Elisabeth A. Lloyd

Getting the Hologenome Concept Right: an Eco-Evolutionary Framework for Hosts and Their Microbiomes

Given the complexity of host-microbiota symbioses, scientists and philosophers are asking questions at new biological levels of hierarchical organization—what is a holobiont and hologenome? When should this vocabulary be applied? Are these concepts a null hypothesis for host-microbe systems or limited to a certain spectrum of symbiotic interactions such as host-microbial coevolution? Critical discourse is necessary in this nascent area, but productive discourse requires that skeptics and proponents use the same lexicon. ABSTRACT Given the complexity of host-microbiota symbioses, scientists and philosophers are asking questions at new biological levels of hierarchical organization—what is a holobiont and hologenome? When should this vocabulary be applied? Are these concepts a null hypothesis for host-microbe systems or limited to a certain spectrum of symbiotic interactions such as host-microbial coevolution? Critical discourse is necessary in this nascent area, but productive discourse requires that skeptics and proponents use the same lexicon. For instance, critiquing the hologenome concept is not synonymous with critiquing coevolution, and arguing that an entity is not a primary unit of selection dismisses the fact that the hologenome concept has always embraced multilevel selection. Holobionts and hologenomes are incontrovertible, multipartite entities that result from ecological, evolutionary, and genetic processes at various levels. They are not restricted to one special process but constitute a wider vocabulary and framework for host biology in light of the microbiome.

Female Sexual Arousal: Genital Anatomy and Orgasm in Intercourse

In men and women sexual arousal culminates in orgasm, with female orgasm solely from sexual intercourse often regarded as a unique feature of human sexuality. However, orgasm from sexual intercourse occurs more reliably in men than in women, likely reflecting the different types of physical stimulation men and women require for orgasm. In men, orgasms are under strong selective pressure as orgasms are coupled with ejaculation and thus contribute to male reproductive success. By contrast, womens orgasms in intercourse are highly variable and are under little selective pressure as they are not a reproductive necessity. The proximal mechanisms producing variability in womens orgasms are little understood. In 1924 Marie Bonaparte proposed that a shorter distance between a womans clitoris and her urethral meatus (CUMD) increased her likelihood of experiencing orgasm in intercourse. She based this on her published data that were never statistically analyzed. In 1940 Landis and colleagues published similar data suggesting the same relationship, but these data too were never fully analyzed. We analyzed raw data from these two studies and found that both demonstrate a strong inverse relationship between CUMD and orgasm during intercourse. Unresolved is whether this increased likelihood of orgasm with shorter CUMD reflects increased penile-clitoral contact during sexual intercourse or increased penile stimulation of internal aspects of the clitoris. CUMD likely reflects prenatal androgen exposure, with higher androgen levels producing larger distances. Thus these results suggest that women exposed to lower levels of prenatal androgens are more likely to experience orgasm during sexual intercourse.

Confirmation and Robustness of Climate Models

Recent philosophical attention to climate models has highlighted their weaknesses and uncertainties. Here I address the ways that models gain support through observational data. I review examples of model fit, variety of evidence, and independent support for aspects of the models, contrasting my analysis with that of other philosophers. I also investigate model robustness, which often emerges when comparing climate models simulating the same time period or set of conditions. Starting from Michael Weisbergs analysis of robustness, I conclude that his approach involves a version of reasoning from variety of evidence, enabling this robustness to be a confirmatory virtue

Clitoral variability compared with penile variability supports nonadaptation of female orgasm

Humans appear relatively unique among animals in that both males and females can experience orgasm as a result of sexual intercourse. However, orgasm during intercourse occurs much less reliably and consistly for females than for males (Lloyd 2005). The significance of this marked sex difference in sexual function is unexplained and of importance to understanding the evolution of female orgasm. The recent revival of the byproduct account of female orgasm (Lloyd 2005), in which the trait is nonadaptive but collateral to selection on the male orgasm, has evoked much debate (Barash 2005; Judson 2005; Zuk 2006). The byproduct account contends that female orgasm arose as the result of shared embryological processes shaped by selection on the male capacity for orgasm thus implying no direct selection on the female form of the trait. The argument is analogous to the presence of male nipples which result from males and females sharing a common embryology and selection for functional nipples in females. The primary evidence that female orgasm is unlikely an adaptation is its high variability in contrast to the almost certainty of male orgasm, suggesting that the female form has been under little selective pressure compared with strong selection for the male form. If this is the case, then one would expect that the genital structures primarily responsible for triggering orgasm in women, the clitoris (Narjani 1924; Masters and Johnson 1966), and in men, the penis, would demonstrate a similar difference in variability to that seen in the occurrence of orgasm. We thus present a comparison in variability of aspects of male and female genital structures that supports differential selection on genitalia and thus likely differential selection on male and female orgasm.

A Semantic Approach to the Structure of Population Genetics

A precise formulation of the structure of modern evolutionary theory has proved elusive. In this paper, I introduce and develop a formal approach to the structure of population genetics, evolutionary theorys most developed sub-theory. Under the semantic approach, used as a framework in this paper, presenting a theory consists in presenting a related family of models. I offer general guidelines and examples for the classification of population genetics models; the defining features of the models are taken to be their state spaces, parameters, and laws. The suggestions regarding the various aspects of the characterization of population genetics models provide an outline for further detailed research.

