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Papers by steven orzack
Significance, Feb 1, 2016
The human sex ratio – the ratio of males to females – has long fascinated biologists and statisti... more The human sex ratio – the ratio of males to females – has long fascinated biologists and statisticians alike. Steven Hecht Orzack presents a potted history, from the earliest interpretations to the most recent – and surprising – conclusions The sex ratio Understanding the ratio of males to females has long fascinated biologists and statisticians, says Steven Hecht Orzack
The notion of homeostasis, an organism's ability to maintain a constant expression of a pheno... more The notion of homeostasis, an organism's ability to maintain a constant expression of a phenotypic character despite environmental change, is central to many arguments in biology. Most workers have presumed that homeostasis is beneficial and therefore the object of selection in natural populations. For example, Lewontin (1957, p. 402) asserts that "genotypes may arise with very wide adaptive norms, so wide in fact, that genetic polymorphism can add little to the adaptation of the population of which they are a part. Should such homeostatic genotypes alise, intrapopulational selection will favor them since they must, in a world of fluctuating environment, leave more offspring than their more specialized sibs." Similarly, Emerson (1961, p. 118) states that "Improved homeostasis seems to be a universal evolutionary trend and is basic to the concepts of adaptation and adaptability applied to all levels of biological and cultural organization." The picture of adaptation contained within all of these works is that of organisms buffering themselves against changes in the environment (see Caswell 1983). It is important to point out, as have Thoday (1953), Lewontin (1957), and especially Bradshaw (1965), that this notion of plasticity could only apply a priori to homeostasis of "fitness" traits. Any realistic view of homeostasis must encompass the realization that decreased biochemical, morphological, or physiological variability could be associated with increased or decreased "fitness" homeostasis. Some aspects of an organism's biology must vary in order to allow other aspects to remain constant (Cannon 1932). Under the classical view, an apparent lack of homeostatic ability is ascribed to the absence of selection rather than as a possible outcome of selection. Therefore, the focus of this paper is on the benefit to an organism arising from homeostasis of survivorship and reproductive schedules. I will argue that there is no universal benefit to such homeostasis. Indeed, at first glance it seems difficult to decide whether genotypes which "ignore" the environment are better off than those which "pay attention" to it. Such a possibility has been suggested previously by Levins (1963) and Bradshaw (1965). Bradshaw writes (p. 127), "During its life an annual suffers changes in its environment, but from generation to generation the
Theoretical Population Biology, Dec 1, 1980
ABSTRACT
Oxford University Press eBooks, Oct 25, 2001
Understanding the allocation of energy is the goal of the evolutionary analysis of sex allocation... more Understanding the allocation of energy is the goal of the evolutionary analysis of sex allocation. Whether one is concerned with the relative sizes of male and female flower parts in plants like those discussed by Campbell (1998), the ratio of males and females in insects like those discussed by Orzack et al. (1991), or the relative sizes of male and female reproductive organs in hermaphroditic fish like those discussed by Leonard (1993), one is concerned with how energy allocated toward reproduction is apportioned into one sex as opposed to the other (or more in the case of some kinds of organisms). Here, the sexes are entities that at regular or irregular intervals produce gametes, some of which come together to produce zygotes. The abstract nature of this description underscores the degree to which there are common evolutionary aspects to all of these problems, despite the fact that the biological details involved are so diverse. One of the most influential and important agendas for evolutionary studies of sex allocation was laid out by Charnov (1982). He described the underlying evolutionary similarities between phenomena as diverse as sex change in shrimp and sex ratio in vertebrates like us. Even more important, he promoted sex allocation as a central evolutionary problem by describing how seemingly unrelated allocation problems could all be analyzed with a kind of mathematical approach elaborated by Shaw and Mohler (1953). I consider in turn four important examples of this approach. Shaw and Mohler’s goal was to understand the evolution of the proportions of males and females. This problem of the sex ratio was most famously addressed by Darwin in his 1871 book, The Descent of Man, and Selection in Relation to Sex, as well as by others in the subsequent decades. The most influential analysis is that of Fisher (1930); however, Carl Düsing, who worked in the 1880s, can rightly be regarded as the progenitor of modern sex ratio theory (see Edwards 1998).
