Two welcome extensions of evolutionary thinking have come to prominence over the last thirty years: the so-called “extended evolutionary synthesis” (EES) and debate about biological kinds and individuals. These two agendas have, however, remained orthogonal to one another. The EES has mostly restricted itself to widening the explanations of adaptation offered by the preceding “modern evolutionary synthesis” by including additional mechanisms of inheritance and variation; while discussion of biological kinds has turned toward philosophical questions of essential vs. contingent properties of life forms and realist vs. epistemological approaches to categorization and classification. Here we attempt to broaden the explanatory scope of evolutionary theory by linking these two agendas. We expand on the mechanistic orientation of the EES, using new understandings of networked systems of components in order to engage the distinct intellectual challenge of the origination of
For the last several decades, a set of concerns has exerted increasing pressure on the modern evolutionary synthesis (MES) of the mid-twentieth century, with the goal of broadening the explanatory powers of evolutionary theory. A much-discussed version of this expanded view, the “extended evolutionary synthesis” (EES), builds on but does not repudiate the earlier formation (
Despite these novel agendas, the EES follows the MES closely in one major respect: in each case the aim is to explain adaptations, that is, the fit of organisms to their environments. This shared aim reflects a shared limitation, since one of the main intellectual achievements of the MES was the recognition that the evolution of adaptations and the origin of species are distinct phenomena, requiring different explanatory models (
This notion of clustering introduces a broader problem that has preoccupied much philosophy of biology over the last thirty years: the nature and origination of biological kinds. Because of their shared adaptationist orientation, neither the MES nor the EES has been positioned to engage directly this question. We think, however, that the expanded view of mechanism proposed by the EES is a step in the right direction, one that might point toward a juncture between the EES and the discourse on biological kinds. Across a series of exemplars described in section 2, we will develop an expanded conception of evolutionary mechanisms in order to understand the origination of kinds in both biology and culture, one of the epochal outgrowths of evolution.
To set the stage for our exemplars, we need to situate ourselves briefly in the recent discourse on kinds. Our position is, first of all, an anti-essentialist one. We understand our biological and cultural kinds as reflective not of fixed essences but of processes. This processualism puts us in the camp of theorists who have turned away from metaphysical considerations of kinds (
All processes change through time, and so do the operations of the networked relations that arise within them (
If, however, historical kinds change across time, then they pose a basic question: how can a flexible and changing kind maintain its identity? For us the question of the self-maintenance of kinds in both biology and culture depends once again on mechanisms and their operation and function. Our historical kinds are characterized by the networks central to them of components linked in mutual, reciprocal causal effect and interdependency. These operate at scales ranging from the molecular to the societal, and from their stable operation arise the kinds they define.
Our view of “historiogenic” mechanisms, then, is similar to that advanced by Richard Boyd in support of his “homeostatic property cluster” (HPC) view of biological kinds—for us, one of the foremost interventions in the debates over biological kinds (
The kinds we discern below may be thought of as HPC kinds, and we aim to describe and specify, in several biological and cultural arenas, the homeostatic mechanisms that are at work in defining them. This specification has the advantage of both distinguishing our kinds and assimilating them to one another. That is, it enables us to identify the special processes from which each arises and at the same time points toward deep commonalities among the general features of the mechanisms that function to maintain them.
We speak here of “individual” kinds and of the “individuation” of kinds, but we do not mean by this to enter into the extensive discussion of biological individuals—into, so to speak, the technical use of the word “individual.” This discussion has been mainly an ontological one stimulated by the question of the units that can undergo natural selection (
The processes that establish novel, individuated lineages of descent are subserved by these mechanisms that enable quasi-independent change within a kind. Here we adduce a conceptual distinction that, to our knowledge, was first fully understood in the context of species evolution and origination, namely the distinction between so-called “anagenetic” evolution, modifications that occur along a lineage of descent, and “cladogenetic” evolution, which leads to new lineages (
This latter process of origination needs to be conceived in ways related to but reaching beyond such well-trodden areas as speciation and gene duplication. Elaborating it can help us to organize research into the origin and evolution of cell types, morphological characters, functional processes, behaviors, and patterns of cultural variation and innovation. Even rituals, music, and Paleolithic bead making can be fruitfully conceptualized as historical kinds individuated from other cultural activities and assuming a quasi-independent life and history, partially decoupled from those of other cultural activities or lineages.
