Presentation on theme: "Darwin and His Theory of Evolution by Natural Selection"— Presentation transcript:
1Darwin and His Theory of Evolution by Natural Selection Evolution- changes in the characteristics of groups of organisms over timeCharles Darwin was the first to propose a feasible mechanism for evolution. It is called natural selection.*
2Evolution by Natural Selection is a theory. What is a scientific theory? Scientific Theory- an idea that is strongly supported by evidence. It is generally accepted and used to explain many observations.*Remember: The word “theory” in everyday language and in scientific language mean very different things.In everyday language, people use the word theory to mean a hypothesis or an educated guess.
3Natural Selection- differential success in survival and reproduction of individuals with different phenotypes (physical characteristics) resulting from interactions with their environments
4Conditions Needed for Natural Selection: VISTA VariationThere are a variety of forms of traits or phenotypes.*
5Conditions Needed for Natural Selection: VISTA 2. InheritanceOnly traits that are determined by an organism’s genes will be passed to the next generation.Some variation is caused by the environment, such as the loss of a limb or the building of muscle. These traits are not heritable, so they can’t be selected for in the next generation.*
6What causes genetic variation? 1) Mutations- changes in the DNA sequence can result in new traits 2) Sexual Reproduction- New combinations of traits can be created in gametes during meiosis.The wide variety of gametes created will join together to make diverse offspring.
7Remember natural selection can only act on the heritable variation that EXISTS in a population. *
8Conditions Needed for Natural Selection: VISTA 4. Survival and ReproductionIndividuals compete for limited resources, such as food, shelter, and mates.Individuals with traits best adapted for the environment are able to out compete other individuals for resources, allowing them to survive and reproduce more.*
9“Survival of the Fittest” Evolutionary fitness isn’t a measure of physical fitness but of reproductive fitness.Fitness- Relative ability to survive and produce offspring in an environment*
11Conditions Needed for Natural Selection: VISTA 4) TimeEvolution occurs over generations.
12Conditions Needed for Natural Selection: VISTA 5) Adaptations- an inherited characteristic that increases an organism’s chance of surviving and reproducingOver time, natural selections causes adaptations to become more common in a population.*
13Drug Resistant Bacteria Practice Variation existed in a population of bacteria. Some were resistant to antibiotics, while some weren't.The resistance was an inherited trait caused by a gene.When treated with antibiotic, the resistant bacteria survived and reproduced more than the nonresistant ones, which were killed by the antibiotic.Over time, the adaptation of drug resistance became more common in each generation of bacteria.
14Natural selection can lead to a variety of changes within a population Natural selection can lead to a variety of changes within a population. These changes can be roughly grouped into three categories:Stabilizing Selection: natural selection that favors an intermediate phenotypeExample: Birth weight, Human height
15Natural selection can lead to a variety of changes within a population Natural selection can lead to a variety of changes within a population. These changes can be roughly grouped into three categories:2. Directional Selection: natural selection that favors an extreme phenotype and causes a shift in the distribution curveExample: Birth weight, Human height
16Natural selection can lead to a variety of changes within a population Natural selection can lead to a variety of changes within a population. These changes can be roughly grouped into three categories:3. Disruptive Selection: natural selection that favors two or more extreme phenotypes are favored over any intermediate phenotype
17Since Darwin’s time, several other forces of selection have been explained: 1. Sexual Selection: adaptive changes in males and females that lead to an increased ability to secure a mate.
18Since Darwin’s time, several other forces of selection have been explained: 2. Artificial Selection: adaptive changes in organisms that occur because of human forces.