Human evolutionary developmental biology or informally human evo-devo is the human-specific subset of evolutionary developmental biology. Evolutionary developmental biology is the study of the evolution of developmental processes across different organisms. It is utilized within multiple disciplines, primarily evolutionary biology and anthropology. Groundwork for the theory that "evolutionary modifications in primate development might have led to … modern humans" was laid by Geoffroy Saint-Hilaire, Ernst Haeckel, Louis Bolk, and Adolph Schultz. [1] Evolutionary developmental biology is primarily concerned with the ways in which evolution affects development, [2] and seeks to unravel the causes of evolutionary innovations. [3]
The approach is relatively new, but has roots in Schultz's The physical distinctions of man, from the 1940s. Shultz urged broad comparative studies to identify uniquely human traits. [4]
Brian Hall traces the roots of evolutionary developmental biology in his 2012 paper on its past present and future. He begins with Darwinian evolution and Mendel's genetics, noting the tendency of the followers of both men in the early 20th century to follow separate paths and to set aside and ignore apparently inexplicable problems. [5] Greater understanding of genotypic and phenotypic structures from the 1940s enabled the unification of evolution and genetics in the modern synthesis. Molecular biology then enabled researchers to explore the mechanisms and evolution of embryonic development in molecular detail, including in humans. [5]
Many of the human evolutionary developmental biology studies have been modeled after primate studies and consider the two together in a comparative model. Brain ontogeny and human life history evolution were looked at by Leigh, in a 2006 paper. He compares brain growth patterns for Homo erectus and Homo sapiens to get at the evolution of brain size and weight. Leigh found three different patterns, all of which pointed to the growth rate of H. erectus either matching or exceeding H. erectus. [6] He makes the case that this finding had wide application and relevance to the overall study of human evolution. It is pertinent specifically to the connections between energy expenditure and brain development. These finding are of specific utility in studies on maternal energy expenditure. [6] Comparative study of nonhuman primates, fossils and modern humans to study patterns of brain growth to correlate human life history and brain growth. [6]
Jeremy De Silva and Julie Lesnik examined chimpanzee neonatal brain size to identify implications for brain growth in Homo erectus. This changed the understanding of differences and similarities of post-natal brain growth in humans and chimpanzees. The study found that there was a distinction necessary between growth time and growth rate. The times of growth were strikingly similar, but the rates were not. The paper further advocates the use of fossils to assess brain size in general and in relation to cranial capacity. [7]
Utilization of endocranial volume as a measure for brain size has been a popular methodology with the fossil record since Darwin in the mid 1800s. This measure has been used to access the metabolic requirements for brain growth and the subsequent trade-offs.
Some of the work on human evolutionary developmental biology has centered around the neotenous features that present in humans, but are not shared across the primate spectrum. Steven J. Gould discussed the presentation of neoteny with "terminal additions" in humans. [8] Neoteny is defined as the delayed or slowed development in humans when compared with their non-human primate counterparts. The "terminal additions" were extensions or reductions in the rate and scope of stages of development and growth. [8] [ pages needed ] Gould hypothesized that this process and production of neoteny in humans might be the key feature that ultimately lead to the emotional and communicative nature of humans. He credits this factor as an integral facet of human evolution. However, there have also been cautions against the application of this aspect to group ranking during it inappropriate as a measure of evolutionary achievement. [9]
Early comparative and human studies examined the fossil record to measure features like cranial sizes and capacities so as to infer brain size, growth rate, total growth and potential implications for energy expenditure. Helpful as this is, the static nature of individual fossils presents its own challenge. The phylogenic fossil line is itself a hypothesis, so anything based upon it is equally hypothetical. [10]
Using the fossil record of Neanderthals, modern humans, and chimpanzees, Gunz et al. examined that patterns of endocranial development. [11] They found that there are common features shared between the three, and that modern humans diverge from these common patterns in the first year of life. They concluded that even though much of the developmental results are similar insofar as brain size, the trajectories by which they arrived are not shared. Most of the differences between the two arise post-natally, in the first year, with cognitive development. [11]
There have been a number of studies that not only take incomplete fossil records into consideration, but have attempted to specifically identify the barriers presented by this condition. For example, Kieran McNulty covers the potential utilities and constraints of using incomplete fossil taxa to examine longitudinal development in Australopithecus africanis. [10]
Many studies on development have been human-specific. In his 2011 paper, Bernard Crespi focused on adaptation and genomic conflict in childhood diseases. He considers the evolution of childhood diseases and their risk levels, and finds that both risk and disease have evolved. [12]