All the examples discussed below share structural features that for us define such individuation. They all are embedded in processes of generational replacement, either by direct, material replication, or by indirect, mediated redevelopment and informational transmission, or by both. During the process of replication or reiteration, a historical kind retains a level of coherence and autonomy from other, cognate historical kinds. Coherence and autonomy are two sides of the same coin, the mechanistic stabilizing dynamic that helps to define the kind. And replication with coherence and autonomy not only maintains the kind but also sets in motion processes of historical change along lines of descent, which are determined through competition, among variant types within historical kinds, for representation in succeeding generations.
This return to the idea of selection, finally, calls for a special word on Peter Godfrey-Smith’s Darwinian populations and individuals (
Nevertheless, Godfrey-Smith’s sole criterion—the process that defines his Darwinian populations —is selection, and so this historical kind (if it be such) is at once more general and less specifiable than the kinds we will describe below. Our view recognizes a wider variety of processes from which kinds can arise. This individuation of kinds is not due to the nature of the processes by which they are replicated so much as to the cohesion brought about by functional integration of various sorts—by, again, the stable, causal operation of networked interactions. Our model of historical kinds points more clearly than Godfrey-Smith’s Darwinian individuals toward processes beyond conventional selection that have not yet received their due in evolutionary theory.
Before we proceed to develop our argument, we want to offer a few words about the root of our collaboration, which, after all, is a somewhat extraordinary one between an evolutionary biologist and a musicologist and cultural theorist. Over the last several years, we have independently proposed models of evolutionary and historical origination. GPW published a book on the nature of morphological characters and their origin (
In this section we briefly discuss several examples of putative historical kinds from biology and the social and cultural sciences. We cannot, needless to say, cover all relevant examples. We consciously interleave examples from biology and the cultural sciences in order to highlight the similarities between biological and cultural historical kinds.
The gene is one of the four fundamental ontological units of biology, alongside the cell, the organism, and the species. While there are major disagreements about the ontological status of all of them, scientific practices in biology leave no doubt that biologists attribute great importance to them, including the gene and related subsidiary concepts. Genes are a repository, though not the only one, of biological information accumulated over evolutionary history. There are two complementary ways to introduce the gene concept, each reflecting a part of the history of our understanding of inheritance and evolution. These are the Mendelian or transmission genetic concept and the distinct concept arising from molecular biology. A third concept, the one used in molecular evolution, can be seen as a synthesis of the former two.
In the Mendelian concept, genes are thought of as quasi-atomic or discrete units of inheritance, or parts of the “germ plasma” that 1) cause a specific phenotypic difference (e.g., yellow or green coloration of peas) and 2) are transmitted independently from other such pieces of heritable material and remain unchanged during transmission between generations (except when mutations occur). This Mendelian concept bears an obvious similarity to other nineteenth-century atomic concepts. It only makes sense, however, in species with sexual reproduction and recombination of their genetic material. Organisms without regular recombination, for instance bacteria, do not have “genes,” at least not in the Mendelian sense of the concept.
