In biology, reciprocal causation arises when developing organisms are both products of evolution as well as causes of evolution. [1] [2] [3] [4] [5] [6] Formally, reciprocal causation exists when process A is a cause of process B and, subsequently, process B is a cause of process A, with this feedback potentially repeated. Some researchers, particularly advocates of the extended evolutionary synthesis, promote the view that causation in biological systems is inherently reciprocal. [7]
Harvard evolutionary biologist Ernst Mayr (1961) [8] suggested that there are two fundamentally different types of causation in biology, ‘ultimate’ and ‘proximate’. Ultimate causes (e.g. natural selection) were seen as (i) providing historical accounts for the existence of an organism's features, and (ii) explaining the function or ‘goal-directedness’ of living beings. In contrast, proximate causes (e.g. physiology) were seen as explaining how biological systems work. According to Mayr, the evolutionary sciences study ultimate causes and the rest of biology studies proximate causes. In some of his works, Mayr considered these domains autonomous:
“The clarification of the biochemical mechanism by which the genetic program is translated into the phenotype tells us absolutely nothing about the steps by which natural selection has built up the particular genetic program.”
Mayr, 1980 [9]
There has been widespread acceptance of the proximate-ultimate dichotomy within the evolutionary sciences. However, many biologists, psychologists and philosophers have taken issue with Mayr's corollary that the proximate-ultimate distinction implies that development is irrelevant to evolution. For instance, evolutionary biologist Mary Jane West-Eberhard writes:
“The proximate-ultimate distinction has given rise to a new confusion, namely, a belief that proximate causes of phenotypic variation have nothing to do with ultimate, evolutionary explanation.”
West-Eberhard, 2003 [3]
Mayr's position implied a unidirectional or linear conception of causation for both development and evolution: genotypes cause phenotypes (proximate causation), whilst through natural selection, changes in environments cause changes in organisms (ultimate causation). Reciprocal causation was proposed as an alternative to this linear characterization. [2] [4] [6] (see also [3] [10] [11] [12] ) It emphasizes how causation cycles through biological systems recursively, allowing proximate causes to feed back and thereby feature in ultimate explanations.
Reciprocal causation features in several explanations within contemporary evolutionary biology, including sexual selection theory, coevolution, habitat selection, and frequency-dependent selection. In these examples, the source of selection on a trait coevolves with the trait itself, therefore causation is reciprocal and developmental processes potentially become relevant to evolutionary accounts. For instance, a peacock’s tail evolves through mating preferences in peahens, and those preferences coevolve with the male trait. The ‘ultimate explanation’ for the male trait is the prior existence of female preferences, proximately manifest in differential peahen mate choice decisions, whilst the ‘ultimate explanation’ for the peahens’ mating preferences is the prior existence of variation in the peacock's tail associated with fitness. This example illustrates how reciprocal causation is not a rejection of the proximate-ultimate distinction itself, but instead a rejection of the implication that developmental processes should not feature in evolutionary explanations.
Reciprocal causation also applies in other domains of evolutionary biology. The extended evolutionary synthesis emphasizes how developmental events, including both the causal effects of environments on organisms (for instance, arising through developmental plasticity, or epigenetic inheritance) and the causal effects of organisms on environments (e.g. niche construction), can direct the course of evolution. Developmental plasticity, niche construction, extra-genetic forms of inheritance and developmental bias are recognized as playing evolutionary roles that cannot be reduced to natural selection of genetically encoded characters or strategies. Proximate causes are not autonomous from natural selection, but rather feed back to influence the rate and direction of adaptive evolution. This goes beyond the recognition that ontogenetic processes can impose constraints on the action of selection, or that proximate and ultimate processes interact. Rather, developmental processes are also seen as a source of evolutionary novelty, initiators of evolutionary episodes, and co-directors of patterns of evolutionary change. [7]
Acceptance or rejection of Mayr's proximate-ultimate distinction may lie at the centre of several major debates within contemporary biology, concerning evo devo (evolutionary developmental biology), niche construction, cultural evolution, human cooperation, and the evolution of language. According to some biologists and philosophers, these disputes share a common pattern. On one side are researchers who consider that interaction and feedback processes traditionally characterized as ‘proximate’ have explanatory value for ‘ultimate’ evolutionary questions. [2] [3] [4] [6] [11] [12] [13] Their concern is that the proximate-ultimate distinction has discouraged consideration of the manner in which developmental processes can set the evolutionary agenda, for instance, by introducing innovations, channeling phenotypic variation, or initiating evolutionary episodes through modifying selection pressures. One the other side are researchers who largely adopt Mayr's stance with a clean separation of proximate and ultimate causation. For the latter, a failure to respect Mayr's dichotomy is considered a sign of confusing an evolutionary explanation with a mechanistic explanation. [14] [15] [16] [17] [18]
Evolutionary developmental biology is a field of biological research that compares the developmental processes of different organisms to infer how developmental processes evolved.
