Issues Of Rhetoric And Risk
From October 16th to 19th of 1980, a conferenceon the subject of macroevolution was held at the Field Museum ofNatural History in Chicago, Illinois. Shortly thereafterin theNovember 21, 1980 issue of Sciencean exciting reporton some events of the conference was published . Thereport was entitled Evolutionary Theory under Fire, andit prompted a cascade of responses in the Letters section ofSciencean exchange of scientific correspondence thatcontinued for almost two decades. Whatever the motives behind theheadlining of the report, it is empirically evident that the chosentitle was inflammatory.
The February 21, 1981 issue of Science included no fewer than5 separate contributions . The February 4, 1983 issue of Sciencecontained a letter by critics of PE and areply . In the March 11 issue of that same year both priorparties were accused of prolonging a fruitless discussion of aphilosophically intractable and dubiouspseudoquestion . In April, onecorrespondent wrote in agreement with Grant and anotherchided him for failing to explore and appreciate the latestblooming in the desert of dogma . To put itmildly, and purely descriptively: many of the responses elicited bythe original report were impassioned and emotive.
Genetic Variation And Drift
Figure 1. The distribution of phenotypes in this litter of kittens illustrates population variation.
Individuals of a population often display different phenotypes, or express different alleles of a particular gene, referred to as polymorphisms. Populations with two or more variations of particular characteristics are called polymorphic. The distribution of phenotypes among individuals, known as the population variation, is influenced by a number of factors, including the populations genetic structure and the environment . Understanding the sources of a phenotypic variation in a population is important for determining how a population will evolve in response to different evolutionary pressures.
Why The Increased Focus On The Evolution Of Pathways Of Metabolism
A number of factors have resulted in an increased interest in the evolution of intermediary metabolism, most notably: increasing appreciation of the importance of integrative, multi-level investigations an increasing shift to network or systems thinking and recent technological developments that allow multiple components of pathways to be characterized simultaneously. Since the 1980s there has been an increasing focus in evolutionary biology on integrative studies that link investigations across multiple levels of the biological hierarchy, often from the gene to whole organism . In these studies, intermediary metabolism often occupies a central gateway position, providing the link between molecular variation and variation in whole-organism performance.
Finally, the development of various omics approaches has produced an unprecedented wealth of information on variation in components of intermediary metabolism. This information, in turn, has provided the opportunity to investigate evolutionary changes in whole pathways, which has made an important contribution to the increased interest in adaptive changes in pathways of metabolism . In the following section, I focus on five prominent areas of recent research on the microevolution of intermediary metabolism.
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Can Macroevolution Happen Without Microevolution
Macroevolution is really only microevolution which has occurred over a longer period of time. Macroevolution is used very often, even in the scientific literature. However, I posit that separating micro and macro is a false dichotomy. Both are the same process, changes in allele frequency with time.
Success Of Asexual Species In Habitats With Extreme Conditions
The plasticity of asexual species should be greater in habitats that are poor in resources or where survival is limited by unfavorable abiotic factors. Here, the main criterion of evolutionary success is how well the species can change its phenotype in response to environmental requirements. It is noteworthy that asexual species or asexual lineages of otherwise sexual species are found primarily in habitats with extreme conditions in habitats that are extremely dry, cold or poisonous. The proportion of asexual species increases, for example, with increasing altitude and latitude, or where the soil contains high concentrations of poisonous heavy metals . On the other hand, elastic sexual species should be better off in an environment rich in resources and with many competing species where the rate of evolutionary responses in the coevolutionary arm-race plays the crucial role. The fact that they retain most of their genetic polymorphism enables them to rapidly respond to any selection pressures by shifting the frequencies of their alleles without needing to wait for rare advantageous mutations.
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Theory Accommodation And Change
One meta-scientific issue raised by these macroevolutionary disputesis just how much a scientific theory can flex and change before iteither becomes a different theory altogether, or it becomes a badscientific theory .
As an illustrative example, consider punctuated equilibrium, which hascertainty been articulated in many and varying ways. The two initialpublications by Eldredge and Eldredge and Gould areundoubtedly the founding ones, but there are other crucial moments inthe development of the theory . At times theshifting nature of PE has been a target of criticism .
Another dynamic theoretical dimension of PE, hierarchical theory, andthe like is how radically these scientific notions areperceivedeven by their own creators. In 1982, for instance,Gould first asked and then answered:
What would a fully elaborated, hierarchically based evolutionarytheory be called? It would neither be Darwinism, as usuallyunderstood, nor a smoothly continuous extension of Darwinism, for itviolates directly the fundamental reductionist tradition embodied inDarwins focus on organisms as units of selection.
But in 2002, Gould wrote
I do believe that the Darwinian framework, and not just thefoundation, persists in the emerging structure of a more adequateevolutionary theory.
