The Quarterly Review of Biology

Published by University of Chicago Press
Online ISSN: 1539-7718
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Article
This paper was given before the Genetics Section of the Moscow Society of Natural Science on November 26, 1957; before the joint session of the Geographical Society of USSR and the All-Union Botanical Society in Leningrad, December 6, 1957; and in Moscow on January 11, 1958 before the students of the Timiryazev Academy. A review, by I. Grebenschikova and F. Schultz, was printed in Der Zuchter, 28 (4): 161-166 (1958).
 
Article
The Soviet biophysical literature has been the subject of an extensive and critical review. The subject matter has been subdivided into sections on techniques, effect sof ionizing radiation, effects of light radiation, photosynthesis, effects of ultrasonics, paramagnetic resonance, microorganisms, viruses, cell structure, proteins, nucleic acids, and muscle, nerve, vision and taste. A bibliography of 520 entries is included. The work which has been reviewed covers the best and worst in Soviet science. In general those experiments and concepts in fields that are close to physics are excellent. Examples are the work in paramagnetic resonance, energy transfer mechanism in photosynthesis systems, the properties of structural proteins such as procollagen, and the coding properties of DNA. The average paper concerned with more biological subject matter, such as microorganisms, viruses, and proteins, seems outdated in concept and lacking in controlled experiments or adequate data. Recent reviews (which contain mostly references to Western literature) indicate that Soviet scientists are well acquainted with in Western countries and that the role of DNA as a carrier of genetic information is now fully appreciated.
 
Article
Pregnancy has commonly been viewed as a cooperative interaction between a mother and her fetus. The effects of natural selection on genes expressed in fetuses, however, may be opposed by the effects of natural selection on genes expressed in mothers. In this sense, a genetic conflict can be said to exist between maternal and fetal genes. Fetal genes will be selected to increase the transfer of nutrients to their fetus, and maternal genes will be selected to limit transfers in excess of some maternal optimum. Thus a process of evolutionary escalation is predicted in which fetal actions are opposed by maternal countermeasures. The phenomenon of genomic imprinting means that a similar conflict exists within fetal cells between genes that are expressed when maternally derived, and genes that are expressed when paternally derived. During implantation, fetally derived cells (trophoblast) invade the maternal endometrium and remodel the endometrial spiral arteries into low-resistance vessels that are unable to constrict. This invasion has three consequences. First, the fetus gains direct access to its mother's arterial blood. Therefore, a mother cannot reduce the nutrient content of blood reaching the placenta without reducing the nutrient supply to her own tissues. Second, the volume of blood reaching the placenta becomes largely independent of control by the local maternal vasculature. Third, the placenta is able to release hormones and other substances directly into the maternal circulation. Placental hormones, including human chorionic gonadotropin (hCG) and human placental lactogen (hPL), are predicted to manipulate maternal physiology for fetal benefit. For example, hPL is proposed to act on maternal prolactin receptors to increase maternal resistance to insulin. If unopposed, the effect of hPL would be to maintain higher blood glucose levels for longer periods after meals. This action, however, is countered by increased maternal production of insulin. Gestational diabetes develops if the mother is unable to mount an adequate response to fetal manipulation. Similarly, fetal genes are predicted to enhance the flow of maternal blood through the placenta by increasing maternal blood pressure. Preeclampsia can be interpreted as an attempt by a poorly nourished fetus to increase its supply of nutrients by increasing the resistance of its mother's peripheral circulation.
 
Article
Tithonus asked Aurora for eternal life, when he meant eternal youth. Modern gerontological research makes the same mistake in its preoccupation with death, as if it were a programmed event in an organism's life history. Gerontology ought instead to investigate senescence, the decreasing effectiveness of mechanisms by which adult organisms avoid death or loss of fitness. Such studies should measure rates of decline in a diversity of adaptations and compare them within and between individuals and relate these rates and their correlations to genetic and environmental factors. The death of a studied organism must necessarily end its usefulness in providing valuable data. It is of little scientific significance.
 
Article
The 1890s and the first decades of the twentieth century saw a vigorous debate about the mechanisms of evolutionary change. On one side, August Weismann defended the selectionist hypothesis; on the other, Herbert Spencer defended neo-Lamarckian theory. Supporters of Spencer, notably the American paleontologist and evolutionary theorist Henry Fairfield Osborn, recognized that the questions raised by Weismann and Spencer could only be settled experimentally. They called for the application of experimental methods, and the establishment of a new institution for the purpose of confirming the inheritance of acquired characters. To a great extent, the experimental program championed by Osborn and others was implemented and, although it failed to reveal soft inheritance and was soon eclipsed by Mendelian and chromosomal genetics, it did make significant and lasting contributions to evolutionary biology. Thus the importance of methodological and institutional innovation and theoretical pluralism to the progress of science is illustrated and underscored.
 
