Ohno presented the hypothesis in , and it is about the logic of gene duplication events in evolutionary history. When a gene gets copied or duplicated in a genome , the new gene lacks the functional constraints of the old gene. In such cases, the duplicated copy can accumulate beneficial or neutral mutations with little deleterious effect on the overall fitness of the organism. This accumulation can lead to the re-arrangement of genetic elements, so that existing structures can acquire new functions.
This hypothesis of genomic change, Jacob argues, illustrates the process of tinkering. According to Jacob, molecular biologists have shown that most morphological change in vertebrates has not resulted from new structural genes , but rather it is the consequence of a change in the regulation of genetic components, including events like heterotopy, a change in the spatial location of developmental events, and heterochrony, a change in the timing of developmental events.
Jacob argues that these events occur in embryonic development according to the precise schedule of a genetic program, suggesting that gene regulation is the key factor in the generation of animals' forms and functions. In the ninth section, Jacob outlines two consequences of the metaphor of evolution as a process of tinkering. First, if his analogy holds, then biologists should expect to find similarities in the underlying molecular elements of different species.
For example, Jacob argues, biochemists have discovered hormone peptides that trigger a variety of chemical reactions in cells from organisms in different species. Second, biologists should expect to see many imperfections or redundancies in the design of organisms.
For instance, Jacob explains, the human reproductive system illustrates a less than perfect mechanism in which almost half of the total number of conceptions result in no viable fetuses. Jacob ends his essay with a final example of tinkering, arguing that the human brain is a product of highly contingent, historical events. Jacob contends that, in humans , the addition of the neo-cortex to the rhinencephalon, a primitive part of the brain responsible for the sense of smell and theorized to control instinct, has set the conditions for the evolution of the human brain.
The human brain is thus the result of an imperfect patchwork of a structure controlling visceral or emotional drives, the rhinencephalon, and a structure controlling more sophisticated cognitive abilities, the neo-cortex. This case can be extrapolated, Jacob argues, to a general rule for evolution : evolution is the net result of a particular sequence of historical opportunities. Jacob's essay had, at first, a mixed reception. Many biologists said that the description of evolution by natural selection as a process of tinkering was blatantly obvious.
In Walter Gehring and his team at the University of Basel in Basel, Switzerland, discovered of a standard set of DNA sequences called the Homeobox in genes that controlled the embryonic development of body plans of animals. Scientists soon found the Homeobox in genes of diverse organisms from flies to humans. Given those results, scientists explicitly began referring to Jacob's essay and to his concept of tinkering.
In , Jacob published a series of lectures given at the University of Washington in Seattle, Washington, under the title The Possible and the Actual , which includes a slightly modified version of his original essay, "Evolution and Tinkering," as well as some essays expounding his philosophy of science.
In , the Novartis Foundation in London, United Kingdom, held a symposium on the concept of tinkering in evolution and development. By the second decade of the twenty-first century, scientists had cited "Evolution and Tinkering" thousands of times. Keywords: bricolage , tinkering. Sources Artmann, Stefan. Carroll, Sean B. Endless Forms Most Beautiful. The Possible and the Actual.
Seattle: University of Washington Press, Laubichler, Manfred. New York: John Wiley, 20— Bmc Evolutionary Biology. Let's face it--complex traits are just not that simple. Craniofacial morphometric analysis of individuals with X-linked hypohidrotic ectodermal dysplasia.
Shape-shift: semicircular canal morphology responds to selective breeding for increased locomotor activity. Evolution; International Journal of Organic Evolution. Facial morphometrics of children with non-syndromic orofacial clefts in Tanzania. Bmc Oral Health. Embryonic bauplans and the developmental origins of facial diversity and constraint.
Stem cell-derived endochondral cartilage stimulates bone healing by tissue transformation. Effects of growth hormone on the ontogenetic allometry of craniofacial bones. Fine tuning of craniofacial morphology by distant-acting enhancers. Science New York, N. Genomic correlates of relationship QTL involved in fore- versus hind limb divergence in mice.
Genome Biology and Evolution.
Quantification of shape and cell polarity reveals a novel mechanism underlying malformations resulting from related FGF mutations during facial morphogenesis. Human Molecular Genetics. The effect of hypoxia on facial shape variation and disease phenotypes in chicken embryos. Anatomical Sciences Education. Heterotopic mineralization ossification or calcification in tendinopathy or following surgical tendon trauma. International Journal of Experimental Pathology. The generation of variation and the developmental basis for evolutionary novelty.
