In progress
140-425: Daisyworld (originally "Daisy World"), a term of reference in evolutionary and population ecology , derives from research on aspects of "coupling" between an ecosphere's biota and its planetary environment, in particular via mathematical modeling and computer simulation , research dating to a series of 1982-1983 symposia presentations and primary research reports by James E. Lovelock and colleagues aimed to address
280-487: A DNA sequence within a chromosome is known as a locus . If the DNA sequence at a locus varies between individuals, the different forms of this sequence are called alleles. DNA sequences can change through mutations, producing new alleles. If a mutation occurs within a gene, the new allele may affect the trait that the gene controls, altering the phenotype of the organism. However, while this simple correspondence between an allele and
420-570: A GC-biased E. coli mutator strain in 1967, along with the proposal of the neutral theory , established the plausibility of mutational explanations for molecular patterns, which are now common in the molecular evolution literature. For instance, mutation biases are frequently invoked in models of codon usage. Such models also include effects of selection, following the mutation-selection-drift model, which allows both for mutation biases and differential selection based on effects on translation. Hypotheses of mutation bias have played an important role in
560-487: A big role in the heating and cooling effects of albedo, high insolation areas like the tropics will tend to show a more pronounced fluctuation in local temperature when local albedo changes. Arctic regions notably release more heat back into space than what they absorb, effectively cooling the Earth . This has been a concern since arctic ice and snow has been melting at higher rates due to higher temperatures, creating regions in
700-514: A chromosome becoming duplicated (usually by genetic recombination ), which can introduce extra copies of a gene into a genome. Extra copies of genes are a major source of the raw material needed for new genes to evolve. This is important because most new genes evolve within gene families from pre-existing genes that share common ancestors. For example, the human eye uses four genes to make structures that sense light: three for colour vision and one for night vision ; all four are descended from
840-400: A climate trade-off: increased carbon uptake from afforestation results in reduced albedo . Initially, this reduction may lead to moderate global warming over a span of approximately 20 years, but it is expected to transition into significant cooling thereafter. Water reflects light very differently from typical terrestrial materials. The reflectivity of a water surface is calculated using
980-535: A consequence of land transformation" and can reduce surface temperature increases associated with climate change. Albedo is not directly dependent on the illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth's surface at that location (e.g. through melting of reflective ice). However, albedo and illumination both vary by latitude. Albedo
1120-456: A dark surface is thought to be indicative of a primitive and heavily space weathered surface containing some organic compounds . The overall albedo of the Moon is measured to be around 0.14, but it is strongly directional and non- Lambertian , displaying also a strong opposition effect . Although such reflectance properties are different from those of any terrestrial terrains, they are typical of
1260-536: A far simpler ecosystem—a planet at the lowest limit of its biota orbiting a star whose radiant energy was slowly changing—as a means to mimic a fundamental element of the interaction of all of the Earth's biota with the Sun. In the original 1983 works, Daisyworld made a wide variety of simplifying assumptions, and had white and black daisies as its only organisms, which were presented for their abilities to reflect or absorb light , respectively. The original simulation modeled
1400-741: A greater fraction of their foliage for direct interception of incoming radiation in the upper canopy. The result is that wavelengths of light not used in photosynthesis are more likely to be reflected back to space rather than being absorbed by other surfaces lower in the canopy. Studies by the Hadley Centre have investigated the relative (generally warming) effect of albedo change and (cooling) effect of carbon sequestration on planting forests. They found that new forests in tropical and midlatitude areas tended to cool; new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming. Research in 2023, drawing from 176 flux stations globally, revealed
1540-446: A low albedo because the majority of the ultraviolet and visible spectrum is absorbed through photosynthesis . For this reason, the greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate impacts of deforestation ). In other words: The climate change mitigation effect of carbon sequestration by forests is partially counterbalanced in that reforestation can decrease
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#17328561638191680-407: A major part of the astronomical field of photometry . For small and far objects that cannot be resolved by telescopes, much of what we know comes from the study of their albedos. For example, the absolute albedo can indicate the surface ice content of outer Solar System objects, the variation of albedo with phase angle gives information about regolith properties, whereas unusually high radar albedo
1820-402: A manner similar to a sequence of letters spelling out a sentence. Before a cell divides, the DNA is copied, so that each of the resulting two cells will inherit the DNA sequence. Portions of a DNA molecule that specify a single functional unit are called genes; different genes have different sequences of bases. Within cells, each long strand of DNA is called a chromosome . The specific location of
1960-413: A marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt because more radiation is being absorbed by the snowpack (the ice–albedo positive feedback ). In Switzerland, the citizens have been protecting their glaciers with large white tarpaulins to slow down the ice melt. These large white sheets are helping to reject the rays from the sun and defecting
2100-435: A net cooling impact, and the net climate impact of albedo and evapotranspiration changes from deforestation depends greatly on local climate. Mid-to-high-latitude forests have a much lower albedo during snow seasons than flat ground, thus contributing to warming. Modeling that compares the effects of albedo differences between forests and grasslands suggests that expanding the land area of forests in temperate zones offers only
2240-509: A number of useful predictions of how Earth's biosphere may respond to, for example, human interference. Later adaptations of Daisyworld (discussed below), which added many layers of complexity, still showed the same basic trends of the original model. One prediction of the simulation is that the biosphere works to regulate the climate , making it habitable over a wide range of solar luminosity. Many examples of these regulatory systems have been found on Earth. Evolution Evolution
2380-405: A nutrient in a long-term laboratory experiment , Flavobacterium evolving a novel enzyme that allows these bacteria to grow on the by-products of nylon manufacturing, and the soil bacterium Sphingobium evolving an entirely new metabolic pathway that degrades the synthetic pesticide pentachlorophenol . An interesting but still controversial idea is that some adaptations might increase
