137-477: Peng Chau is a small island located off the north-eastern coast of Lantau Island , Hong Kong . It is known locally for its temples, fishing industry and seafood . Peng Chau has an area of 0.99 km (0.38 sq mi) and a perimeter of about 5 km (3.1 mi). The tallest point of the island is Finger Hill (手指山), which is 95 m (312 ft) in height. In 2003, the island underwent land degradation restorative work. Politically, Peng Chau
274-420: A synonymous substitution . However, many mutations in non-coding DNA have deleterious effects. Although both mutation rates and average fitness effects of mutations are dependent on the organism, a majority of mutations in humans are slightly deleterious. Some mutations occur in "toolkit" or regulatory genes . Changes in these often have large effects on the phenotype of the individual because they regulate
411-457: A "Nature" which would do the selection. At the time, other mechanisms of evolution such as evolution by genetic drift were not yet explicitly formulated, and Darwin believed that selection was likely only part of the story: "I am convinced that Natural Selection has been the main but not exclusive means of modification." In a letter to Charles Lyell in September 1860, Darwin regretted the use of
548-451: A "commuting" distance to an island that has enough resources to be sustainable. The presence of an island is marked by seabirds , differences in cloud and weather patterns, as well as changes in the direction of waves. It is also possible for human populations to have gone extinct on islands, evidenced by explorers finding islands that show evidence of habitation but no life. Not all islands were or are inhabited by maritime cultures. In
685-514: A "rafting event". This phenomenon is known as oceanic dispersal . Tropical storms have the capacity to transport species over great distances. Animals like tortoises can live for weeks without food or water, and are able to survive floating on debris in the sea. One case study showed that in 1995, fifteen iguanas survived a 300 km journey to Anguilla in the Caribbean , an island which no iguana had lived on previously. They survived floating on
822-519: A chromosome. During the formation of gametes, recombination reshuffles the alleles. The chance that such a reshuffle occurs between two alleles is inversely related to the distance between them. Selective sweeps occur when an allele becomes more common in a population as a result of positive selection. As the prevalence of one allele increases, closely linked alleles can also become more common by " genetic hitchhiking ", whether they are neutral or even slightly deleterious. A strong selective sweep results in
959-426: A detailed review of 1,288 islands found that they were home to 1,189 highly-threatened vertebrate species, which was 41 percent of the global figure. Coral bleaching is expected to occur with more frequency, threatening marine ecosystems, some of which island economies are dependent on. Some islands that are low-lying may cease to exist given high enough amounts of sea level rise. Tuvalu received media attention for
1096-554: A different, incompatible allele of the same gene. Selection against the heterozygote would then directly create reproductive isolation, leading to the Bateson–Dobzhansky–Muller model , further elaborated by H. Allen Orr and Sergey Gavrilets . With reinforcement , however, natural selection can favor an increase in pre-zygotic isolation, influencing the process of speciation directly. Natural selection acts on an organism's phenotype, or physical characteristics. Phenotype
1233-614: A few meters high, and are usually temporary. Changes in the flow speed, water level, and sediment content of the river may effect the rate of fluvial island formation and depletion. Permanent river islands also exist, the largest of which (that is completely inland) is Bananal Island in the Tocantins of Brazil, which has a maximum width of 55 kilometers. Lakes form for a variety of reasons, including glaciers , plate tectonics, and volcanism. Lake islands can form as part of these processes. The field of insular biogeography studies
1370-402: A higher carrying capacity also have more genetic diversity , which promotes speciation . Oceanic islands, ones that have never been connected to shore, are only populated by life that can cross the sea. This means that any animals present on the island had to have flown there, in the case of birds or bats , were carried by such animals, or were carried in a sea current in what is known as
1507-477: A loss of almost all the infrastructure in Dominica. Sea level rise and other climate changes can reduce freshwater reserves, resulting in droughts . These risks are expected to decrease the habitability of islands, especially small ones. Beyond risks to human life, plant and animal life are threatened. It has been estimated that almost 50 percent of land species threatened by extinction live on islands. In 2017,
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#17327727667851644-403: A mass of uprooted trees from a storm. Plant species are thought to be able to travel great distances of ocean. New Zealand and Australia share 200 native plant species, despite being separated by 1500 km. Continental islands, islands that were at one point connected to a continent, are expected to share a common history of plant and animal life up until the point that the island broke away from
1781-837: A minimum. Some islands became host to humans due to a land bridge or a continental island splitting from the mainland. Today, up to 10% of the world's population lives on islands. Islands are popular targets for tourism due to their perceived natural beauty, isolation, and unique cultures. Islands became the target of colonization by Europeans, resulting in the majority of islands in the Pacific being put under European control. Decolonization has resulted in some but not all island nations becoming self-governing , with lasting effects related to industrialisation , invasive species , nuclear weapons testing , and tourism . Islands and island countries are threatened by climate change . Sea level rise threatens to submerge nations such as Maldives ,
1918-743: A minority. Cultural attitudes related to communal ownership of land as well as a lack of individualistic decision-making may make some island cultures less compatible with the global capitalist economy, causing these nations to experience less economic growth. Islands have long been a popular target for tourism , thanks to their unique climates, cultures, and natural beauty. However, islands may suffer from poor transportation connectivity from airplanes and boats and strains on infrastructure from tourist activity. Islands in colder climates often rely on seasonal tourists seeking to enjoy nature or local cultures, and may only be one aspect of an island's economy. In contrast, tourism on tropical islands can often make up
2055-613: A permanent caisson , a steel or concrete structure built in a closed loop and then filled with sand. Some modern islands have been constructed by pouring millions of tons of sand into the sea, such as with Pearl Island in Qatar or the Palm Islands in Dubai. These islands are usually created for real estate development , and are sold for private ownership or construction of housing. Offshore oil platforms have also been described as
2192-524: A phenomenon where new oceanic crust is formed, pushing away older crust. Islands sitting on the continental shelf may be called continental islands. Other islands, like those that make up New Zealand , are what remains of continents that shrank and sunk beneath the sea. It was estimated that Zealandia , the continent-like area of crust that New Zealand sits on, has had 93% of its original surface area submerged. Some islands are formed when coral reefs grow on volcanic islands that have submerged beneath