Microarchitecture, but not bone mechanical properties, is rescued with growth hormone treatment in a mouse model of growth hormone deficiency. International Journal of Endocrinology. Signaling by SHH rescues facial defects following blockade in the brain. Epigenetic integration of the developing brain and face. Craniofacial defect regeneration using engineered bone marrow mesenchymal stromal cells.
Journal of Biomedical Materials Research. Part A. Estimating cell count and distribution in labeled histological samples using incremental cell search. International Journal of Biomedical Imaging. Pioneering paradigms and magnificent manifestos--Leigh Van Valen's priceless contributions to evolutionary biology.
The FaceBase Consortium: a comprehensive program to facilitate craniofacial research. Developmental Biology. Mechanisms that underlie co-variation of the brain and face. Genesis New York, N. An assessment of orofacial clefts in Tanzania. Modularity in the skull and cranial vasculature of laboratory mice: implications for the evolution of complex phenotypes.
Quantitative analyses link modulation of sonic hedgehog signaling to continuous variation in facial growth and shape.
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The coevolution of human hands and feet. The Neocortex. Organization and evolution of the avian forebrain. Part A. Laminar and columnar auditory cortex in avian brain. Revised nomenclature of avian telencephalon and some related brainstem nuclei. The limbic system of tetrapods: a comparative analysis of cortical and amygdalar populations. Brain Behav. Bruce LL. Evolution of the reptilian brain.
In: Kaas JH, editor. Evolution of Nervous Systems , Vol 2. Non-mammalian Vertebrates. Academic Press; Oxford: Striedter GF. The telencephalon of tetrapods in evolution. Puelles L. Kuwana E, Bulfone A, et al. Pallial and subpallial derivatives in the embryonic chick and mouse telencephalon, traced by the expression of the genes Dlx-2, Emx-1, Nkx Expression of Dbx1, neurogenin 2, semaphorin 5A, cadherin 8 , and Emx1 distinguish ventral and lateral pallial histogenetic divisions in the developing mouse claustroamygdaloid complex.
Olfactory and amygdalar structures of the chicken ventral pallium based on the combinatorial expression patterns of LIM and other developmental regulatory genes. Intratelencephalic projections of the visual Wulst in pigeons Columba livia. Wild JM.
The avian somatosensory system: connections of regions of body representation in the forebrain of the pigeon. Medina L, Reiner A. Do birds possess homologues of mammalian primary visual, somatosensory and motor cortices? Trends Neurosci. The concept of homology and the evolution of the nervous system.
Northcutt RG. Evolution of the vertebrate central nervous system: patterns and processes. Central nervous system phylogeny: evaluation of hypotheses.
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Homology in the nervous system: of characters, embryology and levels of analysis. Homology, Novartis Foundation Symposium Defining sameness: historical, biological, and generative homology. Puelles L, Medina L. Field homology as a way to reconcile genetic and developmental variability with adult homology. The pallial amygdala of amniote vertebrates: evolution of the concept, evolution of the structure. Development and evolution of the collopallium in amniotes: a new hypothesis of field homology.
Smith HM. Biological similarities and homologies. Boord RL. Ascending projections of the primary cochlear nuclei and nucleus laminaris in the pigeon. The anatomy of the avian auditory system. Adiciones a nuestros trabajos sobre los centros opticos de las aves. Ramon y Cajal S. Histologie du Systeme Nerveux de l'Homme et des Vertebres. Maloine; Paris: Thalamotelencephalic projections in the turtle Pseudemys scripta.
Ulinski PS. Organization of corticogeniculate projections in the turtle, Pseudemys scripta. Telencephalic connections in lizards: I. Projections to cortex. A lacertilian dorsal retinorecipient thalamus: a re-investigation in the Old World lizard Podarcis hispanica. Organization of thalamic afferents to anterior dorsal ventricular ridge in turtles: I. Projections of thalamic nuclei. Telencephalic connections in lizards.
Projections to anterior dorsal ventricular ridge. The connections and laminar organization of the optic tectum in a reptile Iguana iguana. Nucleus rotundus in a snake, Thamnophis sirtalis : an analysis of a non-retinotopic projection. Pritz MB. Anatomical identification of a telencephalic visual area in crocodiles: ascending connections of nucleus rotundus in Caiman crocodilus. The organization of central auditory pathways in a reptile, Iguana iguana.
