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Contingency (evolutionary Biology)
In evolutionary biology, contingency describes how the outcome of evolution may be affected by the history of a particular lineage. Overview Evolution is a historical process, and the outcomes of history can be sensitive to the details of the interactions and events that preceded them. Contingency was especially emphasized by Stephen Jay Gould, particularly in his 1989 book '' Wonderful Life''. Gould used the thought experiment of rewinding the "tape of life" to the distant past, and argued that even small changes to history would result in evolutionary outcomes very different from our world. Gould's thought experiment has inspired real experiments in the lab and in the field, as well as study of living and extinct organisms as natural experiments. These studies have found that repeatability in evolution is common, particularly in cases of similar founding populations, when defining repeatability broadly, and over the timescales observable in experiments. Convergent evolution ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolutionary Biology
Evolutionary biology is the subfield of biology that studies the evolutionary processes such as natural selection, common descent, and speciation that produced the diversity of life on Earth. In the 1930s, the discipline of evolutionary biology emerged through what Julian Huxley called the Modern synthesis (20th century), modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology. The investigational range of current research has widened to encompass the genetic architecture of adaptation, molecular evolution, and the different forces that contribute to evolution, such as sexual selection, genetic drift, and biogeography. The newer field of evolutionary developmental biology ("evo-devo") investigates how embryogenesis is controlled, thus yielding a wider synthesis that integrates developmental biology with the fields of study covered by the earlier evolutionary synthesis. Subfields ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Biodiversity Of New Zealand
The biodiversity of New Zealand, a large island country located in the south-western Pacific Ocean, is varied and distinctive. The species of New Zealand accumulated over many millions of years as lineages evolved in the local circumstances. New Zealand's pre-human biodiversity exhibited high levels of species endemism, but has experienced episodes of biological turnover. Global extinction approximately 65 Ma (million years ago) resulted in the loss of fauna such as non-avian dinosaurs, pterosaurs and marine reptiles e.g. mosasaurs, elasmosaurs and plesiosaurs. The ancient fauna is not well known, but at least one species of terrestrial mammal existed in New Zealand around 19 Ma. For at least several million years before the arrival of humans, the islands had no terrestrial mammals except for bats and seals, the main component of the terrestrial fauna being insects and birds. It was not until the 14th century that new species were introduced by humans. New Zealand has develo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Burgess Shale
The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fossil beds containing soft-part imprints. The rock unit is a black shale and crops out at a number of localities near the town of Field in Yoho National Park and the Kicking Horse Pass. Another outcrop is in Kootenay National Park 42 km to the south. History and significance The Burgess Shale was discovered by palaeontologist Charles Walcott on 30 August 1909, towards the end of the season's fieldwork. He returned in 1910 with his sons, daughter, and wife, establishing a quarry on the flanks of Fossil Ridge. The significance of soft-bodied preservation, and the range of organisms he recognised as new to science, led him to return to the quarry almost every year until 1924. At that point, aged 74, he had amassed over 65,000 s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extinction Event
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity. The "Big Five" mass extinctions In a landmark paper published in 1982, Jack Sepkoski and David M. Raup identified five particular geological intervals with excessive diversity loss. They were originally identified as outliers on a general trend of decreasing extinction rates during the Phanerozoic, but as more stringent statistical tests have been applied t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the Heredity, heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with selective breeding, artificial selection, which is intentional, whereas natural selection is not. Genetic diversity, Variation of traits, both Genotype, genotypic and phenotypic, exists within all populations of organisms. However, some traits are more likely to facilitate survival and reproductive success. Thus, these traits are passed the next generation. These traits can also become more Allele frequency, common within a population if the environment that favours these traits remains fixed. If new traits become more favoured due to changes in a specific Ecological niche, niche, microevolution occurs. If new traits become more favoured due to changes in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equus (genus)
''Equus'' () is a genus of mammals in the perissodactyl family (biology), family Equidae, which includes wild horse, horses, Asinus, asses, and zebras. Within the Equidae, ''Equus'' is the only recognized Extant taxon, extant genus, comprising seven living species. Like Equidae more broadly, ''Equus'' has numerous extinct species known only from fossils. The genus originated in North America and dispersed into the Old World and South America during the Early and Middle Pleistocene. Equinae, Equines are odd-toed ungulates with slender legs, long heads, relatively long necks, manes (erect in most subspecies), and long tails. All species are herbivorous, and mostly grazers, with simpler digestive systems than Ruminantia, ruminants but able to subsist on lower-quality vegetation. While the domestic horse and donkey (along with their feral horse, feral descendants) exist worldwide, wild equine populations are limited to Africa and Asia. Wild equine social systems are in two forms; a H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eohippus