2520-611: A phenomenon termed de novo gene birth . The generation of new genes can also involve small parts of several genes being duplicated, with these fragments then recombining to form new combinations with new functions ( exon shuffling ). When new genes are assembled from shuffling pre-existing parts, domains act as modules with simple independent functions, which can be mixed together to produce new combinations with new and complex functions. For example, polyketide synthases are large enzymes that make antibiotics ; they contain up to 100 independent domains that each catalyse one step in
2660-437: A planetary temperature close to the optimum for daisy growth. Lovelock sought to demonstrate the stability of Daisyworld by making its sun evolve along the main sequence , taking it from low to high solar constant . This perturbation of Daisyworld's receipt of solar radiation caused the balance of daisies to gradually shift from black to white but the planetary temperature was always regulated back to this optimum (except at
2800-535: A population are therefore more likely to be replaced by the offspring of parents with favourable characteristics for that environment. In the early 20th century, competing ideas of evolution were refuted and evolution was combined with Mendelian inheritance and population genetics to give rise to modern evolutionary theory. In this synthesis the basis for heredity is in DNA molecules that pass information from generation to generation. The processes that change DNA in
2940-575: A population include natural selection, genetic drift, mutation , and gene flow . All life on Earth—including humanity —shares a last universal common ancestor (LUCA), which lived approximately 3.5–3.8 billion years ago. The fossil record includes a progression from early biogenic graphite to microbial mat fossils to fossilised multicellular organisms . Existing patterns of biodiversity have been shaped by repeated formations of new species ( speciation ), changes within species ( anagenesis ), and loss of species ( extinction ) throughout
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#17328561638193080-430: A population is not critical, but instead a measure known as the effective population size. The effective population is usually smaller than the total population since it takes into account factors such as the level of inbreeding and the stage of the lifecycle in which the population is the smallest. The effective population size may not be the same for every gene in the same population. It is usually difficult to measure
3220-433: A population through neutral transitions due to the principles of excess capacity, presuppression, and ratcheting, and it has been applied in areas ranging from the origins of the spliceosome to the complex interdependence of microbial communities . The time it takes a neutral allele to become fixed by genetic drift depends on population size; fixation is more rapid in smaller populations. The number of individuals in
3360-499: A range of genes from bacteria, fungi and plants. Viruses can also carry DNA between organisms, allowing transfer of genes even across biological domains . Large-scale gene transfer has also occurred between the ancestors of eukaryotic cells and bacteria, during the acquisition of chloroplasts and mitochondria . It is possible that eukaryotes themselves originated from horizontal gene transfers between bacteria and archaea . Some heritable changes cannot be explained by changes to
3500-430: A reduction in scope when it was discovered that (1) GC-biased gene conversion makes an important contribution to composition in diploid organisms such as mammals and (2) bacterial genomes frequently have AT-biased mutation. Contemporary thinking about the role of mutation biases reflects a different theory from that of Haldane and Fisher. More recent work showed that the original "pressures" theory assumes that evolution
3640-510: A regulatory framework derived by natural selection amongst species , where one being's harmful waste becomes low energy food for members of another guild. For instance, research on the Redfield ratio of nitrogen to phosphorus suggests that local biotic processes might regulate global systems. Later extension of the Daisyworld simulations which included rabbits , foxes and other species, led to
3780-552: A result of shifts in the popularions of the two plant varieties. Wood and colleagues, in a 2008 review citing the two 1983 Lovelock primary research papers on Daisyworld (still Daisy World or the same in lower case, at that point), describe it as being formulated in response to early criticism of Lovelock's Gaia hypothesis, specifically, being a model "invented to demonstrate that planetary self-regulation can emerge automatically from physically realistic feedback between life and its environment, without any need for foresight or planning on
3920-452: A single ancestral gene. New genes can be generated from an ancestral gene when a duplicate copy mutates and acquires a new function. This process is easier once a gene has been duplicated because it increases the redundancy of the system; one gene in the pair can acquire a new function while the other copy continues to perform its original function. Other types of mutations can even generate entirely new genes from previously noncoding DNA,
4060-419: A single chromosome compared to expectations , which is called their linkage disequilibrium . A set of alleles that is usually inherited in a group is called a haplotype . This can be important when one allele in a particular haplotype is strongly beneficial: natural selection can drive a selective sweep that will also cause the other alleles in the haplotype to become more common in the population; this effect
4200-443: A so-called ocean planet – the average temperature on the planet would rise to almost 27 °C (81 °F). In 2021, scientists reported that Earth dimmed by ~0.5% over two decades (1998–2017) as measured by earthshine using modern photometric techniques. This may have both been co-caused by climate change as well as a substantial increase in global warming. However, the link to climate change has not been explored to date and it
4340-420: A species or population, in particular shifts in allele frequency and adaptation. Macroevolution is the outcome of long periods of microevolution. Thus, the distinction between micro- and macroevolution is not a fundamental one—the difference is simply the time involved. However, in macroevolution, the traits of the entire species may be important. For instance, a large amount of variation among individuals allows
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4480-544: A species to rapidly adapt to new habitats , lessening the chance of it going extinct, while a wide geographic range increases the chance of speciation, by making it more likely that part of the population will become isolated. In this sense, microevolution and macroevolution might involve selection at different levels—with microevolution acting on genes and organisms, versus macroevolutionary processes such as species selection acting on entire species and affecting their rates of speciation and extinction. A common misconception
4620-411: A striking example are people with the inherited trait of albinism , who do not tan at all and are very sensitive to sunburn . Heritable characteristics are passed from one generation to the next via DNA , a molecule that encodes genetic information. DNA is a long biopolymer composed of four types of bases. The sequence of bases along a particular DNA molecule specifies the genetic information, in
4760-472: A system in which organisms interact with every other element, physical as well as biological , in their local environment. Eugene Odum , a founder of ecology, defined an ecosystem as: "Any unit that includes all of the organisms...in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles (i.e., exchange of materials between living and nonliving parts) within
