Popper, falsifiability, and evolutionary biology

First, a brief history is provided of Popper's views on the status of evolutionary biology as a science. The views of some prominent biologists are then canvassed on the matter of falsifiability and its relation to evolutionary biology. Following that, I argue that Popper's programme of falsifiability does indeed exclude evolutionary biology from within the circumference of genuine science, that Popper's programme is fundamentally incoherent, and that the correction of this incoherence results in a greatly expanded and much more realistic concept of what is empirical, resulting in the inclusion of evolutionary biology. Finally, this expanded concept of empirical is applied to two particular problems in evolutionary biology — viz., the species problem and the debate over the theory of punctuated equilibria — and it is argued that both of them are still mainly metaphysical.     

Discussion: Leo Buss's The Evolution of Individuality

In his book The Evolution of Individuality, Leo Buss attacks a central dogma of the neo-Darwinian (or synthetic) theory of evolution, the idea that the individual is the sole unit of selection, by arguing that individuals themselves emerged as the result of selective forces that regulated the replication of cell lineages for the benefit of the whole organism. Buss also argues that metazoan developmental patterns and life cycles are the products of selection operating on different units of selection, and that there have been transitions between different units of selection during the history of life. Despite the revolutionary character of this book, The Evolution of Individuality in many ways reflects the adaptationist thinking often associated with the synthetic theory. Buss' framework could be improved by giving further consideration to chance factors in the evolution of development, and examining the details of the evolution of ontogeny in more depth.I am grateful to an anonymous reviewer from Biology and Philosophy for helpful comments and criticism.     

Stabilizing selection of protein function and distribution of selection coefficient among sites

In this study, I take a new approach to modeling the evolutionary constraint of protein sequence, introducing the stabilizing selection of protein function into the nearly-neutral theory. In other words, protein function under stabilizing selection generates the evolutionary conservation at the sequence level. With the help of random mutational effects of nucleotides on protein function, I have derived the distribution of selection coefficient among sites, called the S-distribution whose parameters have clear biological interpretations. Moreover, I have studied the inverse relationship between the evolutionary rate and the effective population size, showing that the number of molecular phenotypes of protein function, i.e., independent components in the fitness of the organism, may play a key role for the molecular clock under the nearly-neutral theory. These results are helpful for having a better understanding of the underlying evolutionary mechanism of protein sequences, as well as human disease-related mutations.     

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.     

How Could Language Have Evolved?

The evolution of the faculty of language largely remains an enigma. In this essay, we ask why. Language''s evolutionary analysis is complicated because it has no equivalent in any nonhuman species. There is also no consensus regarding the essential nature of the language “phenotype.” According to the “Strong Minimalist Thesis,” the key distinguishing feature of language (and what evolutionary theory must explain) is hierarchical syntactic structure. The faculty of language is likely to have emerged quite recently in evolutionary terms, some 70,000–100,000 years ago, and does not seem to have undergone modification since then, though individual languages do of course change over time, operating within this basic framework. The recent emergence of language and its stability are both consistent with the Strong Minimalist Thesis, which has at its core a single repeatable operation that takes exactly two syntactic elements a and b and assembles them to form the set {a, b}.It is uncontroversial that language has evolved, just like any other trait of living organisms. That is, once—not so long ago in evolutionary terms—there was no language at all, and now there is, at least in Homo sapiens. There is considerably less agreement as to how language evolved. There are a number of reasons for this lack of agreement. First, “language” is not always clearly defined, and this lack of clarity regarding the language phenotype leads to a corresponding lack of clarity regarding its evolutionary origins. Second, there is often confusion as to the nature of the evolutionary process and what it can tell us about the mechanisms of language. Here we argue that the basic principle that underlies language''s hierarchical syntactic structure is consistent with a relatively recent evolutionary emergence.     

Risk management in biological evolution

I present a framework to study the evolution of traits that allow an organism to survive life-threatening but rare risks. Specifically, I am concerned with risks so rare that any one individual in a population may not experience the risk-causing event in its lifetime. A theory of rare risk management is virtually absent in evolutionary biology, although it is well developed in economics. This is surprising because of the great influence economics had on evolutionary biology, and because biology is full of examples for evolved risk management traits. They include the ability of bacteria to sporulate, of pathogens to survive antibiotic treatment, of temperate bacteriophages to enter a lytic life cycle, as well as traits that allow higher organisms to survive rare environmental disasters, such as sporadic wildfires and irregular flooding. I make predictions about the sustenance of risk management traits under two scenarios, one where the catastrophic events cause individual deaths, and another one where catastrophic events cause population extinction. A well-developed theory of risk management will not only predict the distribution of risk management traits, but may also serve other purposes, such as to reconstruct the spectrum of environments that an organism encountered in its evolutionary history from the record stored in its genome's memory.     