Article
Correlations of social structure, life-history patterns, and ecology among the seventeen species of grouse exemplify some general patterns in the evolution of mating systems among higher vertebrates. The species of grouse differ in the aggregation of displaying males, the permanence of heterosexual affiliations, the contributions of males to parental care, and the breeding sex ratio. Promiscous species (no durable heterosexual affiliation) are probably all polynous (the breeding sex ratio less than unity), but fall into two groups depending on whether the displaying males congregate at leks or disperse relatively evenly. In all of these promiscuous, polygymous species and in three monogramous species, the female cares for the young; dual parental care appears only in one monogamous species. During their first year, the males of polynous species do not mate or mate much less frequently, although females normally breed at one year of age, a situation termed sexual bimaturism. At least among birds and mammal...
 
Article
Gene flow between different reproductive units such as bacterial plasmids and chromosomes presents unusual problems for evolutionary analysis. Far more than in eukaryotes, reproductive advantages at several levels of selection--genes, transposons, plasmids, cells, and clones--must be considered simultaneously to understand plasmid evolution. No level consistently prevails in conflict situations, and some reproductive units carry genes that restrain their own reproduction or survival, apparently to enhance the reproduction or survival of the higher-level reproductive units that carry them. Despite gene flow between plasmids and chromosomes, genes for certain functions show strong tendencies to occur on plasmids while others consistently occur on chromosomes. Functions generally associated with plasmids are diverse, but all are useful only in locally restricted contexts; it is argued that the selective consequences of the greater horizontal (within generation) transmission of plasmids are responsible for this pattern. The tendency for prokaryote transposons, which are also horizontally mobile, to carry genes similar to those commonly on plasmids supports this argument. The apparent trends in eukaryote plasmids and transposons to lack these same characters also accords with predictions of the local adaptation hypothesis, because genes on these genetic units are generally no more horizontally mobile than chromosomal genes. There are theoretical reasons to expect that plasmid genes tend to evolve more rapidly than chromosomal genes. "The selfish interests of genes have manifestly produced 'vehicles' in the forms of organelles, cells, individuals and yet higher units. If evolution is to predict as well as describe, then selfish interests must be understood in the framework of the constraints and opportunities generated by these 'vehicles'" (Buss, 1987, p. 182).
 
Article
The review discusses some consequences of the widespread partial uncoupling of the reproduction of organelle DNA from that of nuclear DNA. I propose that in certain circumstances natural selection favors intraorganismal reproductive competition between different varieties of organelle DNA, and in other circumstances selection favors competition between organelle and nuclear DNA. Evidence is marshalled to show that such competition occurs in nature. Situations which would lead to selection for both kinds of competition are described and are shown to be relatively common. A number of examples of apparent competition of predicted kinds are presented. Several testable predictions are made from the theory, and it is shown that the available data are in accord with them. Similar kinds of reproductive competition are predicted to occur in some other symbiotic relationships, and possible examples are presented for two of them: bacterial plasmids and endozoic algae.
 
Article
Several features of the evolution of eyes and photoreceptors are examined in an effort to explore the relative roles of adaptation and historical and developmental constraints. Optical design shows clear evidence of adaptation, which in some respects approaches optima predictable from physics. The primate fovea, on the other hand, illustrates how adaptation can be channeled by developmental heritage. The primary structures of opsins reveal multiple evolutionary lineages within both Drosophila and humans. The pigments of vertebrae rods comprise a subset of opsins whose evolutionary relationships map onto the phylogeny of the parent species. The evolutionary reasons for why most rod pigments absorb maximally at 500 +/- 10 nm are obscure, as there is no convincing explanation based on adaptation alone. Rods are appropriately distinguished from cones on the basis of which opsin gene is expressed. This criterion is likely to be in conflict with other definitions in phyletic lines (e.g., geckos, snakes) that have long diurnal or nocturnal histories accompanied by loss of one or more opsin genes, followed by a secondary adaptation to life in a different photic environment. Color vision--a generalizable perception associated with the spectral composition of light--is usefully distinguished from wavelength-specific behaviors. The latter are also based on multiple visual pigments and more than one spectral class of receptors but cannot be altered by learning. The distinction is particularly forceful in bees, which exhibit both kinds of behavior. The evolution of primate color vision has been shaped by historical factors involving an extensive period of early mammalian nocturnality. Birds, by contrast, have more elaborate cones and a richer set of visual pigments. Avian color space can be represented in a tetrahedron.
 