4900-480: A temporary mitigation benefit. In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily. Deciduous trees have an albedo value of about 0.15 to 0.18 whereas coniferous trees have a value of about 0.09 to 0.15. Variation in summer albedo across both forest types is associated with maximum rates of photosynthesis because plants with high growth capacity display
5040-428: A trait works in some cases, most traits are influenced by multiple genes in a quantitative or epistatic manner. Evolution can occur if there is genetic variation within a population. Variation comes from mutations in the genome, reshuffling of genes through sexual reproduction and migration between populations ( gene flow ). Despite the constant introduction of new variation through mutation and gene flow, most of
5180-425: A warm air mass ), the raised albedo and lower temperature would maintain the current snow and invite further snowfall, deepening the snow–temperature feedback. However, because local weather is dynamic due to the change of seasons , eventually warm air masses and a more direct angle of sunlight (higher insolation ) cause melting. When the melted area reveals surfaces with lower albedo, such as grass, soil, or ocean,
5320-454: Is directional selection , which is a shift in the average value of a trait over time—for example, organisms slowly getting taller. Secondly, disruptive selection is selection for extreme trait values and often results in two different values becoming most common, with selection against the average value. This would be when either short or tall organisms had an advantage, but not those of medium height. Finally, in stabilising selection there
5460-442: Is more noticeable . Indeed, the evolution of microorganisms is particularly important to evolutionary research since their rapid reproduction allows the study of experimental evolution and the observation of evolution and adaptation in real time. Adaptation is the process that makes organisms better suited to their habitat. Also, the term adaptation may refer to a trait that is important for an organism's survival. For example,
5600-644: Is +0.2 W m , with a range +0.1 to +0.4 W m . Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo. In astronomy, the term albedo can be defined in several different ways, depending upon the application and the wavelength of electromagnetic radiation involved. The albedos of planets , satellites and minor planets such as asteroids can be used to infer much about their properties. The study of albedos, their dependence on wavelength, lighting angle ("phase angle"), and variation in time composes
5740-427: Is a byproduct of this process that may sometimes be adaptively beneficial. Gene flow is the exchange of genes between populations and between species. It can therefore be a source of variation that is new to a population or to a species. Gene flow can be caused by the movement of individuals between separate populations of organisms, as might be caused by the movement of mice between inland and coastal populations, or
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5880-417: Is an inherited characteristic and an individual might inherit the "brown-eye trait" from one of their parents. Inherited traits are controlled by genes and the complete set of genes within an organism's genome (genetic material) is called its genotype . The complete set of observable traits that make up the structure and behaviour of an organism is called its phenotype . Some of these traits come from
6020-464: Is based on standing variation: when evolution depends on events of mutation that introduce new alleles, mutational and developmental biases in the introduction of variation (arrival biases) can impose biases on evolution without requiring neutral evolution or high mutation rates. Several studies report that the mutations implicated in adaptation reflect common mutation biases though others dispute this interpretation. Recombination allows alleles on
6160-407: Is called deep homology . During evolution, some structures may lose their original function and become vestigial structures. Such structures may have little or no function in a current species, yet have a clear function in ancestral species, or other closely related species. Examples include pseudogenes , the non-functional remains of eyes in blind cave-dwelling fish, wings in flightless birds,
6300-692: Is called genetic hitchhiking or genetic draft. Genetic draft caused by the fact that some neutral genes are genetically linked to others that are under selection can be partially captured by an appropriate effective population size. A special case of natural selection is sexual selection, which is selection for any trait that increases mating success by increasing the attractiveness of an organism to potential mates. Traits that evolved through sexual selection are particularly prominent among males of several animal species. Although sexually favoured, traits such as cumbersome antlers, mating calls, large body size and bright colours often attract predation, which compromises
6440-497: Is generally to cool the planet; the indirect effect (the particles act as cloud condensation nuclei and thereby change cloud properties) is less certain. Another albedo-related effect on the climate is from black carbon particles. The size of this effect is difficult to quantify: the Intergovernmental Panel on Climate Change estimates that the global mean radiative forcing for black carbon aerosols from fossil fuels
6580-735: Is highest near the poles and lowest in the subtropics, with a local maximum in the tropics. The intensity of albedo temperature effects depends on the amount of albedo and the level of local insolation ( solar irradiance ); high albedo areas in the Arctic and Antarctic regions are cold due to low insolation, whereas areas such as the Sahara Desert , which also have a relatively high albedo, will be hotter due to high insolation. Tropical and sub-tropical rainforest areas have low albedo, and are much hotter than their temperate forest counterparts, which have lower insolation. Because insolation plays such
6720-469: Is indicative of high metal content in asteroids . Enceladus , a moon of Saturn, has one of the highest known optical albedos of any body in the Solar System, with an albedo of 0.99. Another notable high-albedo body is Eris , with an albedo of 0.96. Many small objects in the outer Solar System and asteroid belt have low albedos down to about 0.05. A typical comet nucleus has an albedo of 0.04. Such
6860-594: Is measured by an organism's ability to survive and reproduce, which determines the size of its genetic contribution to the next generation. However, fitness is not the same as the total number of offspring: instead fitness is indicated by the proportion of subsequent generations that carry an organism's genes. For example, if an organism could survive well and reproduce rapidly, but its offspring were all too small and weak to survive, this organism would make little genetic contribution to future generations and would thus have low fitness. If an allele increases fitness more than
7000-517: Is modified by feedbacks: increased by "self-reinforcing" or "positive" feedbacks and reduced by "balancing" or "negative" feedbacks . The main reinforcing feedbacks are the water-vapour feedback , the ice–albedo feedback , and the net effect of clouds. When an area's albedo changes due to snowfall, a snow–temperature feedback results. A layer of snowfall increases local albedo, reflecting away sunlight, leading to local cooling. In principle, if no outside temperature change affects this area (e.g.,
7140-400: Is not only determined by properties of the surface itself, but also by the spectral and angular distribution of solar radiation reaching the Earth's surface. These factors vary with atmospheric composition, geographic location, and time (see position of the Sun ). While directional-hemispherical reflectance factor is calculated for a single angle of incidence (i.e., for a given position of
