Darwin's beautiful notion: sexual selection and the plurality of moral codes

One of the explicit objectives of Darwin's Descent of Man, and Selection in Relation to Sex was to explain cultural differences seen in human beings. Such an explanation, Darwin believed, was to rest upon an understanding of sexual selection. I examine the role that the beautiful plays within the mechanism of sexual selection as it works to differentiate isolated groups. It is suggested that an examination of the relationship between sexual selection and artificial selection--a relationship mediated by the beautiful--will illuminate key issues of the Descent as well as contemporary debates regarding the relationship between evolution and ethics. The beautiful, originally rooted in sexual selection, can become de-coupled from sexual selection and utilized in some selective process which is conscious.     

A sexual selection model for hominid evolution

The following paper develops a sexual selection model for the evolution of bipedal locomotion, canine reduction, brain enlargement, language and higher intelligence. The model involves an expansion of Darwin’s ideas about human evolution based on recent elaborations of sexual selection theory. Modern notions about intrasexual competition and female and male choice and their ecological correlates are summarized along with a new model for the role of sexual selection in speciation. Rapid evolution of bipedal locomotion as a male adaptation for nuptial feeding of females is proposed as a model for ape-hominid divergence through sexual selection; canine reduction is attributed to selection for associated epigamic displays. The analogy with male specialization through sexual selection speciation in hamadryas baboons is noted. Subsequent changes in female reproductive physiology are attributed to female competition for increased male parental investment during the time of early Homo andHomo erectus. The origin of higher intellectual and language abilities inHomo sapiens is attributed to male competition through technology and rule production to control resources and females; intellectual abilities involved in social manipulation are attributed to female competition for male parental investment and maintenance of polyandry. The course of hominid evolution is characterized as involving a trend from a promiscuous mating system toward increasing intensity of adaptations for male control of females, and by increasing intensity of female adaptation to maintain male parental investment while circumventing male control.     

Evolutionary Developmental Biology and Human Language Evolution: Constraints on Adaptation

A tension has long existed between those biologists who emphasize the importance of adaptation by natural selection and those who highlight the role of phylogenetic and developmental constraints on organismal form and function. This contrast has been particularly noticeable in recent debates concerning the evolution of human language. Darwin himself acknowledged the existence and importance of both of these, and a long line of biologists have followed him in seeing, in the concept of ??descent with modification??, a framework naturally able to incorporate both adaptation and constraint. Today, the integrated perspective of modern evolutionary developmental biology (??evo-devo??) allows a more subtle and pluralistic approach to these traditional questions, and has provided several examples where the traditional notion of ??constraint?? can be cashed out in specific, mechanistic terms. This integrated viewpoint is particularly relevant to the evolution of the multiple mechanisms underlying human language, because of the short time available for novel aspects of these mechanisms to evolve and be optimized. Comparative data indicate that many cognitive aspects of human language predate humans, suggesting that pre-adaptation and exaptation have played important roles in language evolution. Thus, substantial components of what many linguists call ??Universal Grammar?? predate language itself. However, at least some of these older mechanisms have been combined in ways that generate true novelty. I suggest that we can insightfully exploit major steps forward in our understanding of evolution and development, to gain a richer understanding of the principles that underlie human language evolution.     

The relative importance of intra- and intersexual selection on human male sexually dimorphic traits

Recent evidence suggests that in sexual selection on human males, intrasexual competition plays a larger role than female choice. In a sample of men (N?=?164), we sought to provide further evidence on the effects of men's physical dominance and sexual attractiveness on mating success and hence in sexual selection. Objective measures and subjective ratings of male sexually dimorphic traits purportedly under sexual selection (height, vocal and facial masculinity, upper body size from 3D scans, physical strength, and baseline testosterone) and observer perceptions of physical dominance and sexual attractiveness based on self-presentation video recordings were assessed and associated with mating success (sociosexual behaviour and number of potential conceptions) in a partly longitudinal design. Results from structural equation models and selection analyses revealed that physical dominance, but not sexual attractiveness, predicted mating success. Physical dominance mediated associations of upper body size, physical strength, as well as vocal and facial physical dominance and attractiveness with mating success. These findings thus suggest a greater importance of intrasexual competition than female choice in human male sexual selection.     