Organisms without regular genetic recombination can, however, be considered to have genes according to the gene concept of contemporary molecular biology. In this concept the gene is no longer a simple atomic unit of inheritance but instead a complex functional system, with different parts ensuring the expression of the gene at the right time and place and allowing for different outputs in response to different inputs. For example, a gene that codes for a protein consists of a nucleotide sequence that can be translated into an amino acid sequence as well as sequence elements necessary to initiate and terminate its transcription onto an RNA molecule. A coding gene, then, is not a discrete material element, but a segment of a more extensive DNA molecule that includes a number of functional elements such that the segment is used by the cell to produce a certain protein. Mutations of this DNA segment are either neutral, i.e., functionally inconsequential, or they affect the production of the protein, thus affecting also those aspects of the organism that rely on the protein’s function. As a consequence, in transmission between generations, the gene appears both as a unit of inheritance and a unit of function; but this dual appearance is an emergent property, arising from the relations of component parts of a system and not based on a unitary, structurally stable and delimited entity.
These two views of the gene, the transmission/genetic and the functional, are merged and connected to evolutionary theory in the gene concept employed in molecular evolution, the study of the history of genes and genomes (
In a genome, the inheritance-with-competition among the alleles and the absence of competition between different genes together form the basis for the quasi-independent evolutionary history of each gene; each, in whatever variant alleles arise, forms a lineage across this history. Replacement can occur between functionally equivalent variants, in the process called “neutral evolution” or “genetic drift,” but natural selection involves replacement on the basis of functional differences between the alleles. It is evident, then, that the allele lineages created in natural selection and drift depend not solely on replicated segments of DNA, but in addition on the functional interdependencies among the different parts of the genomic region that we recognize as “the gene.”
Of course, there can be more complicated situations that are not captured in this simple model, for instance the possibility of stable polymorphisms, where two alleles are maintained by natural selection in the population because the heterozygote genotype is more fit than either of the homozygote genotypes. In such cases, for example the stable polymorphism of the sickle cell anemia allele of hemoglobin in areas with malaria infestation, each allele has its own evolutionary history for as long as the stable polymorphism is maintained. Stable polymorphisms can be immensely long-lasting, as the polymorphism at the alcohol dehydrogenase locus in
A comparison of genes within particular species’ genomes reveals that some genes within a genome can be more closely related to each other than to other genes in the same genome; instances are the different kinds of Hox genes, i.e., transcription factor genes that control parts of bilaterian animal development (
The fact that genes can be more closely related to each other than to other genes in their own genomes points to evolutionary events in which a gene was duplicated and each copy subsequently took on its own, quasi-independent evolutionary history or lineage of descent. Thus individuation of the sort that gives rise to historical kinds can occur at the genetic level. Genes can show the patterns of evolutionary change that we argue are characteristic for all historical kinds, namely one process of evolutionary modification along a line of descent, and another process that leads to the origination of new lines of descent. The latter is much rarer than the former. In the case of genes, the origination of a new line of descent comes about through gene duplication or gene fusion. The evolutionary history of the new genes thus created, their loss or maintenance, is complicated and cannot be adequately dealt with here (
In general, then, the conventional story of gene duplication, mutation, and natural selection outlined above omits an aspect of the biology that explains the historical, functional cohesion of what molecular biologists think of as genes. Insertions and deletions of small fragments of DNA are frequent occurrences in evolution, and so any DNA segment might diffuse into the genome and eventually become untraceable, as happens with large chunks of intergenic DNA. In the case of functionally relevant parts of the genome, however, the functional integration among the parts of a gene creates an emergent cohesion that prevents the loss of identity over evolutionary time. This integration manifests itself in various ways and mechanisms. For instance, an insertion or deletion in a coding region of a gene that does not respect the reading frame (which maps codons, triplets of nucleotides, to amino acids) has a high chance of leading to a non-functional or even toxic protein product. In other cases, a protein coding region might acquire non-coding sequences, so-called introns. But this is only tolerated by natural selection if the intron contains sequence elements that guarantee the removal of this sequence by splicing from the transcript before it is used for making a protein. Even the sequences around the coding region have to meet selective expectations, such that the transcription is initiated at the right time and place, the translation is properly terminated, and the stability of the mRNA is appropriate for the RNA turnover rate and adequate for the cell’s metabolism. All of these and other mechanisms ensure that a functional part of the genome remains a recognizable and coherent unit of genomic change.
