Some metabolic pathways are nearly ubiquitous among organisms: the genes encoding the enzymes for such pathways must therefore be ancient and essential. De novo pyrimidine biosynthesis is an example of one such metabolic pathway. In animals a single protein called CADAbbreviations: CAD, trifunctional protein catalyzing the first three steps of de novo pyrimidine biosynthesis in higher eukaryotes; CPS, carbamyl phosphate synthetase domain; CPSase, carbamyl phosphate synthetase activity; ATC, aspartate transcarbamylase domain; ATCase, aspartate transcarbamylase activity; DHO, dihydroorotase domain; DHOase, dihydroorotase activity; (...) GLN, glutaminase subdomain or subunit of carbamyl phosphate synthetase, GL Nase, glutaminase activity; SYN, synthetase subdomain or subunit of carbamyl phosphate synthetase; SYNase, synthetase activity. carries the first three steps of this pathway. The same three enzymes in prokaryotes are associated with separate proteins. The CAD gene appears to have evolved through a process of gene duplication and DNA rearrangement, leading to an in‐frame gene fusion encoding a chimeric protein. A driving force for the creation of eukaryotic genes encoding multienzymatic proteins such as CAD may be the advantage of coordinate expression of enzymes catalyzing steps in a biosynthetic pathway. The analogous structure in bacteria is the operon. Differences in the translational mechanisms of eukaryotes and prokaryotes may have dictated the different strategies used by organisms to evolve coordinately regulated genes. (shrink)

The evolutionary history of muscle development in the paired fins of teleost fish and the limbs of tetrapod vertebrates is still, to a large extent, uncertain. There has been a consensus, however, that in the vertebrate clade the ancestral mechanism of fin and limb muscle development involves the extension of epithelial tissues from the somite into the fin/limb bud. This mechanism has been documented in chondrichthyan, dipnoan, chondrostean and teleost fishes. It has also been assumed that in amniotes, (...) in contrast, individual progenitor cells of muscles migrate from the somites into the limb buds. Neyt et al.(1) now present the exciting finding that in zebrafishes this presumably derived mechanism involving individual cell migration, is present. They conclude, based on data on sharks, zebrafishes, chickens, quails and mice that the derived mechanism was present in the sarcopterygians. This conclusion, however, may be premature in the light of further data available in the literature, which show a highly mosaic distribution of this character in the vertebrate clade. Furthermore, a developmental mode exists that is intermediate between the supposed ancestral and derived modes in teleosts, reptiles and possibly amphibians. BioEssays 23:383–387, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

Staphylococcus aureus ST45 is a major global MRSA lineage with huge strain diversity and a high clinical impact. It is one of the most prevalent carrier lineages but also frequently causes severe invasive disease, such as bacteremia. Little is known about its evolutionary history. In this study, we used whole-genome sequencing to analyze a large collection of 451 diverse ST45 isolates from 6 continents and 26 countries. De novo-assembled genomes were used to understand genomic plasticity and to perform (...) coalescent analyses. The ST45 population contained two distinct sublineages, which correlated with the isolates’ geographical origins. One sublineage primarily consisted of European/North American isolates, while the second sublineage primarily consisted of African and Australian isolates. Bayesian analysis predicted ST45 originated in northwestern Europe about 500 years ago. Isolation time, host, and clinical symptoms did not correlate with phylogenetic groups. Our phylogenetic analyses suggest multiple acquisitions of the SCCmec element and key virulence factors throughout the evolution of the ST45 lineage. (shrink)

In the last thirty years systematics has transformed itself from a discipline concerned with classification into a discipline concerned with reconstructing the evolutionary history of life. This transformation has been driven by cladistic analysis, a set of techniques for reconstructing evolutionary trees. Long interested in the large-scale structure of evolutionary history, cladistically oriented systematists have recently begun to apply "tree thinking" to problems near the species level. ¶ In any local ("non-dimensional") situation species are usually (...) well-defined, but across space and time the grouping of populations into species is often problematic. Three views of species are in common use today, the biological species concept, the evolutionary species concept, and the phylogenetic species concept. Each of these has strengths and weaknesses, but no matter which is applied, exact counts of the number of species in any extended area will always be ambiguous no matter how much factual information is available. This ambiguity arises because evolution is an historical process, and the grouping of organisms into species always depends to some extent upon expectations of the future behavior of those organisms and their descendants, expectations that cannot be evaluated in the present. The existence and special character of the species problem is itself one of the central pieces of evidence for evolution. (shrink)

