Book Summary: “The Principles of Social Evolution” by Andrew Bourke


The Principles of Social Evolution

Title: The Principles of Social Evolution
Author: Andrew Bourke
Scope: 5 stars
Readability: 2.5 stars
My personal rating: 4 stars
See more on my book rating system.

Topic of Book

A theoretical explanation for how biological organisms evolved from simple self-replicating molecules to complex human societies.

My Comments

This is dense, academic book that will be difficult for most of us to read, but the author shows some basic principles that help us understand how the simple individuals evolve into the complex groups by means of combination and cooperation. This book enables us to understand how human beings were able to evolve such complex societies full of individualistic, but cooperating, members.

While the author makes only tangential references to human history, it is clear that he believes that we can learn a great deal about human history by studying the evolution of biological organisms.

Key Take-aways

  • Common principles of evolution apply to all major transitions in evolution, from self-replicating molecules to RNA to chromosomes to single-celled organism to multi-celled organisms to animal colonies to primate societies to human societies.
  • Simple organism combine together to form more complex organisms. To do this successfully, they must limit internal conflict.
  • Size-Complexity hypothesis: As populations get bigger, the individual members within that population must learn to cooperate. Individuals that are better at cooperating will tend to reproduce, leading to higher levels of cooperation. This enables social groups to become more cooperative which enables the population to grow further.
  • As group size increases, groups transform from simple, less individualistic ones to complex, more individualistic ones.

Important Quotes from Book

An altogether different view of life’s history overcomes these deficiencies by focusing on the hierarchical organization of the units of life. Genes occur in cells and cells fuse to form other cells. Cells may occur within multicellular organisms, and multicellular organisms occur, at least in some cases, in societies. Since units at each level also occur independently, and each level requires the presence of the lower ones, it follows that in the history of life there were distinct events in which genes grouped into cells, cells grouped to become a different type of cell, cells further grouped into multicellular organisms, and multicellular organisms grouped into societies.

Fundamentally, the history of life has been the history of the grouping of biological units into higher-level units and the subsequent consolidation of the new higher-level units into integrated collectives, with this process, once started, having been repeated several times to generate the biological hierarchy we observe today. The concepts of the evolution of individuality and major transitions are themselves underpinned by a key insight whose roots stretch back to the early 1960s, being based in the gene’s-eye (or ‘selfish gene’) view of natural selection and, by implication, in inclusive fitness theory (Hamilton 1963 ; Dawkins 1976, 1982). This insight is that the individuality emerging at each major evolutionary transition is a contingent state.

Specifically, it is contingent upon the absence or suppression of within-individual Conflict…  For, if the level of internal conflict is too great, the higher level of organization either fails to emerge or is unstable and collapses. The challenge has been to understand what kinds of process contribute to the stable evolution of each new level in the hierarchy of major transitions.

The ‘major transitions view’ of evolution offers a more profound and scientifically satisfying vision of life’s fundamental evolutionary history than its rivals for several reasons. First, it provides an evolutionary explanation for the biological hierarchy itself (Maynard Smith and Szathmáry 1995 ; Okasha 2006 ). It does this by viewing the hierarchy as the cumulative product of selection on organisms to form higher-level collectives. In the case of the level of the multicellular organism in particular, this is a substantial insight. Multicellular organisms are such a salient feature of life that it is easy to take their existence for granted. But the hierarchical view, aided by a gene’s eye interpretation of natural selection, demonstrates that the multicellular organism cannot be taken as a ‘given’. It is not a form of biological organization that living matter must inevitably adopt, but an evolved construct in its own right, and as such its existence requires explanation.

Second, the major transitions view helps explain the increase in the complexity of living things over evolutionary time…

It does this in two ways. One arises simply because a nested hierarchy is necessarily more complex than each of its lower-level constituents. The other comes about because each major transition creates conditions for the evolution of mechanisms for excluding would-be exploiters and for reducing internal conflict, which themselves add to the overall complexity of the new level ( Chapters 5 , 6 ). In the same way, to use an analogy from Dawkins ( 1982 ) , computer systems in a world with malicious hackers are more complex than they would be in a solely well-intentioned world.

The major transitions view does not, however, propose that an increase in life’s complexity over time is inevitable. Instead, each step in a major transition depends only on the selective conditions prevailing at the time of its occurrence. It is entirely possible that, within any one lineage, the right conditions never occur, with the result that neither does the next transition. In short, there need be no directional bias driving individuals to associate into new and higher levels of organization, and indeed the fossil record provides little evidence for such bias.

Lastly, the major transition view of life’s history has immense potential to provide a unified explanation for the evolution of a huge range of biological systems. The field of study that equips us to investigate the conditions for a stable transition to a new level of individuality is social evolution. To put this another way, the problem of how individuality arises and is maintained is the problem of the evolution of cooperation.