On the relationship between evolutionary and psychological definitions of altruism and selfishness

I examine the relationship between evolutionary definitions of altruism that are based on fitness effects and psychological definitions that are based on the motives of the actor. I show that evolutionary altruism can be motivated by proximate mechanisms that are psychologically either altruistic or selfish. I also show that evolutionary definitions do rely upon motives as a metaphor in which the outcome of natural selection is compared to the decisions of a psychologically selfish (or altruistic) individual. Ignoring the precise nature of both psychological and evolutionary definitions has obscured many important issues, including the biological roots of psychological altruism.     

Experimental evolution reveals differences between phenotypic and evolutionary responses to population density

Group living can select for increased immunity, given the heightened risk of parasite transmission. Yet, it also may select for increased male reproductive investment, given the elevated risk of female multiple mating. Trade‐offs between immunity and reproduction are well documented. Phenotypically, population density mediates both reproductive investment and immune function in the Indian meal moth, Plodia interpunctella. However, the evolutionary response of populations to these traits is unknown. We created two replicated populations of P. interpunctella, reared and mated for 14 generations under high or low population densities. These population densities cause plastic responses in immunity and reproduction: at higher numbers, both sexes invest more in one index of immunity [phenoloxidase (PO) activity] and males invest more in sperm. Interestingly, our data revealed divergence in PO and reproduction in a different direction to previously reported phenotypic responses. Males evolving at low population densities transferred more sperm, and both males and females displayed higher PO than individuals at high population densities. These positively correlated responses to selection suggest no apparent evolutionary trade‐off between immunity and reproduction. We speculate that the reduced PO activity and sperm investment when evolving under high population density may be due to the reduced population fitness predicted under increased sexual conflict and/or to trade‐offs between pre‐ and post‐copulatory traits.     

Delayed selfing in relation to the availability of a mating partner in the cestode Schistocephalus solidus

Abstract A hermaphroditic individual that prefers to outbreed but that has the potential of selfing faces a dilemma: in the absence of a partner, should it wait for one to arrive or should it produce offspring by selfing? Recent theory on this question suggests that the evolutionary solution is to find an optimal delay of reproduction that balances the potential benefit of outcrossing and the cost of delaying the onset of reproduction. Assuming that resources retained from breeding can be reallocated to future reproduction, isolated individuals, compared with individuals with available mates, are predicted to delay their age at first reproduction to wait for future outcrossing. Here, I present empirical support for this idea with experimental data from the hermaphroditic cestode Schistocephalus solidus. I show that individuals breeding alone delay their reproduction and initially produce their eggs at a slow rate relative to cestodes breeding in pairs. This delay is partly compensated for by a later higher egg production, although singly breeding cestodes still pay a cost of overall lower egg production.     

Reproductive suppression in female primates: A review

Reproductive performance is the currency of evolution. All things being equal, an organism should reproduce as often as possible. The puzzling questions in evolutionary biology, therefore, are not how and why an organism does reproduce, but rather how and why an organism does not reproduce. It is difficult to understand why any individual, particularly a female, might forestall reproduction when one of the biggest limitations for female mammalian reproduction is time (that is, reproductive lifespan). 1 The answer, now widely cited throughout behavioral ecology is quite simple: Reproductive suppression can be an adaptive strategy. 2     

Patterns and Trends in Primate Pair Bonds

Pair-bonding may be a significant feature of the social repertoire of some primate species. However, discerning inter- and intraspecific pair bonds is problematic. I present an overview of the general behavior and ecology of species reported to occur in two-adult, pair-bonded groups. There is no two-adult grouped nonhuman primate species in Africa and only two types in Asia. Behavioral and ecological data suggest that the two-adult group or pair-bonding or both may have evolved separately 4–7 times. I propose that two pair-bond components—social pair bond and sexual pair bond—occur and can be defined and described in such a manner that facilitates comparative analysis across primate taxa. The evolution of grouping patterns in many two-adult grouped primates may be best modeled via evolutionary scenarios relying on direct dietary/energetic constraints, predation, and possibly mate-guarding. There is little support for the infanticide prevention and bodyguard hypotheses of female-choice models.     