2329-479: A precursor to speciation . Alternatively, selection can be divided according to its effect on genetic diversity . Purifying or negative selection acts to remove genetic variation from the population (and is opposed by de novo mutation , which introduces new variation. In contrast, balancing selection acts to maintain genetic variation in a population, even in the absence of de novo mutation, by negative frequency-dependent selection . One mechanism for this
2466-423: A press conference publicizing the ongoing submerging of the island country. Tuvalu signed a cooperation agreement with Australia agreeing to annually allow 280 of its citizens to become permanent residents of Australia. The Marshall Islands, a country of 1,156 islands, have also been identified as a country that may be existentially threatened by rising seas. Increasing intensity of tropical storms also increases
2603-483: A priority target of conservation efforts, to prevent the extinction of these species. Despite high levels of endemism, the total species richness , the total number of unique species in a region, is lower on islands than on mainlands. The level of species richness on islands is proportional to the area of that island, a phenomenon known as the species-area relationship . This is because larger areas have more resources and thus can support more organisms. Populations with
2740-441: A region of the genome where the positively selected haplotype (the allele and its neighbours) are in essence the only ones that exist in the population. Selective sweeps can be detected by measuring linkage disequilibrium , or whether a given haplotype is overrepresented in the population. Since a selective sweep also results in selection of neighbouring alleles, the presence of a block of strong linkage disequilibrium might indicate
2877-430: A relatively high probability of surviving to adulthood. Natural selection can act on any heritable phenotypic trait , and selective pressure can be produced by any aspect of the environment, including sexual selection and competition with members of the same or other species. However, this does not imply that natural selection is always directional and results in adaptive evolution; natural selection often results in
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#17327727667853014-458: A reproductive advantage regardless of whether or not the trait is heritable. Following Darwin's primary usage, the term is used to refer both to the evolutionary consequence of blind selection and to its mechanisms. It is sometimes helpful to explicitly distinguish between selection's mechanisms and its effects; when this distinction is important, scientists define "(phenotypic) natural selection" specifically as "those mechanisms that contribute to
3151-411: A restricted set of natural resources. However, these nations control some of the largest fisheries in the world, deposits of copper , gold , and nickel , as well as oil deposits . The natural beauty of island nations also makes them a magnet for tourism . Islands also have geopolitical value for naval bases , weapons testing , and general territorial control. One such example is French Polynesia ,
3288-476: A selection pressure for smaller animals that require less food. Having fewer predators would mean these animals did not need not be large to survive. Charles Darwin formulated the theory of natural selection through the study of island ecology. The species he observed on the Galápagos Islands , including tanager birds, contributed to his understanding of how evolution works. He first traveled to
3425-454: A species were uninteresting departures from their Platonic ideals (or typus ) of created kinds . However, the theory of uniformitarianism in geology promoted the idea that simple, weak forces could act continuously over long periods of time to produce radical changes in the Earth's landscape. The success of this theory raised awareness of the vast scale of geological time and made plausible
3562-559: A specific niche , microevolution occurs. If new traits become more favored due to changes in the broader environment, macroevolution occurs. Sometimes, new species can arise especially if these new traits are radically different from the traits possessed by their predecessors. The likelihood of these traits being 'selected' and passed down are determined by many factors. Some are likely to be passed down because they adapt well to their environments. Others are passed down because these traits are actively preferred by mating partners, which
3699-509: A specific property known as adaptive radiation . In this process, a species that arrives on a group of islands rapidly becomes more diverse over time, splitting off into new species or subspecies. A species that reaches an island ecosystem may face little competition for resources, or may find that the resources that they found in their previous habitat are not available. These factors together result in individual evolutionary branches with different means of survival. The classical example of this
3836-414: A territory that receives substantial military expenditure and aid from France. Since the first discoveries of Polynesian, Micronesian , and other islands by Westerners, these nations have been the subject of colonization. Islands were the target of Christian missionaries . These missionaries faced resistance, but found success when some local chiefs used European support to centralize power. Beginning in
3973-519: A tree that is present in Australia, New Zealand, parts of South American, and New Guinea, places that today are geographically distant. A possible explanation for this phenomenon is that these landmasses were once all part of the continent Gondwana and separated by tectonic drift. However, there are competing theories that suggest this species may have reached faraway places by way of oceanic dispersal. Species that colonize island archipelagos exhibit
4110-616: A type of island. Some atolls have been covered in concrete to create artificial islands for military purposes, such as those created by China in the South China Sea . These atolls were previously low-tide elevations, landmasses that are only above water during low tide . The United Nations Convention on the Law of the Sea indicates that these islands may not have the same legal status as a naturally occurring island, and as such may not confer
4247-483: A well-documented example involves the spread of a gene in the butterfly Hypolimnas bolina suppressing male-killing activity by Wolbachia bacteria parasites on the island of Samoa , where the spread of the gene is known to have occurred over a period of just five years. A prerequisite for natural selection to result in adaptive evolution, novel traits and speciation is the presence of heritable genetic variation that results in fitness differences. Genetic variation
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4384-515: Is Darwin's finches , a group of up to fifteen tanager species that are endemic to the Galápagos Islands. These birds evolved different beaks in order to eat different kinds of food available on the islands. The large ground finch has a large bill used to crack seeds and eat fruit. The Genovesa cactus finch prefers cacti as a food source, and has a beak adapted for removing pulp and flowers from cacti. The green warbler-finch (in
4521-532: Is heterozygote advantage , where individuals with two different alleles have a selective advantage over individuals with just one allele. The polymorphism at the human ABO blood group locus has been explained in this way. Another option is to classify selection by the life cycle stage at which it acts. Some biologists recognise just two types: viability (or survival) selection , which acts to increase an organism's probability of survival, and fecundity (or fertility or reproductive) selection, which acts to increase