Cultural kinds, like biological kinds, are historical entities that emerge through evolutionary processes as units of function, forming quasi-independent lineages of these units. Discerning cultural kinds is a powerful strategy for understanding biocultural evolution. In this and two more cultural sections below we will show why this is so.
All animal cultures are founded on fundamental processes and adapted capacities that underlie these processes. Two basic processes define culture: learning and transmission (
The adapted capacities underlying these cultural processes include attention, the ability to focus on specific stimuli from the external world while ignoring others (
Repeated cultural gestures, formations, activities, and so forth can form systems of cultural content defined by the functions emergent from the networked linkages of their parts. It is these systems, not the adaptations required for culture to arise, that in our view form cultural kinds and, when they are transmitted across generations, lineages of cultural kinds (
The replication of cultural systems through generations is not, however, “semi-conservative” copying in the manner of genetic replication—not, at least, in the cultures of
All animal culture is an outgrowth of more basic and widespread animal sociality, which is a supra-individual phenomenon that plays itself out in relation to the environments inhabited by social species. Cultural forms and gestures are all instances of social niche construction, and the emergence of historical kinds in culture starts from this central plank in the platform of the EES (Odling-Smee, et al. 2005;
The individuation of a cultural kind depends on the joining of system components in stable ways that transform them by virtue of their participation in the system as a whole.
An example of such individuation is offered by our first instance of a cultural kind: bead making, an activity widespread among Middle Paleolithic
Competition among historical kinds in culture can be seen, across the evolutionary time-spans through which they persist, as biocultural selection of them. Analyses of cultural selection since the 1980s have used the mathematics of population genetics to model the changing frequencies of isolated cultural traits, in effect treating units of culture as if they were genetic alleles (
By including the interrelation of contents of cultural systems in this picture, we complicate and finally revise these earlier, simpler models. We add to them a functional dimension that redefines cultural patterns and canalizes their evolution, and we focus on the specific mechanisms that work together to fix such systemic functioning in persisting lineages. In our example of bead making, cultural selectionist accounts might posit selective advantages accruing to groups able to muster more complex social structure than other groups, and niche-constructive accounts might isolate the use of material signs of rank or position in organizing such complexity. But neither kind of account can describe the emergence of a historical kind whose function alters the potency of the marking of social difference itself and channels this new force into further cultural evolution.
Debate over the nature of biological species is complex and has a long history. This issue was clarified in the 1990s by the discerning of homeostatic property cluster (HPC) natural kinds described in our introduction (
The species concept reflects the fact that living things overwhelmingly come in distinct clusters of similarity. The nature of species is that they form population level units of evolutionary change and for that reason are genetically and often phenotypically distinct from other species. Oak trees and blue whales come with very few intermediate forms, and this is the rule despite the existence of so-called “sister species” (
This “species as individuals” conception, however, hardens a distinction between individuals and kinds and does not offer any processual explanation for the delimitation of a species. A considerable softening of the individual/kind opposition and a turn toward causal processes were both achieved in Boyd’s HPC natural kinds (
In an idealized model, a biological species consists of a lineage of populations that evolve quasi-independently from other such sets of populations, regardless of whether this is due to genetic incompatibilities, as in the case of sexually reproducing species, or to ecological or demographic factors. A consequence of this view is that we need to distinguish two distinct evolutionary processes similar to the ones we distinguished above in the evolution of genes. On the one hand is the evolutionary transformation of populations along a particular lineage, called in an older literature “anagenetic” evolution. On the other hand is the splitting of a lineage to form two independent lineages, or two species. This process has been called “cladogenetic” evolution (
Anagenetic evolution can be largely explained by the two major population genetic processes, natural selection and genetic drift. Natural selection explains the evolution of adaptations, while genetic drift explains random change, which nevertheless can lead to directional changes such as the trends in genome organization noticed in recent decades (
As we made clear in the introduction, we believe that this is a general feature of historical kinds: they are what they are because of the role they play in evolutionary/historical processes, not because of how they took on a form that could assume that role. This general feature, then, characterizes not only species but also our other examples of historical kinds, biological and cultural. Moreover, once a species has attained quasi-independence, its historical coherence is maintained through processes similar to those that maintain the historical coherence of genes, cell types (see below), and cultural kinds, namely the operation of functionally integrated mechanisms. In the case of sexually reproducing species, for example, the integration results from the requirement that haploid genomes from the two parents, united during fertilization, be functionally compatible.
