An evolutionary perspective on physical attractiveness

Everyday experience suggests that physical attractiveness is important in personal—and especially sexual—relationships. This impression is confirmed by a large body of social psychological research.^1,2 Cross-cultural surveys and ethnographic accounts show that concern with the attractiveness of potential mates is also common in non-Western societies and in tribal and peasant cultures.³ However, social psychologists and anthropologists have often had a hard time explaining why attractiveness should count for so much, or why some features rather than others should seem particularly attractive. The theoretical difficulties in accounting for physical attraction are brought out in a Brazilian saying, “Beleza nâo pôe na mesa” (“Good looks don't put anything on the table”), which points to the absence of any evident practical advantage to choosing an attractive mate. Faced with these difficulties, a growing number of researchers in biology, psychology, and anthropology have turned to the modern theory of sexual selection, which has been highly successful in explaining nonhuman animals attractions to traits of no direct ecological utility. In this article, I survey recent efforts to apply the theory of sexual selection to human physical attraction.     

Yawning: An evolutionary perspective

Yawning is a ubiquitous activity among humans, nonhuman primates, mammals, birds and other vertebrates. Comparative analysis suggests that yawning has two major features: (1) communication — whereby the behavior of other individuals is affected, and (2) direct physiological benefit — whereby the organism is receiving some direct physiological benefit from yawning. Various functional hypotheses used to explain yawning in an evolutionary context are reviewed. The contagious nature in humans and the manifest lack of contagion in other species suggests that yawning in humans has a different and as yet poorly understood evolutionary history.     

An evolutionary perspective on panic disorder and agoraphobia

Panic, when viewed ethologically, is not pathological in itself; it is rather an adaptation that evolved to facilitate escape in dangerous situations. Patients with panic disorder have panic with normal form, but the attacks occur in the absence of real danger. The agoraphobia syndrome can be understood as a related adaptation that is expected after repeated panic attacks. These hypotheses account for many aspects of panic and agoraphobia that are difficult for proximate theories to explain, and they suggest new research questions and strategies.     

Forcible rape: An evolutionary perspective

In humans, forcible rape is usually defined as copulation achieved by violence or threat of violence without the free consent of the female. Although rape is universally considered a heinous and punishable crime, it remains a serious and growing problem in many modern cultures. Rape has been perceived as the pathological result of (1) the psychological dysfunction of individual rapists or (2) the sexism inherent in male-dominated societies. Both sociocultural hypotheses recommend that rape be controlled through the rehabilitation of diseased rapists, diseased societies, or both. Exploration of rape in nonhuman animals and a wider application of evolutionary principles to human behavior have generated an alternative evolutionary view of rape as a potentially adaptive rather than a necessarily pathological act. The expanded biological model explores both the ultimate consequences of rape, in terms of a cost/benefit analysis of its expected effects on inclusive fitness, and its immediate proximate control, in terms of the intrinsic motivating variables and external stimuli that determine its probability of occurrence for specific individuals in specific instances. Ultimately, rape is expected to occur only when its potential benefit (production of an extra offspring) exceeds its potential cost (energy expended and risk taken owing to some probability of resistance or retribution that would reduce a rapist's reproductive success). We agree with the sociocultural view that rape is a violent rather than a sexual act. Proximately, rape appears to be motivated by male hostility, with increasing hostility increasing the probability of rape. The external stimulus for rape is a sufficiently vulnerable female. Here vulnerability varies inversely with the probability and severity of resistance or retribution expected by a rapist (i.e., the expected cost of rape in inclusive fitness). Both the frequency and patterns of rape observed in nature are either equally or more consistent with the sociobiological predictions than with the sociocultural predictions. The biological perspective implies that a society can most effectively control rape by ensuring that a rapist can expect to pay a sufficient cost to outweigh any potential benefit.     

An evolutionary perspective of biological invasions

The workshop on the Evolutionary Perspective of Biological Invasions in Terrestrial Ecosystems was held in Halle, Germany from 30 September to 3 October 2002.     

An evolutionary perspective on the systems of adaptive immunity

We propose an evolutionary perspective to classify and characterize the diverse systems of adaptive immunity that have been discovered across all major domains of life. We put forward a new function‐based classification according to the way information is acquired by the immune systems: Darwinian immunity (currently known from, but not necessarily limited to, vertebrates) relies on the Darwinian process of clonal selection to ‘learn’ by cumulative trial‐and‐error feedback; Lamarckian immunity uses templated targeting (guided adaptation) to internalize heritable information on potential threats; finally, shotgun immunity operates through somatic mechanisms of variable targeting without feedback. We argue that the origin of Darwinian (but not Lamarckian or shotgun) immunity represents a radical innovation in the evolution of individuality and complexity, and propose to add it to the list of major evolutionary transitions. While transitions to higher‐level units entail the suppression of selection at lower levels, Darwinian immunity re‐opens cell‐level selection within the multicellular organism, under the control of mechanisms that direct, rather than suppress, cell‐level evolution for the benefit of the individual. From a conceptual point of view, the origin of Darwinian immunity can be regarded as the most radical transition in the history of life, in which evolution by natural selection has literally re‐invented itself. Furthermore, the combination of clonal selection and somatic receptor diversity enabled a transition from limited to practically unlimited capacity to store information about the antigenic environment. The origin of Darwinian immunity therefore comprises both a transition in individuality and the emergence of a new information system – the two hallmarks of major evolutionary transitions. Finally, we present an evolutionary scenario for the origin of Darwinian immunity in vertebrates. We propose a revival of the concept of the ‘Big Bang’ of vertebrate immunity, arguing that its origin involved a ‘difficult’ (i.e. low‐probability) evolutionary transition that might have occurred only once, in a common ancestor of all vertebrates. In contrast to the original concept, we argue that the limiting innovation was not the generation of somatic diversity, but the regulatory circuitry needed for the safe operation of amplifiable immune responses with somatically acquired targeting. Regulatory complexity increased abruptly by genomic duplications at the root of the vertebrate lineage, creating a rare opportunity to establish such circuitry. We discuss the selection forces that might have acted at the origin of the transition, and in the subsequent stepwise evolution leading to the modern immune systems of extant vertebrates.     