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#17328561638197280-456: Is one that is not particularly prevalent in the real world). Evolutionary biologists often criticize the original model for this reason." The Gaia hypothesis has otherwise attracted a substantial amount of criticism from scientists, e.g., Richard Dawkins, who argued that planet-level thermoregulation was impossible without planetary natural selection, which might involve evidence of dead planets that did not thermoregulate. W. Ford Doolittle rejected
7420-421: Is selection against extreme trait values on both ends, which causes a decrease in variance around the average value and less diversity. This would, for example, cause organisms to eventually have a similar height. Natural selection most generally makes nature the measure against which individuals and individual traits, are more or less likely to survive. "Nature" in this sense refers to an ecosystem , that is,
7560-429: Is that evolution has goals, long-term plans, or an innate tendency for "progress", as expressed in beliefs such as orthogenesis and evolutionism; realistically, however, evolution has no long-term goal and does not necessarily produce greater complexity. Although complex species have evolved, they occur as a side effect of the overall number of organisms increasing, and simple forms of life still remain more common in
7700-447: Is the nearly neutral theory , according to which a mutation that would be effectively neutral in a small population is not necessarily neutral in a large population. Other theories propose that genetic drift is dwarfed by other stochastic forces in evolution, such as genetic hitchhiking, also known as genetic draft. Another concept is constructive neutral evolution (CNE), which explains that complex systems can emerge and spread into
7840-500: Is the change in the heritable 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
7980-406: Is the fraction of sunlight that is diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects all incident radiation). Surface albedo is defined as the ratio of radiosity J e to the irradiance E e (flux per unit area) received by a surface. The proportion reflected
8120-495: Is the more common means of reproduction among eukaryotes and multicellular organisms. The Red Queen hypothesis has been used to explain the significance of sexual reproduction as a means to enable continual evolution and adaptation in response to coevolution with other species in an ever-changing environment. Another hypothesis is that sexual reproduction is primarily an adaptation for promoting accurate recombinational repair of damage in germline DNA, and that increased diversity
8260-439: Is the process by which traits that enhance survival and reproduction become more common in successive generations of a population. It embodies three principles: More offspring are produced than can possibly survive, and these conditions produce competition between organisms for survival and reproduction. Consequently, organisms with traits that give them an advantage over their competitors are more likely to pass on their traits to
8400-431: Is unclear whether or not this represents an ongoing trend. For land surfaces, it has been shown that the albedo at a particular solar zenith angle θ i can be approximated by the proportionate sum of two terms: with 1 − D {\displaystyle {1-D}} being the proportion of direct radiation from a given solar angle, and D {\displaystyle {D}} being
8540-522: Is used to translate a sample set of satellite reflectance measurements into estimates of directional-hemispherical reflectance and bi-hemispherical reflectance (e.g., ). These calculations are based on the bidirectional reflectance distribution function (BRDF), which describes how the reflectance of a given surface depends on the view angle of the observer and the solar angle. BDRF can facilitate translations of observations of reflectance into albedo. Earth's average surface temperature due to its albedo and
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#17328561638198680-462: Is valuable. This finding was supported by a 1994 primary research report on species composition , dynamics, and diversity in successional and native grasslands in Minnesota by David Tilman and John A. Downing , which concluded that "primary productivity in more diverse plant communities is more resistant to, and recovers more fully from, a major drought". They go on to add that their "results support
8820-496: The Fresnel equations . At the scale of the wavelength of light even wavy water is always smooth so the light is reflected in a locally specular manner (not diffusely ). The glint of light off water is a commonplace effect of this. At small angles of incident light, waviness results in reduced reflectivity because of the steepness of the reflectivity-vs.-incident-angle curve and a locally increased average incident angle. Although
8960-498: The contrails of heavy commercial airliner traffic. A study following the burning of the Kuwaiti oil fields during Iraqi occupation showed that temperatures under the burning oil fires were as much as 10 °C (18 °F) colder than temperatures several miles away under clear skies. Aerosols (very fine particles/droplets in the atmosphere) have both direct and indirect effects on Earth's radiative balance. The direct (albedo) effect
9100-419: The energy budget of a planet populated by two different types of plants, black daisies and white daisies. The colour of the daisies influences the albedo of the planet such that black daisies absorb light and warm the planet, while white daisies reflect light and cool the planet. Competition between the daisies (based on temperature-effects on growth rates) leads to a balance of populations that tends to favour
9240-412: The greenhouse effect is currently about 15 °C (59 °F). If Earth were frozen entirely (and hence be more reflective), the average temperature of the planet would drop below −40 °C (−40 °F). If only the continental land masses became covered by glaciers, the mean temperature of the planet would drop to about 0 °C (32 °F). In contrast, if the entire Earth was covered by water –
9380-425: The neutral theory of molecular evolution most evolutionary changes are the result of the fixation of neutral mutations by genetic drift. In this model, most genetic changes in a population are thus the result of constant mutation pressure and genetic drift. This form of the neutral theory has been debated since it does not seem to fit some genetic variation seen in nature. A better-supported version of this model
9520-454: The product of a gene , or prevent the gene from functioning, or have no effect. About half of the mutations in the coding regions of protein-coding genes are deleterious — the other half are neutral. A small percentage of the total mutations in this region confer a fitness benefit. Some of the mutations in other parts of the genome are deleterious but the vast majority are neutral. A few are beneficial. Mutations can involve large sections of
9660-463: The regolith surfaces of airless Solar System bodies. Two common optical albedos that are used in astronomy are the (V-band) geometric albedo (measuring brightness when illumination comes from directly behind the observer) and the Bond albedo (measuring total proportion of electromagnetic energy reflected). Their values can differ significantly, which is a common source of confusion. In detailed studies,
9800-574: The urban heat island effect. An estimate in 2022 found that on a global scale, "an albedo increase of 0.1 in worldwide urban areas would result in a cooling effect that is equivalent to absorbing ~44 Gt of CO 2 emissions." Intentionally enhancing the albedo of the Earth's surface, along with its daytime thermal emittance , has been proposed as a solar radiation management strategy to mitigate energy crises and global warming known as passive daytime radiative cooling (PDRC). Efforts toward widespread implementation of PDRCs may focus on maximizing