4658-726: Is a piece of land, distinct from a continent, completely surrounded by water. There are continental islands, which were formed by being split from a continent by plate tectonics , and oceanic islands, which have never been part of a continent. Oceanic islands can be formed from volcanic activity, grow into atolls from coral reefs , and form from sediment along shorelines, creating barrier islands . River islands can also form from sediment and debris in rivers. Artificial islands are those made by humans, including small rocky outcroppings built out of lagoons and large-scale land reclamation projects used for development. Islands are host to diverse plant and animal life. Oceanic islands have
4795-598: Is actually a cognate of Swedish ö and German Aue , and more distantly related to Latin aqua (water). The spelling of the word was modified in the 15th century because of a false etymology caused by an association with the Old French loanword isle , which itself comes from the Latin word insula . Islands often are found in archipelagos or island chains, which are collections of islands. These chains are thought to form from volcanic hotspots , areas of
4932-405: Is all the parts of one whole) happened like as if they were made for the sake of something, these were preserved, having been appropriately constituted by an internal spontaneity, and whatsoever things were not thus constituted, perished, and still perish. But Aristotle rejected this possibility in the next paragraph, making clear that he is talking about the development of animals as embryos with
5069-500: Is central to natural selection. In broad terms, individuals that are more "fit" have better potential for survival, as in the well-known phrase " survival of the fittest ", but the precise meaning of the term is much more subtle. Modern evolutionary theory defines fitness not by how long an organism lives, but by how successful it is at reproducing. If an organism lives half as long as others of its species, but has twice as many offspring surviving to adulthood, its genes become more common in
5206-455: Is determined by an organism's genetic make-up (genotype) and the environment in which the organism lives. When different organisms in a population possess different versions of a gene for a certain trait, each of these versions is known as an allele . It is this genetic variation that underlies differences in phenotype. An example is the ABO blood type antigens in humans, where three alleles govern
5343-456: Is increased, which means that it leaves more offspring. If the traits that give these individuals a reproductive advantage are also heritable , that is, passed from parent to offspring, then there will be differential reproduction, that is, a slightly higher proportion of fast rabbits or efficient algae in the next generation. Even if the reproductive advantage is very slight, over many generations any advantageous heritable trait becomes dominant in
5480-476: Is intentional, whereas natural selection is not. Variation of traits, both 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 onto the next generation. These traits can also become more common within a population if the environment that favours these traits remains fixed. If new traits become more favored due to changes in
5617-438: Is intrinsic to the concept of a species that hybrids are selected against, opposing the evolution of reproductive isolation, a problem that was recognised by Darwin. The problem does not occur in allopatric speciation with geographically separated populations, which can diverge with different sets of mutations. E. B. Poulton realized in 1903 that reproductive isolation could evolve through divergence, if each lineage acquired
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5754-543: Is known as sexual selection . Female bodies also prefer traits that confer the lowest cost to their reproductive health, which is known as fecundity selection . Natural selection is a cornerstone of modern biology . The concept, published by Darwin and Alfred Russel Wallace in a joint presentation of papers in 1858 , was elaborated in Darwin's influential 1859 book On the Origin of Species by Means of Natural Selection, or
5891-788: Is linked to Tai Lei Island by a bridge. The bridge is part of Peng Lei Road. It is a popular fishing spot. Peng Chau is in Primary One Admission (POA) School Net 99, which contains two aided schools: Holy Family School in Peng Chau and SKH Wei Lun Primary School in Discovery Bay ; no government primary schools are in this net. The 2015 Hong Kong film Wong Ka Yan was set in Peng Chau, starring Wong You Nam and Karena Ng . 22°17′7″N 114°2′19″E / 22.28528°N 114.03861°E / 22.28528; 114.03861 Island An island or isle
6028-483: Is lowered by the presence of another. This may be because both rely on a limited supply of a resource such as food, water, or territory . Competition may be within or between species , and may be direct or indirect. Species less suited to compete should in theory either adapt or die out , since competition plays a powerful role in natural selection, but according to the "room to roam" theory it may be less important than expansion among larger clades . Competition
6165-555: Is modelled by r/K selection theory , which is based on Robert MacArthur and E. O. Wilson 's work on island biogeography . In this theory, selective pressures drive evolution in one of two stereotyped directions: r - or K -selection. These terms, r and K , can be illustrated in a logistic model of population dynamics : d N d t = r N ( 1 − N K ) {\displaystyle {\frac {dN}{dt}}=rN\left(1-{\frac {N}{K}}\right)\qquad \!} where r
6302-461: Is natural selection via any means other than sexual selection, such as kin selection, competition, and infanticide . Following Darwin, natural selection is sometimes defined as ecological selection, in which case sexual selection is considered a separate mechanism. Sexual selection as first articulated by Darwin (using the example of the peacock 's tail) refers specifically to competition for mates, which can be intrasexual , between individuals of
6439-835: Is part of Peng Chau & Hei Ling Chau constituency of the Islands District Council . The executive branch of the government of the island included department of the Islands District Office of the Home Affairs Department . The local police station belongs to the Cheung Chau Division of the Marine Police . There are several temples on Peng Chau, including: The island is also the site of the, now defunct, Peng Chau Theatre ( 坪洲戲院 ). There are remains of
6576-410: Is selection favoring extreme trait values over intermediate trait values. Disruptive selection may cause sympatric speciation through niche partitioning . Some forms of balancing selection do not result in fixation, but maintain an allele at intermediate frequencies in a population. This can occur in diploid species (with pairs of chromosomes) when heterozygous individuals (with just one copy of
6713-412: Is slowed by the competition. The variant which is a candidate for a beneficial mutation in this limited carrying capacity environment must first out-compete the "less fit" variants in order to accumulate the requisite number of replications for there to be a reasonable probability of that beneficial mutation occurring. In biology, competition is an interaction between organisms in which the fitness of one
6850-461: Is still often used by non-biologists, modern biologists avoid it because it is tautological if "fittest" is read to mean "functionally superior" and is applied to individuals rather than considered as an averaged quantity over populations. Natural selection relies crucially on the idea of heredity, but developed before the basic concepts of genetics . Although the Moravian monk Gregor Mendel ,