Cambridge University Press eBooks, May 5, 2013
The American Naturalist, Apr 1, 1985
Page 1. Vol. 125, No. 4 The American Naturalist April 1985 POPULATION DYNAMICS IN VARIABLE ENVIRO... more Page 1. Vol. 125, No. 4 The American Naturalist April 1985 POPULATION DYNAMICS IN VARIABLE ENVIRONMENTS V. THE GENETICS OF HOMEOSTASIS REVISITED Steven Hecht Orzack Population Genetics, Museum ...
Genetics, May 1, 1985
ABSTRACT We detected genetic variation for the sex ratio in the parasitoid wasp Nasonia vitripenn... more ABSTRACT We detected genetic variation for the sex ratio in the parasitoid wasp Nasonia vitripennis by analysis of inbred lines and with an artificial selection experiment. Sex ratios differed significantly among five independently isolated lines. Furthermore, sex ratio in broods produced by single females in single hosts shifted from 80-90% female to 50-55% female in 13 to 15 generations in each of two replicate selection lines. The final sex ratios of both selection lines were significantly lower than any of the inbred line sex ratios. Backcrosses revealed that the selection response was due to nuclear genes acting through the female parent. In light of known facultative sex ratio behavior and major genes affecting sex ratio in Nasonia, our results suggest that population and individual sex ratios in this species are molded by processes at both genetic and behavioral levels.
Trends in Ecology and Evolution, Sep 1, 1996
Evolution and Diversity of Sex Ratio, 1993
Proceedings of the Royal Society B: Biological Sciences
Non peer reviewe
Understanding modeling in biology requires understanding how biology is organized as a discipline... more Understanding modeling in biology requires understanding how biology is organized as a discipline and how this organization influences the research practices of biologists. Biology includes a wide range of sub-disciplines, such as cell biology, population biology, evolutionary biology, molecular biology, and systems biology among others. Biologists in sub-disciplines such as cell, molecular, and systems biology believe that the use of a few experimental models allows them to discover biological universals, whereas biologists in sub-disciplines such as ecology and evolutionary biology believe that the use of many different experimental and mathematical models is necessary in order to do this. Many practitioners of both approaches misunderstand best practices of modeling, especially those related to model testing. We stress the need for biologists to better engage with best practices and for philosophers of biology providing normative guidance for biologists to better engage with curr...
The Quarterly Review of Biology, 2000
Trends in Ecology & Evolution, 1995
Population and Development Review
The Quarterly Review of Biology, 2014
Significance, Feb 1, 2016
The human sex ratio – the ratio of males to females – has long fascinated biologists and statisti... more The human sex ratio – the ratio of males to females – has long fascinated biologists and statisticians alike. Steven Hecht Orzack presents a potted history, from the earliest interpretations to the most recent – and surprising – conclusions The sex ratio Understanding the ratio of males to females has long fascinated biologists and statisticians, says Steven Hecht Orzack
The notion of homeostasis, an organism's ability to maintain a constant expression of a pheno... more The notion of homeostasis, an organism's ability to maintain a constant expression of a phenotypic character despite environmental change, is central to many arguments in biology. Most workers have presumed that homeostasis is beneficial and therefore the object of selection in natural populations. For example, Lewontin (1957, p. 402) asserts that "genotypes may arise with very wide adaptive norms, so wide in fact, that genetic polymorphism can add little to the adaptation of the population of which they are a part. Should such homeostatic genotypes alise, intrapopulational selection will favor them since they must, in a world of fluctuating environment, leave more offspring than their more specialized sibs." Similarly, Emerson (1961, p. 118) states that "Improved homeostasis seems to be a universal evolutionary trend and is basic to the concepts of adaptation and adaptability applied to all levels of biological and cultural organization." The picture of adaptation contained within all of these works is that of organisms buffering themselves against changes in the environment (see Caswell 1983). It is important to point out, as have Thoday (1953), Lewontin (1957), and especially Bradshaw (1965), that this notion of plasticity could only apply a priori to homeostasis of "fitness" traits. Any realistic view of homeostasis must encompass the realization that decreased biochemical, morphological, or physiological variability could be associated with increased or decreased "fitness" homeostasis. Some aspects of an organism's biology must vary in order to allow other aspects to remain constant (Cannon 1932). Under the classical view, an apparent lack of homeostatic ability is ascribed to the absence of selection rather than as a possible outcome of selection. Therefore, the focus of this paper is on the benefit to an organism arising from homeostasis of survivorship and reproductive schedules. I will argue that there is no universal benefit to such homeostasis. Indeed, at first glance it seems difficult to decide whether genotypes which "ignore" the environment are better off than those which "pay attention" to it. Such a possibility has been suggested previously by Levins (1963) and Bradshaw (1965). Bradshaw writes (p. 127), "During its life an annual suffers changes in its environment, but from generation to generation the