The modern synthesis was the early 20th-century synthesis of Charles Darwin's theory of evolution and Gregor Mendel's ideas on heredity into a joint mathematical framework. Julian Huxley coined the term in his 1942 book, Evolution: The Modern Synthesis.
Allele frequency, or gene frequency, is the relative frequency of an allele at a particular locus in a population, expressed as a fraction or percentage. Specifically, it is the fraction of all chromosomes in the population that carry that allele over the total population or sample size. Microevolution is the change in allele frequencies that occurs over time within a population.
Niche construction is the process by which an organism alters its own local environment. These alterations can be a physical change to the organism’s environment or encompass when an organism actively moves from one habitat to another to experience a different environment. Examples of niche construction include the building of nests and burrows by animals, and the creation of shade, influencing of wind speed, and alternation of nutrient cycling by plants. Although these alterations are often beneficial to the constructor, they are not always.
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the population during that process. Thirdly, it is a phenotypic trait or adaptive trait, with a functional role in each individual organism, that is maintained and has evolved through natural selection.
In evolutionary biology, the Baldwin effect, a phenotype-first theory of evolution, describes the effect of learned behaviour on evolution. James Mark Baldwin and others suggested during the eclipse of Darwinism in the late 19th century that an organism's ability to learn new behaviours will affect its reproductive success and will therefore have an effect on the genetic makeup of its species through natural selection. Though this process appears similar to Lamarckism, that view proposes that living things inherited their parents' acquired characteristics. The Baldwin effect has been independently proposed several times, and today it is generally recognized as part of the modern synthesis.
A proximate cause is an event which is closest to, or immediately responsible for causing, some observed result. This exists in contrast to a higher-level ultimate cause which is usually thought of as the "real" reason something occurred.
The theory of facilitated variation demonstrates how seemingly complex biological systems can arise through a limited number of regulatory genetic changes, through the differential re-use of pre-existing developmental components. The theory was presented in 2005 by Marc W. Kirschner and John C. Gerhart.
Evolutionary developmental psychology (EDP) is a research paradigm that applies the basic principles of evolution by natural selection, to understand the development of human behavior and cognition. It involves the study of both the genetic and environmental mechanisms that underlie the development of social and cognitive competencies, as well as the epigenetic processes that adapt these competencies to local conditions.
In biology, saltation is a sudden and large mutational change from one generation to the next, potentially causing single-step speciation. This was historically offered as an alternative to Darwinism. Some forms of mutationism were effectively saltationist, implying large discontinuous jumps.
Genetic assimilation is a process described by Conrad H. Waddington by which a phenotype originally produced in response to an environmental condition, such as exposure to a teratogen, later becomes genetically encoded via artificial selection or natural selection. Despite superficial appearances, this does not require the (Lamarckian) inheritance of acquired characters, although epigenetic inheritance could potentially influence the result. Waddington stated that genetic assimilation overcomes the barrier to selection imposed by what he called canalization of developmental pathways; he supposed that the organism's genetics evolved to ensure that development proceeded in a certain way regardless of normal environmental variations.
Tinbergen's four questions, named after 20th century biologist Nikolaas Tinbergen, are complementary categories of explanations for animal behaviour. These are also commonly referred to as levels of analysis. It suggests that an integrative understanding of behaviour must include: ultimate (evolutionary) explanations, in particular the behaviour (1) adaptive function and (2) phylogenetic history; and the proximate explanations, in particular the (3) underlying physiological mechanisms and (4) ontogenetic/developmental history.
The history of molecular evolution starts in the early 20th century with "comparative biochemistry", but the field of molecular evolution came into its own in the 1960s and 1970s, following the rise of molecular biology. The advent of protein sequencing allowed molecular biologists to create phylogenies based on sequence comparison, and to use the differences between homologous sequences as a molecular clock to estimate the time since the last common ancestor. In the late 1960s, the neutral theory of molecular evolution provided a theoretical basis for the molecular clock, though both the clock and the neutral theory were controversial, since most evolutionary biologists held strongly to panselectionism, with natural selection as the only important cause of evolutionary change. After the 1970s, nucleic acid sequencing allowed molecular evolution to reach beyond proteins to highly conserved ribosomal RNA sequences, the foundation of a reconceptualization of the early history of life.