The bridge of iconicity: from a world of experience to the experience of language

Iconicity, a resemblance between properties of linguistic form (both in spoken and signed languages) and meaning, has traditionally been considered to be a marginal, irrelevant phenomenon for our understanding of language processing, development and evolution. Rather, the arbitrary and symbolic nature of language has long been taken as a design feature of the human linguistic system. In this paper, we propose an alternative framework in which iconicity in face-to-face communication (spoken and signed) is a powerful vehicle for bridging between language and human sensori-motor experience, and, as such, iconicity provides a key to understanding language evolution, development and processing. In language evolution, iconicity might have played a key role in establishing displacement (the ability of language to refer beyond what is immediately present), which is core to what language does; in ontogenesis, iconicity might play a critical role in supporting referentiality (learning to map linguistic labels to objects, events, etc., in the world), which is core to vocabulary development. Finally, in language processing, iconicity could provide a mechanism to account for how language comes to be embodied (grounded in our sensory and motor systems), which is core to meaningful communication.     

Imitation and conventional communication

To the extent that language is conventional, non-verbal individuals, including human infants, must participate in conventions in order to learn to use even simple utterances of words. This raises the question of which varieties of learning could make this possible. In this paper I defend Tomasello’s (The cultural origins of human cognition. Harvard UP, Cambridge, 1999, Origins of human communication. MIT, Cambridge, 2008) claim that knowledge of linguistic conventions could be learned through imitation. This is possible because Lewisian accounts of convention have overstated what one must know to participate in conventions; and because the required knowledge could be learned imitatively. The imitation claim that I defend is consistent with what we know about both the proliferation of conventional behaviours in human children, who are skilful imitators, and the comparative absence of such behaviours in non-human great apes, who are poor at imitative learning.     

The actions of others act as a pseudo-reward to drive imitation in the context of social reinforcement learning

While there is no doubt that social signals affect human reinforcement learning, there is still no consensus about how this process is computationally implemented. To address this issue, we compared three psychologically plausible hypotheses about the algorithmic implementation of imitation in reinforcement learning. The first hypothesis, decision biasing (DB), postulates that imitation consists in transiently biasing the learner’s action selection without affecting their value function. According to the second hypothesis, model-based imitation (MB), the learner infers the demonstrator’s value function through inverse reinforcement learning and uses it to bias action selection. Finally, according to the third hypothesis, value shaping (VS), the demonstrator’s actions directly affect the learner’s value function. We tested these three hypotheses in 2 experiments (N = 24 and N = 44) featuring a new variant of a social reinforcement learning task. We show through model comparison and model simulation that VS provides the best explanation of learner’s behavior. Results replicated in a third independent experiment featuring a larger cohort and a different design (N = 302). In our experiments, we also manipulated the quality of the demonstrators’ choices and found that learners were able to adapt their imitation rate, so that only skilled demonstrators were imitated. We proposed and tested an efficient meta-learning process to account for this effect, where imitation is regulated by the agreement between the learner and the demonstrator. In sum, our findings provide new insights and perspectives on the computational mechanisms underlying adaptive imitation in human reinforcement learning.

This study investigates imitation from a computational perspective; three experiments show that, in the context of reinforcement learning, imitation operates via a durable modification of the learner''s values, shedding new light on how imitation is computationally implemented and shapes learning and decision-making.     

Epistemology, necessity, and evolution: a critical review of Michael Ruse��s Philosophy After Darwin

Michael Ruse??s new anthology Philosophy After Darwin provides great history and background in the major impacts Darwinism has had on philosophy, especially in ethics and epistemology. This review focuses on epistemology understood through the lens of evolution by natural selection. I focus on one of Ruse??s own articles in the collection, which responds to two classic articles by Konrad Lorenz and David Hull on the two major forms of evolutionary epistemology. I side with Ruse against Lorenz??s account of the necessity we think our principles of reasoning have, though I disagree with Ruse??s particular example. I also argue that Ruse??s alternative explanation is lacking. Against Hull, I side with Ruse in his doubts that a sociobiological approach to science will prove fruitful, though I point out that it has certain advantages other approaches do not have. Although I side with Ruse on the issue, I conclude that the two views do not really come into direct conflict and so one needs not reject either. Finally, I discuss Ruse??s positive view and raise questions for his conception of evolutionary epistemology. I conclude that his arguments are insufficient to overcome opposing views and his view has at least as many unintuitive conclusions as the alternatives.     