Lower Viability And Fertility Of Decorative Breeds
The same negative correlation between departure of a phenotype from the original state and the mean fitness could explain the lower viability and fertility of most decorative breeds of practically any domesticated species. When the populations of pure-bred animals are left to their fate, members of the population return to the phenotype of their wild predecessors within a few generations. This phenomenon differs from the return of the phenotype to an original wild form in the case of crosses between two different races. In crosses, the almost immediate return to the original phenotype is caused by a breakdown of the unique combination of alleles as a consequence of recombination and segregation of alleles. In members of the same race, there is a gradual return to the wild phenotype as a consequence of the action of natural selection which, during a few subsequent generations, removes from the population the individuals with reduced viability and fertility, i.e. with the phenotype of the human-bred race.
Correlation Between The Rate Of Molecular Evolution And The Speciation Rate
The correlation between the rates of anagenesis and speciation can be detected even on a molecular level. A molecular study has shown that a relatively large part of the variability in the substitution rate can be explained by differences in the speciation rate between evolutionary lineages. Of course, a large part of the monitored nucleotide substitutions are neutral mutations known to be fixed by means of genetic drift and genetic draft and not by selection. Drift probably operates at the same rate in frozen, elastic and plastic species, however, the genetic draft operates more effectively during plastic phase of evolution when many neutral and nearly neutral mutations are being fixed with positive mutations by genetic hitchhiking. Approximately 35% of the substitutions was shown to occur in brief periods of speciation. It is worth mentioning that we are not aware of how many speciation events actually occur in the studied, seemingly unbranched lineages. Therefore, the published estimates of speciation-associated substitution rates represent only the lower margin of the real figures.
Electron Transport Hybrid Breakdown And Speciation
Since the 1930s, the genetic mechanisms responsible for reproductive isolation and speciation have been a central focus of evolutionary biology . The classic model of allopatric speciation proposes that reduced genetic exchange between geographically separated populations leads to genetic divergence and the evolution of population-specific epistatic interactions among alleles at different loci . Numerous studies have shown that hybrid breakdown commonly occurs in the F2 generation of interpopulational crosses, which has been interpreted as resulting from the breakdown of these co-adapted complexes as a result of genetic recombination . However, few studies have investigated in detail the functional basis of these negative genetic interactions in natural populations. Recently, Burton and colleagues have conducted a long-term, functional study of F2 hybrid breakdown, focusing on epistatic interactions between mitochondrial and nuclear genes that encode subunits of enzymes of the mitochondrial electron transport system .
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Intermediary Metabolism And Population Adaptation In Drosophila Melanogaster
A number of detailed studies of population genetics have focused on the microevolution of pathways of intermediary metabolism in Drosophila melanogaster, an important genetic model in evolutionary research. These studies comprise two major research thrusts. The first and more extensive involves studies of genetic differences in enzymes and pathway features in the context of adaptation of natural populations to different climates. A second approach involves quantitative, genetic analyses of genetic variation in pathway output , correlations with underlying enzymatic activities, and effects on fitness components in the laboratory . Because of space constraints, only the first approach will be considered here.
The ADH polymorphism was one of the first, and remains one of the most extensively studied, enzyme polymorphisms in natural populations with respect to effects of enzyme activity on pathway flux from the perspective of MCA . These studies illustrate the importance and complexities involved in ascertaining the relationship between enzyme activity and pathway flux.
Relationship between alcohol dehydrogenase activity and flux from ethanol to lipid biosynthesis in larval Drosophila melanogaster . The slope of the line is the flux control coefficient of ADH. Various pathways of metabolism of radiolabeled ethanol in larval D. melanogaster .
Main Difference Microevolution Vs Macroevolution
Microevolution and macroevolution are two terms that describe the two scales of evolutionary changes in organisms. Microevolution refers to the small scale changes, particularly at gene level that cause the evolution of the species. On the other hand, macroevolution refers to the changes occurring above species level that contribute to the large-scale evolutionary process. This can be considered as the main difference between Microevolution and Macroevolution. Microevolution happens through processes such as mutation, selection, gene flow, and genetic drift. However, macroevolution is the final result of such microevolutionary changes.
The Evolution Of Sirenians
The sirenians are a group of mammals within the placental mammals, consisting of the manatees and the Dugong, as well as other extinct species.
Also known as the sea cows, the sirenians feed solely on sea grass and are the only herbivorous aquatic mammals. They share a common ancestor with the elephants and the extinct mammoths, in a taxonomic group called the Tethytheria. The evidence for the macroevolution that has separated these groups of animals comes from vestigial structures within their bodies.
Firstly, the flippers of sirenians have internal bone structures that are homologous to the bone structure of all other terrestrial tetrapods . Each flipper contains an upper arm bone two forearm bones, wrist bones, hand bones and five finger bones. On the external tips of their flippers the sirenians have toenails, which are the same as those seen in elephants.
The image shows the skeleton of a manatee. The homologous bone structures are visible in the flippers. Like all other terrestrial mammals, manatees have five finger bones although they have no fingers!
Furthermore, manatees dont have hind limbs but they do have pelvic bones, which are usually used to support the hind limbs in other tetrapods. Because they lack hind limbs they also dont have femurs but they have vestigial hip sockets where the femur attaches to the pelvis.
