Hybridization, ecological races and the nature of species: empirical evidence for the ease of speciation

Species are generally viewed by evolutionists as 'real' distinct entities in nature, making speciation appear difficult. Charles Darwin had originally promoted a very different uniformitarian view that biological species were continuous with 'varieties' below the level of species and became distinguishable from them only when divergent natural selection led to gaps in the distribution of morphology. This Darwinian view on species came under immediate attack, and the consensus among evolutionary biologists today appears to side more with the ideas of Ernst Mayr and Theodosius Dobzhansky, who argued 70 years ago that Darwin was wrong about species. Here, I show how recent genetic studies of supposedly well-behaved animals, such as insects and vertebrates, including our own species, have supported the existence of the Darwinian continuum between varieties and species. Below the level of species, there are well-defined ecological races, while above the level of species, hybridization still occurs, and may often lead to introgression and, sometimes, hybrid speciation. This continuum is evident, not only across vast geographical regions, but also locally in sympatry. The existence of this continuum provides good evidence for gradual evolution of species from ecological races and biotypes, to hybridizing species and, ultimately, to species that no longer cross. Continuity between varieties and species not only provides an excellent argument against creationism, but also gives insight into the process of speciation. The lack of a hiatus between species and ecological races suggests that speciation may occur, perhaps frequently, in sympatry, and the abundant intermediate stages suggest that it is happening all around us. Speciation is easy!     

Organisms as natural purposes: the contemporary evolutionary perspective

Kant's conception of organisms as natural purposes raises a challenge to the adequacy of mechanistic explanation in biology. Certain features of organisms appear to be inexplicable by appeal to mechanical law alone. Some biological phenomena, it seems, can only be accounted for teleologically. Contemporary evolutionary biology has by and large ignored this challenge. It is widely held that Darwin's theory of natural selection gives us an adequate, wholly mechanical account of the nature of organisms. In contemporary biology, the category of the organism plays virtually no explanatory role. Contemporary evolutionary biology is a science of sub-organismal entities-replicators. I argue that recent advances in developmental biology demonstrate the inadequacy of sub-organismal mechanism. The category of the organism, construed as a 'natural purpose' should play an ineliminable role in explaining ontogenetic development and adaptive evolution. According to Kant the natural purposiveness of organisms cannot be demonstrated to be an objective principle in nature, nor can purposiveness figure in genuine explain. I attempt to argue, by appeal to recent work on self-organization, that the purposiveness of organisms is a natural phenomenon, and, by appeal to the apparatus of invariance explanation, that biological purposiveness provides genuine, ineliminable biological explanations.     

"Curiously parallel": analogies of language and race in Darwin's Descent of man. A reply to Gregory Radick

In the second chapter of The descent of man (1871), Charles Darwin interrupted his discussion of the evolutionary origins of language to describe ten ways in which the formation of languages and of biological species were 'curiously' similar. I argue that these comparisons served mainly as analogies in which linguistic processes stood for aspects of biological evolution. Darwin used these analogies to recapitulate themes from On the origin of species (1859), including common descent, genealogical classification, the struggle for existence, and natural selection, among others. Skeptical of this interpretation, Gregory Radick sees the naturalistic account of language formation in the Descent comparisons as reinforcing Darwin's idea that languages and the races of mankind have both undergone progressive development. (The opposite view was that modern-day primitive peoples had degenerated from an originally civilized condition.) Yet the details of Darwin's language-species comparisons, as well as the polemical context in which they appear, show that they were not aimed at so limited a function. Rather, they addressed issues related to species transmutation in general.     

Darwin's explanation of races by means of sexual selection

In Darwin's Sacred Cause, Adrian Desmond and James Moore contend that "Darwin would put his utmost into sexual selection because the subject intrigued him, no doubt, but also for a deeper reason: the theory vindicated his lifelong commitment to human brotherhood" (2009: p. 360). Without questioning Desmond and Moore's evidence, I will raise some puzzles for their view. I will show that attention to the structure of Darwin's arguments in the Descent of Man shows that they are far from straightforward. As Desmond and Moore note, Darwin seems to have intended sexual selection in non-human animals to serve as evidence for sexual selection in humans. However, Darwin's account of sexual selection in humans was different from the canonical cases that Darwin described at great length. If explaining the origin of human races was the main reason for introducing sexual selection, and if sexual selection was a key piece of Darwin's anti-slavery arguments, then it is puzzling why Darwin would have spent so much time discussing cases that did not really support his argument for the origin of human races, and it is also puzzling that his argument for the origin of human races would be so (atypically) poor.     