Genes must cooperate to form a genome within a cell, cells must cooperate to form a multicellular organism, and multicellular organisms must cooperate to form a society. In a phrase that Lachmann et al. ( 2003 ) applied to organisms, each hierarchical level is ‘composed of layers upon layers of cooperation’.

The working hypothesis of this book is that, as proposed by previous authors… common principles of social evolution apply at each step in the evolution of individuality, regardless of the taxa involved and regardless of the level within the hierarchy of organization.

This is an important and grand vision that conceptually unifi es an immense range of superficially different phenomena in diverse taxa under the banner of social evolution.

My overall aim in this book is to present a fresh synthesis of this expanded view of social evolution. Specifically, I seek to articulate its theoretical basis and its principles as fully as possible, to investigate the extent to which its principles are applicable across different taxa and hierarchical levels, and to highlight new or little-appreciated principles, in addition to those already recognized.

I aim to place inclusive fitness theory centre-stage in the analysis of the major transitions as a whole.

Major transitions in evolution:

Replicating molecules ⇒ Populations of molecules in compartments

Independent replicators ⇒ Chromosomes

RNA as gene and enzyme ⇒ DNA + protein (genetic code)

Prokaryotes ⇒ Eukaryotes

Asexual clones ⇒ Sexual populations

Protists ⇒ Animals, plants, fungi (cell differentiation)

Solitary individuals ⇒ Colonies (non-reproductive castes)

Primate societies ⇒ Human societies (language)

I identify six major transitions involving the evolution of individuality. All involve groupings of previously separate entities (e.g. genes, cells, organisms, species) to form higher-level, stable collectives (e.g. genomes, multicellular organisms, eusocial societies, interspecific mutualisms).

In this book I take the view that a fundamental problem posed by the evolution of cooperation has been solved by Hamilton’s (1964) inclusive fitness theory. Hamilton’s theory addresses the evolution of four types of social behaviour, namely cooperation (narrow sense), altruism, selfishness, and spite. These represent all possible types of social behaviour as formally defined by the nature of the costs and benefits experienced by social partners.

Stepping back, one can begin to see that Hamilton’s rule implies that organisms are selected to perform social actions as if they valued others according to how closely related they are, with the reproduction of others being valued more highly the greater the degree of relatedness.

Following Bonner, I term the idea that an increase in the size of social groups causes complexity, whether in multicellular organisms or eusocial societies, the size-complexity hypothesis.

In essence, the extended version of the size-complexity hypothesis proposes the following (Fig. 6.1). First, external ecological and evolutionary drivers tend to favour increased size in social groups (Section 6.3). Second, increased size selects for the syndrome of social traits that (independently of size itself) collectively define social complexity (Section 6.4). Third, via positive feedback (i.e. through self-reinforcing social evolution), these traits promote further increases in group size (Section 6.5).

The result is the transformation of small, simple social groups with one suite of traits, which collectively amount to a lesser degree of individuality, into large, complex social groups with another, which collectively confer greater individuality.

The size-complexity hypothesis proposes that, in multicellular organisms and eusocial societies, social group transformation occurs when the number of members per group increases. As group size increases, groups transform from simple, less individualistic ones to complex, more individualistic ones. Hence, social complexity is associated with a greater degree of reproductive and non-reproductive division of labour.

Once formed, social groups are selected to increase in size as a result of a variety of external drivers. If external drivers cause social groups to become larger, groups are then selected to become more complex.

Social complexity allows social groups to become more productive, and so, in a process of positive feedback, promotes further increases in group size. An important component of this process is the saving of the costs of conflict as power shifts away from single group members to collectives of group members (or to the virtual dominant) as group size increases.

Larger colony size also allows self-organization of workers’ labour to occur, again enhancing colony productivity and so leading to yet larger colonies.

By enhancing reproductive and non-reproductive division of labour within social groups, increased group size creates more interdependence between group members, and hence increases group-level individuality.

I sought to address two key unresolved issues (Section 1.5). The first concerned the extent to which common principles operate at each stage of a major transition across all levels in the biological hierarchy, and the strength of the empirical evidence for their operation. The conclusion is, resoundingly, that common principles operate to a very large extent. Each stage in a major transition to individuality (social group formation, maintenance, and transformation) frequently involves the same social evolutionary principles acting in analogous ways at the different hierarchical levels (Table 7.1). In addition, as earlier chapters have explored in detail, the empirical evidence for the operation of these principles is very considerable.

The main conclusion here is that, at least in social groups of relatives, it is likely to have occurred via the steps defined by the size-complexity hypothesis.

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