Hotchberg and Belsky incorporate a life-history perspective, looking at adolescence. Substantial variation in phenotypic paths and presentations suggest significant environmental influence. They focus on plasticity between stages of development and the factors that shape it. Rate of maturation, fecundity, and fertility were all impacted by environmental circumstances. They argue that early maturation can be positive, reflecting opportunistic actions within specific conditions. [13]
Technological advances that have allowed better and better access to the growth of the human form in utero have proven particularly formative in studies involving focus on genetic and epigenetic development. Bakker et al. look at the interconnected nature of developmental processes and attempt to use fetal vertebral abnormalities as an indicator for other malformations. They found that the origin of the cells was not nearly as highly correlated as the observed developmental signals. [14] In utero development and malformations were correlated in severity. [14]
Freiston and Galis look at the development of ribs, digits, and mammalian asymmetry. They argue that this construction is relevant for the study of disease, the consistency in evolution of body plans, and understanding of developmental constraints. [15] Sexual dimorphism in prenatal digit ratio was found as early as 14 weeks and was maintained whether or not the fleshy finger part was included. [15]
Languages and cognitive function have also been subjects of evolutionary studies. Insofar as language and evolutionary developmental biology, there is tension from the gate. Much of this contention has centered around whether to view and study language as an adaptation in and of itself, or as a by-product of other adaptations. Jackendoff and Pinker have argued for language as an adaptation owing to the interdependent social nature of humans. To support these claims, he points to things like the bi-directionality in language usage and comprehension. [16] This is a counter to the claims by theorists like Noam Chomsky, who argued against language as a human specific adaptation. [17]
Adaptation and adaptive theory has been argued even separate from its utility in the study of language. Gould and Lewontin engage with what they saw as flaws in adaptive theory using the analogy of the spandrels of San Marco. Among the issues identified is the lack of distinction between what trait developed and how it is used, and the underlying reasons or forces that created the novel trait initially. [18] This is particularly difficult to access in intangible language and cognition.
This debate has continued over decades and most often presents in the form of a response and published dialogue between theorists. This continued debate has prompted efforts to marry the two perspectives in a useful way. Fitch argues that these two approaches can be rectified with the study of "neutral computation and mammalian brain development". [19] It may be more useful to consider specific components of neural computation and development, what has been selected for, and to what end. [19]
Ploeger and Galis tackled modular evolvability and developmental constraints in human and other primate evolutionary trajectories. They argue that these should be treated with an interdisciplinary approach across the cognitive sciences. They frame this in the context of:
Human evolution is the evolutionary process within the history of primates that led to the emergence of Homo sapiens as a distinct species of the hominid family that includes all the great apes. This process involved the gradual development of traits such as human bipedalism, dexterity, and complex language, as well as interbreeding with other hominins, indicating that human evolution was not linear but weblike. The study of the origins of humans involves several scientific disciplines, including physical and evolutionary anthropology, paleontology, and genetics; the field is also known by the terms anthropogeny, anthropogenesis, and anthropogony.
Homininae, is a subfamily of the family Hominidae (hominids). This subfamily includes two tribes, Hominini and Gorillini, both having extant species as well as extinct species.
Dollo's law of irreversibility, proposed in 1893 by Belgian paleontologist Louis Dollo states that, "an organism never returns exactly to a former state, even if it finds itself placed in conditions of existence identical to those in which it has previously lived ... it always keeps some trace of the intermediate stages through which it has passed."
Encephalization quotient (EQ), encephalization level (EL), or just encephalization is a relative brain size measure that is defined as the ratio between observed and predicted brain mass for an animal of a given size, based on nonlinear regression on a range of reference species. It has been used as a proxy for intelligence and thus as a possible way of comparing the intelligence levels of different species. For this purpose, it is a more refined measurement than the raw brain-to-body mass ratio, as it takes into account allometric effects. Expressed as a formula, the relationship has been developed for mammals and may not yield relevant results when applied outside this group.
In evolutionary developmental biology, heterochrony is any genetically controlled difference in the timing, rate, or duration of a developmental process in an organism compared to its ancestors or other organisms. This leads to changes in the size, shape, characteristics and even presence of certain organs and features. It is contrasted with heterotopy, a change in spatial positioning of some process in the embryo, which can also create morphological innovation. Heterochrony can be divided into intraspecific heterochrony, variation within a species, and interspecific heterochrony, phylogenetic variation, i.e. variation of a descendant species with respect to an ancestral species.