Pritz ME. Ascending connections of a thalamic auditory area in a crocodile, Caiman crocodilus. Somatosensory representation in the anterior Wulst of the owl Speotyto cunicularia. Connectivity of the rat amygdaloid complex. In: Aggleton JP, editor. The Amygdala.
Oxford University Press; Oxford. UK: Rat's claustrum shows two main cortico-related zones. The avian tectofugal visual pathway: projections of its telencephalic target ectostriatal complex. Husband SA, Shimizu T. Efferent projections of the ectostriatum in the pigeon Columba livia. Definition and novel connections of the entopallium in the pigeon Columba livia. Scheich H. Two columnar systems in the auditory neostriatum of the chick: evidence from 2-deoxyglucose. Connections of the auditory forebrain in the pigeon Columba livia. Simpson GG. Principles of Animal Taxonomy.
Columbia University Press; New York: Organization of the tectofugal visual pathway in the pigeon: a retrograde transport study. Two distinct populations of tectal neurons have unique connections within the retinotectorotundal pathway of the pigeon Columba livia. Bottlebrush dendritic endings and large dendritic fields: motion-detecting neurons in tectofugal pathway. Bottlebrush dendritic endings and large dendritic fields: motion-detecting neurons in the mammalian tectum.
Chattering and differential signal processing in identified motion-sensitive neurons of parallel visual pathways in the chick tectum. The organization of the pulvinar in the grey squirrel Sciurus carolinensis : I. Cytoarchitecture and connections. Lugo-Garcia N, Kicliter E. Superior colliculus efferents to five subcortical visual system structures in the ground squirrel.
Kuljis RO, Fernandez V. On the organization of the retino-tecto-thalamo-telencephalic pathways in a Chilean rodent; the Octodon degus. Anatomical and functional organization of pathway from superior colliculus to lateral posterior nucleus in hamster. A new view of the oranization of the pulvinar nucleus in Tupaia as revealed by tectopulvinar and pulvinar-cortical projections.
Trojanowski JQ, Jacobson S. Peroxidase labeled subcortical afferents to pulvinar in rhesus monkey.
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Benevento LA, Rezak M. The cortical projections of the inferior pulvinar and adjacent lateral pulvinar in the rhesus monkey Macaca mulatta : an autoradiographic study. Laminar origin of projections from the superficial layers of the superior colliculus in the tree shrew, Tupaia glis. Graham J, Berman N. Origins of the projections of the superior colliculus to the dorsal lateral geniculate nucleus and pulvinar in the rabbit. Organization of projections from the superior colliculus to the thalamic lateral posterior nucleus in the rat.
The organization of projections of the retinorecipient and nonretinorecipient nuclei of the pretectal complex and layers of the superior colliculus to the lateral pulvinar and medial pulvinar in the macaque monkey. Sublamination within the superficial gray layer of the squirrel monkey: an analysis of the tectopulvinar projection using anterograde and retrograde transport methods. Synaptic organization of the tectorecipient zone of the rat lateral posterior nucleus.
Multiple pathways from the superior colliculus to the extrageniculate visual thalamus of the cat. Nucleus isthmi, pars semilunaris as a key component of the tectofugal visual system in pigeons. Yamamoto K, Reiner A. Is the avian dorsal ventricular ridge DVR homologous to the mammalian cerebral cortex or to the amygdala? Evaluating hypotheses by assessing homologous projection pathways to the telencephalon.
Integration of Comparative Neuroanatomy and Cognition. Keio University Press; Tokyo: Immunochemical heterogeneity in the tecto-LP pathway of the rat. Projection status of calbindin- and parvalbumin-immunoreactive neurons in the superficial layers of the rat's superior colliculus. Graham J. An autoradiographic study of the efferent connections of the superior colliculus in the cat. Behan M, Appell PP. Intrinsic connectivity in the cat superior colliculus: projections from the superficial layers. The ascending projections of the superior colliculus in the rhesus monkey Macaca mulatta.
GABAergic inputs to the nucleus rotundus pulvinar inferior of the pigeon Columba livia. Ultrastructural analysis of projections to the pulvinar nucleus of the cat. II: pretectum.