9940-492: The Sun), albedo is the directional integration of reflectance over all solar angles in a given period. The temporal resolution may range from seconds (as obtained from flux measurements) to daily, monthly, or annual averages. Unless given for a specific wavelength (spectral albedo), albedo refers to the entire spectrum of solar radiation. Due to measurement constraints, it is often given for the spectrum in which most solar energy reaches
10080-519: The ability of organisms to generate genetic diversity and adapt by natural selection (increasing organisms' evolvability). Adaptation occurs through the gradual modification of existing structures. Consequently, structures with similar internal organisation may have different functions in related organisms. This is the result of a single ancestral structure being adapted to function in different ways. The bones within bat wings, for example, are very similar to those in mice feet and primate hands, due to
10220-402: The adaptation of horses' teeth to the grinding of grass. By using the term adaptation for the evolutionary process and adaptive trait for the product (the bodily part or function), the two senses of the word may be distinguished. Adaptations are produced by natural selection. The following definitions are due to Theodosius Dobzhansky: Adaptation may cause either the gain of a new feature, or
10360-420: The albedo and surface temperature of a planet. Ice is very reflective, therefore it reflects far more solar energy back to space than the other types of land area or open water. Ice–albedo feedback plays an important role in global climate change . Albedo is an important concept in climate science . Any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of
10500-642: The albedo effect of the colour of external clothing. Albedo can affect the electrical energy output of solar photovoltaic devices . For example, the effects of a spectrally responsive albedo are illustrated by the differences between the spectrally weighted albedo of solar photovoltaic technology based on hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si)-based compared to traditional spectral-integrated albedo predictions. Research showed impacts of over 10% for vertically (90°) mounted systems, but such effects were substantially lower for systems with lower surface tilts. Spectral albedo strongly affects
10640-531: The albedo of surfaces from very low to high values, so long as a thermal emittance of at least 90% can be achieved. The tens of thousands of hectares of greenhouses in Almería, Spain form a large expanse of whitened plastic roofs. A 2008 study found that this anthropogenic change lowered the local surface area temperature of the high-albedo area, although changes were localized. A follow-up study found that "CO2-eq. emissions associated to changes in surface albedo are
10780-493: The albedo of various areas around the globe. Human impacts to "the physical properties of the land surface can perturb the climate by altering the Earth’s radiative energy balance" even on a small scale or when undetected by satellites. Urbanization generally decreases albedo (commonly being 0.01–0.02 lower than adjacent croplands ), which contributes to global warming . Deliberately increasing albedo in urban areas can mitigate
10920-544: The albedo to 0.9. Cloud albedo has substantial influence over atmospheric temperatures. Different types of clouds exhibit different reflectivity, theoretically ranging in albedo from a minimum of near 0 to a maximum approaching 0.8. "On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth." Albedo and climate in some areas are affected by artificial clouds, such as those created by
11060-507: The alleles are subject to sampling error . This drift halts when an allele eventually becomes fixed, either by disappearing from the population or by replacing the other alleles entirely. Genetic drift may therefore eliminate some alleles from a population due to chance alone. Even in the absence of selective forces, genetic drift can cause two separate populations that begin with the same genetic structure to drift apart into two divergent populations with different sets of alleles. According to
11200-429: The arctic that are notably darker (being water or ground which is darker color) and reflects less heat back into space. This feedback loop results in a reduced albedo effect. Albedo affects climate by determining how much radiation a planet absorbs. The uneven heating of Earth from albedo variations between land, ice, or ocean surfaces can drive weather . The response of the climate system to an initial forcing
11340-441: The biosphere. For example, the overwhelming majority of species are microscopic prokaryotes , which form about half the world's biomass despite their small size and constitute the vast majority of Earth's biodiversity. Simple organisms have therefore been the dominant form of life on Earth throughout its history and continue to be the main form of life up to the present day, with complex life only appearing more diverse because it
11480-488: The change over time in this genetic variation. The frequency of one particular allele will become more or less prevalent relative to other forms of that gene. Variation disappears when a new allele reaches the point of fixation —when it either disappears from the population or replaces the ancestral allele entirely. Mutations are changes in the DNA sequence of a cell's genome and are the ultimate source of genetic variation in all organisms. When mutations occur, they may alter
11620-402: The darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body . When seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4. The average albedo of Earth is about 0.3. This is far higher than for
11760-403: The descent of all these structures from a common mammalian ancestor. However, since all living organisms are related to some extent, even organs that appear to have little or no structural similarity, such as arthropod , squid and vertebrate eyes, or the limbs and wings of arthropods and vertebrates, can depend on a common set of homologous genes that control their assembly and function; this
11900-400: The development of thinking about the evolution of genome composition, including isochores. Different insertion vs. deletion biases in different taxa can lead to the evolution of different genome sizes. The hypothesis of Lynch regarding genome size relies on mutational biases toward increase or decrease in genome size. However, mutational hypotheses for the evolution of composition suffered
12040-490: The direct control of genes include the inheritance of cultural traits and symbiogenesis . From a neo-Darwinian perspective, evolution occurs when there are changes in the frequencies of alleles within a population of interbreeding organisms, for example, the allele for black colour in a population of moths becoming more common. Mechanisms that can lead to changes in allele frequencies include natural selection, genetic drift, and mutation bias. Evolution by natural selection
12180-478: The directional reflectance properties of astronomical bodies are often expressed in terms of the five Hapke parameters which semi-empirically describe the variation of albedo with phase angle , including a characterization of the opposition effect of regolith surfaces. One of these five parameters is yet another type of albedo called the single-scattering albedo . It is used to define scattering of electromagnetic waves on small particles. It depends on properties of
