5.2: Natural Selection
*Outline the process of evolution through natural selection.* Understanding: Natural selection can only occur if there is variation among members of the same species.
1. populations produce more offspring than can survive; 2. individuals show variation in heritable traits; 3. there is a struggle for survival, often due to competition for resources; 4. some individuals are better suited to the environment and survive; 5. the most fit individuals survive to reproduce; 6. the advantageous variation is passed on to the next generation; 7. over time, the advantageous variation increases in frequency in the population;
*Outline how mutation leads to genetic variation.* Understanding: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
A mutation is a random change in DNA. A change in DNA may cause phenotypic variation. Mutations can occur when the DNA is replicated or as the result of environmental factors (such as UV light and cigarette smoke). Only mutations in the DNA of germ cells or gametes effect evolution. Mutations in somatic cell DNA cannot be passed on to offspring and therefore do not matter for evolution.
*Define “selective pressure" as related to natural selection.* Understanding: Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
A selective pressure is any phenomena that impacts the survival and/or reproduction of organisms living within a given environment. Selective pressures can be divided into two types of pressure: biotic or abiotic.
*Describe an example of evolution through natural selection.* Understanding: Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
*1. A named example of a species;* //Anole lizards.// *2. An outline of the different variations of a relevant trait;* //Variation in the limb length and toepad surface area which affects clinging ability.// *3. A statement that the variation is genetically inherited.* //Limb length and toepad surface area are genetically controlled traits.// *4. A statement of the selective pressure;* //Hurricanes in the habitat.// *5. Consequence of the selective pressure;* //Lizards that can better cling onto branches are more likely to survive hurricanes.// *6. More reproduction by better adapted individuals;* //Surviving lizards are able to reproduce after the hurricane.// *7. The change in the population that results.* //The surviving lizard populations have larger toe pads, longer forelimbs and shorter hind limbs on average than before the storms.//
*Explain how natural selection leads to changes in antibiotic resistance.* Application: Evolution of antibiotic resistance in bacteria.
*1. A named example of a species;* //Bacteria, such as Staphylococcus aureus.// *2. An outline of the different variations of a relevant trait;* //Within populations, bacteria vary in their resistance to antibiotics. Some varieties are more resistant to antibiotics than others;// *3. A statement that the variation is genetically inherited.* //Antibiotic resistance arises by random DNA gene mutation. Resistance is passed through binary fission to subsequent generations or transferred to other bacteria by plasmids.// *4. A statement of the selective pressure;* //Antibiotics, which are chemicals used to treat bacterial diseases. // *5. Consequence of the selective pressure;* //Antibiotic-sensitive bacteria are killed. Antibiotic resistant bacteria survive.// *6. More reproduction by better adapted individuals;* //Antibiotic resistant bacteria reproduce and pass on resistance gene(s) to the next generation.// *7. The change in the population that results.* //A larger proportion of the bacteria population is antibiotic-resistant. It becomes difficult to treat some infections.//
*Explain how natural selection leads to changes in the beaks of Galapagos finches with changes in weather conditions.* Application: Changes in beaks of finches on Daphne Major.
*1. A named example of a species;* //Medium ground finches// *2. An outline of the different variations of a relevant trait;* //Variation in beak size and shape// *3. A statement that the variation is genetically inherited.* //Beak size and shape are genetically controlled traits.// *4. A statement of the selective pressure;* //A drought occurred in 1977. For 551 days the island received no rain. Plants withered and the tiny seeds the medium ground finches were accustomed to eating grew scarce. // *5. Consequence of the selective pressure;* //Medium ground finches with larger beaks could take advantage of alternate food sources because they could crack open larger seeds. The smaller-beaked birds couldn't do this, so they died of starvation.// *6. More reproduction by better adapted individuals;* //Surviving birds are able to reproduce.// *7. The change in the population that results.* //The Grant's measured the offspring and compared their beak size to that of the pre-drought generations. They found the offsprings' beaks to be 3 to 4% larger than their grandparents'.//
*List examples of abiotic selective pressures.* Understanding: Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
Abiotic selective pressure are non-living factors within the organism's environment (such as light, wind, temperature and pollutants) that influence the survival and reproduction of the affected organism.
*Outline why only inherited characteristics can be acted upon by natural selection.* Understanding: Individuals that reproduce pass on characteristics to their offspring.
Acquired traits are not within the genetic material of an individual and therefore they cannot be passed down to offspring during reproduction. In order to be acted upon natural selection, the trait must be able to be inherited by the subsequent generation.
*Define "adaptation."* Understanding: Adaptations are characteristics that make an individual suited to its environment and way of life.
Adaptation is the result of natural selection. An adaptation is a physical structure or behavior of an organism that is common in a population because it provides some improved survival or reproduction in the habitat..
*Outline a plant example to illustrate the potential for overproduction of offspring in a population.* Understanding: Species tend to produce more offspring than the environment can support.