Consideration of the evolutionary and cross-cultural history of childbirth reveals many differences between the ways in which most human females have experienced childbirth and the ways in which most women in contemporary industrialized obstetric settings experience the event. In this paper I review two of these differences: the pain and anxiety of labor and delivery and the discontinuity of care provided for the mother and infant. I argue that much of the dissatisfaction with birth practices in the United (...) States results from the failure of modern obstetric practice to meet the evolved needs of mothers and infants. (shrink)

In the context of macroevolutionary transitions, environmental changes prompted vertebrates already bearing genetic variations to undergo gradual adaptations resulting in profound anatomical, physiological, and behavioral adaptations. The emergence of new genes led to the genetic variation essential in metazoan evolution, just as was gene loss, both sources of genetic variation resulting in adaptive phenotypic diversity. In this context, F12‐coding protein with defense and hemostatic roles emerged some 425 Mya, and it might have contributed in aquatic vertebrates to the transition from (...) water‐to‐land. Conversely, the F12 loss in marine, air‐breathing mammals like cetaceans has been associated with phenotypic adaptations in some terrestrial mammals in their transition to aquatic lifestyle. More recently, the advent of technological innovations in western lifestyle with blood‐contacting devices and harmful environmental nanoparticles, has unfolded new roles of FXII. Environment operates as either a positive or a relaxed selective pressure on genes, and consequently genes are selected or lost. FXII, an old dog facing environmental novelties can learn new tricks and teach us new therapeutic avenues. (shrink)

In Romans 5, St. Paul claims that death came into the world through Adam's sin. Many have taken this to foist on us a fundamentalist reading of Genesis. If death is the result of human sin, then, apparently, there cannot have been death in the world prior to human sin. This, however, is inconsistent with contemporary evolutionary biology, which requires that death predates the existence of modern humans. Although the relationship between Romans 5, Genesis, and contemporary science has been (...) much discussed—often with goal of dissipating the idea that the two are in conflict—the specific issue of death entering the world through sin has remained difficult to resolve. I argue that the Eastern Orthodox tradition has the resources to respect both Romans 5 and contemporary science. Appealing to a broadly Irenaean notion of soul‐making, and to the idea of theosis, opens up space for an understanding of these passages that is both scientifically informed and Orthodox. (shrink)

Critics of evolutionary psychology object that it is not rigorous science compared to other evolutionary science. Advocates reply that it is rigorous science, and that the critics are uninformed. Still, informed people having opposing preconceptions of what counts as rigor may reach opposing evaluative conclusions. I shall clarify the very idea of rigorous evolutionary histories in relation to the basic objection that “evolution without history” is not rigorous.

How genomic innovation translates into organismal organization remains largely unanswered. Possessing the largest invertebrate nervous system, in conjunction with many species‐specific organs, coleoid cephalopods (octopuses, squids, cuttlefishes) provide exciting model systems to investigate how organismal novelties evolve. However, dissecting these processes requires novel approaches that enable deeper interrogation of genome evolution. Here, the existence of specific sets of genomic co‐evolutionary signatures between expanded gene families, genome reorganization, and novel genes is posited. It is reasoned that their co‐evolution has contributed (...) to the complex organization of cephalopod nervous systems and the emergence of ecologically unique organs. In the course of reviewing this field, how the first cephalopod genomic studies have begun to shed light on the molecular underpinnings of morphological novelty is illustrated and their impact on directing future research is described. It is argued that the application and evolutionary profiling of evolutionary signatures from these studies will help identify and dissect the organismal principles of cephalopod innovations. By providing specific examples, the implications of this approach both within and beyond cephalopod biology are discussed. (shrink)

Accounts of the evolutionary past have as much in common with works of narrative history as they do with works of science. Awareness of the narrative character of evolutionary writing leads to the discovery of a host of fascinating and hitherto unrecognized problems in the representation of evolutionary history, problems associated with the writing of narrative. These problems include selective attention, narrative perspective, foregrounding and backgrounding, differential resolution, and the establishment of a canon of important (...) events. The narrative aspects of evolutionary writing, however, which promote linearity and cohesiveness in conventional stories, conflict with the underlying chronicle of evolution, which is not linear, but branched, and which does not cohere, but diverges. The impulse to narrate is so great, however, and is so strongly reinforced by traditional schemes of taxonomic attention, that natural historians have more often abandoned the diverging tree than they have abandoned the narrative mode of representation. If we are to understand the true nature of the evolutionary past then we must adopt tree thinking, and develop new and creative ways, both narrative and non-narrative, of telling the history of life. (shrink)