12320-416: The diversity stability hypothesis but not the alternative hypothesis that most species are functionally redundant". Because Daisyworld is so simplistic, having for example, no atmosphere , no animals, only one species of plant life, and only the most basic population growth and death models, it should not be directly compared to Earth. This was stated very clearly by the original authors. Even so, it provided
12460-408: The effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating. Snow albedo is highly variable, ranging from as high as 0.9 for freshly fallen snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow. Over Antarctica snow albedo averages a little more than 0.8. If
12600-526: The effects of small errors in the measurement of albedo, can lead to large errors in energy estimates. Because of this, in order to reduce the error of energy estimates, it is important to measure the albedo of snow-covered areas through remote sensing techniques rather than applying a single value for albedo over broad regions. Albedo works on a smaller scale, too. In sunlight, dark clothes absorb more heat and light-coloured clothes reflect it better, thus allowing some control over body temperature by exploiting
12740-489: The evolutionary history of life on Earth. Morphological and biochemical traits tend to be more similar among species that share a more recent common ancestor , which historically was used to reconstruct phylogenetic trees , although direct comparison of genetic sequences is a more common method today. Evolutionary biologists have continued to study various aspects of evolution by forming and testing hypotheses as well as constructing theories based on evidence from
12880-483: The extreme ends of solar evolution). This situation is very different from the corresponding abiotic world, where temperature is unregulated and rises linearly with solar output. Daisyworld was designed to refute the idea that there was something inherently mystical about the Gaia hypothesis that Earth's surface displays homeostatic and homeorhetic properties similar to those of a living organism; specifically, thermoregulation
13020-430: The fact that although it is often used as an analogy for Earth, the original simulation leaves out many important details of the true Earth system. For example, the hypothetical system requires an ad-hoc death rate (γ) to sustain homeostasis, and does not take into account the difference between species-level phenomena and individual level phenomena. Detractors of the simulation believed inclusion of these details would cause
13160-414: The field or laboratory and on data generated by the methods of mathematical and theoretical biology . Their discoveries have influenced not just the development of biology but also other fields including agriculture, medicine, and computer science . Evolution in organisms occurs through changes in heritable characteristics—the inherited characteristics of an organism. In humans, for example, eye colour
13300-427: The fitness of an allele is not a fixed characteristic; if the environment changes, previously neutral or harmful traits may become beneficial and previously beneficial traits become harmful. However, even if the direction of selection does reverse in this way, traits that were lost in the past may not re-evolve in an identical form. However, a re-activation of dormant genes, as long as they have not been eliminated from
13440-491: The fraction of incident radiation reflected by the surface ], which is, in turn, influenced by the coverage of the two daisy types. This hypothetical construction produces, in its mathematical modeling, a nonlinear system "with interesting self-regulating properties". The purpose of the model is to demonstrate that feedback mechanisms can evolve from the actions or activities of self-interested organisms, rather than through classic group selection mechanisms. Daisyworld examines
13580-472: The genome and were only suppressed perhaps for hundreds of generations, can lead to the re-occurrence of traits thought to be lost like hindlegs in dolphins, teeth in chickens, wings in wingless stick insects, tails and additional nipples in humans etc. "Throwbacks" such as these are known as atavisms . Natural selection within a population for a trait that can vary across a range of values, such as height, can be categorised into three different types. The first
13720-479: The genome of a species is very similar among all individuals of that species. However, discoveries in the field of evolutionary developmental biology have demonstrated that even relatively small differences in genotype can lead to dramatic differences in phenotype both within and between species. An individual organism's phenotype results from both its genotype and the influence of the environment it has lived in. The modern evolutionary synthesis defines evolution as
13860-465: The heat. Although this method is very expensive, it has been shown to work, reducing snow and ice melt by 60%. Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water. Sea water absorbs more solar radiation than would the same surface covered with reflective snow. When sea ice melts, either due to a rise in sea temperature or in response to increased solar radiation from above,
14000-640: The idea of developmental bias . Haldane and Fisher argued that, because mutation is a weak pressure easily overcome by selection, tendencies of mutation would be ineffectual except under conditions of neutral evolution or extraordinarily high mutation rates. This opposing-pressures argument was long used to dismiss the possibility of internal tendencies in evolution, until the molecular era prompted renewed interest in neutral evolution. Noboru Sueoka and Ernst Freese proposed that systematic biases in mutation might be responsible for systematic differences in genomic GC composition between species. The identification of
14140-450: The interaction of its genotype with the environment while others are neutral. Some observable characteristics are not inherited. For example, suntanned skin comes from the interaction between a person's genotype and sunlight; thus, suntans are not passed on to people's children. The phenotype is the ability of the skin to tan when exposed to sunlight. However, some people tan more easily than others, due to differences in genotypic variation;
14280-512: The level of the individual organism are genes called transposons , which can replicate and spread throughout a genome. Selection at a level above the individual, such as group selection , may allow the evolution of cooperation. Genetic drift is the random fluctuation of allele frequencies within a population from one generation to the next. When selective forces are absent or relatively weak, allele frequencies are equally likely to drift upward or downward in each successive generation because
14420-452: The longer term, evolution produces new species through splitting ancestral populations of organisms into new groups that cannot or will not interbreed. These outcomes of evolution are distinguished based on time scale as macroevolution versus microevolution. Macroevolution refers to evolution that occurs at or above the level of species, in particular speciation and extinction, whereas microevolution refers to smaller evolutionary changes within
14560-405: The loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to antibiotic selection, with genetic changes causing antibiotic resistance by both modifying the target of the drug, or increasing the activity of transporters that pump the drug out of the cell. Other striking examples are the bacteria Escherichia coli evolving the ability to use citric acid as
14700-497: The material ( refractive index ), the size of the particle, and the wavelength of the incoming radiation. An important relationship between an object's astronomical (geometric) albedo, absolute magnitude and diameter is given by: A = ( 1329 × 10 − H / 5 D ) 2 , {\displaystyle A=\left({\frac {1329\times 10^{-H/5}}{D}}\right)^{2},} where A {\displaystyle A}
