Variation and Natural Selection

Evolution Basics Changes that occur in living organisms over many generations (time). – Evolution only happens to populations of living organisms. – It can only happen with characteristics that are inherited (genes, DNA)

Adaptation All living are adapted to their habitat Adaptations – are characteristics plants and animal have to help them be suited to their environment

Adaptation Adaptations are the characteristics/ features that helps a plant and animals do the following: Obtain food Avoid being eaten reproduction conserve water Survive

Animals and Plants are fit into their habitat through their adaptations, just like a puzzle piece fits into a puzzle through its shape

Adaptations to Habitat How is this shark adapted to its habitat?

Natural Variation Natural variation - definition differences among individuals of a species that is found in all organisms.

Variation and Gene Pools There are Two Main Sources of Variation: 1.Genetic Mutation 2.Genetic Shuffling from sexual reproduction

Sources of Genetic Variation – Mutations A mutation is any change in a sequence of DNA. Mutations occur because of mistakes in DNA replication or as a result of radiation or chemicals in the environment.

Natural Variation

Variation is a result of genes (DNA) that we inherit from our parents.

Inheritance Living Organisms pass their characteristics on to their offspring (babies) Inheritance is getting characteristics/ features from your parents

Inheritance Living organisms that sexually reproduce (example: most mammals) inherit half their traits from the mothers and half from their fathers. More on this later in the genetics unit.

Variation Leads to Difference in Reproductive Success Some individuals in a population have characteristics/ adaptation that help them survive better than others. We call the difference in reproduction success.

Why do you think it is an advantage to be a brown beetle in this situation? Variation Leads to Difference in Reproductive Success

Overproduction Overproduction: Organism produce a far greater number of offspring than ever survive to adulthood. –The number of individuals within a species remains relatively constant/ same –Therefore, there must be a high mortality/ death rate –Because of overproduction, there is a struggle for existence. Some individual will die and some will survive. Because of variation within a population, some individual are better adapted to their environment. These individuals tend to survive and reproduce. This is Natural selection. The better adapted individuals pass on their characteristics to their offspring via genes.

Differences in Reproductive Success

Difference in Reproductive Success: Joe is Blue & Jim is green. If Joe and Jim were the last people of the planet describe what would happen to the blue characteristic.

Variation Leads to Difference in Reproductive Success: Explain what you think would happen to the short characteristic over time and explain why?

Evolution Define An Introduction to Evolution Biological evolution, is descent with modification 1. small-scale evolution (changes in gene frequency in a population from one generation to the next) Example: A population of bacteria will evolve a resistance to antibiotic medicine.

Evolution Define An Introduction to Evolution Biological evolution, is descent with modification 2. large-scale evolution (the descent of different species from a common ancestor over many generations) Example: The species Homo sapiens evolved from Home erectus

Evolution Define The explanation Biological evolution is not simply a matter of change over time. trees lose their leaves, mountain ranges rise and erode, but they aren't examples of biological evolution because they don't involve descent through genetic inheritance

Evolution – by Natural Selection Evolution is defined as descent with modification from a common ancestor, but exactly what has been modified? Evolution only occurs when there is a change in gene frequency within a population over time.

Evolution – by Natural Selection These genetic differences are heritable and can be passed on to the next generation — which is what really matters in evolution: long term change.

Natural Selection – Define Based on the idea that because of natural variation within a population some individuals will have more success reproducing than other Over generations, this results in increased ‘fitness’ of a population.

Natural Selection – Is “survival of the fittest” – Meaning individuals that successfully reproduce before they die are “the fittest”

Natural Selection – Define Natural selection is a mindless process Natural selection is a process that acts on the variation of a population. Based on the idea that because of natural variation within a population some individuals will have more success reproducing than others

Formula for Natural Selection Variation + Differences in Reproductive Success + Heredity

Real Life Example of Natural Selection In England the pepper moth is both white and black moth. Before the industrial revolution there were more white moths than black moths. Then after the industrial revolution the black allele frequency was higher

The Case of the Peppered Moth (Biston betularia) Before 1848: Trees where they rested were covered with off-white lichen. Moths were white, therefore camouflaged from the predation of birds-best adapted Occasionally a black moth would appear and thus would have a very high chance of being eaten by a bid before reproducing.

The Case of the Peppered Moth (Biston betularia) After 1848: Coal-based industry covered trees with soot. White moths were easily spotted and eaten. The black moth now had the advantage and became predominant- best adapted. (95%)

The Case of the Peppered Moth (Biston betularia) Now: Reduced use of coal has made trees green (covered in algae). Both forms of moth are common

NEW SPECIES A new species may evolve, if a population is divided into geographically isolated subpopulations One or both populations may undergo evolutionary change during the period of separation

LE 24-5 Allopatric speciation Sympatric speciation

LE 24-6 A. harrisi A. leucurus