All species overproduce, since they have more offspring than can realistically reach reproductive age, based on the resources available. For example, cottonwood trees release millions of seeds all at once, though only a fraction will germinate. Oak trees release thousands of acorn seeds each year but very few will grow to become full-sized trees.
*Outline an animal example to illustrate the potential for overproduction of offspring in a population.* Understanding: Species tend to produce more offspring than the environment can support.
All species overproduce, since they have more offspring than can realistically reach reproductive age, based on the resources available. For example, many species of fish lay millions of eggs at one time, though only a fraction of those survive. Sea turtles can lay anywhere from 70 to 190 eggs at a time, though only about one out of 100 typically survive. Oysters can also lay 60 to 80 million eggs at a time, but again, only a few survive to reproduce themselves.
*State an example of an animal adaptation.* Understanding: Adaptations are characteristics that make an individual suited to its environment and way of life.
Animal camouflage is adaptation to avoid detection by both predator and prey species.
*Outline the role of competition as a selective pressure.* Understanding: Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
Because populations produce more offspring than the environment can support., individuals often must compete for resources required for survival and reproduction. Habitats usually have a limited supply of at least one resource (such as food, water, territory, or mates) which can lead to competition for the resource.
*Define "variation."* Understanding: Natural selection can only occur if there is variation among members of the same species.
Biological variation is the genetic differences among individuals. The genetic difference can produce differences in observable phenotypes and be inherited between generations.
*List examples of biotic selective pressures.* Understanding: Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
Biotic selective pressures that affect an organism are other organisms within the same ecosystem that interact with the affected organism in a way that influences its survival or reproduction. The interaction can be between members of the same species (for example intraspecies competition for food) or between different species (for example predator and prey).
*Outline the characteristics of Daphne Major.* Application: Changes in beaks of finches on Daphne Major.
Daphne Major is a small island in the Galapagos archipelago. An intensive study of ground finches was conducted here by biologists Peter and Rosemary Grant over a period of 25+ years. Daphne Major serves as an ideal site for research because the finches have few predators or competitors. The major factor selective pressure influencing survival of the finch is the weather, and thus the availability of food.
*Use an example to outline the role of natural selection in the formation of new species.* Understanding: Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
Different species of Galápagos finches live on different islands in the Galápagos islands, located in the Pacific Ocean off South America. The finches are geographically isolated from one another by the ocean. Each island has unique habitat and food resources. Over millions of years, each species of finch developed a unique beak that is especially adapted to the kinds of food found on the island it inhabits. Some finches have large, blunt beaks that can crack the hard shells of nuts and seeds. Other finches have long, thin beaks that can probe into cactus flowers. Still other finches have medium-size beaks that can catch and grasp insects. Natural selection increased the frequency of traits in each finch populations that best enabled the bird to survive and reproduce given the selective pressure of food availability. Because they are isolated, the birds don’t breed with one another and have developed into unique species with unique characteristics.
*Define "evolution."* Understanding: Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
Evolution is the change in the heritable characteristics of a population over time. Natural selection is one mechanism of evolution. Though evolution, new species can arise from pre-existing species.
*Outline the role of natural selection in formation of new species.* Understanding: Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
For a variety of reasons (temporal/behavioural/geographic isolation), members of the same species will be split into separate populations resulting in a lack of interbreeding between the populations (reproductive isolation). Each population may be exposed to different selective pressures, so natural selection will act differently on the two populations, selecting for different variations in each population. Over generations, the original populations will have diverged to the point of not being able to create viable, fertile offspring if a mating was attempted. New species will have been formed.
*List sources of genetic variation.* Understanding: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
Genetic variation is a result of random mutation and sexual reproduction (meiosis and random fertilization).
*Define "heritable trait."* Understanding: Individuals that reproduce pass on characteristics to their offspring.
Heritable traits are those that are entirely based in genetics.
*Compare the use of the word theory in daily language and scientific language.* Nature of Science: Use theories to explain natural phenomena- the theory of evolution by natural selection can explain the development of antibiotic resistance in bacteria.
In daily use: a theory is a guess, there is doubt. In scientific use: a theory has been shown to be true through repeated observations and experiments. There is no current doubt*. As of yet, no evidence has been collected that does not support the idea.
*Describe how independent assortment during meiosis leads to genetic variation.* Understanding: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
Independent assortment is the process where the chromosomes move randomly to separate poles during meiosis. Independent assortment means that each gamete will have one of many different possible combinations of chromosomes.
*Explain the effect of the selective pressure on the more and less adapted individuals in a population.* Understanding: Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
Individuals more adapted to the selective pressure will will be able to survive and reproduce, passing on the trait to the subsequent generation. The frequency of the more adapted trait will increase in the population. Individuals less adapted to the selective pressure will not survive and/or reproduce. The frequency of the less adapted trait will decrease in the population.