Adaptation is one of the central concepts in evolutionary theory, which nonetheless has been given different definitions. Some scholars support a historical definition of adaptation, considering it as a trait that is the outcome of natural selection, whereas others support an ahistorical definition, considering it as a trait that contributes to the survival and reproduction of its possessors. Finally, adaptation has been defined as a process, as well. Consequently, two questions arise: the first is a philosophical one and focuses (...) on what adaptation actually is; the second is a pedagogical one and focuses on what science teachers and educators should teach about it. In this article, the various definitions of adaptation are discussed and their uses in some textbooks are presented. It is suggested that, given elementary students’ intuitions about purpose and design in nature and secondary students’ teleological explanations for the origin of adaptations, any definition of adaptation as a trait should include some information about its evolutionary history. (shrink)

Comparative genomics has proven a fruitful approach to acquire many functional and evolutionary insights into core cellular processes. Here it is argued that in order to perform accurate and interesting comparative genomics, one first and foremost has to be able to recognize, postulate, and revise different evolutionary scenarios. After all, these studies lack a simple protocol, due to different proteins having different evolutionary dynamics and demanding different approaches. The authors here discuss this challenge from a practical (what (...) are the observations?) and conceptual (how do these indicate a specific evolutionary scenario?) viewpoint, with the aim to guide investigators who want to analyze the evolution of their protein(s) of interest. By sharing how the authors draft, test, and update such a scenario and how it directs their investigations, the authors hope to illuminate how to execute molecular evolution studies and how to interpret them. Also see the video abstract here https://youtu.be/VCt3l2pbdbQ. (shrink)

Among monkeys and apes, both the recognition and classification of individuals and the recognition and classification of vocalizations constitute discrete combinatorial systems. One system maps onto the other, suggesting that during human evolution kinship classifications and language shared a common cognitive precursor.

Katz denies that organisms created in a lab as part of a de-extinction attempt will be authentic members of the extinct species, on the basis that they will lack the original species’ defining biological and evolutionary history. Against Katz, I note that an evolutionary lineage is conferred on an organism through its inheriting genes from forebears already possessed of such a lineage, and that de-extinction amounts to a delayed, human-assisted reproductive process, in which genes are inherited from (...) forebears long dead. My conclusion is that de-extinct organisms can perfectly well have an ancient evolutionary history, contrary to what Katz claims. (shrink)

Accounts of the evolutionary past have as much in common with works of narrative history as they do with works of science. Awareness of the narrative character of evolutionary writing leads to the discovery of a host of fascinating and hitherto unrecognized problems in the representation of evolutionary history, problems associated with the writing of narrative. These problems include selective attention, narrative perspective, foregrounding and backgrounding, differential resolution, and the establishment of a canon of important (...) events. The narrative aspects of evolutionary writing, however, which promote linearity and cohesiveness in conventional stories, conflict with the underlying chronicle of evolution, which is not linear, but branched, and which does not cohere, but diverges. The impulse to narrate is so great, however, and is so strongly reinforced by traditional schemes of taxonomic attention, that natural historians have more often abandoned the diverging tree than they have abandoned the narrative mode of representation. If we are to understand the true nature of the evolutionary past then we must adopt “tree thinking”, and develop new and creative ways, both narrative and non-narrative, of telling the history of life. (shrink)

Many phylogenetic systematists have criticized the Biological Species Concept (BSC) because it distorts evolutionary history. While defenses against this particular criticism have been attempted, I argue that these responses are unsuccessful. In addition, I argue that the source of this problem leads to previously unappreciated, and deeper, fatal objections. These objections to the BSC also straightforwardly apply to other species concepts that are not defined by genealogical history. What is missing from many previous discussions is the fact (...) that the Tree of Life, which represents phylogenetic history, is independent of our choice of species concept. Some species concepts are consistent with species having unique positions on the Tree while others, including the BSC, are not. Since representing history is of primary importance in evolutionary biology, these problems lead to the conclusion that the BSC, along with many other species concepts, are unacceptable. If species are to be taxa used in phylogenetic inferences, we need a history-based species concept. (shrink)