6987-503: Is the apple snail , initially introduced to the U.S. by aquarium owners. It has since been transported by hurricanes across the Gulf Coast and neighboring islands. These species compete for resources with native animals, and some may grow so densely that they displace other forms of existing life. For hundreds of years, islands have been created through land reclamation . One of the first recorded instances of this when people of
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#17327727667857124-634: Is the giant tortoise of the Seychelles , though it is unknown if it grew in size before or after reaching the island. Larger animals such as the hippopotamus tend to become smaller, such as in the case of the pygmy hippopotamus . This is known as insular dwarfism . In the case of smaller animals, it has been hypothesized that animals on islands may have fewer predators and competitors, resulting in selection pressure towards larger animals. Larger animals may exhaust food resources quickly due to their size, causing malnutrition in their young, resulting in
7261-405: Is the growth rate of the population ( N ), and K is the carrying capacity of its local environmental setting. Typically, r -selected species exploit empty niches , and produce many offspring, each with a relatively low probability of surviving to adulthood. In contrast, K -selected species are strong competitors in crowded niches, and invest more heavily in much fewer offspring, each with
7398-435: Is the result of mutations, genetic recombinations and alterations in the karyotype (the number, shape, size and internal arrangement of the chromosomes ). Any of these changes might have an effect that is highly advantageous or highly disadvantageous, but large effects are rare. In the past, most changes in the genetic material were considered neutral or close to neutral because they occurred in noncoding DNA or resulted in
7535-542: The Atlantic Ocean in search of an alternate route to the East Indies . These historians theorize that successful explorers were rewarded with recognition and wealth, leading others to attempt possibly dangerous expeditions to discover more islands, usually with poor results. About 10% of the world's population lives on islands. The study of the culture of islands is known as island studies . The interest in
7672-474: The Industrial Revolution , many of the trees on which the moths rested became blackened by soot , giving the dark-coloured moths an advantage in hiding from predators. This gave dark-coloured moths a better chance of surviving to produce dark-coloured offspring, and in just fifty years from the first dark moth being caught, nearly all of the moths in industrial Manchester were dark. The balance
7809-577: The Marshall Islands , and Tuvalu completely. Increases in the frequency and intensity of tropical cyclones can cause widespread destruction of infrastructure and animal habitats. Species that live exclusively on islands are some of those most threatened by extinction . An island is an area of land surrounded by water on all sides that is distinct from a continent. There is no standard of size that distinguishes islands and continents . Continents have an accepted geological definition – they are
7946-507: The Polynesians . Many of the previous island settlements required traveling distances of less than 100 km (62 mi), whereas Polynesians may have traveled 2,000–3,200 km (1,200–2,000 mi) to settle islands such as Tahiti . They would send navigators to sail the ocean without the aid of navigational instruments to discover new islands for settlement. Between 1100 and 800 BC, Polynesians sailed East from New Guinea and
8083-551: The Roman poet Lucretius , expressed the idea that nature produces a huge variety of creatures, randomly, and that only those creatures that manage to provide for themselves and reproduce successfully persist. Empedocles' idea that organisms arose entirely by the incidental workings of causes such as heat and cold was criticised by Aristotle in Book II of Physics . He posited natural teleology in its place, and believed that form
8220-863: The Sing Lei Hap Gei Lime Kiln Factory , established in the 19th century, and the Great China Match Company Factory , built in 1938. The main mode of transportation on the island is the bicycle, or on foot. Motor vehicles are not permitted on the island except emergency services, construction and village vehicles used for the transport of goods around the island. Peng Chau is accessible by ferry ( Hong Kong & Kowloon Ferry ) from Central on Hong Kong Island , or by ferry from Cheung Chau via Mui Wo and Chi Ma Wan ( Sun Ferry ), or by Kai-to ferry from Discovery Bay on Lantau Island. Helicopters are sometimes used in medical emergencies. Peng Chau
8357-891: The Solomon Islands and reached the islands that make up the modern-day Fiji and Samoa . The furthest extent of this migration would be Easter Island in the East, and New Zealand in the South, with New Zealand's first settlements between 1250 and 1300. Historians have sought to understand why some remote islands have always been uninhabited, while others, especially in the Pacific Ocean , have long been populated by humans. Generally, larger islands are more likely to be able to sustain humans and thus are more likely to have been settled. Small islands that cannot sustain populations on their own can still be habitable if they are within
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#17327727667858494-499: The Solomon Islands created eighty such islands by piling coral and rock in the Lau Lagoon . One traditional way of constructing islands is with the use of a revetment . Sandbags or stones are dropped with a barge into the sea to bring the land level slightly out of the water. The island area is then filled with sand or gravel, followed by a construction of this revetment to hold it together. Islands have also been constructed with
8631-524: The founder effect in initially small new populations. When genetic variation does not result in differences in fitness, selection cannot directly affect the frequency of such variation. As a result, the genetic variation at those sites is higher than at sites where variation does influence fitness. However, after a period with no new mutations, the genetic variation at these sites is eliminated due to genetic drift. Natural selection reduces genetic variation by eliminating maladapted individuals, and consequently
8768-434: The genetic regulatory programs which control the development of the embryo at molecular level. Natural selection is here understood to act on embryonic development to change the morphology of the adult body. The term natural selection is most often defined to operate on heritable traits, because these directly participate in evolution. However, natural selection is "blind" in the sense that changes in phenotype can give
8905-414: The lithosphere where the mantle is hotter than the surrounding area. These hotspots would give rise to volcanoes whose lava would form the rock the islands are made of. For some islands, the movement of tectonic plates above stationary hotspots would form islands in a linear chain, with the islands further away from the hotspot being progressively older and more eroded , before disappearing under
9042-424: The modern synthesis of the mid-20th century. The addition of molecular genetics has led to evolutionary developmental biology , which explains evolution at the molecular level. While genotypes can slowly change by random genetic drift , natural selection remains the primary explanation for adaptive evolution . Several philosophers of the classical era , including Empedocles and his intellectual successor,