Article
A large fraction, sometimes the largest fraction, of a eukaryotic genome consists of repeated DNA sequences. Copy numbers range from several thousand to millions per diploid genome. All classes of repetitive DNA sequences examined to date exhibit apparently general, but little studied, patterns of "concerted evolution." Historically, concerted evolution has been defined as the nonindependent evolution of repetitive DNA sequences, resulting in a sequence similarity of repeating units that is greater within than among species. This intraspecific homogenization of repetitive sequence arrays is said to take place via the poorly understood mechanisms of "molecular drive." The evolutionary population dynamics of molecular drive remains largely unstudied in natural populations, and thus the potential significance of these evolutionary dynamics for population differentiation is unknown. This review attempts to demonstrate the potential importance of the mechanisms responsible for concerted evolution in the differentiation of populations. It contends that any natural grouping that is characterized by reproductive isolation and limited gene flow is capable of exhibiting concerted evolution of repetitive DNA arrays. Such effects are known to occur in protein and RNA-coding repetitive sequences, as well as in so-called "junk DNA," and thus have important implications for the differentiation and discrimination of natural populations.
 
Article
Seven general kinds of life cycles are known among crickets; they differ chiefly in overwintering (diapause) stage and number of generations per season, or diapauses per generation. Some species with broad north-south ranges vary in these respects, spannig wholly or in part certain of the gaps between cycles and suggesting how some of the differences orgininated. Species with a particular cycle have predictable responses to photoperiod and temperature regimes that affect behavior, development time, wing length, boyd size, and other characteristics. Some polymorphic tendencies also correlate with habitat permanence, and some are influenced by population density. Genera and subfamilies with several kinds of life cycles usually have proportionately more species in temperate regions than those with but one or two cycles, although numbers of species in all widely distributed groups diminish toward the higher latitudes. The tendency of various field cricket species to become double-cycled at certain latitudes a...
 
Article
Ribosomal DNA (rDNA) sequences have been aligned and compared in a number of living organisms, and this approach has provided a wealth of information about phylogenetic relationships. Studies of rDNA sequences have been used to infer phylogenetic history across a very broad spectrum, from studies among the basal lineages of life to relationships among closely related species and populations. The reasons for the systematic versatility of rDNA include the numerous rates of evolution among different regions of rDNA (both among and within genes), the presence of many copies of most rDNA sequences per genome, and the pattern of concerted evolution that occurs among repeated copies. These features facilitate the analysis of rDNA by direct RNA sequencing, DNA sequencing (either by cloning or amplification), and restriction enzyme methodologies. Constraints imposed by secondary structure of rRNA and concerted evolution need to be considered in phylogenetic analyses, but these constraints do not appear to impede seriously the usefulness of rDNA. An analysis of aligned sequences of the four nuclear and two mitochondrial rRNA genes identified regions of these genes that are likely to be useful to address phylogenetic problems over a wide range of levels of divergence. In general, the small subunit nuclear sequences appear to be best for elucidating Precambrian divergences, the large subunit nuclear sequences for Paleozoic and Mesozoic divergences, and the organellar sequences of both subunits for Cenozoic divergences. Primer sequences were designed for use in amplifying the entire nuclear rDNA array in 15 sections by use of the polymerase chain reaction; these "universal" primers complement previously described primers for the mitochondrial rRNA genes. Pairs of primers can be selected in conjunction with the analysis of divergence of the rRNA genes to address systematic problems throughout the hierarchy of life.
 