What are we to make of the concept of race?: Thoughts of a philosopher–scientist

Discussions about the biological bases (or lack thereof) of the concept of race in the human species seem to be never ending. One of the latest rounds is represented by a paper by Neven Sesardic, which attempts to build a strong scientific case for the existence of human races, based on genetic, morphometric and behavioral characteristics, as well as on a thorough critique of opposing positions. In this paper I show that Sesardic’s critique falls far short of the goal, and that his positive case is exceedingly thin. I do this through a combination of analysis of the actual scientific findings invoked by Sesardic and of some philosophical unpacking of his conceptual analysis, drawing on a dual professional background as an evolutionary biologist and a philosopher of science.     

The biological roots of morality

The question whether ethical behavior is biologically determined may refer either to thecapacity for ethics (e.i., the proclivity to judge human actions as either right or wrong), or to the moralnorms accepted by human beings for guiding their actions. My theses are: (1) that the capacity for ethics is a necessary attribute of human nature; and (2) that moral norms are products of cultural evolution, not of biological evolution.Humans exhibits ethical behavior by nature because their biological makeup determines the presence of the three necessary, and jointly sufficient, conditions for ethical behavior: (i) the ability to anticipate the consequences of one's own actions; (ii) the ability to make value judgements; and (iii) the ability to choose between alternative courses of action. Ethical behavior came about in evolution not because it is adaptive in itself, but as a necessary consequece of man's eminent intellectual abilities, which are an attribute directly promoted by natural selection.Since Darwin's time there have been evolutionists proposing that the norms of morality are derived from biological evolution. Sociobiologists represent the most recent and most subtle version of that proposal. The sociobiologists' argument is that human ethical norms are sociocultural correlates of behaviors fostered by biological evolution. I argue that such proposals are misguided and do not escape the naturalistic fallacy. The isomorphism between the behaviors promoted by natural selection and those sanctioned by moral norms exist only with respect to the consequences of the behaviors; the underlying causations are completely disparate.This article is based on a paper presented at the International Symposium onBiological Models of Human Action, Palma de Mallorca, Spain, 16–18 December 1985.     

Kant goes fishing: Kant and the right to property in environmental resources

We can observe a connection between some serious environmental problems caused by the overexploitation of environmental resources and the particular conceptions of property rights that are claimed to hold with regard to these resources. In this paper, I investigate whether Kant's conception of property rights might constitute a basis for justifying property regimes that would overcome some of these environmental problems. Kant's argument for the right to property, put forward in his Doctrine of right, is complex. In Section , I attempt an interpretation. Section works out the defining characteristics of the conception of property rights that Kant's argument establishes and investigates their implications for determining property regimes in environmental resources. Kant proposes a minimalist notion of the right to property as a triadic relation between persons with regard to an object, justified only on the condition that it is universalizable in the given circumstances. I argue that this notion offers a promising account for determining property relations with regard to environmental resources. By way of illustration, in Section , I focus on an example of Kantian property rights in one type of environmental resource: the marine fisheries.     

Kant on biological teleology: Towards a two-level interpretation

According to Kant's Critique of the power of judgment, teleological considerations are unavoidable for conceptualizing organisms. Does this mean that teleology is more than merely heuristic? Kant stresses the regulative status of teleological attributions, but sometimes he seems to treat teleology as a constitutive condition for biology. To clarify this issue, the concept of natural purpose and its role for biology are examined. I suggest that the concept serves an identificatory function: it singles out objects as natural purposes, whereby the special science of biology is constituted. This relative constitutivity of teleology is explicated by means of a distinction of levels: on the object level of biological science, teleology is taken as constitutive, though it is merely regulative on the philosophical meta level. This distinction also concerns the place of Aristotelian teleology in Kant: on the object level, the Aristotelian view is accepted, whereas on the meta level, an agnostic stance is taken concerning teleology.     