9179-450: The sea as a natural barrier to the introduction of new species, causing the species that do reach the island to evolve in isolation. Continental islands share animal and plant life with the continent they split from. Depending on how long ago the continental island formed, the life on that island may have diverged greatly from the mainland due to natural selection . Humans have lived on and traveled between islands for thousands of years at
9316-468: The "principle by which each slight variation [of a trait], if useful, is preserved". The concept was simple but powerful: individuals best adapted to their environments are more likely to survive and reproduce. As long as there is some variation between them and that variation is heritable , there will be an inevitable selection of individuals with the most advantageous variations. If the variations are heritable, then differential reproductive success leads to
9453-496: The "upper power" but instead are generated in different forms naturally and then selected for reproduction by their compatibility with the environment. The more recent classical arguments were reintroduced in the 18th century by Pierre Louis Maupertuis and others, including Darwin's grandfather, Erasmus Darwin . Until the early 19th century, the prevailing view in Western societies was that differences between individuals of
9590-537: The 16th century, European states placed most of Oceania in under colonial administration . Pohnpei was colonized by Spain as early as 1526. It changed hands from Germany to Japan to the United States before joining the Federated States of Micronesia in 1982, maintaining a "free association" status with the U.S. Guam was a Spanish territory until 1898, and now is a unincorporated territory of
9727-511: The Hawaiian islands being home to irrigated fields of taro, whereas in some islands, like Tahiti, breadfruit was more widely cultivated and fermented in order to preserve it. There is archeological evidence that Canary Islanders would chew the roots of ferns for sustenance, a practice that wore heavily on their molars . These islanders would also grow barley and raised livestock such as goats . Many island nations have little land and
9864-433: The Origin of Species (1942). W. D. Hamilton conceived of kin selection in 1964. This synthesis cemented natural selection as the foundation of evolutionary theory, where it remains today. A second synthesis was brought about at the end of the 20th century by advances in molecular genetics , creating the field of evolutionary developmental biology ("evo-devo"), which seeks to explain the evolution of form in terms of
10001-629: The Origin of Species . The first evidence of humans colonizing islands probably occurred in the Paleolithic era, 100,000 to 200,000 years ago. Reaching the Indonesian islands of Flores and Timor would have required crossing distances of water of at least 29 km (18 mi). Some islands, such as Honshu , were probably connected to the mainland with a land bridge that allowed humans to colonize it before it became an island. The first people to colonize distant oceanic islands were
10138-678: The Preservation of Favoured Races in the Struggle for Life . He described natural selection as analogous to artificial selection, a process by which animals and plants with traits considered desirable by human breeders are systematically favoured for reproduction. The concept of natural selection originally developed in the absence of a valid theory of heredity; at the time of Darwin's writing, science had yet to develop modern theories of genetics. The union of traditional Darwinian evolution with subsequent discoveries in classical genetics formed
10275-481: The U.S. The decolonization era saw many island states achieve independence or some form of self-governance . Nuclear weapons testing on the Marshall Islands left many atolls destroyed or uninhabitable, causing the forced displacement of people from their home islands as well as increases in cancer rates due to radiation . Colonization has resulted in a decline of observance of traditional cultural practices in places such as Hawaii, where Native Hawaiians are now
10412-441: The adult population of the next generation. Though natural selection acts on individuals, the effects of chance mean that fitness can only really be defined "on average" for the individuals within a population. The fitness of a particular genotype corresponds to the average effect on all individuals with that genotype. A distinction must be made between the concept of "survival of the fittest" and "improvement in fitness". "Survival of
10549-551: The allele is fixed and the entire population shares the fitter phenotype. Far more common is stabilizing selection, which lowers the frequency of alleles that have a deleterious effect on the phenotype—that is, produce organisms of lower fitness. This process can continue until the allele is eliminated from the population. Stabilizing selection conserves functional genetic features, such as protein-coding genes or regulatory sequences , over time by selective pressure against deleterious variants. Disruptive (or diversifying) selection
10686-427: The allele) have a higher fitness than homozygous individuals (with two copies). This is called heterozygote advantage or over-dominance, of which the best-known example is the resistance to malaria in humans heterozygous for sickle-cell anaemia . Maintenance of allelic variation can also occur through disruptive or diversifying selection , which favours genotypes that depart from the average in either direction (that is,
10823-544: The antlers of stags , which are used in combat with other stags. More generally, intrasexual selection is often associated with sexual dimorphism , including differences in body size between males and females of a species. Natural selection is seen in action in the development of antibiotic resistance in microorganisms . Since the discovery of penicillin in 1928, antibiotics have been used to fight bacterial diseases. The widespread misuse of antibiotics has selected for microbial resistance to antibiotics in clinical use, to
10960-404: The apparently vestigial structure may retain a limited functionality, or may be co-opted for other advantageous traits in a phenomenon known as preadaptation . A famous example of a vestigial structure, the eye of the blind mole-rat , is believed to retain function in photoperiod perception. Speciation requires a degree of reproductive isolation —that is, a reduction in gene flow. However, it
11097-442: The assumption that groups replicate and mutate in an analogous way to genes and individuals. There is an ongoing debate over the degree to which group selection occurs in nature. Finally, selection can be classified according to the resource being competed for. Sexual selection results from competition for mates. Sexual selection typically proceeds via fecundity selection, sometimes at the expense of viability. Ecological selection
11234-450: The best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection. Once he had his theory, Darwin was meticulous about gathering and refining evidence before making his idea public. He was in the process of writing his "big book" to present his research when
11371-476: The concept of the "cost" of natural selection. Sewall Wright elucidated the nature of selection and adaptation. In his book Genetics and the Origin of Species (1937), Theodosius Dobzhansky established the idea that mutation, once seen as a rival to selection, actually supplied the raw material for natural selection by creating genetic diversity. Ernst Mayr recognised the key importance of reproductive isolation for speciation in his Systematics and
11508-406: The continent. For example, the presence of freshwater fish on an island surrounded by ocean would indicate that it once was attached to a continent, since these fish cannot traverse the ocean on their own. Over the course of time, evolution and extinction changes the nature of animal life on a continental island, but only once it splits from the mainland. An example is that of the southern beech ,