Parallels between the persistence of genes and species and the persistence of cultural systems are apparent in the wake of this discussion. Like genes and species, historical kinds in culture are units of evolutionary change (in this case, biocultural evolution,
The maintenance of the coherence of its systemic network renders a cultural historical kind recognizable across evolutionary history. The coherence also marks off cultural kinds from the cultural contexts in which they occur, giving them varying degrees of autonomy. This is clear in the case of the tool making system just mentioned, or in the bead making discussed above. There the shell-as-insignia occupies a place in a bead-making culture that is determined by its relations to the other elements of the system and for this reason set apart from the shell-as-byproduct of harvesting. A similar autonomy is clear also in many different cultural kinds involving communication in non-human cultures. The “songs” of songbirds, for example, are complex patterns of vocalized sounds with roles in territorial marking and mate attraction. As a biocultural system making up a cultural kind, these songs comprise an intergenerational, social pedagogy, a sonic medium, distinctive combinatorial structures in their design, and a dedicated biological substrate in the birds’ bodies and brains that enables their learning, production, and cognitive processing (
Such coherence and autonomy are evident in the case of ritual in hominin societies, and we can consider ritual a class of historical kinds that is pervasive in human culture. A ritual comes about through the formation of a system of gestures and expressions—of practices—that sets itself apart from the quotidian expressions and gestures around it. The construction of such autonomy is characteristic of the process of ritualization (
But rituals also call for something more, another defining trait of this class of kinds as a whole. The internal system of gestures and expressions that makes up a ritual must be repeatable and, moreover, repeatable in specific, socially determined moments. This means that the ritual system must point in systematized ways beyond itself—that ritualization is a process pointing both inward toward an enclosed system and outward toward a fixed relation with institutions, power structures, and cosmologies (
The circumstances that evoke the full, dual systematization of ritual in modern human societies, and that must have evoked it also among our ancestors, are often life-cycle events consequential in marking the structures of a society and its place in the world. They include today the marking of kinship and affiliation, of rites of passage into maturity, of pair-bonding, of death, of successful communal provisioning, of shared belief, and the like. Rituals marking such events are very ancient, and it is likely that ritualization predated
This pre-sapient emergence makes it also likely that ritual kinds took shape before language and music, features of all sapient cultures today, assumed their modern forms. Ritual without modern language may seem a puzzling concept, but to see this likelihood we need only picture social complexities among hominins as far back as half a million years ago, which involved pedagogies of tool making, divisions of labor in organized hunting or scavenging, communal sharing of the resulting spoils, and other similar behavioral patterns. The absence of modern language in such societies need not have blocked the coalescing of ritual, because they possessed well-developed vocal and bodily communicative resources referred to today as “protolanguage” or “protodiscourse.” Long before the syntax and lexicon of modern languages appeared, hominin ritual could have relied on these communicative means and even canalized their own further development toward modern forms. We return to protodiscourse, language, and music below.
