The Process of Evolution: Understanding Natural Selection and Genetic Diversity
This guide explores the fundamental principles of evolution, highlighting how natural selection drives both the diversity and unity of life. It discusses key observations made by evolutionary biologist Ernst Mayr, such as population stability despite potential exponential growth and the struggle for existence due to limited resources. It also explains the significance of genetic variation and mutation in natural selection, as well as the Hardy-Weinberg principle that outlines genetic equilibrium. Understanding these concepts is crucial for grasping the complexities of evolutionary processes.
The Process of Evolution: Understanding Natural Selection and Genetic Diversity
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Presentation Transcript
BIG IDEA 1 The process of evolution drives the diversity and unity of life.
Enduring understanding 1.A Change in the genetic makeup of a population over time is evolution.
Essential knowledge 1.A.1 Natural selection is a major mechanism of evolution.
Evolutionary Biologist Ernst Mayr • OBSERVATION # 1 • For any species, population sizes would increase exponentially if all individuals that are born reproduced successfully (pg 445, fig 22.8) • OBSERVATION # 2 • Nonetheless, populations tend to remain stable in size, except for seasonal fluctuations
OBSERVATION # 3 • Resources are limited • INFERENCE # 1 • Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving each generation.
OBSERVATION # 4 • Members of a population vary extensively in their characteristics; no two individuals are exactly alike (pg 445, fig 22.9) • INFERENCE # 2 • Survival depends in part on inherited traits. Individuals whose inherited traits give them a high probability of surviving and reproducing in a given environment • These individuals have higher fitness and are likely to leave more offspring than less fit individuals
INFERENCE # 3 • This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over generations. • The environment determines which variations are more favorable. More favorable traits are thereby passed on to the population as a whole.
Darwin’s Theory of Natural Selection • Individuals with favorable phenotypes • More likely to survive and produce more offspring • Passing traits to subsequent generations • Evolutionary fitness is measured by reproductive success
Genetic variation and mutation play roles in natural selection • A diverse gene pool is important for the survival of a species in a changing environment • Form and Function
Environments • Evolutionary rate and direction depends on the stability of the environment • Article for opinion
Adaptation • Genetic variation that is favored by selection • Manifested as a trait that provides an advantage to an organism in a particular environment
In addition to natural selection • Chance • Random events • Influence the evolutionary process, especially for small populations. • What are some random events that can influence the evolutionary process?
Darwin’s ideas • Mendel’s ideas • Modern Synthesis –ideas from others – still expanding and evolving
Gene pools and Allele frequencies • Population – • A localized group of individuals that are capable of interbreeding and producing fertile offspring • May or may not be isolated
Gene pool • Aggregate of genes in a population at any one time • All alleles and all gene loci in all individuals of the population • Fixed allele – one allele exists at a particular loci (homozygous_ • 2 or more alleles for a particular locus in a population may be homozygous or heterozygous
Each allele has a frequency (proportion) in the population • Population of flowers with 2 alleles for color
Conditions for Hardy-Weinberg Equilibrium • For a population or an allele • (1) a large population size • (2) absence of migration • (3) no net mutations • (4) random mating • (5) absence of selection • These conditions are seldom met.
The Hardy-Weinberg principle describes genetic equilibrium • A. Godfrey Hardy, an English mathematician, and Wilhelm Weinberg, a German physician, derived this model in 1908 • B. The Hardy-Weinberg principle describes the situation of no evolution (e.g., genetic equilibrium) • C. p is the frequency of the dominant allele, and q is the frequency of the recessive allele; frequencies range from 0 to 1
D. p + q = 1; therefore (p + q )2= 1 • E. p 2+ 2 pq + q 2= 1; p 2is the frequency of the dominant homozygote, 2 pq is the frequency of the heterozygote, and q 2is the frequency of the recessive homozygote • F. Any sexually reproducing population in which the allele frequencies conform to this equation is at genetic equilibrium
51.4 cont. • Laboratory Studies of Drosophila Foraging Behavior • Read section in text • Analyze fig 51.20 on pg 1120 • Migratory Patterns in Blackcaps • Read section in text • Create an approximate view of what the graph would look like if you knew the quantitative data
Natural selection favors behaviors that increase survival and reproductive success • Foraging Behavior • includes not only eating, but also mechanisms used to recognize, search for, and capture food items • Compromise between obtaining food and the energy spent or hazards faced when obtaining food (avoiding predators)
Foraging • Energy Costs and Benefits • Cost-benefit analysis of feeding behavior • Pacific Northwest crows and welk shells • fig 51.22, pg 1122 • Bluegill sunfish and Daphnia • Fig 51.23, pg 1123 • Risk of Predation • Influence of Predation risk on Foraging behavior • Idaho mule deer • Fig 51.24, pg 1123
Optimal Foraging Theory • There is a compromise between the benefits of nutrition and the costs of obtaining food • Costs include energy expenditures and risk of being eaten by a predator • Natural selection should favor foraging behavior that minimizes the costs of foraging and maximizes the benefits
http://www.thewildclassroom.com/biodiversity/birds/aviantopics/optimalforagingtheory.htmlhttp://www.thewildclassroom.com/biodiversity/birds/aviantopics/optimalforagingtheory.html
Mating Behavior and Mate Choice • Seeking or attracting mates • Choosing among potential mates • Competing for mates • http://www.bbc.co.uk/nature/adaptations/Courtship_display#p003x6x1
Mating Systems and Parental Care • Differs from species to species • Promiscuous • Remaining together • Monogamous • Polygamous – usually one male with many females • Polygyny vs polyandry • Figs 51.25, pg 1124 • http://evolution.berkeley.edu/evolibrary/search/lessonsummary.php?audience_level%5B3%5D=9-12&topic_id=&keywords=&type_id=&sort_by=audience_rank&Submit=Search&thisaudience=9-12&resource_id=100
Applying Game Theory • Pg 1127 • Read and summarize information • Side-blotched lizard • “Paper-Rock-Scissors”
The concept of inclusive fitness can account for most altruistic social behavior
Altruism • Selflessness • Squirrels • Bees • Naked mole rats • Pg 1128
Inclusive Fitness • In addition to altruistic behavior, close relatives or “kin” further their genes by inclusive fitness • Helping close relatives to produce offspring • Hamilton’s Rule – mathematical formula for • Applying a quantitative measure for predicting when natural selection favors altruism
Social Learning • Learning through observing others
Social learning • Mate choice copying • Alarm calls • Different sounds for different dangers • Fig 51.37, pg 1132
Evolution and Human Culture • Sociobiology • Certain behaviors occur because they are expressions of genes that have been furthered by natural selection • Edward O. Wilson – behavior is controlled more by our genes than learned behavior
Essential knowledge 1.A.1 To know: Benchmarks a – h See Unit Organization Handout