14840-458: The mechanics in developmental plasticity and canalisation . Heritability may also occur at even larger scales. For example, ecological inheritance through the process of niche construction is defined by the regular and repeated activities of organisms in their environment. This generates a legacy of effects that modify and feed back into the selection regime of subsequent generations. Other examples of heritability in evolution that are not under
14980-408: The movement of pollen between heavy-metal-tolerant and heavy-metal-sensitive populations of grasses. Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer . Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring; this is most common among bacteria. In medicine, this contributes to
15120-427: The next generation than those with traits that do not confer an advantage. This teleonomy is the quality whereby the process of natural selection creates and preserves traits that are seemingly fitted for the functional roles they perform. Consequences of selection include nonrandom mating and genetic hitchhiking . The central concept of natural selection is the evolutionary fitness of an organism. Fitness
15260-402: The notion of planetary regulation because it seemed to require a "secret consensus" among organisms, thus some sort of inexplicable purpose on a planetary scale. Others countered the criticism that some "secret consensus" would be required for planetary regulation, suggesting that thermoregulation of a planet beneficial to the two species arises naturally. Later criticism of Daisyworld centers on
15400-563: The ocean primarily because of the contribution of clouds. Earth's surface albedo is regularly estimated via Earth observation satellite sensors such as NASA 's MODIS instruments on board the Terra and Aqua satellites, and the CERES instrument on the Suomi NPP and JPSS . As the amount of reflected radiation is only measured for a single direction by satellite, not all directions, a mathematical model
15540-499: The offspring of sexual organisms contain random mixtures of their parents' chromosomes that are produced through independent assortment. In a related process called homologous recombination , sexual organisms exchange DNA between two matching chromosomes. Recombination and reassortment do not alter allele frequencies, but instead change which alleles are associated with each other, producing offspring with new combinations of alleles. Sex usually increases genetic variation and may increase
15680-456: The other alleles of that gene, then with each generation this allele has a higher probability of becoming common within the population. These traits are said to be "selected for ." Examples of traits that can increase fitness are enhanced survival and increased fecundity . Conversely, the lower fitness caused by having a less beneficial or deleterious allele results in this allele likely becoming rarer—they are "selected against ." Importantly,
15820-578: The overall process, like a step in an assembly line. One example of mutation is wild boar piglets. They are camouflage coloured and show a characteristic pattern of dark and light longitudinal stripes. However, mutations in the melanocortin 1 receptor ( MC1R ) disrupt the pattern. The majority of pig breeds carry MC1R mutations disrupting wild-type colour and different mutations causing dominant black colouring. In asexual organisms, genes are inherited together, or linked , as they cannot mix with genes of other organisms during reproduction. In contrast,
15960-438: The part of the organisms", Given the impossibility of fully representing the "coupling" of the whole of the Earth's biota and its environment , the hypothetical model is an imaginary grey world orbiting, at a similar distance to the Earth, a star like our Sun that gets brighter with time. The environment... is reduced to one variable, temperature, and the biota consist of two types of life, black and white daisies, which share
16100-563: The performance of bifacial solar cells where rear surface performance gains of over 20% have been observed for c-Si cells installed above healthy vegetation. An analysis on the bias due to the specular reflectivity of 22 commonly occurring surface materials (both human-made and natural) provided effective albedo values for simulating the performance of seven photovoltaic materials mounted on three common photovoltaic system topologies: industrial (solar farms), commercial flat rooftops and residential pitched-roof applications. Forests generally have
16240-474: The plausibility of the Gaia hypothesis . Also later referred to as a modeling of geosphere–biosphere interactions, Lovelock 's 1983 reports focused on a hypothetical planet with biota (in the original work, daisies) whose growth fluctuates as the planet's exposure to its sun's rays fluctuate, i.e., a pair of daisy varieties , whose differing colours drive a difference in interaction with their environment (in particular,
16380-527: The presence of hip bones in whales and snakes, and sexual traits in organisms that reproduce via asexual reproduction. Examples of vestigial structures in humans include wisdom teeth , the coccyx , the vermiform appendix , and other behavioural vestiges such as goose bumps and primitive reflexes . However, many traits that appear to be simple adaptations are in fact exaptations : structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in
16520-464: The process. One example is the African lizard Holaspis guentheri , which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree—an exaptation. Within cells, molecular machines such as the bacterial flagella and protein sorting machinery evolved by
16660-424: The proportion of diffuse illumination, the actual albedo α {\displaystyle {\alpha }} (also called blue-sky albedo) can then be given as: This formula is important because it allows the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface. Human activities (e.g., deforestation, farming, and urbanization) change
16800-419: The proposal that the larger the number of species, the greater thermoregulartory improvement for the entire planet, results suggesting that such a hypothetical system was robust and stable even when perturbed. Daisyworld simulations where environments were stable gradually became less diverse over time; in contrast gentle perturbations led to bursts of species richness, lending support to the idea that biodiversity
16940-494: The rate of evolution. The two-fold cost of sex was first described by John Maynard Smith . The first cost is that in sexually dimorphic species only one of the two sexes can bear young. This cost does not apply to hermaphroditic species, like most plants and many invertebrates . The second cost is that any individual who reproduces sexually can only pass on 50% of its genes to any individual offspring, with even less passed on as each new generation passes. Yet sexual reproduction
17080-407: The recruitment of several pre-existing proteins that previously had different functions. Another example is the recruitment of enzymes from glycolysis and xenobiotic metabolism to serve as structural proteins called crystallins within the lenses of organisms' eyes. Albedo Albedo ( / æ l ˈ b iː d oʊ / al- BEE -doh ; from Latin albedo 'whiteness')
17220-500: The reflection of sunlight (albedo). In the case of evergreen forests with seasonal snow cover, albedo reduction may be significant enough for deforestation to cause a net cooling effect. Trees also impact climate in extremely complicated ways through evapotranspiration . The water vapor causes cooling on the land surface, causes heating where it condenses, acts as strong greenhouse gas, and can increase albedo when it condenses into clouds. Scientists generally treat evapotranspiration as