Darwin and the linguists: the coevolution of mind and language, Part 1. Problematic friends

In his book The descent of man (1871), Charles Darwin paid tribute to a trio of writers (Hensleigh Wedgwood, F. W. Farrar, and August Schleicher) who offered naturalistic explanations of the origin of language. Darwin's concurrence with these figures was limited, however, because each of them denied some aspect of his thesis that the evolution of language had been coeval with and essential to the emergence of humanity's characteristic mental traits. Darwin first sketched out this thesis in his theoretical notebooks of the 1830s and then clarified his position in Descent, where he argued that mind-language coevolution had occurred prior to the rise of distinct racial groups. He thus opposed the view of August Schleicher and Ernst Haeckel, who (along with Alfred Russel Wallace) taught that speech had originated subsequent to the geographical and racial dispersion of humanity's ancestors. As Darwin argued in Descent, this quasi-polygenetic version of coevolution was unable to explain primeval man's initial dominance over rival ape-like populations. Drawing inspiration from British anthropologists, Darwin made the early development of language, hence mental monogenesis, central to his account of human evolution.     

Is the Naturalistic Fallacy Dead (and If So,Ought It Be?)

Much of modern moral philosophy argued that there are is's in this world, and there are oughts, but that the two are entirely independent of one another. What this meant was that morality had nothing to do with man's biological nature, and could not be derived from it. Any such attempt was considered to be a categorical mistake, and plain foolish. Most philosophers still believe this, but a growing group of neo-naturalist thinkers are now challenging their assumptions. Here I consider the latest work of one of them, Patricia Churchland, on what neurobiology teaches us about morality, and ask whether her challenge means that the naturalistic fallacy, as it is known, should be laid to rest. I argue that while there may be no such thing as a human trait divorced from human biology, this does not necessarily mean that our natures produce constraints that are relevant to specific moral dilemmas.     

The importance of cryptic species and subspecific populations in classic biological control of weeds: a North American perspective

Classical biological control of weeds depends on finding agents that are highly host-specific. This requires not only correctly understanding the identity of the target plant, sometimes to subspecific levels, in order to find suitable agents, but also identifying agents that are sufficiently specific to be safe and effective. Behavioral experiments and molecular genetic tools have revealed that some arthropod species previously thought to be polyphagous really consist of multiple cryptic species, host races or biotypes, some of which are more host-specific than others. Whereas true species are reproductively isolated, individuals from subspecific populations may potentially interbreed with those of other populations if they should encounter them. Furthermore, biotypes may consist of individuals sharing a genotype that is not fixed within a monophyletic group, and thus may not be evolutionarily stable. This raises the question of how such populations should be classified, and how to confirm the identity of live arthropods before releasing them as classical biological control agents. The existence of host races or cryptic species may greatly increase the number of prospective biological control agents available. However, it may also create new challenges for governmental regulation. These issues are discussed using pertinent examples, mainly from North America.     

Egg colour mimicry in the common cuckoo Cuculus canorus as revealed by modelling host retinal function

Some parasite cuckoo species lay eggs that, to the human eye, appear to mimic the appearance of the eggs of their favourite hosts, which hinders discrimination and removal of their eggs by host species. Hitherto, perception of cuckoo-host egg mimicry has been estimated based on human vision or spectrophotometry, which does not account for what the receivers' eye (i.e. hosts) actually discriminates. Using a discrimination model approach that reproduces host retinal functioning, and museum egg collections collected in the south of Finland, where at least six different races of the European cuckoo (Cuculus canorus) coexist, I first assess whether the colour design of cuckoo eggs of different races maximizes matching for two favourite avian hosts, viz. the redstart (Phoenicurus phoenicurus) and the pied wagtail (Motacilla alba). Second, I assess the role of nest luminosity on host perception of mimicry by the same two hosts. Phoenicurus-cuckoo eggs showed a better chromatic matching with the redstart-host eggs than other cuckoo races, and in most cases can not be discriminated. Sylvia-cuckoo eggs, however, showed better achromatic matching with redstart-host eggs than Phoenicurus-cuckoo eggs. Also, Motacilla-cuckoo eggs showed poorer chromatic and achromatic matching with pied wagtail-host eggs than Sylvia-cuckoo eggs. Nest luminosity affected chromatic and achromatic differences between cuckoo and host eggs, although only minimally affected the proportion of cuckoo eggs discriminated by chromatic signals. These results reveal that cuckoo races as assessed by humans do not entirely match with host perception of matching and that achromatic mechanisms could play a main role in the discrimination of cuckoo eggs at low-light levels.     