Estimating the strength of sexual selection from Y-chromosome and mitochondrial DNA diversity

We show that a sex difference in the opportunity for selection results in sex differences in the strength of random genetic drift and thus creates different patterns of genetic diversity for maternally and paternally inherited haploid genes. We derive the effective population size Ne for a male-limited or female-limited haploid gene in terms of I, the "opportunity for selection" or the variance in relative fitness. Because the variance in relative fitness of males can be an order of magnitude larger than that of females, the Ne is much smaller for males than it is for females. We derive both nonequilibrium and equilibrium expressions for F(ST) in terms of I and show how the portion of I owing to sexual selection, Imates, that is, the variation among males in mate numbers, is a simple function of the F's for cytoplasmic (female inherited) and Y-linked (male inherited) genes. Because multiple, transgenerational data are lacking to apply the nonequilibrium expression, we apply only the equilibrium model to published data on Y chromosome and mitochondrial sequence divergence in Homo sapiens to quantify the opportunity for sexual selection. The estimate suggests that sexual selection in humans represents a minimum of 54.8% of total selection, supporting Darwin's proposal that sexual selection has played a significant role in human evolution and the recent proposal regarding a shift from polygamy to monogamy in humans.     

Inheritance and mapping of the ore gene controlling the quantity of β-carotene in cucumber (Cucumis sativus L.) endocarp

The metabolic precursor of vitamin A, ??-carotene, is essential for human health. The gene(s) controlling ??-carotene quantity (Q??C) has been introgressed from Xishuangbanna gourd (XIS, possessing ??-carotene; Cucumis sativus L. var. xishuangbannanesis Qi et Yuan; 2n?=?2x?=?14) into cultivated cucumber (no ??-carotene; Cucumis sativus L.). To determine the inheritance of Q??C in cucumber fruit endocarp, F1 progeny and a set of 124 F7 recombinant inbred lines (RILs) derived from the cultivated cucumber line CC3 and XIS line SWCC8 were evaluated for Q??C during 2009 and 2010 in Nanjing, China. Segregation analysis revealed that endocarp Q??C of greenhouse-grown fruit was controlled by a single recessive gene. Further, marker analysis indicated the gene controlling Q??C was linked to seven SSR markers on linkage group 3, where their order was SSR20710?CSSR19511?CSSR15419?CSSR07706?Core?CSSR23231?CSSR11633?CSSR20270. These markers and the putative candidate gene were mapped to cucumber chromosome 3DS. An evaluation of 30 genetically diverse cucumber lines indicated that marker SSR07706 has utility in further genetic analyses of the Q??C orange endocarp gene, designated ore. Moreover, the markers defined herein may have utility for marker-assisted selection directed towards the development of cucumber germplasm with high fruit ??-carotene content.     

Darwin on woman

In his 1871 book The Descent of Man, Darwin exposed the idea of sexual selection as a major principle of human evolution. His main hypothesis, which was already briefly presented in The Origin of Species, is that there exists, besides “natural selection”, another form of selection, milder in its effect, but no less efficient. This selection is operated by females to mate and reproduce with some partners that are gifted with more qualities than others, and more to their taste. At more evolved stages, sexual selection was exerted by men who became able to choose the women most attractive to their taste. However, Darwin insists, sexual selection in the human species is limited by a certain number of cultural practices. If Darwin's demonstration sometimes carried the prejudices of his times regarding gender differences he was the first who took into account the importance of sexual choices in his view on evolution, and who insisted on the evolutionary role of women at the dawn of humanity. Thus, he opened the space for a rich reflection, which after him was widely developed and discussed in anthropological and gender studies.     