What Diseases Are Caused By Mutations
But the mutations we hear about most often are the ones that cause disease. Some well-known inherited genetic disorders include cystic fibrosis, sickle cell anemia, Tay-Sachs disease, phenylketonuria and color-blindness, among many others. All of these disorders are caused by the mutation of a single gene.
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What’s An Example Of Mutation
Other common mutation examples in humans are Angelman syndrome, Canavan disease, color blindness, cri-du-chat syndrome, cystic fibrosis, Down syndrome, Duchenne muscular dystrophy, haemochromatosis, haemophilia, Klinefelter syndrome, phenylketonuria, PraderWilli syndrome, TaySachs disease, and Turner syndrome.
Selective And Environmental Pressures
Natural selection only acts on the populations heritable traits: selecting for beneficial alleles and thus increasing their frequency in the population, while selecting against deleterious alleles and thereby decreasing their frequencya process known as adaptive evolution. Natural selection does not act on individual alleles, however, but on entire organisms. An individual may carry a very beneficial genotype with a resulting phenotype that, for example, increases the ability to reproduce , but if that same individual also carries an allele that results in a fatal childhood disease, that fecundity phenotype will not be passed on to the next generation because the individual will not live to reach reproductive age. Natural selection acts at the level of the individual it selects for individuals with greater contributions to the gene pool of the next generation, known as an organisms evolutionary fitness.
Fitness is often quantifiable and is measured by scientists in the field. However, it is not the absolute fitness of an individual that counts, but rather how it compares to the other organisms in the population. This concept, called relative fitness, allows researchers to determine which individuals are contributing additional offspring to the next generation, and thus, how the population might evolve.
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So What Is A Living Thing
There are varying definitions for something to be physically alive. Some helpful distinctions include2:
Lets compare and contrast a living and non-living thing.
Now that weve defined living, lets look at the various facets of biology.
Microevolutionary Elasticity And Adaptation To Past Condition
According to the classical gradualistic theories, all species respond to selection as if they were plasticine while, according to punctuational theories, most species are resistant to selection as if they were lead or respond to selection as though they were rubber at first, they respond readily to selection pressure however, as the average phenotype of the organism deviates from its original state, selection is less and less effective and, at a certain point, the response ceases . According to class IV and class V punctuational theories, the average phenotype returns to the original state when the selection stops .
There are several critical implications: in the world of species that do not respond to selection, organisms are not optimally adapted to the conditions of their current environment but to those present during the evolutionary plasticity of the particular species. This should be true especially for evolutionarily old species, as their environmental conditions probably differ most from those existing during their origination. For example, algae , which originated in the Paleozoic when days lasted about 21 hours, are known to better synchronize their circadian rhythms with shorter lightdark cycles than the current 24-hour cycle .
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What Youll Learn To Do: Recognize That Mutations Are The Basis Of Microevolution And That Adaptations Enhance The Survival And Reproduction Of Individuals In A Population
Weve already learned about DNA and mutations, now well learn about how these mutations can drive evolution. This type of evolution falls under the category of microevolution.
Microevolution is the change in allele frequencies that occurs over time within a population. This change is due to five different processes: mutation, selection , gene flow, gene migration and genetic drift. This change happens over a relatively short amount of time compared to the changes termed macroevolution which is where greater differences in the population occur.
Population genetics is the branch of biology that provides the mathematical structure for the study of the process of microevolution. Ecological genetics concerns itself with observing microevolution in the wild. Typically, observable instances of evolution are examples of microevolution for example, bacterial strains that have antibiotic resistance.
Microevolution over time leads to speciation or the appearance of novel structure, sometimes classified as macroevolution. Macro and microevolution describe fundamentally identical processes on different scales.
Examples Of Microevolution In A Sentence
microevolution Smithsonian Magazinemicroevolution Smithsonian MagazinemicroevolutionSmithsonian MagazinemicroevolutionThe Atlanticmicroevolution Quanta MagazinemicroevolutionNew York Times
These example sentences are selected automatically from various online news sources to reflect current usage of the word ‘microevolution.’ Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
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Punctuational Evolution And The Origin Of Evolutionary Trends
The class II-V punctuational models of evolution also offer a new explanation for the existence of evolutionary trends, the slow directional phenotypic changes in organisms of particular phylogenetic lineages that endure much longer than the individual species involved. The trends are too slow to be geared by selection the change in the value of the trait per generation is so small that it is completely invisible for selection , p. 835. According to gradualistic evolutionary theories, the selection pressure has to be sufficiently strong to overcome genetic drift. However, this type of selection should result in far more rapid changes than those that emerge as trends in the paleontological record. Punctuational theories suggest a new solution to the paradox of very slow evolutionary trends. According to punctuational theories, the trend could, in fact, be a product of a relatively strong and long-term selective pressure to which species can respond, however, only in the brief and rare periods of their evolutionary plasticity.