Evolution of social behaviour

Nowak et al.1 wish to explain why the version of kin selection theory that is summarised by the formula R>c/b (c=cost of performing 'altruistic' act, b=benefit derived by recipient of act, R=relatedness between the two) is of little utility for understanding the evolution of eusociality. But in trying to do so they omit much that is relevant and risk misrepresenting the issue to anyone who is not familiar with the literature. A fairer account would include the following facts

George Gamow and the genetic code

On February 28, 1953, in a pub in Cambridge, Francis Crick was telling everyone who cared to listen that he and James Watson had just discovered the secret of life. The April 25 issue of the journal Nature carried the same news in the form of their first, and most famous, paper, "A Structure for Deoxyribose Nucleic Acid". In it they announced that DNA, the molecular basis of heredity, was a right-handed double helix. It consisted of two intertwined, anti-parallel helical strands. Each strand was a long molecule made up of subunits which contained a sugar, deoxyribose, a phosphate group, and one of the four bases adenine (A), guanine (G), thymine (T) and cytosine (C). The two strands specified each other; they were 'complementary'. This was because they were held together by hydrogen bonds formed between adenine and thymine (A-T) and between guanine and cytosine (G-C). On May 30 there was a follow-up by Watson and Crick in the same journal, entitled "Genetical Implications of the Structure of Deoxyribonucleic Acid" It was seen by Luis Alvarez and brought by him to the attention of George Gamow, then visiting the University of California at Berkeley

John Maynard Smith (1920-2004) "One of the last grand evolutionary theorists of the 20th Century"

There is virtually no area of evolutionary biology to which John Maynard Smith did not make a significant contribution. In this essay I try to present a flavour of his accomplishments

The origin of species after 150 years: one hundred and fifty years without Darwin are enough

A happy accident enabled the young Charles Darwin to go on a voyage of exploration a round the world. Among the outcomes of that voyage was a book, The Origin of Species, which was published in 1859. In it Darwin developed aperspective of the living world that, as we have come to realise, encapsulates its essence. By viewing plants and animals as dynamical entities that were subject to external forces, he was able to show convincingly that they had evolved, on the whole by a process known as natural selection. In doing so he made the point that the living world was explainable on the basis of natural laws and, at the same time, that biology can lay claim to an autonomous status among the natural sciences. Paradoxically, he a ccomplished all this with out knowing how heredity worked or variations occurred. This article attempts to look at The Origin of Species from the vantage point of the present. Anaccount of the events that led to the writing of the book will be followed by a quick run through its contents. The essay ends with a mention of some issues that continue to engage evolutionary biologists today

Phenotypic plasticity can potentiate rapid evolutionary change

Using a computational model of string-like haploid genotypes, we verify the conjecture (J. Theor. Biol. 188 (1997) 153) that phenotypic plasticity can speed up evolution. The corresponding real-life situation was realized by Waddington in experiments carried out on the fruit fly Drosophila. Waddington found that after selecting for an environmentally induced trait over a number of generations, a new, true-breeding phenotype resulted that was absent in the starting population. The phenomenon, termed 'genetic assimilation', continues to attract interest because of the rapidity of the effect and because of its seemingly Lamarckian implications. By making use of a genetic algorithm-based approach developed previously, we show that conventional Darwinian selection acting on regulatory genes can account for genetic assimilation. The essential assumption in our model is that a structural gene can be in either of three allelic states. These correspond to its being (a) 'on' or 'off' constitutively or (b) in a plastic state in which the probability that it is 'on' or 'off' is influenced by regulatory loci in a dosage-dependent manner

Why are most mutations recessive?

It is a long-standing observation that most mutations are recessive. That is, they do not lead to visible phenotypic effects when in heterozygous combination with the wild-type allele. The reason for this has long been debated. Fisher (1930) attributed the observed dominance of the wild type to the action of natural selection at modifier loci. Wright (1929) on the other hand asserted that dominance did not have a selective functionper se, but was a more-or-less automatic offshoot of genetic regulatory mechanisms. The present essay discusses these explanations from a contemporary standpoint and suggests that neither is likely to be valid exclusively. In particular, even when physiology appears to offer a sufficient explanation, evolution of dominance cannot be ruled out

J. B. S. Haldane, Ernst Mayr and the Beanbag genetics dispute

Starting from the early decades of the twentieth century, evolutionary biology began to acquire mathematical overtones. This took place via the development of a set of models in which the Darwinian picture of evolution was shown to be consistent with the laws of heredity discovered by Mendel. The models, which came to be elaborated over the years, define a field of study known as population genetics. Population genetics is generally looked upon as an essential component of modern evolutionary theory. This article deals with a famous dispute between J. B. S. Haldane, one of the founders of population genetics, and Ernst Mayr, a major contributor to the way we understand evolution. The philosophical undercurrents of the dispute remain relevant today. Mayr and Haldane agreed that genetics provided a broad explanatory framework for explaining how evolution took place but differed over the relevance of the mathematical models that sought to underpin that framework. The dispute began with a fundamental issue raised by Mayr in 1959: in terms of understanding evolution, did population genetics contribute anything beyond the obvious? Haldane's response came just before his death in 1964. It contained a spirited defense, not just of population genetics, but also of the motivations that lie behind mathematical modelling in biology. While the difference of opinion persisted and was not glossed over, the two continued to maintain cordial personal relations

Evolutionary questions raised by cellular slime mould development

The cellular slime moulds (CSMs) are amoeboid organisms whose life cycle can be viewed in two ways. Firstly, because free-living amoebae come together to build bodies, they are ideal models for studying multicellular development in terms of the properties of single cells. Secondly, coming together and participating in an integrated unit implies social behaviour. Consequently differentiation (especially in the advanced CSMs) can be seen as a form of division of labour in which only some amoebae get to transmit their genes to the next generation. Viewed thus, their life cycle is ideally suited for studying the evolutionary basis of cooperation with some members of the cooperating group exhibiting altruistic behviour. The present review takes the second approach. We examine alternative explanations for social behaviour (i.e., multicellular development) based on individual-level and group (including kin-group) selection. Non-clonal fruiting bodies are likely to be common in nature; we show a case with at least nine genotypes. The CSMs display both individual and group-level adaptations and both levels of selection operate in their appropriate contexts. The review ends with questions for the future and indicates how studies of CSM development might help to explain the evolution of altruism in this group

Some remarks concerning near-zero g experiments on living systems

In the case of animal systems, gravity probably plays an important role only during early development; this has to do with the determination of embryonic polarity. At other times in the life of an animal, gravity is a hindrance. If animals are to be sent into space, it is clearly necessary to study the effect of zero g on their physiology and behaviour. This apart, there seems to be no basis for thinking that biological experiments conducted in outer space might yield interesting insights into how living systems work

Transposable element copy number and stable polymorphisms

We consider a simple and analytically solvable model for the spread of a transposable element which has deleterious effects on fitness. Two possible modes are treated, one in which transposition occurs in the newly fertilized zygote, and another in which transposition takes place only in the germ line. In effect, transposition precedes selection in the first case and follows it in the second. This has different long-term consequences depending on the rate of transposition and the values of the selection coefficients. Conditions are derived for the existence of a stable polymorphism with respect to element copy number; the conditions are more stringent in the first case than in the second. It is proved that a polymorphism is impossible unless the copy number decreases fitness in a more-than-muitiplicative fashion