Intraspecific Distribution-Abundance Relationships A) Shows the spatial location of individuals of a species. For clarity, we demonstrate sampling with uniform grid cells; alternatives include distributed sampling quadrates, or sites defined by habitat characteristics. B) Distribution and abundance are measured, as the presence/absence and population number in each grid cell. On a larger grid (overlaid), the central areas have larger grid cell occupancy. C) The spatial intraspecific relationship: There is a positive correlation between the cell occupancy and mean local abundance across areas from different parts of the range. D) Depicts the same species sampled at a later point in time where the population size has decreased. E) Repeating the sampling process gives a measure of distribution and abundance at this time. F) The temporal intraspecific relationship: integrating the data from (B) and (E) reveals a positive correlation between the distribution and abundance across time.
The Interspecific Distribution-Abundance Relationship Two co-occurring species are sampled in a similar way to the species in Figure 1. Plotting the distribution and abundance of each species against each other reveals a positive interspecific relationship.
The Relationship between Local Abundance and Proportional Occupany among Danish Birds Data taken from the Danish breeding bird Atlas (Grell 1998; for a description of data selection, see Borregaard and Rahbek 2006) at the 5x5 km scale (black dots), and subsequently resampled by lumping grid cells to 25x25 km cells (white dots). The slopes are significantly different (t 7.14, p 0.001).  
Causality of Distribution-Abundance Relationships The flow diagram illustrates the interlinks between the types of distribution-abundance relationships and the different types of causality. The solid line denominates structural causality, the uniform dashed line represents dynamic causality, and the slashed dotted line indicates measurement effects. (See the text for details.)  
The Relationship between Structural and Dynamic Causal Pathways Different mechanisms affect different aspects of the distribution of species, and may work together to create observed patterns. Here the interaction is demonstrated for the most commonly quoted hypotheses: the resource use hypothesis and meta-population dynamics.  
Article
The positive relationship between a species' geographic distribution and its abundance is one of ecology's most well-documented patterns, yet the causes behind this relationship remain unclear. Although many hypotheses have been proposed to account for distribution-abundance relationships none have attained unequivocal support. Accordingly, the positive association in distribution-abundance relationships is generally considered to be due to a combination of these proposed mechanisms acting in concert. In this review, we suggest that much of the disparity between these hypotheses stems from differences in terminology and ecological point of view. Realizing and accounting for these differences facilitates integration, so that the relative contributions of each mechanism may be evaluated. Here, we review all the mechanisms that have been proposed to account for distribution-abundance relationships, in a framework that facilitates a comparison between them. We identify and discuss the central factors governing the individual mechanisms, and elucidate their effect on empirical patterns.
 
Article
Since 1813, when Crampton first described the ciliary muscle of the avian eye, there has been little agreement on how birds are able to change the focus of their eyes. Numerous lata studies on the eyes of a variety of bird species contradicted earlier findings or proposed new accommodative mechanisms. The resulting confusion persists today, and a number of significant works on the avian eye perpetuate many of the myths developed during the 1800s. There is little consensus on avian accommodation; the early literature contains many accurate descriptions qi the mechanisms, along with elegant experimental evidence to support them. Much of the early literature, however, is in German and has remained obscure. Further, among the mechanistic descriptions of avian accommodation are many that are incorrect. The current confusion can be attributed in part to the fact that some birds have both corneal and lenticular accommodation. It is unclear to what extent different bird species employ both mechanisms, or depend on one mechanism or the other. These facts, together with the diversity of bird species, their range of visual requirements, and the numerous anatomical differences in their eyes, mab it impossible to describe a single avian mechanism of accommodation. Our own experience in studying accommodation in the chick eye has led us to review the historical literature in an attempt to provide a new foundation for future studies on visual accommodation in birds.
 
Article
A comprehensive review of women's dietary behavior across the menstrual cycle suggests a drop in caloric intake around the time of ovulation; similar patterns occur in many other mammals. The periovulatory nadir is puzzling, as it is not explicable in terms of changes in the energy budget. Existing explanations in the animal literature operate wholly at the proximate level of analysis and hence do not address this puzzle. In this paper, I offer an ultimate explanation for the periovulatory feeding nadir, arguing that the decrease in the set point for satiation during the fertile period of the female cycle is an adaptation produced by natural selection in order to reduce the motivational salience of goals that compete with those directly or indirectly pertaining to mating. In support of this explanation, I adduce evidence of: a) periovulatory reductions in other ingestive behaviors, and b) periovulatory increases in motor activity and the psychological concomitants thereof.
 
Article
During the 1930s, T.D. Lysenko rose to prominence in Soviet science, with a belief that genes were a myth invented by bourgeois scientists and that chromosomes had nothing to do with heredity. He also accepted inheritance of acquired characters; spontaneous generation; and that one species could suddenly be transformed into another without any intermediate stage. The ideological and scientific background to and implications of the genetic determinism of Lysenko are discussed in four papers (Lysenkoism in Poland, by Gajewski; How I became a Lysenkoist, by Putraments; Difficult years in Soviet genetics, by Gershenson; In defence of Timofeeff-Ressovsky, by Berg), with an explanatory preface by Glass. -P.J.Jarvis
 