This article reports the results of an experiment involving 108 college students with varying backgrounds in biology. Subjects answered questions about the evolutionary history of sets of hominid and equine taxa. Each set of taxa was presented in one of three diagrammatic formats: a noncladogenic diagram found in a contemporary biology textbook or a cladogram in either the ladder or tree format. As predicted, the textbook diagrams, which contained linear components, were more likely than the cladogram formats to (...) yield explanations of speciation as an anagenic process, a common misconception among students. In contrast, the branching cladogram formats yielded more appropriate explanations concerning levels of ancestry than did the textbook diagrams. Although students with stronger backgrounds in biology did better than those with weaker biology backgrounds, they generally showed the same effects of diagrammatic format. Implications of these results for evolution education and for diagram design more generally are discussed. (shrink)

In this article, I am concerned with the public engagements of Julian Huxley, Lancelot Hogben, and J. B. S. Haldane. I analyze how they used the new insights into the genetics of heredity to argue against any biological foundations for antidemocratic ideologies, be it Nazism, Stalinism, or the British laissez-faire and class system. The most striking fact—considering the abuse of biological knowledge they contested—is that these biologists presented genetics itself as inherently democratic. Arguing from genetics, they developed an understanding of (...) diversity that cuts across divisions of race, class, or gender. Human diversity rightly understood was advantageous for societal progress. Huxley, Hogben, and Haldane did not hold identical political ideals, but they all argued for democratic reforms and increased planning geared toward greater social equality, and they did so under the label of scientific humanism. Huxley took issue with the notion that evolutionary history does not carry any moral lessons for human societies. Rather than being its antithesis, evolution was the basis of human sociality. In fact, the entire future progress of individuals and communities toward a democratic world order needed to be founded on the cosmic principles of evolution—a process that had to be guided by the biological expert with a strong sense of social responsibility. (shrink)

The recent discovery of microRNAs (miRNAs) in unicellular eukaryotes, including miRNAs known previously only from animals or plants, implies that miRNAs have a deep evolutionary history among eukaryotes. This contrasts with the prevailing view that miRNAs evolved convergently in animals and plants. We re‐evaluate the evidence and find that none of the 73 plant and animal miRNAs described from protists meet the required criteria for miRNA annotation and, by implication, animals and plants did not acquire any of their (...) respective miRNA genes from the crown ancestor of eukaryotes. Furthermore, of the 159 novel miRNAs previously identified among the seven species of unicellular protists examined, only 28 from the algae Ectocarpus and Chlamydomonas, meet the criteria for miRNA annotation. Therefore, at present only five groups of eukaryotes are known to possess miRNAs, indicating that miRNAs have evolved independently within eukaryotes through exaptation of their shared inherited RNAi machinery. (shrink)

O objetivo deste ensaio é refletir sobre o significado da expressão “arte do paladar”, enfocando os aspectos da nossa história evolutiva – uma história contemporaneamente biológica e cultural – os quais fizeram de nós os únicos “macacos” capazes de cozinhar o alimento, de produzi-lo de modo sistemático, de escolhê-lo em meio a uma vasta gama de alimentos, com base em diferentes critérios, de atribuir-lhe um valor simbólico e de celebrálo através da linguagem; razões pelas quais o homem pode reivindicar plenamente (...) a invenção dos sabores. Resultado de um longo processo de elaboração da natureza, a arte do paladar é, portanto, o resultado de todos os processos pelos quais transformamos um dos atos mais naturais, isto é, o ato de comer, em um artificial, cultural e intelectual, aplicando um conhecimento, um saber prático, para conceber, imaginar e elaborar novos objetos alimentares, novas sensações para o paladar, novas possibilidades de interação social. Palavras-chave: Arte de alimentos. Sabor. Cozinhar. Culinária. Linguagem. (shrink)

The anthropological scale -- Organ projection -- The first tools -- Limbs and measure -- Apparatuses and instruments -- The inner architecture of the bones -- Steam engines and rail lines -- The electromagnetic telegraph -- The unconscious -- Machine technology -- The fundamental morphological law -- Language -- The state.