''Eohippus'' is an extinct genus of small equid ungulates. The only species is ''E. angustidens'', which was long considered a species of ''Hyracotherium'' (now strictly defined as a member of the Palaeotheriidae rather than the Equidae). Its remains have been identified in North America and date to the Early Eocene (Ypresian stage). Discovery In 1876, Othniel C. Marsh described a skeleton as ''Eohippus validus'', from (, 'dawn') and (, 'horse'), meaning 'dawn horse'. Its similarities with fossils described by Richard Owen were formally pointed out in a 1932 paper by Clive Forster Cooper. ''E. validus'' was moved to the genus ''Hyracotherium'', which had priority as the name for the genus, with ''Eohippus'' becoming a junior synonym of that genus. ''Hyracotherium'' was recently found to be a paraphyletic group of species, and the genus now includes only ''H. leporinum''. ''E. validus'' was found to be identical to an earlier-named species, ''Orohippus angustidens'' Cope, 18 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyracotherium
''Hyracotherium'' ( ; "hyrax-like beast") is an extinction, extinct genus of small (about 60 cm in length) perissodactyl ungulates that was found in the London Clay formation. This small, fox-sized animal is (for some scientists) considered to be the earliest known member of Equidae before the type species, ''H. leporinum'', was reclassified as a palaeothere, a perissodactyl family (biology), family related to both horses and brontotheres. The remaining species are now thought to belong to different genera, such as ''Eohippus'', which had previously been synonymised with ''Hyracotherium''. Description ''Hyracotherium'' averaged 78 cm (2.5 feet) in length and weighed about 9 kg (20 pounds). It had a short face with eye sockets in the middle and a short diastema (the space between the front teeth and the cheek teeth). The skull was long, having 44 low-crowned teeth. Although it had low-crowned teeth, the beginnings of the characteristic horse-like ridges on the molars ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolution Of The Horse
The evolution of the horse, a mammal of the family Equidae, occurred over a geologic time scale of 50 million years, transforming the small, dog-sized, forest-dwelling '' Eohippus'' into the modern horse. Paleozoologists have been able to piece together a more complete outline of the evolutionary lineage of the modern horse than of any other animal. Much of this evolution took place in North America, where horses originated but became extinct about 10,000 years ago, before being reintroduced in the 15th century. The horse belongs to the order Perissodactyla ( odd-toed ungulates), the members of which one will share hooved feet and an odd number of toes on each foot, as well as mobile upper lips and a similar tooth structure. This means that horses share a common ancestry with tapirs and rhinoceroses. The perissodactyls arose in the late Paleocene, less than 10 million years after the Cretaceous–Paleogene extinction event. This group of animals appears to have been origin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
March Of Progress
''The March of Progress'', originally titled ''The Road to Homo Sapiens'', is an illustration that presents 25 million years of human evolution. It was created for the ''Early Man'' volume of the ''Life Nature Library'', published in 1965, and drawn by the artist Rudolph Zallinger. It has been widely parodied and imitated to create images of progress of other kinds. Illustration Context The illustration is part of a section of text and images commissioned by Time-Life Books for the ''Early Man'' volume (1965) of the ''Life Nature Library'', by Francis Clark Howell, F. Clark Howell.Howell, F. Clark and the Editors of Time-Life Books (1965), ''Early Man'', New York City, New York: TIME-LIFE Books, pp. 41–45. The illustration is a spread (typography), foldout entitled "The Road to Homo Sapiens". It shows a sequence of figures, drawn by natural history painter and muralist Rudolph Zallinger (1919–1995). The 15 human evolutionary forebears are lined up as if they were marchin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolution
Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation. The scientific theory of evolution by natural selection was conceived independently by two British naturalists, Charles Darwin and Alfred Russel Wallace, in the mid-19th century as an explanation for why organisms are adapted to their physical and biological environments. The theory was first set out in detail in Darwin's book ''On the Origin of Species''. Evolution by natural selection is established by observable facts about living organisms: (1) more offspring are often produced than can possibly survive; (2) phenotypic variatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Iconography
Iconography, as a branch of art history, studies the identification, description and interpretation of the content of images: the subjects depicted, the particular compositions and details used to do so, and other elements that are distinct from artistic style. The word ''iconography'' comes from the Ancient Greek, Greek ("image") and ("to write" or ''to draw''). A secondary meaning (based on a non-standard translation of the Greek and Russian equivalent terms) is the production or study of the religious images, called "Icon, icons", in the Byzantine art, Byzantine and Eastern Orthodox Churches, Orthodox Christian tradition. This usage is mostly found in works translated from languages such as Greek or Russian, with the correct term being "icon painting". In art history, "an iconography" may also mean a particular depiction of a subject in terms of the content of the image, such as the number of figures used, their placing and gestures. The term is also used in many academic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
