At 800 the idea that species evolve over time with new appearances and extinctions was accepted at an academic level. The evidence for evolution were already known to biologists before Darwin. For example, for the comparative biology wing of the bat, the fin whale and the man's arm has the same structure in common (homologous) because they are derived from the limb of the mammalian quadrupeds. Embryology is known that the early stages of embryonic development are almost identical in many different vertebrate species. Paleontology know what species of animals existing in geological time was far from our diverse and in some cases it is possible to reconstruct the transition.
A half of the 800 did not know the mechanism by which this could happen. In 1859 Charles Darwin published Origin of Species and gave answers on the mechanism of natural selection . The idea of \u200b\u200bDarwin
begins by noting the way in which farmers get different breeds through artificial selection. Farmers select individuals with a salient feature, and if this is hereditary is the next generation. From 1831 to 1836 Darwin traveled around the world on HMS Beagle and experience behind the understanding of natural selection was the observation of adaptation and speciation occurred from the Galapagos finches.
A source from another discipline, economics, came from Thomas Malthus by the Essay on Population who had pointed out how the animal and human populations tend to grow if not limited, tending to occupy geometrically all the space available, the availability of limited resources, the competition among individuals, predation and the spread of disease limit the maximum number of individuals.
in natural selection there is the overproduction : Each species produces more individuals than they reach maturity; limits to growth: each population is limited in number due to limitations of space, food resources, causing a proportion most individuals do not reach maturity and reproduction; variability : individuals show differences, some of these hereditary success ripprodduttivo differential : if a feature allows a greater survival you play more, with the passing of generations, is spreading in the population.
The Natural Selection produces adaptation to the environment. A case of adaptation observed in the act is relative to industrial melanism : butterflies with alleles for the color of light and dark wings with allele survived more clear when the birch trees were clear, here in the dark of the trunk because of the English industrial revolution the trend is opposite. Another form is the act antibiotic resistance in bacteria : resistant bacteria have a chance to reproduce.
Micro and macroevolution At the time of Darwin
dell'eridatarietà mechanisms were not known because the theory of natural selection could not be formalized. Between the wars biologists incorporate population genetics was born in Darwin's theory and the synthetic theory of evolution . In the theory of individual variability arises by mutation and evolution is seen mainly as changes in allele frequencies.
Changes in allelic frequencies in generations is defined microevolution, but can not explain the huge differnza between species this requires other mechanisms.
The principle of Hardy-Weinberg describes the relationship between allyl frequencies and the frequencies of different genotypes for a particular gene. Allows geneticists to determine the frequency of each allele frequencies starting from different genotypes or vice versa, starting from the relative frequency of alleles of a gene in the ideal population. In the ideal population distribution of alleles remains constant. Alter the balance of the Hardy-Weinberg involved 1) the natural selection, 2) the mutation , 3) the gene is derived , 4) the non-random mating , 5) the gene flow .
The mutation is based on which natural selection acts and a significant accumulation of changes affect the balance Hardy-Weinberg.
not random couplings are determined by the proximity of kin, and whether the possibility of incest is avoided (as in mammals), we have an inbreeding. In some species there is a prevalence of assorted mating in which individuals choose partners based on their similarity to the phenotype.
Hardy-Weinberg's law is valid if the population is large to enforce the laws of probability, but people with a few specimens you have the gene for which is derived alleles can be eliminated in generations.
The bottleneck effect is when people become too few and we are witnessing the impoverishment of the gene pool. A special case is
the 'founder effect for which individuals from a larger population colonizes an isolated their gene pool is the only one available.
Gene flow occurs when a population welcomes people from migration by increasing the gene pool. In contrast to the drift and nonrandom mating gene flow increases genetic variability.
Natural selection can be of three types: 1) directional , 2) stabilizing , 3) diversifying . In
stabilizing selection will favor a particular value of a character's extreme detriment. In
directional selection favors one extreme disadvantage is the opposite and the intermediate
In diversifying selection will favor the extreme disadvantage and the intermediate (rare).
Natural selection usually tends to reduce the genetic variability by eliminating characters that do not fit the environment, but in other cases, natural selection may favor the same variable if 1) varies in space and time, when there are 2 ) if there is balanced polymorphism and 3) frequency-dependent selection. The
spatial and temporal variations in natural selection is to favor individuals with different phenotypes depending on where you are (presence or absence of predators) or time (or cold months the warmer months). In skinned human species phenotypes are favored in areas with little sun and dark skin in the area with plenty of sun increasing the variability in the total pool of the human species. The
balanced polymorphism is the preference in some circles to heterozygous individuals, who have that dominant and recessive alleles for the same character. For example, sickle cell anemia. The
frequency dependent selection is a mechanism that favors the individual with the rare phenotype. In some species, including humans, females may prefer dissimilar inbred individuals.
Speciation and extinction
Alone specified processes do not explain the enormous variety of species.
For ' extinction is known that changes in physical conditions (eg weather), parasitic infection, predation, competition won by antagonistic species that makes better use of the ecological niche may be a disappearing species.
For speciation is necessary 1) to form a reproductive barrier between populations, 2) there are distinct ecological niches and different selective pressures. The
speciations are 3 types: 1) allopatric , 2) parapatrica , 3) sympatric . In allopatric speciation
the population is divided into populations isolated geographically, over time these differences will accumulate isolated groups can no longer reproduce with the population base. In parapatrica
speciation, even without barriers, extending the territory included several ecological niches causes the population fits into an ecosystem.
In sympatric speciation occurs when a genetic event in a population so that individuals do differ. Some mature individuals of substantial difference in favor of the habitat and reproduction will be favored with like-minded individuals. So barriers are formed and prezigotiche postzigotiche (economically disadvantaged).
prezigotiche Among the barriers can be a temporal isolation or behavioral. Among the barriers
postzigotiche the individual can manifest sterility or is poorly adapted to the habitat.
Sexual preferences based on the histocompatibility genes
The major histocompatibility complex or MHC is composed of many genes and is implicated in the response immunitraria against non-self, eg. causes the rejection of transplants. Many animals, including humans, recognize different MHC on the basis of smell. In our case this process is completely unconscious, but it can be demonstrated experimentally.
In choosing the male for breeding females based their choice on similarity of MHC.
man the time of ovulation in female prefer individuals with different MHC from their offspring to have greater variability in gene expression, on the other days of the cycle prefer people with similar genes.
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