Theoretical Population Biology, Dec 1, 1980
ABSTRACT
Oxford University Press eBooks, Oct 25, 2001
Understanding the allocation of energy is the goal of the evolutionary analysis of sex allocation... more Understanding the allocation of energy is the goal of the evolutionary analysis of sex allocation. Whether one is concerned with the relative sizes of male and female flower parts in plants like those discussed by Campbell (1998), the ratio of males and females in insects like those discussed by Orzack et al. (1991), or the relative sizes of male and female reproductive organs in hermaphroditic fish like those discussed by Leonard (1993), one is concerned with how energy allocated toward reproduction is apportioned into one sex as opposed to the other (or more in the case of some kinds of organisms). Here, the sexes are entities that at regular or irregular intervals produce gametes, some of which come together to produce zygotes. The abstract nature of this description underscores the degree to which there are common evolutionary aspects to all of these problems, despite the fact that the biological details involved are so diverse. One of the most influential and important agendas for evolutionary studies of sex allocation was laid out by Charnov (1982). He described the underlying evolutionary similarities between phenomena as diverse as sex change in shrimp and sex ratio in vertebrates like us. Even more important, he promoted sex allocation as a central evolutionary problem by describing how seemingly unrelated allocation problems could all be analyzed with a kind of mathematical approach elaborated by Shaw and Mohler (1953). I consider in turn four important examples of this approach. Shaw and Mohler’s goal was to understand the evolution of the proportions of males and females. This problem of the sex ratio was most famously addressed by Darwin in his 1871 book, The Descent of Man, and Selection in Relation to Sex, as well as by others in the subsequent decades. The most influential analysis is that of Fisher (1930); however, Carl Düsing, who worked in the 1880s, can rightly be regarded as the progenitor of modern sex ratio theory (see Edwards 1998).
Cambridge University Press eBooks, May 5, 2013
The American Naturalist, Apr 1, 1985
Page 1. Vol. 125, No. 4 The American Naturalist April 1985 POPULATION DYNAMICS IN VARIABLE ENVIRO... more Page 1. Vol. 125, No. 4 The American Naturalist April 1985 POPULATION DYNAMICS IN VARIABLE ENVIRONMENTS V. THE GENETICS OF HOMEOSTASIS REVISITED Steven Hecht Orzack Population Genetics, Museum ...
Genetics, May 1, 1985
ABSTRACT We detected genetic variation for the sex ratio in the parasitoid wasp Nasonia vitripenn... more ABSTRACT We detected genetic variation for the sex ratio in the parasitoid wasp Nasonia vitripennis by analysis of inbred lines and with an artificial selection experiment. Sex ratios differed significantly among five independently isolated lines. Furthermore, sex ratio in broods produced by single females in single hosts shifted from 80-90% female to 50-55% female in 13 to 15 generations in each of two replicate selection lines. The final sex ratios of both selection lines were significantly lower than any of the inbred line sex ratios. Backcrosses revealed that the selection response was due to nuclear genes acting through the female parent. In light of known facultative sex ratio behavior and major genes affecting sex ratio in Nasonia, our results suggest that population and individual sex ratios in this species are molded by processes at both genetic and behavioral levels.
Trends in Ecology and Evolution, Sep 1, 1996
Evolution and Diversity of Sex Ratio, 1993
Proceedings of the Royal Society B: Biological Sciences
Non peer reviewe
Understanding modeling in biology requires understanding how biology is organized as a discipline... more Understanding modeling in biology requires understanding how biology is organized as a discipline and how this organization influences the research practices of biologists. Biology includes a wide range of sub-disciplines, such as cell biology, population biology, evolutionary biology, molecular biology, and systems biology among others. Biologists in sub-disciplines such as cell, molecular, and systems biology believe that the use of a few experimental models allows them to discover biological universals, whereas biologists in sub-disciplines such as ecology and evolutionary biology believe that the use of many different experimental and mathematical models is necessary in order to do this. Many practitioners of both approaches misunderstand best practices of modeling, especially those related to model testing. We stress the need for biologists to better engage with best practices and for philosophers of biology providing normative guidance for biologists to better engage with curr...
The Quarterly Review of Biology, 2000
Trends in Ecology & Evolution, 1995
Population and Development Review
The Quarterly Review of Biology, 2014