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\"Darwin developed the theory of sexual selection to explain why the animal world abounds in stunning beauty, from the brilliant colors of butterflies and fishes to the songs of birds and frogs. He argued that animals have 'a taste for the beautiful' that drives their potential mates to evolve features that make them more sexually attractive and reproductively successful. But if Darwin explained why sexual beauty evolved in animals, he struggled to understand how. In [this book], Ryan ... tells the remarkable story of how he and other scientists have taken up where Darwin left off and transformed our understanding of sexual selection, shedding new light on human behavior in the process\"--Amazon.com.

The life cycle of a sexually reproducing species starts from the formation of a zygote by fusion of two gametes. In external fertilisers, the survival of an individual organism from a zygote to an adult is precarious and depends largely on the gametic provisioning of resources by its parents (via the female gamete in species where anisogamy has evolved). In evolutionary ecology, this early survival time has been modelled using a variety of zygote survival functions. In evolutionary modelling applications, the fitness of an individual is measured by the number of its offspring that survive to reproductive maturity, making the survival probability of the offspring a key component in these models. Despite their significance, the existing zygote survival functions remain scattered, with little consensus on their theoretical principles and mathematical tools. Here, our aim was to provide clarification and coherence for future theoretical and empirical research. We achieve this by reconstructing the history of zygote survival modelling, analysing existing zygote survival functions and discussing their theoretical details and problems. Systematising existing survival functions will facilitate future modelling work and will decrease duplication of efforts by concentrating theoretical focus into a unified modelling discourse. Tiivistelmä Suvullisesti lisääntyvän lajin elinkierto alkaa, kun kaksi gameettia yhtyy ja muodostaa zygootin. Ulkoisesti hedelmöittyvillä lajeilla yksilön selviytyminen zygootista aikuiseksi on epävarmaa ja riippuu pitkälti resursseista, jotka zygootti saa vanhemmiltaan sukusolujen kautta (anisogamisilla lajeilla munasoluista). Evoluutioekologiassa selviytymistä tässä elämän varhaisessa vaiheessa on mallinnettu käyttämällä erilaisia zygoottien selviytymisfunktioita. Evolutiivisissa mallinnussovelluksissa yksilön kelpoisuutta mitataan yleisesti sukukypsään aikuisuuteen selviävien jälkeläisten lukumäärällä, mikä tekee jälkeläisten selviytymistodennäköisyydestä oleellisen komponentin näissä malleissa. Tärkeydestään huolimatta olemassa olevat zygoottien selviytymisfunktiot muodostavat hajanaisen joukon vailla yksimielisyyttä niiden teoreettisista periaatteista tai matemaattisista menetelmistä. Tavoitteemme tässä artikkelissa oli selkeyttää ja johdonmukaistaa aihepiirin teoreettista ja empiiristä tutkimusta hahmottelemalla zygoottien selviytymisfunktioiden mallintamisen historiaa, analysoimalla olemassa olevia zygoottien selviytymisfunktioita ja keskustelemalla niiden teoreettisista yksityiskohdista ja ongelmista. Olemassa olevien zygoottien selviytymisfunktioiden systematisointi helpottaa tulevaa mallinnusta ja ehkäisee turhaa työtä keskittämällä teoreettisen painopisteen yhtenäistettyyn mallinnusperinteeseen.

Over the last decades, the field of sexual selection underwent a paradigm shift from sexual-stereotype thinking of “eager” males and “coy” females towards a more nuanced perspective acknowledging that not only males but also females can benefit from multiple mating and compete for mating partners. Yet, sexual selection in females is still considered a peculiarity, and the evolution of polyandry is often viewed to result from a higher mating interest of males. Here, we present meta-analytic evidence from 77 species across a broad range of animal taxa to demonstrate that female reproductive success is overall positively correlated with mating success, suggesting that females typically benefit from multiple mating. Importantly, we found that these fitness gains likely promote the evolution of polyandry. Our findings offer support for the idea that sexual selection is widespread in females and to play a key role for the evolution of animal mating systems. Thereby, our results extend our understanding of the evolutionary consequences of sexual reproduction and contribute to a more balanced view of how sexual selection operates in males and females.