Hybridization and regional variation in Pacific Northwestern Impatiens (Balsaminaceae)

Variation patterns ofImpatiens species in the Pacific Northwest are discussed. Much of the variability there is attributed to widespread interspecific hybridization. Taxonomy of the genus is briefly reviewed, and it is suggested that four species should be recognized for the region. An account of natural hybridization betweenI. capensis andI. ecalcarata is given in detail, and it is postulated that the effects of this hybridization may extend beyond the immediate area in which it is detectable on the basis of morphological patterns. It is suggested thatI. aurella may be of hybrid origin since it combines characters of two species in the Pacific Northwest. Although natural hybridization is occurring at the present time, geographical distribution of variant populations of the species suggests that extensive hybridization may have been initiated in late Pleistocene as a result of the ecological disturbances prevalent at that time.     

Getting the most out of Shannon information

Shannon information is commonly assumed to be the wrong way in which to conceive of information in most biological contexts. Since the theory deals only in correlations between systems, the argument goes, it can apply to any and all causal interactions that affect a biological outcome. Since informational language is generally confined to only certain kinds of biological process, such as gene expression and hormone signalling, Shannon information is thought to be unable to account for this restriction. It is often concluded that a richer, teleosemantic sense of information is needed. I argue against this view, and show that a coherent and sufficiently restrictive theory of biological information can be constructed with Shannon information at its core. This can be done by paying due attention some crucial distinctions: between information quantity and its fitness value, and between carrying information and having the function of doing so. From this I construct an account of how informational functions arise, and show that the “subject matter” of these functions can easily be seen as the natural information dealt with by Shannon’s theory.     

Race: a social destruction of a biological concept

It is nowadays a dominant opinion in a number of disciplines (anthropology, genetics, psychology, philosophy of science) that the taxonomy of human races does not make much biological sense. My aim is to challenge the arguments that are usually thought to invalidate the biological concept of race. I will try to show that the way “race” was defined by biologists several decades ago (by Dobzhansky and others) is in no way discredited by conceptual criticisms that are now fashionable and widely regarded as cogent. These criticisms often arbitrarily burden the biological category of race with some implausible connotations, which then opens the path for a quick eliminative move. However, when properly understood, the biological notion of race proves remarkably resistant to these deconstructive attempts. Moreover, by analyzing statements of some leading contemporary scholars who support social constructivism about race, I hope to demonstrate that their eliminativist views are actually in conflict with what the best contemporary science tells us about human genetic variation.     

Janus-faced race: Is race biological,social, or mythical?

As belief in the reality of race as a biological category among U.S. anthropologists has fallen, belief in the reality of race as a social category has risen in its place. The view that race simply does not exist—that it is a myth—is treated with suspicion. While racial classification is linked to many of the worst evils of recent history, it is now widely believed to be necessary to fight back against racism. In this article, I argue that race is indeed a biological fiction, but I critique the claim that race is socially real. I defend a form of anti-realist reconstructionism about race, which says that there are no races, only racialized groups—groups mistakenly believed to be races. I argue that this is the most attractive position about race from a metaphysical perspective, and that it is also the position most conductive to public understanding and social justice.     

Evaluation of Factors Affecting Emotional Responses in Zoo Visitors and the Impact of Emotion on Conservation Mindedness