Fraction of Pathogens Examined that Utilize Cholesterol (N ϭ 32). 
Pathogens for which the Infection Cycle is Maximally Limited by Th1 or Th2 Responses (N ϭ 32). 
Pathogens for which the Infection Cycle is Maximally Enhanced by Th1 or Th2 Responses (N ϭ 13). 
Period of Maximal Negative Impact of Infection Among Pathogens Known to Affect the Course of Pregnancy (N ϭ 15). 
Article
Progesterone and cholesterol are both vital to pregnancy. Among other functions, progesterone downregulates inflammatory responses, allowing for maternal immune tolerance of the fetal allograft. Cholesterol a key component of cell membranes, is important in intracellular transport, cell signaling, nerve conduction, and metabolism Despite the importance of each substance in pregnancy, one exercises an antagonistic effect on the other, as periods of peak progesterone correspond with reductions in cholesterol availability, a consequence of progesterone's negative effects on cholesterol biosynthesis. This arrangement is understandable in light of the threat posed by pathogens early in pregnancy. Progesterone-induced immunomodulation entails increased vulnerability to infection, an acute problem in the first trimester, when fetal development is highly susceptible to insult. Many pathogens rely on cholesterol for cell entry, egress, and replication. Progesterone's antagonistic effects on cholesterol thus partially compensate for the costs entailed by progesterone-induced immunomodulation. Among pathogens to which the host's vulnerability is increased by progesterone's effects, approximately 90% utilize cholesterol, and this is notably true of pathogens that pose a risk during pregnancy. In addition to having a number of possible clinical applications, our approach highlights the potential importance of second-order adaptations, themselves a consequence of the lack of teleology in evolutionary processes.
 
Article
Highly purified preparations of RNA prepared from mature ovarian eggs of Rana catesbeiana contain at least two gross fractions of RNA: one that is soluble in cold 0.5 M perchloric acid (acid-soluble RNA) and another that is insoluble in the same concentration of acid (acid-insoluble RNA). Each Comprises roughly 50 per cent of the total RNA. The two RNA fractions are distinct not only in solubility characteristics but in nucleotide composition as well. A procedure has been developed for the mass isolation of structures morphologically similar to the nucleoli of mature ovarian eggs. These structures contain no DNA, from 8 to 17 per cent RNA, and a large amount of protein. The distribution of P32 in the mononucleotides of cytoplasmic RNA, nuclear RNA, and nucleolar RNA shows that the mononucleotide compositions, based on counts, of nuclear RNA and nucleolar RNA are essentially the same. Nucleolar RNA apparently contains a major component (compound X) which superficially resembles uridylic acid and may be pse...
 
Article
A major goal of research in ecology and evolution is to explain why species richness varies across habitats, regions, and clades. Recent reviews have argued that species richness patterns among regions and clades may be explained by "ecological limits" on diversity over time, which are said to offer an alternative explanation to those invoking speciation and extinction (diversification) and time. Further, it has been proposed that this hypothesis is best supported by failure to find a positive relationship between time (e.g., clade age) and species richness. Here, I critically review the evidence for these claims, and propose how we might better study the ecological and evolutionary origins of species richness patterns. In fact, ecological limits can only influence species richness in clades by influencing speciation and extinction, and so this new "alternative paradigm" is simply one facet of the traditional idea that ecology influences diversification. The only direct evidence for strict ecological limits on richness (i.e., constant diversity over time) is from the fossil record, but many studies cited as supporting this pattern do not, and there is evidence for increasing richness over time. Negative evidence for a relationship between clade age and richness among extant clades is not positive evidence for constant diversity over time, and many recent analyses finding no age-diversity relationship were biased to reach this conclusion. More comprehensive analyses strongly support a positive age-richness relationship. There is abundant evidence that both time and ecological influences on diversification rates are important drivers of both large-scale and small-scale species richness patterns. The major challenge for future studies is to understand the ecological and evolutionary mechanisms underpinning the relationships between time, dispersal, diversification, and species richness patterns.
 
Article
Many of the 200 or so non-protein amino acids synthesized by higher plants are related structurally to the constituents of common proteins. L-Canavanine, the guanidinooxy structural analogue of L-arginine, is representative of this group. It has provided valuable insight into the biological effects and the mode of action of non-protein amino acids which acts as analogues of the protein amino acids. The arginyl-tRNA synthetases of numerous canavanine-free species charge canavanine, and canavanine is subsequently incorporated into the nascent polypeptide chain. Production of canavanine-containing proteins ultimately can disrupt critical reactions of RNA and DNA metabolism as well as protein synthesis. Canavanine also affects regulatory and catalytic reactions of arginine metabolism, arginine uptake, formation of structural components, and other cellular precesses. In these ways, canavanine alters essential biochemical reactions and becomes a potent antimetabolite of arginine in a wide spectrum of species. These deleterious properties of canavanine render it a highly toxic secondary plant constituent that probably functions as an allelochemic agent that deters the feeding activity of phytophagous insects and other herbivores.
 