All life depends on cellular organization, including biological entities that are not cells themselves, like viruses, which are parasites of cellular life. The most fundamental reason for this fact is that life only exists in a state of thermodynamic disequilibrium with its environment, and this necessitates the maintenance of chemical gradients between the inside and outside of life forms. Cells are the fundamental, i.e., atomic, unit of life, and, in our world, only originate from other such units (
Only in recent years has it been fully recognized that cell types form distinct, individuated lineages of descent (
The recent discovery of cell-type lineages was driven in part by the availability of molecular signatures that allowed identification of homologous cell types even in cases where the morphological and functional phenotypes have become unrecognizably different. In these cases the cells have undergone a change of function in the course of evolution, for example, a change from a photoreceptor cell to an interneuron (
A difference between the origination of species or genes and that of cell-types arises at the proximate level, in their mechanisms and modes of inheritance. Genes form lineages of descent based on direct replication of the DNA molecules, in which the descendant copies of the gene have material overlap with their mother copies (
This developmental mediation leads to a number of conceptual difficulties, in particular with respect to the ontological status of cell types. For Peter Godfrey-Smith (personal communication), for example, cell types cannot be historical individuals analogous to species and genes, because they do not directly replicate. Therefore, though it might be granted that we can represent the relationships among cell types in different species in a way similar to a phylogenetic tree, this representation, Godfrey-Smith argues, is illusory. In this argument, however, phenomenon and explanation are conflated. The phenomenon is the treelike pattern of diversification found in genes, species, and also (putatively) in cell types. One model for the formation of the tree is direct replication, which can explain the homology of genes and the relatedness of species. But to say that a phenomenon is an illusion because
If cell types are historical kinds in biology, we require an explanation as to how the individuation proper to them comes about—how, that is, some cells are individuated from other cells in the same body with respect to their development, function, and evolutionary history. If there is no direct replication and transmission of cell type identity from generation to generation, what then endows a cell type with the ability to have its own evolutionary history, quasi-independent from that of other cell types? Some of the answer, certainly, will be and has been found in the genome, but the variability, among species, of the genetic determinants of cell type development renders this answer insufficient (
Different cell types usually perform different functions in multicellular organisms. To be able to do so they express a different, though partially overlapping, set of genes than other cell types. Different genes lead to different gene products, such as enzymes, non-coding RNA, and cytoskeletal proteins, and these determine the cell types’ physiological and morphological phenotypes. The genes that produce the phenotype of cell types can be called “effector genes.” But through what mechanisms do different cell types come to express these different sets of effector genes? At one level the answer lies in the diverse signals a cell receives from other cells in the embryo, which determine its ultimate fate. In many cases, however, the signals, which can be small molecules such as steroid hormones, peptides, or ions, do not directly regulate the effector genes, but instead activate a different set of genes, many of them coding for transcription factor proteins. Several slightly different models suggest that these genes form a small regulatory network, variously called a kernel (
This forms a three-layer model of cell type development, encompassing signals, cell type identity network, and effector genes and/or effector modules. Using this model, we can devise a scenario for the structure of the gene regulatory network that explains the evolutionary individuation of cell types. In order to do so, we need to add one additional feature, critical for what follows. The transcription factor proteins produced by the genes of a cell type identity network do not act singly, but form a physical complex that has been called a “core regulatory complex” or CoRC (
A CoRC regulates the expression of effector genes by binding to specific cis-regulatory elements (CREs), segments of DNA often proximate to their associated effector genes (for instance the mechanisms determining motor neuron identity, Lee,
This model amounts to a mechanistic explanation of how a cell type can maintain its identity and thus historical independence from other cell types, and at the same time evolve a more or less arbitrary phenotype. The cohesion of the cell type, over evolutionary time, can be explained by the coevolution among the transcription factors forming the CoRC. Due to the continuous expression of the CoRC, cells are able to change their phenotype in a gradual manner, by the stepwise addition or loss of effector genes under the transcriptional control of the CoRC. This feature makes the evolutionary history traceable in spite of changes of cell phenotype, through tracing either the expression of the CoRC itself (which is technically difficult) or the gradual change of the cell phenotype.