The Evolution of Language: A Comparative Review

For many years the evolution of language has been seen as a disreputable topic, mired in fanciful “just so stories” about language origins. However, in the last decade a new synthesis of modern linguistics, cognitive neuroscience and neo-Darwinian evolutionary theory has begun to make important contributions to our understanding of the biology and evolution of language. I review some of this recent progress, focusing on the value of the comparative method, which uses data from animal species to draw inferences about language evolution. Discussing speech first, I show how data concerning a wide variety of species, from monkeys to birds, can increase our understanding of the anatomical and neural mechanisms underlying human spoken language, and how bird and whale song provide insights into the ultimate evolutionary function of language. I discuss the “descended larynx” of humans, a peculiar adaptation for speech that has received much attention in the past, which despite earlier claims is not uniquely human. Then I will turn to the neural mechanisms underlying spoken language, pointing out the difficulties animals apparently experience in perceiving hierarchical structure in sounds, and stressing the importance of vocal imitation in the evolution of a spoken language. Turning to ultimate function, I suggest that communication among kin (especially between parents and offspring) played a crucial but neglected role in driving language evolution. Finally, I briefly discuss phylogeny, discussing hypotheses that offer plausible routes to human language from a non-linguistic chimp-like ancestor. I conclude that comparative data from living animals will be key to developing a richer, more interdisciplinary understanding of our most distinctively human trait: language.     

Lipoproteinstoffwechsel und koronare Herzkrankheit

A better understanding of complex diseases and their genetics has been gained by investigating genetic disorders of lipoprotein metabolism. This has resulted in the development of ddrugs to prevent atherosclerosis, the most frequent cause of death in industrialized countries. Thus, analysis of familial hypercholesterinemia (FH), the most frequent cause of which are mutations on the LDLR gene, has contributed to the development of HMG-CoA reductase inhibitors (statins). Meanwhile, in genome-wide association studies (GWAS), variants in over 90 genes have been found to influence the concentration of plasma lipids. However, these explain only a small fraction of the genetic variance of the traits. Taking the classical polymorphism of Apo-E as an example, it is discussed that one possible reason for the ??missing heritability?? may be the selection of the SNPs on the arrays used in the GWAS. Further, this polymorphism demonstrates how interactions may mask a connection between a genotype and a disease. Genetic studies based on the principle of ??Mendelian randomization?? have established the causal role of a high Lp(a) concentration as a risk factor for coronary heart disease (CHD). For patients with end-stage renal disease, however, a polymorphism (KIV-2 CNV) is a better predictor for CHD than Lp(a) concentration.     

Facial attractiveness,developmental stability,and fluctuating asymmetry

Despite robust cross-cultural reliability of human facial attractiveness ratings, research on facial attractiveness has only superficially addressed the connection between facial attractiveness and the history of sexual selection in Homo sapiens. There are reasons to believe that developmental stability and phenotypic quality are related. Recent studies of nonhuman animals indicate that developmental stability, measured as fluctuating asymmetry in generally bilateral symmetrical traits, is predictive of performance in sexual selection: Relatively symmetrical males are advantaged under sexual selection. This pattern is suggested by our study of facial attractiveness and fluctuating asymmetry in seven bilateral body traits in a student population. Overall, facial attractiveness negatively correlated with fluctuating asymmetry; the relation for men, but not for women, was statistically reliable. Possible confounding factors were controlled for in the analysis.     

The adaptive significance of cultural behavior

In this article, I argue that human social behavior is a product of the coevolution of human biology and culture. While critical of attempts by anthropologists to explain cultural practices as if they were independent of the ability of individual human beings to survive and reproduce, I am also leery of attempts by biologists to explain the consistencies between neo-Darwinian theory and cultural behavior as the result of natural selection for that behavior. Instead, I propose that both biological and cultural attributes of human beings result to a large degree from the selective retention of traits that enhance the inclusive fitnesses of individuals in their environments. Aspects of human biology and culture may be adaptive in the same sense despite differences between the mechanisms of selection and regardless of their relative importance in the evolution of a trait. The old idea that organic and cultural evolution are complementary can thus be used to provide new explanations for why people do what they do.This article was prepared from remarks I presented at the Smithsonian Conference on Human Biogeography in April 1974. Help with phenotypic costs came from an NSF Pre-doctoral Fellowship and the University of Michigan Society of Fellows.     