Creating experiences for visitors that increase their biological knowledge and inspire conservation mindedness is a critical task for zoos and aquariums. A growing body of literature suggests that emotional stimulation is affected by characteristics of both the visitor and the visitor's experiences and is important for learning and inspiring pro-environmental sentiment. In this study we explored relationships between emotional experience, the factors that influence it, visitors' predispositions toward nature, and their reports of conservation mindedness after viewing three carnivore exhibits at the Bronx Zoo, USA. We surveyed visitors after they viewed tigers, African wild dogs, and spotted hyenas during baseline conditions or when the animals were given environmental enrichment to stimulate natural behavior and activity. We asked visitors to report their predispositions toward nature, the extent of positive emotional experiences they had while viewing the animals, and how the experience affected their conservation mindedness. Environmental enrichment significantly increased animal behavioral diversity, particularly for African wild dogs, and contributed to visitors reporting having had an up-close encounter with the animals, both of which affected the strength of positive emotional experiences at the exhibits. The extent of eye contact with the animal and the animal species also significantly affected emotional responses. Women reported stronger emotional experiences than men, however younger adults did not experience stronger positive emotional responses than older participants. Visitors' predispositions toward nature and emotional responses were significantly correlated. Strong predispositions toward nature and emotional experiences produced significantly stronger reports of conservation mindedness in visitors as a result of their experience at the exhibit. These findings have implications for animal husbandry, exhibit design, education, and outreach efforts for zoos.     

Host races in plant-feeding insects and their importance in sympatric speciation

The existence of a continuous array of sympatric biotypes - from polymorphisms, through ecological or host races with increasing reproductive isolation, to good species - can provide strong evidence for a continuous route to sympatric speciation via natural selection. Host races in plant-feeding insects, in particular, have often been used as evidence for the probability of sympatric speciation. Here, we provide verifiable criteria to distinguish host races from other biotypes: in brief, host races are genetically differentiated, sympatric populations of parasites that use different hosts and between which there is appreciable gene flow. We recognize host races as kinds of species that regularly exchange genes with other species at a rate of more than ca. 1% per generation, rather than as fundamentally distinct taxa. Host races provide a convenient, although admittedly somewhat arbitrary intermediate stage along the speciation continuum. They are a heuristic device to aid in evaluating the probability of speciation by natural selection, particularly in sympatry. Speciation is thereby envisaged as having two phases: (i) the evolution of host races from within polymorphic, panmictic populations; and (ii) further reduction of gene flow between host races until the diverging populations can become generally accepted as species. We apply this criterion to 21 putative host race systems. Of these, only three are unambiguously classified as host races, but a further eight are strong candidates that merely lack accurate information on rates of hybridization or gene flow. Thus, over one-half of the cases that we review are probably or certainly host races, under our definition. Our review of the data favours the idea of sympatric speciation via host shift for three major reasons: (i) the evolution of assortative mating as a pleiotropic by-product of adaptation to a new host seems likely, even in cases where mating occurs away from the host; (ii) stable genetic differences in half of the cases attest to the power of natural selection to maintain multilocus polymorphisms with substantial linkage disequilibrium, in spite of probable gene flow; and (iii) this linkage disequilibrium should permit additional host adaptation, leading to further reproductive isolation via pleiotropy, and also provides conditions suitable for adaptive evolution of mate choice (reinforcement) to cause still further reductions in gene flow. Current data are too sparse to rule out a cryptic discontinuity in the apparently stable sympatric route from host-associated polymorphism to host-associated species, but such a hiatus seems unlikely on present evidence. Finally, we discuss applications of an understanding of host races in conservation and in managing adaptation by pests to control strategies, including those involving biological control or transgenic parasite-resistant plants.     

Introductory gestures before songbird vocal displays are shaped by learning and biological predispositions

Numerous animal displays begin with introductory gestures. For example, lizards start their head-bobbing displays with introductory push-ups, and many songbirds begin their vocal displays by repeating introductory notes (INs) before producing their learned song. Among songbirds, the acoustic structure and the number of INs produced before song vary considerably between individuals in a species. While similar variation in songs between individuals is a result of learning, whether variations in INs are also due to learning remains poorly understood. Here, using natural and experimental tutoring with male zebra finches, we show that mean IN number and IN acoustic structure are learned from a tutor. Interestingly, IN properties and how well INs were learned, were not correlated with the accuracy of song imitation and only weakly correlated with some features of songs that followed. Finally, birds artificially tutored with songs lacking INs still repeated vocalizations that resembled INs, before their songs, suggesting biological predispositions in IN production. These results demonstrate that INs, just like song elements, are shaped both by learning and biological predispositions. More generally, our results suggest mechanisms for generating variation in introductory gestures between individuals while still maintaining the species-specific structure of complex displays like birdsong.