The nature of Darwin's support for the theory of natural selection

When natural selection theory was presented, much active philosophical debate, in which Darwin himself participated, centered on its hypothetical nature, its explanatory power, and Darwins methodology. Upon first examination, Darwins support of his theory seems to consist of a set of claims pertaining to various aspects of explanatory success. I analyze the support of his method and theory given in the Origin of Species and private correspondence, and conclude that an interpretation focusing on the explanatory strengths of natural selection theory accurately reflects neither Darwins own self-consciously held views, nor the nature of his support. Darwins methodological and philosophical arguments were at once consistently empiricist and more sophisticated than such interpretations credit to him.

Variation in orgasm occurrence by sexual orientation in a sample of U.S. singles.

INTRODUCTION Despite recent advances in understanding orgasm variation, little is known about ways in which sexual orientation is associated with mens and womens orgasm occurrence. AIM To assess orgasm occurrence during sexual activity across sexual orientation categories. METHODS Data were collected by Internet questionnaire from 6,151 men and women (ages 21-65+ years) as part of a nationally representative sample of single individuals in the United States. Analyses were restricted to a subsample of 2,850 singles (1,497 men, 1,353 women) who had experienced sexual activity in the past 12 months. MAIN OUTCOME MEASURES Participants reported their sex/gender, self-identified sexual orientation (heterosexual, gay/lesbian, bisexual), and what percentage of the time they experience orgasm when having sex with a familiar partner. RESULTS Mean occurrence rate for experiencing orgasm during sexual activity with a familiar partner was 62.9% among single women and 85.1% among single men, which was significantly different (F1,2848  = 370.6, P < 0.001, η(2)  = 0.12). For men, mean occurrence rate of orgasm did not vary by sexual orientation: heterosexual men 85.5%, gay men 84.7%, bisexual men 77.6% (F2,1494  = 2.67, P = 0.07, η(2)  = 0.004). For women, however, mean occurrence rate of orgasm varied significantly by sexual orientation: heterosexual women 61.6%, lesbian women 74.7%, bisexual women 58.0% (F2,1350  = 10.95, P < 0.001, η(2)  = 0.02). Lesbian women had a significantly higher probability of orgasm than did either heterosexual or bisexual women (P < 0.05). CONCLUSIONS Findings from this large dataset of U.S. singles suggest that women, regardless of sexual orientation, have less predictable, more varied orgasm experiences than do men and that for women, but not men, the likelihood of orgasm varies with sexual orientation. These findings demonstrate the need for further investigations into the comparative sexual experiences and sexual health outcomes of sexual minorities.

Why the Gene Will Not Return

I argue that four of the fundamental claims of those calling themselves ‘genic pluralists’—Philip Kitcher, Kim Sterelny, and Ken Waters—are defective. First, they claim that once genic selectionism is recognized, the units of selection problems will be dissolved. Second, Sterelny and Kitcher claim that there are no targets of selection (interactors). Third, Sterelny, Kitcher, and Waters claim that they have a concept of genic causation that allows them to give independent genic causal accounts of all selection processes. I argue that each one of these claims is either false or misleading. Moreover, the challenge that arises from the availability of genic causal accounts, namely, the inability to choose on rational grounds among genic and higher‐level accounts, is unsupported.

COMMENTARY: Evolutionary Psychology: A View From Evolutionary Biology

Given the recent explosion of interest in applications of evolutionary biology to understanding human psychology, we think it timely to assure better understanding of modern evolutionary theory among the psychologists who might be using it. We find it necessary to do so because of the very reduced version of evolutionary theorizing that has been incorporated into much of evolutionary psychology so far. Our aim here is to clarify why the use of a reduced version of evolutionary genetics will lead to faulty science and to indicate where other resources of evolutionary biology can be found that might elevate the standard of the evolutionary component of evolutionary psychology.

Objectivity and a comparison of methodological scenario approaches for climate change research

Climate change assessments rely upon scenarios of socioeconomic developments to conceptualize alternative outcomes for global greenhouse gas emissions. These are used in conjunction with climate models to make projections of future climate. Specifically, the estimations of greenhouse gas emissions based on socioeconomic scenarios constrain climate models in their outcomes of temperatures, precipitation, etc. Traditionally, the fundamental logic of the socioeconomic scenarios—that is, the logic that makes them plausible—is developed and prioritized using methods that are very subjective. This introduces a fundamental challenge for climate change assessment: The veracity of projections of future climate currently rests on subjective ground. We elaborate on these subjective aspects of scenarios in climate change research. We then consider an alternative method for developing scenarios, a systems dynamics approach called ‘Cross-Impact Balance’ (CIB) analysis. We discuss notions of ‘objective’ and ‘objectivity’ as criteria for distinguishing appropriate scenario methods for climate change research. We distinguish seven distinct meanings of ‘objective,’ and demonstrate that CIB analysis is more objective than traditional subjective approaches. However, we also consider criticisms concerning which of the seven meanings of ‘objective’ are appropriate for scenario work. Finally, we arrive at conclusions regarding which meanings of ‘objective’ and ‘objectivity’ are relevant for climate change research. Because scientific assessments uncover knowledge relevant to the responses of a real, independently existing climate system, this requires scenario methodologies employed in such studies to also uphold the seven meanings of ‘objective’ and ‘objectivity.’