The sight of the peacock’s tail makes me sick: The early arguments on sexual selection

Why does a peacock have a beautiful train, while a peahen is sober without such flamboyance? Darwin proposed the theory of sexual selection to explain the differences between the sexes of the same species. Recently the study of sexual selection has been one of the most flourishing areas in evolutionary biology. However, the theory met with great resistance from biologists since the publication of the idea and the history of the theory included a lot of misunderstanding and confusion. There are several reasons for this. First, classical Darwinism failed to recognize social competition as an important selective force. Second, the good-for-the-species argument, which persisted in the days after Darwin, made the sexual selection argument more difficult to understand. Compared to the discussions on animals, Darwin’s argument on human sex differences is not satisfactory. The reason probably lies in the debate over human racial differences which prevailed in the 19th century.     

Cripping Safe Sex

Life Goes On (1989?C1993) was the first television series in U.S. history not only to introduce a recurring teenaged HIV-positive character but also to feature an actor with Down syndrome in a leading role. Drawing new connections among disability studies, queer theory, and bioethics, I argue that Life responded to American disability rights activism and the AIDS epidemic of the early 1990s by depicting sex education as disability activism. By portraying fulfilling sexual relationships for its disabled protagonists, Life challenged heteronormative and ableist underpinnings of marriage, sexuality, reproduction, and sex education and imagined transgressive queer/disabled alliances that often surpassed those of activists of its cultural moment. By representing homophobia, AIDS-phobia, and ableism as intertwined oppressions, the series conjured an expansive vision of sexual justice and pleasure, one that included and united teenagers, intellectually disabled people, and seropositive people??populations whose sexualities have generally been regarded as pathological or nonexistent.     

Male genital modification

By modifying the body in meaningful ways, human beings establish their identity and social status. Lip plugs, ear plugs, penis sheaths, cosmetics, ornaments, scarification, body piercings, and genital modifications encode and transmit messages about age, sex, social status, health, and attractiveness from one individual to another. Through sociocultural sexual selection, male genital modification plays an important role as a sociosexual signal in both male competition and female mate choice. The reliability of the signal correlates with the cost of acquiring the trait. Women use a variety of cues to assess male quality. Male genital modification is one way that some women assess their mates. Extreme male genital modifications not only honestly advertise status, sexual potency, and ability to provide sexual satisfaction, they may provide a reliable index of male-female cooperation through the male’s commitment to endure pain and risk.     

Causes of secondary sexual differences in plants — Evidence from extreme leaf dimorphism in Leucadendron (Proteaceae)

In extreme cases leaves in male plants of the dioecious genus Leucadendron (Proteaceae) are up to an order of magnitude smaller than female leaves. This secondary sexual dimorphism (SSD) in leaf size has previously been suggested to be due to intra-male sexual selection, leading to an increase in male allocation to reproduction in dimorphic species. After critically evaluating previous data provided to support this hypothesis, I suggest on both theoretical grounds and on re-analysis that this argument is unlikely and unsupported. Leaf size dimorphism could theoretically evolve directly due to disruptive ecological selection between genders, leading to niche dimorphism either within or between habitats. I test this ecological causation hypothesis by providing data on specific leaf area (sla) and water use efficiency (δ ¹³C) of leaves from males and females of several Leucadendron species. Results confirm the expectation of minimal gender differences. I argue that leaf dimorphism is a consequence of selection on flower size and architecture.     

Peak shifts and extinction under sex-specific selection

A well-known property of sexual selection combined with a cross-sex genetic correlation (r_mf) is that it can facilitate a peak shift on the adaptive landscape. How do these diversifying effects of sexual selection + r_mf balance with the constraints imposed by such sexual antagonism, to affect the macroevolution of sexual dimorphism? Here, I extend existing quantitative genetic models of evolution on complex adaptive landscapes. Beyond recovering classical predictions for the conditions promoting a peak shift, I show that when r_mf is moderate to strong, relatively weak sexual selection is required to induce a peak shift in males only. Increasing the strength of sexual selection leads to a sexually concordant peak shift, suggesting that macroevolutionary rates of sexual dimorphism may be largely decoupled from the strength of within-population sexual selection. Accounting explicitly for demography further reveals that sex-specific peak shifts may be more likely to be successful than concordant shifts in the face of extinction, especially when natural selection is strong. An overarching conclusion is that macroevolutionary patterns of sexual dimorphism are unlikely to be readily explained by within-population estimates of selection or constraint alone.