An evolutionary perspective on the kinome of malaria parasites

Malaria parasites belong to an ancient lineage that diverged very early from the main branch of eukaryotes. The approximately 90-member plasmodial kinome includes a majority of eukaryotic protein kinases that clearly cluster within the AGC, CMGC, TKL, CaMK and CK1 groups found in yeast, plants and mammals, testifying to the ancient ancestry of these families. However, several hundred millions years of independent evolution, and the specific pressures brought about by first a photosynthetic and then a parasitic lifestyle, led to the emergence of unique features in the plasmodial kinome. These include taxon-restricted kinase families, and unique peculiarities of individual enzymes even when they have homologues in other eukaryotes. Here, we merge essential aspects of all three malaria-related communications that were presented at the Evolution of Protein Phosphorylation meeting, and propose an integrated discussion of the specific features of the parasite's kinome and phosphoproteome.     

An evolutionary perspective on the regulation of carpel development

The carpel, or female reproductive organ enclosing the ovules, is one of the major evolutionary innovations of the flowering plants. The control of carpel development has been intensively studied in the model eudicot species Arabidopsis thaliana. This review traces the evolutionary history of genes involved in carpel development by surveying orthologous genes in taxa whose lineages separated from that of A. thaliana at different levels of the phylogenetic tree of the seed plants. Some aspects of the control of female reproductive development are conserved between the flowering plants and their sister group, the gymnosperms, indicating the presence of these in the common ancestor of the extant seeds plants, some 300 million years ago. Gene duplications that took place in the pre-angiosperm lineage, before the evolution of the first flowering plants, provided novel gene clades of potential importance for the origin of the carpel. Subsequent to the appearance of the first flowering plants, further gene duplications have led to sub-functionalization events, in which pre-existing reproductive functions were shared between paralogous gene clades. In some cases, fluidity in gene function is evident, leading to similar functions in carpel development being controlled by non-orthologous genes in different taxa. In other cases, gene duplication events have created sequences that evolved novel functions by the process of neo-functionalization, thereby generating biodiversity in carpel and fruit structures.     

An evolutionary perspective on the 'death hormone'hypothesis in plants

Many plants die after first reproduction, as if committing suicide, a phenomenon known as 'monocarpic senescence'. The process is different from the ageing seen in most animals. A 'death hormone'has been proposed to explain the phenomenon, both for plants and also separately for animals. This paper considers for plants whether and how such a death hormone could have evolved.
Monocarpic senescence has sometimes been attributed to starvation of the vegetative parts for photosynthate or mineral nutrients, by nutrient diversion to developing fruit. In this case, no evolutionary problem arises. In other cases, the phenomenon seems to be one of programmed senescence, since details of the process conflict with an explanation in terms of nutrient diversion, since there is apparently a hormonal senescence signal, and since, e.g., the same type of senescence occurs even in male plants that do not bear fruit.
A range of evolutionary mechanisms are considered, by which a death hormone could have evolved: species selection, kin selection, direct Darwinian selection, pleiotropy, functional correlation, orthogenesis, genetic drift and founder effects. The two most likely are identified as: (1) kin selection, in which the mother plant dies, and thus facilitates establishment of her offspring, and (2) selection for efficiency of assimilate mobilisation. Neither of these explanations seems completely satisfactory.     

An evolutionary perspective on synonymous codon usage in unicellular organisms

Summary Observed patterns of synonymous codon usage are explained in terms of the joint effects of mutation, selection, and random drift. Examination of the codon usage in 165Escherichia coli genes reveals a consistent trend of increasing bias with increasing gene expression level. Selection on codon usage appears to be unidirectional, so that the pattern seen in lowly expressed genes is best explained in terms of an absence of strong selection. A measure of directional synonymous-codon usage bias, the Codon Adaptation Index, has been developed. In enterobacteria, rates of synonymous substitution are seen to vary greatly among genes, and genes with a high codon bias evolve more slowly. A theoretical study shows that the patterns of extreme codon bias observed for someE. coli (and yeast) genes can be generated by rather small selective differences. The relative plausibilities of various theoretical models for explaining nonrandom codon usage are discussed.Presented at the FEBS Symposium on Genome Organization and Evolution, held in Crete, Greece, September 1–5, 1986     

Endopolyploidy in vertebrate liver: An evolutionary perspective

Hepatocyte nuclei in several species of vertebrates were examined, to establish the frequency of polyploidy and related parameters along evolutionary lines. Nuclei were compared in terms of volume, DNA content, ploidy ranges and internal organization. Several trends emerged. When present, heterochromatin occupied 20–25% of nuclear profile areas, irrespective of nuclear volume and ploidy; the volume of heterochromatin, however, increased in direct proportion to ploidy level. Regardless of internal organization, ploidy and species, a direct correlation emerged between the volumes of nuclei and their absolute DNA content. Results are discussed in terms of structural and genic DNA.     

Bigeneric nomina: An historical and evolutionary perspective

It is suggested that the addition of bigeneric or bispecific nomina to designate fossils which are intermediate between two chronogenera or chronospecies is inadvisable, because the use of either of these categories to describe cases involving a single phyletic line, consisting of a continuous chain of time-sequential populations, misrepresents the nature of the evolutionary processes involved; and that in such cases fossils might best be referred to by specimen numbers.