Evolutionary neuroscience is the scientific study of the evolution of nervous systems. Evolutionary neuroscientists investigate the evolution and natural history of nervous system structure, functions and emergent properties. The field draws on concepts and findings from both neuroscience and evolutionary biology. Historically, most empirical work has been in the area of comparative neuroanatomy, and modern studies often make use of phylogenetic comparative methods. Selective breeding and experimental evolution approaches are also being used more frequently.
The evolution of human intelligence is closely tied to the evolution of the human brain and to the origin of language. The timeline of human evolution spans approximately seven million years, from the separation of the genus Pan until the emergence of behavioral modernity by 50,000 years ago. The first three million years of this timeline concern Sahelanthropus, the following two million concern Australopithecus and the final two million span the history of the genus Homo in the Paleolithic era.
Cognitive specialization suggests that certain behaviors, often in the domain of social communication, are passed on to offspring and refined to be maximally beneficial by the process of natural selection. Specializations serve an adaptive purpose for an organism by allowing the organism to be better suited for its habitat. Over time, specializations often become essential to the species' continued survival. Cognitive specialization in humans has been thought to underlie the acquisition, development, and evolution of language, theory of mind, and specific social skills such as trust and reciprocity. These specializations are considered to be critical to the survival of the species, even though there are successful individuals who lack certain specializations, including those diagnosed with autism spectrum disorder or who lack language abilities. Cognitive specialization is also believed to underlie adaptive behaviors such as self-awareness, navigation, and problem solving skills in several animal species such as chimpanzees and bottlenose dolphins.
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.
Mosaic evolution is the concept, mainly from palaeontology, that evolutionary change takes place in some body parts or systems without simultaneous changes in other parts. Another definition is the "evolution of characters at various rates both within and between species".408 Its place in evolutionary theory comes under long-term trends or macroevolution.
In evolutionary biology, a spandrel is a phenotypic trait that is a byproduct of the evolution of some other characteristic, rather than a direct product of adaptive selection. Stephen Jay Gould and Richard Lewontin brought the term into biology in their 1979 paper "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme". Adaptationism is a point of view that sees most organismal traits as adaptive products of natural selection. Gould and Lewontin sought to temper what they saw as adaptationist bias by promoting a more structuralist view of evolution.
Ontogeny and Phylogeny is a 1977 book on evolution by Stephen Jay Gould, in which the author explores the relationship between embryonic development (ontogeny) and biological evolution (phylogeny). Unlike his many popular books of essays, it was a technical book, and over the following decades it was influential in stimulating research into heterochrony, which had been neglected since Ernst Haeckel's theory that ontogeny recapitulates phylogeny had been largely discredited. This helped to create the field of evolutionary developmental biology.
The evolution of the brain refers to the progressive development and complexity of neural structures over millions of years, resulting in the diverse range of brain sizes and functions observed across different species today, particularly in vertebrates.
Homo erectus is an extinct species of archaic human from the Pleistocene, with its earliest occurrence about 2 million years ago. Its specimens are among the first recognizable members of the genus Homo.
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.
In brain anatomy, the lunate sulcus or simian sulcus, also known as the sulcus lunatus, is a fissure in the occipital lobe variably found in humans and more often larger when present in apes and monkeys. The lunate sulcus marks the transition between V1 and V2.
Cognitive genomics is the sub-field of genomics pertaining to cognitive function in which the genes and non-coding sequences of an organism's genome related to the health and activity of the brain are studied. By applying comparative genomics, the genomes of multiple species are compared in order to identify genetic and phenotypical differences between species. Observed phenotypical characteristics related to the neurological function include behavior, personality, neuroanatomy, and neuropathology. The theory behind cognitive genomics is based on elements of genetics, evolutionary biology, molecular biology, cognitive psychology, behavioral psychology, and neurophysiology.
Evolutionary psychology of language is the study of the evolutionary history of language as a psychological faculty within the discipline of evolutionary psychology. It makes the assumption that language is the result of a Darwinian adaptation.
Leslie Crum Aiello is an American paleoanthropologist and professor emeritus of University College London. She was the president of Axel Lennart Wenner-Gren donated Wenner-Gren Foundation for Anthropological Research from 2005 to 2017. In 2014, Aiello was elected to the American Philosophical Society. She is currently president of the American Association of Physical Anthropologists.
Neoteny is the retention of juvenile traits well into adulthood. In humans, this trend is greatly amplified, especially when compared to non-human primates. Neotenic features of the head include the globular skull; thinness of skull bones; the reduction of the brow ridge; the large brain; the flattened and broadened face; the hairless face; hair on the head; larger eyes; ear shape; small nose; small teeth; and the small maxilla and mandible.
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