Sexual selection favours traits that confer advantages in the competition for mates. In many cases, such traits are costly to produce and maintain, because the costs help to enforce the honesty of these signals and cues 1 . Some evolutionary models predict that sexual selection also produces costs at the population level, which could limit the ability of populations to adapt to changing conditions and thus increase the risk of extinction 2 – 4 . Other models, however, suggest that sexual selection should increase rates of adaptation and enhance the removal of deleterious mutations, thus protecting populations against extinction 3 , 5 , 6 . Resolving the conflict between these models is not only important for explaining the history of biodiversity, but also relevant to understanding the mechanisms of the current biodiversity crisis. Previous attempts to test the conflicting predictions produced by these models have been limited to extant species and have thus relied on indirect proxies for species extinction. Here we use the informative fossil record of cytheroid ostracods—small, bivalved crustaceans with sexually dimorphic carapaces—to test how sexual selection relates to actual species extinction. We show that species with more pronounced sexual dimorphism, indicating the highest levels of male investment in reproduction, had estimated extinction rates that were ten times higher than those of the species with the lowest investment. These results indicate that sexual selection can be a substantial risk factor for extinction. Ostracod species (small, bivalved crustaceans) with high sexual dimorphism, and therefore high male investment, had markedly higher extinction rates than low-investment species, indicating that sexual selection can be a substantial risk factor for extinction.

What can explain the incredible diversity of beauty in nature? Richard O. Prum, an award-winning ornithologist, discusses Charles Darwin's second and long-neglected theory--aesthetic mate choice--and what it means for our understanding of evolution. In addition, Prum connects those same evolutionary dynamics to the origins and diversity of human sexuality, offering riveting new thinking about the evolution of human beauty and the role of mate choice, thereby transforming our ancestors from typical infanticidal primates into socially intelligent, pair-bonding caregivers. Prum's book is an exhilarating tour de force that begins in the trees and ends by fundamentally challenging how we understand human evolution and ourselves. -- adapted from dust jacket.

Sexual selection by mate choice is a powerful force that can lead to evolutionary change, and models of why females choose particular mates are central to understanding its effects. Predominant mate choice theories assume preferences are determined solely by genetic inheritance, an assumption still lacking widespread support. Moreover, preferences often vary among individuals or populations, fail to correspond with conspicuous male traits, or change with context, patterns not predicted by dominant models. Here, we propose a new model that explains this mate choice complexity with one general hypothesized mechanism, “Inferred Attractiveness.” In this model, females acquire mating preferences by observing others’ choices and use context-dependent information to infer which traits are attractive. They learn to prefer the feature of a chosen male that most distinguishes him from other available males. Over generations, this process produces repeated population-level switches in preference and maintains male trait variation. When viability selection is strong, Inferred Attractiveness produces population-wide adaptive preferences superficially resembling “good genes.” However, it results in widespread preference variation or nonadaptive preferences under other predictable circumstances. By casting the female brain as the central selective agent, Inferred Attractiveness captures novel and dynamic aspects of sexual selection and reconciles inconsistencies between mate choice theory and observed behavior.

Seminal fluid proteins (SFPs) are a group of reproductive proteins that are among the most evolutionarily divergent known. As SFPs can impact male and female fitness, these proteins have been proposed to evolve under postcopulatory sexual selection (PCSS). However, the fast change of the SFPs can also result from nonadaptive evolution, and the extent to which selective constraints prevent SFPs rapid evolution remains unknown. Using intra-and interspecific sequence information, along with genomics and functional data, we examine the molecular evolution of approximately 300 SFPs in Drosophila. We found that 50–57% of the SFP genes, depending on the population examined, are evolving under relaxed selection. Only 7–12% showed evidence of positive selection, with no evidence supporting other forms of PCSS, and 35–37% of the SFP genes were selectively constrained. Further, despite associations of positive selection with gene location on the X chromosome and protease activity, the analysis of additional genomic and functional features revealed their lack of influence on SFPs evolving under positive selection. Our results highlight a lack of sufficient evidence to claim that most SFPs are driven to evolve rapidly by PCSS while identifying genomic and functional attributes that influence different modes of SFPs evolution.