Article
Dormant ascospores of Neurospora remain quiescent and metabolize at a slow rate unless activated by exposure to high temperatures or to chemicals, including certain furans, pyrroles, thiophenes, or organic solvents. As a result of this treatment, a step-wise series of changes is initiated, resultingin in a greatly increased respiratory rate, a loss in thermal resistance, and a rise in the respiratory quotient. Up to 30 minutes after dormancy is broken, deactivation by incubation at 4⚬ C is possible, but after this time the process is irreversible. The locus of the metabolic activation has been shown not to reside in the cytochrome system and probably not in terminal oxidation. Moreover, pyruvate carboxylase, as well as the steps leading to oxygen, are probably not directly affected by the activation reaction, although there is evidence for an increase in the amount of cytochrome c available to the respiratory apparatus after activation. A study of the endogenous substrates of ascospores reveals that the C...
 
Direct and Indirect Effects on a Larval Phenotype Social insect phenotypes are influenced by a variety of direct and indirect effects. These different influences on a focal larva's phenotype are shown by the arrows. Siblings expressing sib-social care are shown to be smaller than the mother to indicate that only individuals in poor condition express sib-social care. 
Path Diagram for Influences of Direct and Indirect Additive Genetic Effects on a Phenotype of a Second Brood Offspring A mother with folded wings is shown on the left, and her first and second brood female offspring are in the center and right, respectively. Panel A shows a subsocial colony in which offspring of both broods reproduce, disperse (hence the extended wings), and express maternal care genes toward their own offspring (not shown). Panel B shows a eusocial colony in which first brood offspring remain at the natal nest (hence folded wings) and express sib-social genes toward their sibs (second brood dispersing offspring with extended wings) instead of reproducing, dispersing, and expressing maternal care genes toward their own offspring. The first brood offspring is smaller than the other individuals to indicate that it is in poor condition and cannot successfully reproduce on its own. The symbol, A o , is for direct additive genetic effects that influence the phenotype of the individual in which they are expressed, while A m represents maternal additive genetic effects that influence offspring phenotypes through their effect on maternal performance, M. The A s represents sib-social additive genetic effects that influence sibling phenotypes through their effect on sib-social performance, S. Genetic effects in parentheses are not expressed (i.e., the eusocial mother and her second brood offspring express maternal care genes but do not express sib-social care genes, while smaller first brood offspring express sibsocial care genes but do not express maternal care genes). Solid arrows represent influences on a phenotype Z of the second brood offspring. Doubleheaded dotted arrows represent genetic correlations between additive genetic effects due to pleiotropy: (1) r om is the direct maternal additive genetic correlation; (2) r os is the direct sib-social additive genetic correlation; and, (3) r ms is the maternal sib-social additive genetic correlation. In panel A, phenotype Z of the second brood offspring is influenced by maternal and direct effects. In panel B, phenotype Z of the second brood offspring is influenced by maternal and direct effects, as well as by sib-social effects from the first brood offspring. Note that sib-social care initially is merely the pleiotropic expression of maternal care genes, so that at least initially, r os r om and r ms 1. For clarity, no environmental effects, paternal effects, or effects due to competition among sibs are shown. Paths for the transmission of additive genetic effects from mother to offspring weighted by maternal-offspring relatedness (1/2) are also not shown nor is the genetic relatedness between sibs (3/4 in haplodiploids with a singly-mated mother) shown, although relatedness among social partners is accounted for in indirect genetic effect models. 
Article
We discuss the evolutionary origin and elaboration of sociality using an indirect genetic effects perspective. Indirect genetic effects models simultaneously consider zygotic genes, genes expressed in social partners (especially mothers and siblings), and the interactions between them. Incorporation of these diverse genetic effects should lead to more realistic models of social evolution. We first review haplodiploidy as a factor that promotes the evolution of eusociality. Social insect biologists have doubted the importance of relatedness asymmetry caused by haplodiploidy and focused on other predisposing factors such as maternal care. However; indirect effects theory shows that maternal care evolves more readily in haplodiploids, especially with inbreeding and despite multiple mating. Because extended maternal care is believed to be a precondition for the evolution of eusociality, the evolutionary bias towards maternal care in haplodiploids may result in a further bias towards eusociality in these groups. Next, we compare kin selection and parental manipulation and then briefly review additional hypotheses for the evolutionary origin of eusociality. We present a verbal model for the evolutionary origin and elaboration of sib-social care from maternal care based on the modification of the timing of expression of maternal care behaviors. Specifically, heterochrony genes cause maternal care behaviors to be expressed prereproductively towards siblings instead of postreproductively towards offspring. Our review demonstrates that both maternal effect genes (expressed in a parental manipulation manner) and direct effect zygotic genes (expressed in an offspring control manner) are likely involved in the evolution of eusociality. We conclude by describing theoretical and empirical advances with indirect genetic effects and sociogenomics, and we provide specific quantitative genetic and genomic predictions from our heterochrony model for the evolutionary origin and elaboration of eusociality.
 