11645-451: The deposition of sediment by waves . These islands erode and grow as the wind and waves shift. Barrier islands have the effect of protecting coastal areas from severe weather because they absorb some of the energy of large waves before they can reach the shore. A fluvial island is an island that forms from the erosion and sedimentation of debris in rivers; almost all rivers have some form of fluvial islands. These islands may only be
11782-434: The different alleles, or variants of the gene that produces the variants of the trait. Selection can be divided into three classes, on the basis of its effect on allele frequencies: directional , stabilizing , and disruptive selection . Directional selection occurs when an allele has a greater fitness than others, so that it increases in frequency, gaining an increasing share in the population. This process can continue until
11919-426: The distances and frequency with which invasive species may be transported to islands. Floodwaters from these storms may also wash plants further inland than they would travel on their own, introducing them to new habitats. Agriculture and trade also have introduced non-native life to islands. These processes result in an introduction of invasive species to ecosystems that are especially small and fragile. One example
12056-458: The dog-days, but only if we have it in winter. If then, it is agreed that things are either the result of coincidence or for an end, and these cannot be the result of coincidence or spontaneity, it follows that they must be for an end; and that such things are all due to nature even the champions of the theory which is before us would agree. Therefore action for an end is present in things which come to be and are by nature. The struggle for existence
12193-400: The ecological processes that take place on islands, with a focus on what factors effect the evolution , extinction , and richness of species. Scientists often study islands as an isolated model of how the process of natural selection takes place. Island ecology studies organisms on islands and their environment. It has yielded important insights for its parent field of ecology since
12330-579: The evolution of particular populations of a species, and populations that evolve to be sufficiently different eventually become different species. Darwin's ideas were inspired by the observations that he had made on the second voyage of HMS Beagle (1831–1836), and by the work of a political economist, Thomas Robert Malthus , who, in An Essay on the Principle of Population (1798), noted that population (if unchecked) increases exponentially , whereas
12467-399: The extravagant plumage of some male birds such as the peacock. An alternate theory proposed by the same Ronald Fisher in 1930 is the sexy son hypothesis , that mothers want promiscuous sons to give them large numbers of grandchildren and so choose promiscuous fathers for their children. Aggression between members of the same sex is sometimes associated with very distinctive features, such as
12604-512: The father of modern genetics, was a contemporary of Darwin's, his work lay in obscurity, only being rediscovered in 1900. With the early 20th-century integration of evolution with Mendel's laws of inheritance, the so-called modern synthesis , scientists generally came to accept natural selection. The synthesis grew from advances in different fields. Ronald Fisher developed the required mathematical language and wrote The Genetical Theory of Natural Selection (1930). J. B. S. Haldane introduced
12741-473: The fittest" does not give an "improvement in fitness", it only represents the removal of the less fit variants from a population. A mathematical example of "survival of the fittest" is given by Haldane in his paper "The Cost of Natural Selection". Haldane called this process "substitution" or more commonly in biology, this is called "fixation". This is correctly described by the differential survival and reproduction of individuals due to differences in phenotype. On
12878-472: The food supply grows only arithmetically ; thus, inevitable limitations of resources would have demographic implications, leading to a "struggle for existence". When Darwin read Malthus in 1838 he was already primed by his work as a naturalist to appreciate the "struggle for existence" in nature. It struck him that as population outgrew resources, "favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be
13015-421: The formation of new species." Darwin wrote: If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organisation, and I think this cannot be disputed; if there be, owing to the high geometrical powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering
13152-453: The function of many other genes. Most, but not all, mutations in regulatory genes result in non-viable embryos. Some nonlethal regulatory mutations occur in HOX genes in humans, which can result in a cervical rib or polydactyly , an increase in the number of fingers or toes. When such mutations result in a higher fitness, natural selection favours these phenotypes and the novel trait spreads in
13289-502: The habit of true warbler species) consumes spiders and insects that live on plants. Other examples of this phenomenon exist worldwide, including in Hawaii and Madagascar, and are not limited to island ecosystems. Species endemic to islands show a common evolutionary trajectory. Foster's rule (also known as the island rule), states that small mammals such as rodents evolve to become larger, known as island gigantism . One such example
13426-487: The idea that tiny, virtually imperceptible changes in successive generations could produce consequences on the scale of differences between species. The early 19th-century zoologist Jean-Baptiste Lamarck suggested the inheritance of acquired characteristics as a mechanism for evolutionary change; adaptive traits acquired by an organism during its lifetime could be inherited by that organism's progeny, eventually causing transmutation of species . This theory, Lamarckism ,
13563-502: The infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each being's own welfare, in the same way as so many variations have occurred useful to man. But if variations useful to any organic being do occur, assuredly individuals thus characterised will have
13700-457: The islands as a naturalist on HMS Beagle in 1835, as part of a five-year circumnavigation of Earth. He wrote that "the different islands to a considerable extent are inhabited by a different set of beings". Through the study of the finches and other animals he realized that organisms survive by changing to adapt to their habitat. It would be over twenty years before he published his theories in On
13837-643: The largest landmass of a particular tectonic plate . Islands can occur in any body of water, including lakes , rivers , seas . Low-tide elevations , areas of land that are not above the surface during a high tide , are generally not considered islands. Islands that have been bridged or otherwise joined to a mainland with land reclamation are sometimes considered "de-islanded", but not in every case. The word island derives from Middle English iland , from Old English igland (from ig or ieg , similarly meaning 'island' when used independently, and -land carrying its contemporary meaning. Old English ieg
13974-444: The level or unit of selection . Individual selection acts on the individual, in the sense that adaptations are "for" the benefit of the individual, and result from selection among individuals. Gene selection acts directly at the level of the gene. In kin selection and intragenomic conflict , gene-level selection provides a more apt explanation of the underlying process. Group selection , if it occurs, acts on groups of organisms, on