Nucleotide Polymorphism and Within-Gene Recombination in Daphnia magna and D. pulex, Two Cyclical Parthenogens

Theory predicts that partially asexual organisms may make the “best of both worlds”: for the most part, they avoid the costs of sexual reproduction, while still benefiting from an enhanced efficiency of selection compared to obligately asexual organisms. There is, however, little empirical data on partially asexual organisms to test this prediction. Here we examine patterns of nucleotide diversity at eight nuclear loci in continentwide samples of two species of cyclically parthenogenetic Daphnia to assess the effect of partial asexual reproduction on effective population size and amount of recombination. Both species have high nucleotide diversities and show abundant evidence for recombination, yielding large estimates of effective population sizes (300,000–600,000). This suggests that selection will act efficiently even on mutations with small selection coefficients. Divergence between the two species is less than one-tenth of previous estimates, which were derived using a mitochondrial molecular clock. As the two species investigated are among the most distantly related species of the genus, this suggests that the genus Daphnia may be considerably younger than previously thought. Daphnia has recently received increased attention because it is being developed as a model organism for ecological and evolutionary genomics. Our results confirm the attractiveness of Daphnia as a model organism, because the high nucleotide diversity and low linkage disequilibrium suggest that fine-scale mapping of genes affecting phenotypes through association studies should be feasible.     

Asexual reproduction and the turbellarian archetype

The turbellarian archetype is widely believed to have been a hermaphrodite lacking asexual reproduction, and such asexual reproduction as is now seen in the Turbellaria (as paratomy and architomy) is generally assumed to have arisen secondarily several times independently. Asexual reproduction clearly prevails among the most primitive metazoans such as the placozoans, sponges, and radiates, however, and if the Platyhelminthes is indeed an early offshoot of bilaterian evolution, as some have claimed, then it is reasonable to expect asexual reproduction to be a primitive feature of the Turbellaria. Asexual reproduction by paratomy or architomy is found in all three main evolutionary lines of the Turbellaria and is most common among primitive groups such as the Catenulida and Macrostomida. The discovery of a new, apparently primitive marine genus of Macrostomida having paratomy widens the known incidence of asexual reproduction within that order. The presence of a muscle ring around the gut of several distantly related genera of the Macrostomida and similarities this ring shows with septa in the division plane of paratomizing species are evidence that paratomy was a feature of the stem species for this order — a feature only secondarily lost in most macrostomids — and suggest that asexual reproduction is a primitive feature for the Platyhelminthes as a whole.     

Naturalism, evidence and creationism: The case of Phillip Johnson

Phillip Johnson claims that Creationism is a better explanation of the existence and characteristics of biological species than is evolutionary theory. He argues that the only reason biologists do not recognize that Creationist's negative arguments against Darwinism have proven this is that they are wedded to a biased ideological philosophy —Naturalism — which dogmatically denies the possibility of an intervening creative god. However, Johnson fails to distinguish Ontological Naturalism from Methodological Naturalism. Science makes use of the latter and I show how it is not dogmatic but follows from sound requirements for empirical evidential testing. Furthermore, Johnson has no serious alternative type of positive evidence to offer for Creationism, and purely negative argumentation, despite his attempt to legitimate it, will not suffice.     

Pigment–Protein Complexes and the Number of Reaction Centers of the Photosystems in Pea Chlorophyll Mutants

We studied fluorescent and absorption properties of the chloroplasts and pigment–protein complexes isolated by gel electrophoresis from the leaves of pea, the parent cultivar Torsdag and mutants chlorotica 2004 and 2014. Specific fluorescence peaks of chlorophyll forms in individual complexes have been determined from the absorption and fluorescence spectra of the chloroplast chlorophyll and their second derivatives at 23 and –196°C. The mutant chlorotica 2004 proved to have an increased intensity of a long-wave band of the light-harvesting complex I at both 23°C (745 nm) and –196°C (728 nm). At the same time, this mutant manifested a decreased accumulation of the chlorophyll forms making up the nearest-neighbor antenna of the PS I reaction center (at 690, 697, and 708 nm). No spectral differences have been revealed between chlorotica 2014 mutant and the parent cultivar. Gel electrophoresis revealed the synthesis of all chlorophyll–protein complexes in both mutants. At the same time, analysis of photochemical activity of PS I and PS II reaction centers and calculations of their number and the size of the light-harvesting antenna have shown that the number of reaction centers in the PS I of chlorotica 2004 mutant is reduced by a factor of 1.7 because its chlorophyll a–protein complex is disturbed by the mutation. The primary effect of chlorotica 2014 mutation remains unclear. The proportional changes in the content of photosystem complexes in this mutant suggest that they are secondary and result from a 50% decrease in chlorophyll content.     

Predicted fitness changes along an environmental gradient

Summary The relations between enzyme activity and the intensity of selection across an environmental gradient are investigated usingEscherichia coli growing on mixed resources. Experimental results demonstrate that the direction and intensity of natural selection can be predicted solely from a knowledge of the underlying biochemistry, physiology and ecology of the organism. Ecological theory, based on the logistic equation, is unable to use this information to predict the outcome of competition — the best it can do is to fit constants to data points. Our results also suggest that partitioning of the phenotypic variance using quantitative genetics need not correspond to the underlying molecular structure generating phenotypes.     