This scenario is a model only—a schematic simplification that serves to illustrate how cell types can have historical continuity and quasi-independent trajectories of evolution and to explain their tree-like pattern of evolutionary diversification. It suggests, nevertheless, that cell types are endowed with a molecular machinery—i.e., core-regulatory complexes of transcription factor proteins—that enables differential expression of effector genes. It suggests also that this regulatory machinery enables the cell type-specific evolution of the cell phenotype, leading to the evolutionary modification of cell types. The evolution of novel CoRCs or cell type identity networks can thus originate a novel cell type identity, in turn splitting the evolutionary fate of a cell population and leading to two new cell types. The two sister cell types form independent lineages of evolutionary modification because the cell type specific CoRCs control different gene sets having different cis-regulatory elements responsive to different CoRCs. The functional integration of the CoRC ensures its long-term persistence by means of a specific trans-regulatory activity. This mechanistic scenario offers an explanation for the diversification of cell types along trees of phylogenetic relatedness in which direct replication of cell types plays no role. It is important to note, however, that this model is only one possible mechanistic realization and that it is in general better to think in terms of multiple
The model of cell type effector genes, CoRCs, and identity networks described above suggests that a functional system can be endowed with regulatory or control mechanisms that shape or determine its operation. Such mechanisms can assume long-lived stability, coherence, and autonomy. The stable CoRCs, guiding the expression of effector genes with their cis-regulatory elements and thus the differentiation of cell types, show these features. In our view, understanding such emergent control mechanisms represents an important extension of the emphasis placed on feedback networks in the EES. In systems theory, mechanisms controlling the feedback loops of a system but not directly a part of those loops are known as
Emergent control mechanisms of a similar sort arise in cultural systems. Here, as in CoRCs, they take on heightened stability and autonomy, which in this case are played out across the biocultural evolutionary situations in which they are formed. In their heightened autonomy from the cultural kinds that generate them, they exert feedforward influence, controlling effects on the feedback cycles involved in biocultural evolution; for this reason Tomlinson has called them
We have seen that all culture is niche constructive—that is, it manifests itself in the environmentally situated sociality of the animals that create it. The literature on niche construction has treated extensively the feedback cycles between culture and biology. Usually they are viewed this way: cultural practices of a population alter the environment in advantageous ways, giving rise to altered selective pressures on the genomes of the population; selection is favored for genes enabling or fostering the practices that advantageously alter the environment, and this pushes the population as a whole toward enhanced culture-making capacities (
Epicyclic mechanisms add a new dimension to this model. By virtue of their feedforward impact on the feedback cycles of biocultural evolution, they drive culture in a specific direction, not only redoubling its niche-shaping force but also
This begins to describe the dynamic by which cultural epicycles give rise to new kinds, but there is another aspect that is central to it. Because culture is niche constructive, all historical kinds that are individuated in it stand in a relation, more or less mediated, to the affordances and constraints of the environments in which they operate. In reshaping the niche, cultural historical kinds do not merely reflect passively these environmental conditions, but instead alter them in more or less dramatic ways. The epicyclic origination and individuation of a historical kind is an especially marked event in this reshaping of environmental conditions, in which factors that had not previously functioned as affordances or constraints begin to do so. Environmental factors previously insignificant in biocultural evolution take on a new, powerful significance
An example will clarify this epicyclic model. It takes the form of a set of linked inferences aiming to explain the emergence among hominins of some capacities basic to modern human language and music (for fuller accounts, see
Language as a whole and music as a whole thus are distinguished in their particular functional systematizations from other communicative means. Indeed, in understanding language and music as individual cultural kinds it helps to see them in the broader perspective of the cultural communication of many animals—a class of cultural kinds that extends well beyond our species and includes birdsong, the click codes of sperm whales, the songs of humpback whales, and some communicative gestures of great apes (including some vocalizations—“gesture-calls,” as one anthropologist has usefully named them,