While N6‐methyladenosine (m6A) is a well‐known epigenetic modification in bacterial DNA, it remained largely unstudied in eukaryotes. Recent studies have brought to fore its potential epigenetic role across diverse eukaryotes with biological consequences, which are distinct and possibly even opposite to the well‐studied 5‐methylcytosine mark. Adenine methyltransferases appear to have been independently acquired by eukaryotes on at least 13 occasions from prokaryotic restriction‐modification and counter‐restriction systems. On at least four to five instances, these methyltransferases were recruited as RNA methylases. Thus, (...) m6A marks in eukaryotic DNA and RNA might be more widespread and diversified than previously believed. Several m6A‐binding protein domains from prokaryotes were also acquired by eukaryotes, facilitating prediction of potential readers for these marks. Further, multiple lineages of the AlkB family of dioxygenases have been recruited as m6A demethylases. Although members of the TET/JBP family of dioxygenases have also been suggested to be m6A demethylases, this proposal needs more careful evaluation. (shrink)

The ABO histo‐blood group, first discovered over a century ago, is found not only in humans but also in many other primate species, with the same genetic variants maintained for at least 20 million years. Polymorphisms in ABO have been associated with susceptibility to a large number of human diseases, from gastric cancers to immune or artery diseases, but the adaptive phenotypes to which the polymorphism contributes remain unclear. We suggest that variation in ABO has been maintained by frequency‐dependent or (...) fluctuating selection pressures, potentially arising from co‐evolution with gut pathogens. We further hypothesize that the histo‐blood group labels A, B, AB, and O do not offer a full description of variants maintained by natural selection, implying that there are unrecognized, functionally important, antigens beyond the ABO group in humans and other primates. (shrink)

Sex differences in mortality rates stem from genetic, physiological, behavioral, and social causes that are best understood when integrated in an evolutionary life history framework. This paper investigates the Male-to-Female Mortality Ratio (M:F MR) from external and internal causes and across contexts to illustrate how sex differences shaped by sexual selection interact with the environment to yield a pattern with some consistency, but also with expected variations due to socioeconomic and other factors.

The development of evolutionary approaches to psychology from Classical Ethology through Sociobiology to Evolutionary Psychology is outlined and the main tenets of today's Evolutionary Psychology briefly examined: the heuristic value of evolutionary thinking for psychology, the massive modularity thesis and the monomorphic mind thesis.

Philosophical defenses of cognitive/evolutionary psychological accounts of racialism claim that classification based on phenotypical features of humans was common historically and is evidence for a species-typical, cognitive mechanism for essentializing. They conclude that social constructionist accounts of racialism must be supplemented by cognitive/evolutionary psychology. This article argues that phenotypical classifications were uncommon historically until such classifications were socially constructed. Moreover, some philosophers equivocate between two different meanings of “racial thinking.” The article concludes that social constructionist accounts are far (...) more robust than psychological accounts for the origins of racialism. (shrink)

Well into the 1940s, many French biologists rejected both Mendelian genetics and Darwinism in favour of neo-transformism, the claim that evolution proceeds by the inheritance of acquired characteristics. In 1931 the zoologist Maurice Caullery published Le Problème d’évolution, arguing that, while Lamarckian mechanisms could not be demonstrated in the present, they had nevertheless operated in the past. It was in this context that Raymond Aron expressed anxiety about the relationship between biology, history, and human autonomy in his 1938 Introduction (...) à la philosophie de l’histoire: essai sur les limites de l’objectivité historique, in which he rejected both neo-Kantian and biological accounts of human history. Aron aspired to a philosophy of history that could explain the dual nature of human existence as fundamentally rooted in the biological, and at the same time, as a radical transcendence of natural law. I argue that Aron’s encounter with evolutionary theory at this moment of epistemic crisis in evolutionary theory was crucial to the formation of his philosophy of history, and moreover that this case study demonstrates the importance of moving beyond the methodological divisions between intellectual history and history of science. (shrink)

Philosophical defenses of cognitive/evolutionary psychological accounts of racialism claim that classification based on phenotypical features of humans was common historically and is evidence for a species-typical, cognitive mechanism for essentializing. They conclude that social constructionist accounts of racialism must be supplemented by cognitive/evolutionary psychology. This article argues that phenotypical classifications were uncommon historically until such classifications were socially constructed. Moreover, some philosophers equivocate between two different meanings of “racial thinking.” The article concludes that social constructionist accounts are far (...) more robust than psychological accounts for the origins of racialism. (shrink)

