the genome, due to multiple genomes in a cell, due to the presence of symbiotic organelles, or due to the number of cells. Hence it is an indicative measure of organismal complexity, although others have been proposed (eg, see [1] for discussions). The conditions under which such increases in DNA might emerge during evolution have been explored using simple fitness landscape models here. These models can perhaps be seen as a method by which to attempt to explain biology whilst removing as much detail of the biology as possible, and thereby potentially missing key elements. For example, although touched upon for symbiogenesis, that an increase in complexity may subsequently create the opportunity for conflict has not been explored. However, such abstract fitness landscapes enable the consideration of evolution purely as a stochastic process being fed innovations due to (often almost unavoidable) things like copy errors, joining/separation events, etc. as it searches through a multidimensional space containing peaks and troughs. The findings here show how the ruggedness and movement/change within fitness landscapes can be used to explain the emergence of key complexity increasing events.
Larry Bull

Backmatter

Weitere Informationen

Premium Partner

    Marktübersichten

    Die im Laufe eines Jahres in der „adhäsion“ veröffentlichten Marktübersichten helfen Anwendern verschiedenster Branchen, sich einen gezielten Überblick über Lieferantenangebote zu verschaffen. 

    Bildnachweise