Perceptual Processes and the Maintenance of Polymorphism Through Frequency-dependent Predation

One of the key challenges of both ecology and evolutionary biology is to understand the mechanisms that maintain diversity. Negative frequency-dependent selection is a powerful mechanism for maintaining variation in the population as well as species diversity in the community. There are a number of studies showing that this type of selection, where individuals of a rare type (i.e. a rare morph or a rare species) experience higher survival than those of more common type(s). However, it is still not clear how frequency-dependent selection operates. Search image formation has been invoked as a possible, proximate explanation. Although the conceptual link between search image and frequency-dependent predation is often assumed in ecological and evolutionary studies, a review of the literature reveals a paucity of evidence demonstrating the occurrence of both in a natural predator-prey system. Advances in the field of psychology strongly support the existence of search image, yet these findings are not fully recognized in the realm of ecology and evolutionary biology, in part, we feel because of confusion and inconsistencies in terminology. Here we try to simplify the language, clarify the advances in the study of frequency-dependent predation and search image, and suggest avenues for future research. We feel that the investigations of both proximate (perceptual mechanisms) and ultimate (pattern of predation) processes are necessary to fully understand the importance of individual behavioural processes for mediating evolutionary and ecological diversity.Co-ordinating editor: O. Leimar     

An experimental test of density‐dependent selection on temperament traits of activity,boldness and sociability

Temperament traits are seen in many animal species, and recent evolutionary models predict that they could be maintained by heterogeneous selection. We tested this prediction by examining density‐dependent selection in juvenile common lizards Zootoca vivipara scored for activity, boldness and sociability at birth and at the age of 1 year. We measured three key life‐history traits (juvenile survival, body growth rate and reproduction) and quantified selection in experimental populations at five density levels ranging from low to high values. We observed consistent individual differences for all behaviours on the short term, but only for activity and one boldness measure across the first year of life. At low density, growth selection favoured more sociable lizards, whereas viability selection favoured less active individuals. A significant negative correlational selection on activity and boldness existed for body growth rate irrespective of density. Thus, behavioural traits were characterized by limited ontogenic consistency, and natural selection was heterogeneous between density treatments and fitness traits. This confirms that density‐dependent selection plays an important role in the maintenance of individual differences in exploration‐activity and sociability.     

Anemophilous plants select pollen from their own species from the air

In wind-tunnel experiments, Niklas (1985) has demonstrated the ability of anemophilous plants to select pollen from their own species from the airstream. However, there have been no field experiments to establish whether this operates in nature. We surveyed the pollents on the stigmas of four different, coextensive, dioecious anemophilous species surrounded by a Pinus radiata plantation. The alien pine pollen was overrepresented relative to background levels on only one of the four species. For all three indigenous species with both male and female plants in the area, the highest proportion — in all cases more than 40% — of the pollen found on their stigmas came from their own species. One indigenous species lacked male plants in the area; consequently, the results from this species are difficult to interpret. However, for all four species, there was at least 15% pine pollen, and some pollen of other indigenous species. These results suggest that there is some pollen selection, but that the mechanisms are may be not as effective as Niklas has suggested.     

Assessing evolutionary epistemology

There are two interrelated but distinct programs which go by the name evolutionary epistemology. One attempts to account for the characteristics of cognitive mechanisms in animals and humans by a straightforward extension of the biological theory of evolution to those aspects or traits of animals which are the biological substrates of cognitive activity, e.g., their brains, sensory systems, motor systems, etc. (EEM program). The other program attempts to account for the evaluation of ideas, scientific theories and culture in general by using models and metaphors drawn from evolutionary biology (EET program). The paper begins by distinguishing the two programs and discussing the relationship between them. The next section addresses the metaphorical and analogical relationship between evolutionary epistemology and evolutionary biology. Section IV treats the question of the locus of the epistemological problem in the light of an evolutionary analysis. The key questions here involve the relationship between evolutionary epistemology and traditional epistemology and the legitimacy of evolutionary epistemology as epistemology. Section V examines the underlying ontological presuppositions and implications of evolutionary epistemology. Finally, section VI, which is merely the sketch of a problem, addresses the parallel between evolutionary epistemology and evolutionary ethics.This research was supported, in part, by a grant from the National Science Foundation # SES—8308720. I want to thank Richard Lewontin and the Museum of Comparative Zoology, Harvard University for their hospitality and support during Spring 1984. I also want to thank David Hull, Charles Dyke and Michael Ruse for helpful comments on an earlier draft, and Andy Altman for pointing out to me the passage from Inherit the Wind.