14111-404: The mainland, they had no need for boats. The motivation for island exploration has been the subject of research and debate. Some early historians previously argued that early island colonization was unintentional, perhaps by a raft being swept out to sea. Others compare the motivations of Polynesian and similar explorers with those of Christopher Columbus , the explorer who sailed westward over
14248-403: The maintenance of the status quo by eliminating less fit variants. Selection can be classified in several different ways, such as by its effect on a trait, on genetic diversity, by the life cycle stage where it acts, by the unit of selection, or by the resource being competed for. Selection has different effects on traits. Stabilizing selection acts to hold a trait at a stable optimum, and in
14385-589: The majority of the local economy and built environment . These islands sometimes also require consistent foreign aid on top of tourism in order to ensure economic growth. This reliance can result in social inequality and environmental degradation . During tourism downturns, these economies struggle to make up the lost inflow of cash with other industries. Climate change threatens human development on islands due to sea level rise , more dangerous tropical cyclones , coral bleaching , and an increase in invasive species . For example, in 2017 Hurricane Maria caused
14522-406: The mutations that caused the maladaptation. At the same time, new mutations occur, resulting in a mutation–selection balance . The exact outcome of the two processes depends both on the rate at which new mutations occur and on the strength of the natural selection, which is a function of how unfavourable the mutation proves to be. Genetic linkage occurs when the loci of two alleles are close on
14659-546: The naturalist Alfred Russel Wallace independently conceived of the principle and described it in an essay he sent to Darwin to forward to Charles Lyell . Lyell and Joseph Dalton Hooker decided to present his essay together with unpublished writings that Darwin had sent to fellow naturalists, and On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection
14796-410: The opposite of over-dominance), and can result in a bimodal distribution of trait values. Finally, balancing selection can occur through frequency-dependent selection, where the fitness of one particular phenotype depends on the distribution of other phenotypes in the population. The principles of game theory have been applied to understand the fitness distributions in these situations, particularly in
14933-412: The other hand, "improvement in fitness" can occur in an environment where "survival of the fittest" is also acting. Richard Lenski 's classic E. coli long-term evolution experiment is an example of adaptation in a competitive environment, ("improvement in fitness" during "survival of the fittest"). The probability of a beneficial mutation occurring on some member of the lineage to give improved fitness
15070-405: The other hand, "improvement in fitness" is not dependent on the differential survival and reproduction of individuals due to differences in phenotype, it is dependent on the absolute survival of the particular variant. The probability of a beneficial mutation occurring on some member of a population depends on the total number of replications of that variant. The mathematics of "improvement in fitness
15207-529: The past, some societies were found to have lost their seafaring ability over time, such as the case of the Canary Islands , which were occupied by an indigenous people since the island's first discovery in the first century until being conquered by the Spanish Empire in 1496. It has been hypothesized that since the inhabitants had little incentive for trade and had little to any contact with
15344-404: The phenotype. Some traits are governed by only a single gene, but most traits are influenced by the interactions of many genes. A variation in one of the many genes that contributes to a trait may have only a small effect on the phenotype; together, these genes can produce a continuum of possible phenotypic values. When some component of a trait is heritable, selection alters the frequencies of
15481-511: The phrase survival of the fittest , which became a popular summary of the theory. The fifth edition of On the Origin of Species published in 1869 included Spencer's phrase as an alternative to natural selection, with credit given: "But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient." Although the phrase
15618-441: The phrase "either invariably or normally come about", not the origin of species: ... Yet it is impossible that this should be the true view. For teeth and all other natural things either invariably or normally come about in a given way; but of not one of the results of chance or spontaneity is this true. We do not ascribe to chance or mere coincidence the frequency of rain in winter, but frequent rain in summer we do; nor heat in
15755-688: The point that the methicillin-resistant Staphylococcus aureus (MRSA) has been described as a "superbug" because of the threat it poses to health and its relative invulnerability to existing drugs. Response strategies typically include the use of different, stronger antibiotics; however, new strains of MRSA have recently emerged that are resistant even to these drugs. This is an evolutionary arms race , in which bacteria develop strains less susceptible to antibiotics, while medical researchers attempt to develop new antibiotics that can kill them. A similar situation occurs with pesticide resistance in plants and insects. Arms races are not necessarily induced by man;
15892-406: The population. Established traits are not immutable; traits that have high fitness in one environmental context may be much less fit if environmental conditions change. In the absence of natural selection to preserve such a trait, it becomes more variable and deteriorate over time, possibly resulting in a vestigial manifestation of the trait, also called evolutionary baggage . In many circumstances,
16029-563: The population. In this way the natural environment of an organism "selects for" traits that confer a reproductive advantage, causing evolutionary change, as Darwin described. This gives the appearance of purpose, but in natural selection there is no intentional choice. Artificial selection is purposive where natural selection is not, though biologists often use teleological language to describe it. The peppered moth exists in both light and dark colours in Great Britain, but during
16166-527: The rate of reproduction, given survival. Others split the life cycle into further components of selection. Thus viability and survival selection may be defined separately and respectively as acting to improve the probability of survival before and after reproductive age is reached, while fecundity selection may be split into additional sub-components including sexual selection, gametic selection, acting on gamete survival, and compatibility selection, acting on zygote formation. Selection can also be classified by
16303-403: The same legal rights. 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 heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection , which
16440-421: The same sex, that is male–male competition, or intersexual , where one gender chooses mates , most often with males displaying and females choosing. However, in some species, mate choice is primarily by males, as in some fishes of the family Syngnathidae . Phenotypic traits can be displayed in one sex and desired in the other sex, causing a positive feedback loop called a Fisherian runaway , for example,