Several attempts have been made recently to apply Darwinian evolutionary theory to the study of culture change and social history. The essential elements in such a theory are that variations occur in population, and that a process of selective retention operates during their replication and transmission. Location of such variable units in the semantic structure of cognition provides the individual psychological basis for an evolutionary theory of history. Selection operates on both the level of cognition and (...) on its phenotypic expression in action in relation to individual preferred sources of psychological satisfaction. Social power comprises the principal selective forces within the unintended consequences of action and through the struggle of individuals and groups in pursuit of opposing interests. The implication for historiography are methodological in that evolutionary theory of history sharpens the focus of explanatory situational analysis, and interpretive in that it provides a paradigmatic metanarrative for the understanding of historical change. (shrink)

Evolutionary explanations are not only common in the biological sciences, but also widespread outside biology. But an account of how evolutionary explanations perform their explanatory work is still lacking. This paper develops such an account. I argue that available accounts of explanations in evolutionary science miss important parts of the role of history in evolutionary explanations. I argue that the historical part of evolutionary science should be taken as having genuine explanatory force, and that (...) it provides how‐possibly explanations sensu Dray. I propose an account of evolutionary explanations as comparative‐composite explanations consisting of two distinct kinds of explanations, one processual and one historical, that are connected via the explanandum's evolvability to show how the explanandum is the product of its evolutionary past. The account is both a reconstruction of how evolutionary explanations in biology work and a guideline specifying what kind of explanations evolutionary research programs should develop. (shrink)

Several attempts have been made recently to apply Darwinian evolutionary theory to the study of culture change and social history. The essential elements in such a theory are that variations occur in a population, and that a process of selective retention operates during their replication and transmission. Location of such variable “units” in the semantic structure of cognition provides the individual psychological basis for an evolutionary theory of history. Selection operates on both the level of cognition (...) and on its “phenotypic” expression in action in relation to individual preferred sources of psychological satisfaction. Social power comprises the principal selective forces within the sociocultural environment. Sociocultural evolution takes place both as a result of the unintended consequences of action and through the struggle of individuals and groups in pursuit of opposing interests. The implications for historiography are methodological in that evolutionary theory of history sharpens the focus of explanatory situational analysis, and interpretive in that it provides a paradigmatic metanarrative for the understanding of historical change. (shrink)

Originally published anonymously in 1844, Vestiges proved to be as controversial as its author expected. Integrating research in the burgeoning sciences of anthropology, geology, astronomy, biology, economics, and chemistry, it was the first attempt to connect the natural sciences to a history of creation. The author, whose identity was not revealed until 1884, was Robert Chambers, a leading Scottish writer and publisher. Vestiges reached a huge popular audience and was widely read by the social and intellectual elite. It sparked (...) debate about natural law, setting the stage for the controversy over Darwin's Origin. In response to the surrounding debate and criticism, Chambers published Explanations: A Sequel, in which he offered a reasoned defense of his ideas about natural law, castigating what he saw as the narrowness of specialist science. With a new introduction by James Secord, a bibliography of reviews, and a new index, this volume adds to Vestiges and Explanations Chambers's earliest works on cosmology, an essay on Darwin, and an autobiographical essay, raising important issues about the changing meanings of popular science and religion and the rise of secular ideologies in Western culture. (shrink)

This paper presents an analysis of the characteristics of men who become stepfathers, and their subsequent fertility patterns and lifetime reproductive success. Because women who already have children are ranked lower in the marriage market than women without children, men who marry women with children (e.g., stepfathers) are likely to have lower rankings in the marriage market as well. Using retrospective fertility and marital histories from the Panel Study of Income Dynamics (PSID), I show that men who become stepfathers have (...) lower levels of education, less income, and are more likely to have been divorced before and to already have children, all characteristics that lower their rankings in the marriage market. Men with one or two stepchildren are just as likely to have children within a marriage as non-stepfathers, although men with three stepchildren show decreased fertility. Among men age 45 and older, stepfathers have lower lifetime fertility than non-stepfathers, although the difference disappears when men’s age at first marriage is controlled for. Additionally, stepfathers have significantly higher fertility than men who never marry. The results suggest that some men become stepfathers to procure mates and fertility benefits that they would otherwise have been unlikely to obtain; for these men, raising other men’s children serves as a form of mating effort. (shrink)