*Compare the reproductive success of better and less well adapted individuals in a population.* Understanding: Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
Individuals more adapted to the selective pressure will will be able to survive and reproduce, passing on the trait to the subsequent generation. The frequency of the more adapted trait will increase in the population. Individuals less adapted to the selective pressure will not survive and/or reproduce. The frequency of the less adapted trait will decrease in the population.
*Explain the cause of the change in frequency of traits in a population through natural selection.* Understanding: Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
Individuals that are better adapted for a selective pressure will be able to survive and reproduce, passing on the beneficial variation to the next generation. The frequency of the best fit variation will increase in the population and the frequency of the least fit variation will decrease in the population.
*Contrast acquired characteristics with inheritable characteristics.* Understanding: Individuals that reproduce pass on characteristics to their offspring.
Inherited characteristics are those that are genetically passed down from parents to their offspring. Acquired characteristic are those gained by an organism after birth due to environmental influence.
*State an example of a plant adaptation.* Understanding: Adaptations are characteristics that make an individual suited to its environment and way of life.
Many plants found in arid environments have spines rather than leaves. The spines minimise the surface area of the cactus reducing water loss.
*Outline how meiosis leads to genetic variation.* Understanding: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
Meiosis creates variation in the gametes, the sperms and eggs. Because of recombination and independent assortment in meiosis, each gamete contains a different set of DNA.
*Explain why natural selection can only function if there is variation in a species.* Understanding: Natural selection can only occur if there is variation among members of the same species.
Natural selection acts on the genetic variation between individuals in a population. Some individuals will have advantageous variations that are better adapted to the environmental conditions. Individuals with the beneficial variation will have a greater chance of survival and reproduction than others. The favorable genetic variation will be inherited by offspring in the next generation.
*Define "natural selection."* Understanding: Natural selection can only occur if there is variation among members of the same species.
Natural selection is a process of evolution in which organisms better adapted to their environment tend to survive and produce more offspring.
*Outline the role of Charles Darwin in the study of Galapagos finches.* Application: Changes in beaks of finches on Daphne Major.
On his visit to the Galapagos Islands (1835), Charles Darwin discovered several species of finches that varied from island to island. His observations of the variation in forms and habitats in which the birds were found helped him to develop his theory of evolution by natural selection. He theorized that the 13 distinct species were all descendants of a common ancestor which had adapted over time to each islands unique habitats and resources.
*Explain the consequences of populations producing more offspring than the environment can support.* Understanding: Species tend to produce more offspring than the environment can support.
Overproduction of offspring can lead to competition (between offspring) for limited resources (such as water, space or food) in the habitat. Competition for resources can be a selective pressure. Some individuals will have a variation that is more suited for the environmental conditions and will be more likely to survive and reproduce. With overproduction, the population is more likely to produce a variant that can survive the environmental conditions.
*Outline the role of Peter and Rosemary Grant in the study of Galapagos finches.* Application: Changes in beaks of finches on Daphne Major.
Peter and Rosemary Grant study the evolution of the medium ground finch on the small island of Daphne Major. The Grants have been collecting data on the birds for 25+ years and have witnessed natural selection in action.
*Describe how recombination during meiosis leads to genetic variation.* Understanding: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
Recombination (crossing over) occurs during prophase I of meiosis. Homologous chromosomes pair along their lengths, gene by gene. Breaks occur along the chromosomes, and they rejoin, trading some of their alleles. This produces a unique combination of alleles on the chromosome.
*Outline how sexual reproduction leads to genetic variation.* Understanding: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
Sexual reproduction involves the combination of genetic material from two parents, resulting in new combinations of paternal and maternal chromosomes present in the zygote formed at fertilization. New combinations of genetic material is a source of genetic variation within the population.
*Define "species."* Understanding: Natural selection can only occur if there is variation among members of the same species.
The biological species concept defines a species as organisms that can (actually or potentially) interbreed with each other to produce fertile offspring and cannot breed with others. In other words, the organisms of the species are reproductively isolated.
*List reasons why evolution of antibiotic resistance has been rapid.* Application: Evolution of antibiotic resistance in bacteria.
The rapid emergence of bacterial strains resistant to multiple antibiotics is posing a growing public health risk. Evolution of antibiotic resistance has been rapid because bacteria reproduce very rapidly and have high mutation rate. Additionally, there has been extensive use of antibiotics since they were first discovered (for example, in hospitals, animal feed, inappropriate prescriptions and not finishing prescriptions).
*Outline how a selective pressure acts on the variation in a population.* Understanding: Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
There is genetic variation of the traits within a population. A selective pressure causes a struggle for survival and/or reproduction. Organisms with the variation that best adapt them to survive given the selective pressure in the environment will be able to survive and reproduce, passing on the trait to the subsequent generation.