Schematic Relationship Between Increasing Stress and Resulting Damage Within an Individual Cell or Organism There is an implied time component, in assuming that the increasing stress develops slowly enough that protective stress responses can develop.
Effect of Increasing Stress on Pathogens and the Host If pathogens (dashed curve) are more stressed than the host (solid curve), any additional induced stress (e.g., Points 1, 2, or 3) will cause more damage to the pathogens (P) than to the host (H). Host benefit occurs for every induced stress beyond the crossover point of the two curves (X).  
Immune Brinksmanship Model of the APR Systemic stressors of the APR affect the entire body (outer circle) containing both host cells and pathogens. However, pathogens, being localized to the infected area (dark inner oval), are subject to additional vulnerabilities (listed in the arrow).  
Article
The acutephase response (APR) is a systemic response to severe trauma, infection, and cancer, although many of the numerous cytokine-mediated components of the APR are incompletely understood. Some of these components, such as fever, reduced availability of iron and zinc, and nutritional restriction due to anorexia, appear to be stressors capable of causing harm to both the pathogen and the host. We review how the host benefits from differences in susceptibility to stress between pathogens and the host. Pathogens, infected host cells, and neoplastic cells are generally more stressed or vulnerable to additional stress than the host because: (a) targeted local inflammation works in synergy with APR stressors; (b) proliferation/growth increases vulnerability to stress; (c) altered pathogen physiology results in pathogen stress or vulnerability; and (d) protective heat shock responses are partially abrogated in pathogens since their responses are utilized by the host to enhance immune responses. Therefore, the host utilizes a coordinated system of endogenous stressors to provide additional levels of defense against pathogens. This model of immune brinksmanship can explain the evolutionary basis for the mutually stressful components of the APR.
 
MECHANISTIC AND HISTORICAL AXES A. Mechanistic axis. This represents the causal interactions among the parts. Here the lever and the gears work together to produce a torque. Variation in torque is a mechanistic consequence of variation in the moment arm and variation in the gear ratio. This axis does not tell us how these variables change and what actual patterns exist in nature. This dimension lacks history. B. Historical axis. This represents patterns of change in isolated parts over evolutionary time. By itself, this axis cannot provide strong inferences about the mechanistic causes of change. In this example, ancestral state is large gears, small moment arm, and low torque performance. In the derived condition, the gears have become smaller, the moment arm has become larger, and there is an increase in torque. Why did torque increase? One could explain this by correlated change in any of the variables. Possibly the smaller gears increase torque, or possibly the larger arm increases torque. It is not possible to tell without adding the mechanistic dimension. In this example the gear ratio remains the same, so change in gear sizes have no effect on torque.  
Article
Adding a causal, mechanistic dimension to the study of character evolution will increase the strength of inferences regarding the evolutionary history of characters and their adaptive consequences. This approach has the advantage of illuminating mechanism and testing evolutionary hypotheses rigorously. We consider the advantages of combining mechanistic and historical biology in the study of behavior, physiology, and development. We present six examples to illustrate the advantages: (1) preexisting biases in sound perception in frogs; (2) preexisting biases in visual cues in swordtailfishes; (3) exploitation of prey location behavior for attraction of mates in water mites; (4) heterospecific mating in asexual molly fishes; (5) developmental foundation of morphological diversification in amphibian digits; and (6) locomotor performance at low temperature and the evolution of nocturnality in geckos. In each of these examples, the dominant role of history, combined with organismal integration, makes ignoring history a risky proposition.
 
Article
For many animals, the best defense against harsh environmental conditions is an escape to a hypometabolic or dormant state. Facultative metabolic rate depression is the common adaptive strategy of anaerobiosis, hibernation, and estivation, as well as a number of other arrested states. By reducing metabolic rate by a factor ranging from 5 to 100 fold or more, animals gain a comparable extension of survival time that can support months or even years of dormancy. The present review focuses on the molecular control mechanisms that regulate and coordinate cellular metabolism for the transition into dormancy. These include reversible control over the activity state of enzymes via protein phosphorylation or dephosphorylation reactions, pathway regulation via the association or dissociation of particle-bound enzyme complexes, and fructose-2,6-bisphosphate regulation of the use of carbohydrate reserves for biosynthetic purposes. These mechanisms, their interactions, and the regulatory signals (e.g., second messenger molecules, pH) that coordinate them form a common molecular basis for metabolic depression in anoxia-tolerant vertebrates (goldfish, turtles) and invertebrates (marine molluscs), hibernation in small mammals, and estivation in land snails and terrestrial toads.
 