Gerd B. Müller is an Austrian biologist who is emeritus professor at the University of Vienna where he was the head of the Department of Theoretical Biology in the Center for Organismal Systems Biology. His research interests focus on vertebrate limb development, evolutionary novelties, evo-devo theory, and the Extended Evolutionary Synthesis. He is also concerned with the development of 3D based imaging tools in developmental biology.
Ecological inheritance is the passing on to descendants of inherited resources and conditions, and associated modified selection pressures, through niche construction. For instance, many organisms build, choose or provision nursery environments, such as nests, for their offspring. The recurrence of traits across life cycles results in part from parents constructing developmental conditions for their descendants. Richard Lewontin stresses how by modifying the availability of biotic and abiotic resources, niche-constructing organisms can cause organisms to coevolve with their environments.
Evolutionary psychiatry, also known as Darwinian psychiatry, is a theoretical approach to psychiatry that aims to explain psychiatric disorders in evolutionary terms. A branch of the field of evolutionary medicine, it is distinct from the medical practise of psychiatry in its emphasis on providing scientific explanations rather than treatments for mental disorder. This often concerns questions of ultimate causation. For example, psychiatric genetics may discover genes associated with mental disorders, but evolutionary psychiatry asks why those genes persist in the population. Other core questions in evolutionary psychiatry are why heritable mental disorders are so common how to distinguish mental function and dysfunction, and whether certain forms of suffering conveyed an adaptive advantage. Disorders commonly considered are depression, anxiety, schizophrenia, autism, eating disorders, and others. Key explanatory concepts are of evolutionary mismatch and the fact that evolution is guided by reproductive success rather than health or wellbeing. Rather than providing an alternative account of the cause of mental disorder, evolutionary psychiatry seeks to integrate findings from traditional schools of psychology and psychiatry such as social psychology, behaviourism, biological psychiatry and psychoanalysis into a holistic account related to evolutionary biology. In this sense, it aims to meet the criteria of a Kuhnian paradigm shift.
The extended evolutionary synthesis consists of a set of theoretical concepts argued to be more comprehensive than the earlier modern synthesis of evolutionary biology that took place between 1918 and 1942. The extended evolutionary synthesis was called for in the 1950s by C. H. Waddington, argued for on the basis of punctuated equilibrium by Stephen Jay Gould and Niles Eldredge in the 1980s, and was reconceptualized in 2007 by Massimo Pigliucci and Gerd B. Müller. Notably, Dr. Müller concluded from this research that Natural Selection has no way of explaining speciation, saying: “selection has no innovative capacity...the generative and the ordering aspects of morphological evolution are thus absent from evolutionary theory.”
In biology, constructive development refers to the hypothesis that organisms shape their own developmental trajectory by constantly responding to, and causing, changes in both their internal state and their external environment. Constructive development can be contrasted with programmed development, the hypothesis that organisms develop according to a genetic program or blueprint. The constructivist perspective is found in philosophy, most notably developmental systems theory, and in the biological and social sciences, including developmental psychobiology and key themes of the extended evolutionary synthesis. Constructive development may be important to evolution because it enables organisms to produce functional phenotypes in response to genetic or environmental perturbation, and thereby contributes to adaptation and diversification.
Karola Stotz was a German scholar of philosophy of biology, cognitive science, and philosophy of science. With Paul E. Griffiths, she pioneered the use of experimental philosophy methods in the field of philosophy of science.
Kevin Neville Laland is an English evolutionary biologist who is Professor of Behavioural and Evolutionary Biology at the University of St Andrews in Scotland. Educated at the University of Southampton and University College London, he was a Human Frontier Science Program fellow at the University of California, Berkeley before joining the University of St Andrews in 2002. He is one of the co-founders of niche construction theory and a prominent advocate of the extended evolutionary synthesis. He is a fellow of the Royal Society of Edinburgh and the Society of Biology. He has also received a European Research Council Advanced Grant, a Royal Society Wolfson Research Merit Award, and a John Templeton Foundation grant. President of the European Human Behaviour and Evolution Association from 2007 to 2010.