But how were language and music, distinctive human historical kinds of communication, individuated in our deep history? In each case, several cultural epicycles arose that not only biased ongoing cultural evolution but also redefined environmental or ontological constraints on communication. There is space here to outline only one of these, which militated toward the distinct forms of discrete cognitive processing that characterize language in one fashion and music in another (for more, see
As early as half a million years ago, as we remarked in the discussion of ritual, at least some hominins lived in social groups complex enough to require well-developed communicative codes. These protolanguages or protodiscourses, to judge from archaeological reconstruction and the communication of apes and monkeys in the world today, involved varieties of bodily gesture and vocalization (
The development of indexical protodiscourse progressed in tandem with the sociality around it, the one nudging the other toward greater complexity as the niche-constructive advantages of such complexity came to be felt. This led to an increase in the number and variety of the signs employed. In vocalization—to judge, again, from non-human mammal vocalizations in the world today—the indexes were at first deployed along a graded, analogue spectrum, with continuously modulated intonational shapes, amplitudes, onsets and decays, and timbral patterns. But the multiplication of such indexes brought them up against a new constraint, not relevant to simpler protodiscourse: the ontological constraint, on any graded spectrum, that increasing the number of events will decrease the distance between them. Each index, as their number multiplied, became more and more like the ones near to it on the spectrum. Communicative clarity was compromised as the number of signs increased.
This new constraint, together with the conditions that brought it into play, formed a cultural epicycle that militated for discrete, not graded, distinctions between signs. The altered niche, the advantageous structuring of which now depended on the enlarged vocabulary of signs in the protodiscourse, created a general selection for capacities that enhanced the production and comprehensibility of these signs; but at the same time the newly active ontological constraint made discrete production and processing an important part of those capacities. The epicycle acted as a control, biasing biocultural evolution and driving protodiscourse toward discreteness, and this feature would eventually come to be fundamental in the emergence of both language and music. Discreteness of timbre and onset and decay would mark off one uttered unit from another in the vowels, phonemes, and syllables of modern language, while discreteness of pitch would set off a cascade of new capacities, leading to the relative pitch perception, octave duplication, and scales of music today.
Historical kinds are fundamental in both biology and culture, and these two perspectives converge on questions of the systems that characterize individual kinds. The view of the origination of historical kinds offered here depends on the coalescing of systems and the functional integration that emerges from it. The mechanisms of this integration come to control or regulate the kind, giving it its character of quasi-independence or autonomy, and this character is basic to the force of any system to define a historical kind. But the historical kind is determined not only by this coalescing and autonomy, but also by the persistence of its functional integration and thus its ability to form a lineage of descent. Our view is through and through a processual one, since the functional integration of components in our historical kinds, from cell type regulatory networks to hominin protodiscourse, is an ongoing process of interaction of the elements in any given kind.
We are struck by the deep-seated similarities of emergence and function extending across the historical kinds we have described. From molecular regulatory systems to cultural epicycles, there are constancies of pattern in the emergence, control, and stabilizing of these systems. These reveal that biological and cultural evolutions are foundationally connected to one another, but not in a way that is limited to structural analogies of natural and cultural selection. Instead they are linked in their patterns of emergence of systemic regulation and integration. In order to understand this the mechanisms of both biological and cultural systems must be understood at the deepest level. It is the functionalized content of these systems—the components that mesh, the manners in which they mesh, and the emergent functional qualities that take shape in the meshing—that must be attended to.
Finally, we think that these systemic constancies amount to something more than ontological accidents and point to the most general ways in which stable kinds can take shape within historical, evolving dynamics. The appearance of similar systems dynamics across vast ontological distances, from molecular biology to human culture, encourages us to suggest that the concept of historical kinds as we use it here can shed light on the unified field on which all systems evolution takes place.
The authors thank our colleagues, Drs. Richard Prum, Stephen Stearns, Mihaela Pavličev, James DiFrisco and Alan Love, for discussions as well as Professor John Dupré and an anonymous referee for advice on this paper.
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