17360-408: The reflectivity of water is very low at low and medium angles of incident light, it becomes very high at high angles of incident light such as those that occur on the illuminated side of Earth near the terminator (early morning, late afternoon, and near the poles). However, as mentioned above, waviness causes an appreciable reduction. Because light specularly reflected from water does not usually reach
17500-408: The relative importance of selection and neutral processes, including drift. The comparative importance of adaptive and non-adaptive forces in driving evolutionary change is an area of current research . Mutation bias is usually conceived as a difference in expected rates for two different kinds of mutation, e.g., transition-transversion bias, GC-AT bias, deletion-insertion bias. This is related to
17640-413: The same optimum temperature for growth and limits to growth. The soil of Daisyworld is sufficiently well watered and laden with nutrients for temperature alone to determine the growth rate of the daisies. The planet has a negligible atmospheric greenhouse , so its surface temperature is simply determined by... [the hypothetical star's] luminosity and its [the planet's] overall albedo [ reflective power,
17780-417: The same strand of DNA to become separated. However, the rate of recombination is low (approximately two events per chromosome per generation). As a result, genes close together on a chromosome may not always be shuffled away from each other and genes that are close together tend to be inherited together, a phenomenon known as linkage . This tendency is measured by finding how often two alleles occur together on
17920-552: The sequence of nucleotides in the DNA. These phenomena are classed as epigenetic inheritance systems. DNA methylation marking chromatin , self-sustaining metabolic loops, gene silencing by RNA interference and the three-dimensional conformation of proteins (such as prions ) are areas where epigenetic inheritance systems have been discovered at the organismic level. Developmental biologists suggest that complex interactions in genetic networks and communication among cells can lead to heritable variations that may underlay some of
18060-636: The snow-covered surface is reduced, and more surface of sea water is exposed, so the rate of energy absorption increases. The extra absorbed energy heats the sea water, which in turn increases the rate at which sea ice melts. As with the preceding example of snowmelt, the process of melting of sea ice is thus another example of a positive feedback. Both positive feedback loops have long been recognized as important for global warming . Cryoconite , powdery windblown dust containing soot, sometimes reduces albedo on glaciers and ice sheets. The dynamical nature of albedo in response to positive feedback, together with
18200-406: The spread of antibiotic resistance , as when one bacteria acquires resistance genes it can rapidly transfer them to other species. Horizontal transfer of genes from bacteria to eukaryotes such as the yeast Saccharomyces cerevisiae and the adzuki bean weevil Callosobruchus chinensis has occurred. An example of larger-scale transfers are the eukaryotic bdelloid rotifers , which have received
18340-420: The stability of the homeostasis . More recently, other research, modeling real biochemical cycles of Earth, and using various types of organisms (e.g. photosynthesisers , decomposers , herbivores and primary and secondary carnivores ) also argues to have produced Daisyworld-like regulation and stability, in support of ideas related to planetary biological diversity . This enables nutrient recycling within
18480-464: The sun). Reference to Daisyworld types of experiments have come to more broadly refer to extensions of that early work, and to further hypothetical systems involving similar and unrelated species. More specifically, given the impossibility of mathematically modeling the interactions of the full array of the biota of Earth with the full array of their environmental inputs, Lovelock introduced the idea of (and mathematical models and simulations approach to)
18620-411: The surface (between 0.3 and 3 μm). This spectrum includes visible light (0.4–0.7 μm), which explains why surfaces with a low albedo appear dark (e.g., trees absorb most radiation), whereas surfaces with a high albedo appear bright (e.g., snow reflects most radiation). Ice–albedo feedback is a positive feedback climate process where a change in the area of ice caps , glaciers , and sea ice alters
18760-640: The survival of individual males. This survival disadvantage is balanced by higher reproductive success in males that show these hard-to-fake , sexually selected traits. Evolution influences every aspect of the form and behaviour of organisms. Most prominent are the specific behavioural and physical adaptations that are the outcome of natural selection. These adaptations increase fitness by aiding activities such as finding food, avoiding predators or attracting mates. Organisms can also respond to selection by cooperating with each other, usually by aiding their relatives or engaging in mutually beneficial symbiosis . In
18900-491: The system to become unstable, making it a false analogy. These criticisms were countered by Timothy Lenton and James Lovelock in 2001, who argued that including further factors can improve climate regulation on later versons of Daisyworld. Later versions of Daisyworld, identifying the research area as "tutorial modelling of geosphere–biosphere interactions", introduced a range of grey daisies, as well as populations of grazers and predators , and found that these further increased
19040-642: The system...." Each population within an ecosystem occupies a distinct niche , or position, with distinct relationships to other parts of the system. These relationships involve the life history of the organism, its position in the food chain and its geographic range. This broad understanding of nature enables scientists to delineate specific forces which, together, comprise natural selection. Natural selection can act at different levels of organisation , such as genes, cells, individual organisms, groups of organisms and species. Selection can act at multiple levels simultaneously. An example of selection occurring below
19180-415: The two daisy populations—which combined to determine the planet's overall reflective power (fraction of incident radiation reflected by its surface)—and Daisyworld's surface temperature, as a function of changes in the hypothetical star's luminosity ; in doing so Lovelock demonstrated that the surface temperature of the simple Daisyworld system remained nearly constant over a broad range of solar fluctuations,
19320-410: The viewer, water is usually considered to have a very low albedo in spite of its high reflectivity at high angles of incident light. Note that white caps on waves look white (and have high albedo) because the water is foamed up, so there are many superimposed bubble surfaces which reflect, adding up their reflectivities. Fresh 'black' ice exhibits Fresnel reflection. Snow on top of this sea ice increases
19460-420: Was addressed. Wood and colleagues noted in 2008 that a key element in the hypothetical construct of Daisyworld was that the species of focus, "the daisies alter the same environmental variable (temperature) in the same direction at the local level and the global level. Hence what is selected for at the individual level is directly linked to its global effects. This makes the original model a special case (and it
19600-887: 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) traits vary among individuals with respect to their morphology , physiology , and behaviour; (3) different traits confer different rates of survival and reproduction (differential fitness ); and (4) traits can be passed from generation to generation ( heritability of fitness). In successive generations, members of
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