16577-789: The sea entirely. An example is the Hawaiian Islands , with the oldest island being 25 million years old, and the youngest, Hawaii , still being an active volcano . However, not all island chains are formed this way. Some may be formed all at once by fractures in the tectonic plates themselves, simultaneously creating multiple islands. One supporting piece of evidence is that of the Line Islands , which are all estimated to be 8 million years old, rather than being different ages. Other island chains form due to being separated from existing continents. The Japanese archipelago may have been separated from Eurasia due to seafloor spreading ,
16714-469: The selection of individuals that reproduce", without regard to whether the basis of the selection is heritable. Traits that cause greater reproductive success of an organism are said to be selected for , while those that reduce success are selected against . Natural variation occurs among the individuals of any population of organisms. Some differences may improve an individual's chances of surviving and reproducing such that its lifetime reproductive rate
16851-444: The simplest case all deviations from this optimum are selectively disadvantageous. Directional selection favours extreme values of a trait. The uncommon disruptive selection also acts during transition periods when the current mode is sub-optimal, but alters the trait in more than one direction. In particular, if the trait is quantitative and univariate then both higher and lower trait levels are favoured. Disruptive selection can be
16988-549: The study of islands is due to their unique cultures and natural environments that differ from mainland cultures. This is for a few reasons: First, the obvious political and geographic isolation from mainland cultures. Second, unique restraints on resources and ecology creating marine-focused cultures with a focus on fishing and sailing. Third, a lasting historical and political significance of islands. The Polynesian diet got most of its protein from fishing. Polynesians were known to fish close to shore, as well as in deep water. It
17125-494: The study of kin selection and the evolution of reciprocal altruism . A portion of all genetic variation is functionally neutral, producing no phenotypic effect or significant difference in fitness. Motoo Kimura 's neutral theory of molecular evolution by genetic drift proposes that this variation accounts for a large fraction of observed genetic diversity. Neutral events can radically reduce genetic variation through population bottlenecks . which among other things can cause
17262-450: The surface. When these coral islands encircle a central lagoon , the island is known as an atoll . The formation of reefs and islands related to those reefs is aided by the buildup of sediment in shallow patches of water. In some cases, tectonic movements lifting a reef out of the water by as little as 1 meter can cause sediment to accumulate and an island to form. Barrier islands are long, sandy bars that form along shorelines due to
17399-407: The term "Natural Selection", preferring the term "Natural Preservation". For Darwin and his contemporaries, natural selection was in essence synonymous with evolution by natural selection. After the publication of On the Origin of Species , educated people generally accepted that evolution had occurred in some form. However, natural selection remained controversial as a mechanism, partly because it
17536-438: The time of Charles Darwin . In biology, endemism is defined as the phenomenon where species or genus is only found in a certain geographical area. Islands isolate land organisms from others with water, and isolate aquatic organisms living on them with land. Island ecosystems have the highest rates of endemism globally. This means that islands contribute heavily to global biodiversity . Areas with high lives of biodiversity are
17673-518: The useful forms survived: So what hinders the different parts [of the body] from having this merely accidental relation in nature? as the teeth, for example, grow by necessity, the front ones sharp, adapted for dividing, and the grinders flat, and serviceable for masticating the food; since they were not made for the sake of this, but it was the result of accident. And in like manner as to the other parts in which there appears to exist an adaptation to an end. Wheresoever, therefore, all things together (that
17810-421: Was achieved for a purpose, citing the regularity of heredity in species as proof. Nevertheless, he accepted in his biology that new types of animals, monstrosities (τερας), can occur in very rare instances ( Generation of Animals , Book IV). As quoted in Darwin's 1872 edition of The Origin of Species , Aristotle considered whether different forms (e.g., of teeth) might have appeared accidentally, but only
17947-611: Was an influence on the Soviet biologist Trofim Lysenko 's ill-fated antagonism to mainstream genetic theory as late as the mid-20th century. Between 1835 and 1837, the zoologist Edward Blyth worked on the area of variation, artificial selection, and how a similar process occurs in nature. Darwin acknowledged Blyth's ideas in the first chapter on variation of On the Origin of Species . In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. He defined natural selection as
18084-482: Was described by Kleinman. An empirical example of "improvement in fitness" is given by the Kishony Mega-plate experiment. In this experiment, "improvement in fitness" depends on the number of replications of the particular variant for a new variant to appear that is capable of growing in the next higher drug concentration region. Fixation or substitution is not required for this "improvement in fitness". On
18221-493: Was later described by the Islamic writer Al-Jahiz in the 9th century, particularly in the context of top-down population regulation, but not in reference to individual variation or natural selection. At the turn of the 16th century Leonardo da Vinci collected a set of fossils of ammonites as well as other biological material. He extensively reasoned in his writings that the shapes of animals are not given once and forever by
18358-429: Was perceived to be too weak to explain the range of observed characteristics of living organisms, and partly because even supporters of evolution balked at its "unguided" and non- progressive nature, a response that has been characterised as the single most significant impediment to the idea's acceptance. However, some thinkers enthusiastically embraced natural selection; after reading Darwin, Herbert Spencer introduced
18495-751: Was read to the Linnean Society of London announcing co-discovery of the principle in July 1858. Darwin published a detailed account of his evidence and conclusions in On the Origin of Species in 1859. In the 3rd edition of 1861 Darwin acknowledged that others—like William Charles Wells in 1813, and Patrick Matthew in 1831—had proposed similar ideas, but had neither developed them nor presented them in notable scientific publications. Darwin thought of natural selection by analogy to how farmers select crops or livestock for breeding, which he called " artificial selection "; in his early manuscripts he referred to
18632-470: Was reported that Rapa Nui people were known to fish as far as 500 km (310 mi) from shore at coral reefs. Spear , line , and net fishing were all used, to catch tuna as well as sharks and stingrays . Island cultures also cultivate native and non-native crops. Polynesians grew the native yam , taro , breadfruit , banana , coconut and other fruits and vegetables. Different island climates made different resources more important, such as
18769-487: Was reversed by the effect of the Clean Air Act 1956 , and the dark moths became rare again, demonstrating the influence of natural selection on peppered moth evolution . A recent study, using image analysis and avian vision models, shows that pale individuals more closely match lichen backgrounds than dark morphs and for the first time quantifies the camouflage of moths to predation risk. The concept of fitness
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