Article
Organisms typically "discount the future" in their decision making, but the extent to which they do so varies across species, sexes, age classes, and circumstances. This variability has been studied by biologists, economists, psychologists, and criminologists. We argue that the conceptual framework required for an interdisciplinary synthesis of knowledge in this area is the evolutionary adaptationist analysis of reproductive effort scheduling pioneered by George Williams.
 
Article
In his classic Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought (1966), George Williams showed definitively that our understanding of adaptation, a central concept of evolutionary theory, must be gene-centered. The purpose of adaptations is to further the replication of genes. Genes are machines for turning out more genes; and adaptations are the means by which genes pluck resources from the world to promote this self-replication. Thus adaptations transform potential resources from part of the indifferent world-at-large into tailor-made environments, environments brimming with resources for organisms' distinctive adaptive needs. Systematically dif ferent adaptive problems therefore give rise to different environments; and so different species, for example, have different environments. Thus a gene-centered analysis of adaptations implies a gene-centered theory of environments. Without genes to specify what constitutes an environment, environments would not exist. Rather than being separate from biology, an autonomous, independent force, environments are themselves the products of biology. So a gene-centered view, far from depreciating the environment, furnishes a rich and precise understanding of its importance.
 
Comparative Analysis of the Correlation Between Sexual Dimorphism in Home Range Size and Sexual Dimorphism in Spatial Ability Across Species A) The phylogeny of the species used in the comparative analysis. Estimated divergence times are placed next to the branch lengths. Note that the branch lengths are not drawn to scale. In brackets at the tips of the tree before the species names are the species averages for home range and spatial ability dimorphism, respectively, from Table 1. B) The raw correlation without any transformation to adjust for phylogenetic relatedness. 
Article
In the past few decades, sex differences in spatial cognition have often been attributed to adaptation in response to natural selection. A common explanation is that home range size differences between the sexes created different cognitive demands pertinent to wayfinding in each sex and resulted in the evolution of sex differences in spatial navigational ability in both humans and nonhuman mammals. However, the assumption of adaptation as the appropriate mode of explanation was nearly simultaneous with the discovery and subsequent verification of the male superiority effect, even without any substantive evidence establishing a causal role for adaptation. An alternate possibility that the sex difference in cognition is a genetic or hormonal side effect has not been rigorously tested using the comparative method. The present study directly evaluates how well the range hypothesis fits the available data on species differences in spatial ability by use of a phylogenetically based, cross-species, comparative analysis. We find no support for the hypothesis that species differences in home range size dimorphism are positively associated with parallel differences in spatial navigation abilities. The alternative hypothesis that sex differences in spatial cognition result as a hormonal side effect is better supported by the data.
 
Article
A cell's decision whether to undergo apoptosis (cell suicide) is examined here from an adaptationist perspective, rather than a mechanistic one. External and internal inputs to the cell's protein-based information processing network are used in making this decision, with the cell factoring in its replaceability. A system in which each cell takes primary responsibility for deciding its own fate has great adaptive value because it harnesses each cell's self-knowledge rather than waiting for external cues to be recognized by other cells. Cell self-destruction can be an important selective mechanism, potentially leading to better performance of tissues over time. However, reliance on cells to monitor themselves has a flaw, since cells may incur selfish mutations that impair their apoptotic responsibility. The tight control exerted over somatic cells serves to check selfish genes involved in neoplasia and viral infections. Germ cells appear to be similarly monitored, both by other germ cells and by supporting follicular or Sertoli cells, thus maintaining the advantages offered by an apoptotic system. The adaptationist approach views the limited replacement of neurons and cardiac myocytes as likely to have net survival value. The linkage of these cells into a network with their neighbors throughout a lifetime allows for a precisely functioning team of cells expected to compensate for gradual declines in individual cell functionality. Replacement of apoptotic cells with naive cells might decrease brain functionality and might risk upsetting the conduction of cardiac impulses. The evolutionary viewpoint lends itself to new hypotheses, but only the boldest speculator would have predicted a system in which cells are given primary responsibility for deciding whether to kill themselves when they deem it beneficial to the organism.
 
Top-cited authors
Robert Trivers
  • Chapman University
Robert E. Ziemba
  • Arizona State University
Alison Bell
  • University of Illinois, Urbana-Champaign
James Chadwick Johnson
  • Arizona State University
Andrew Sih
  • University of California, Davis