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Darwin and His Theory of Evolution by Natural Selection Evolution- changes in the characteristics of groups of organisms over time Charles Darwin was the.

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Presentation on theme: "Darwin and His Theory of Evolution by Natural Selection Evolution- changes in the characteristics of groups of organisms over time Charles Darwin was the."— Presentation transcript:

1 Darwin and His Theory of Evolution by Natural Selection Evolution- changes in the characteristics of groups of organisms over time Charles Darwin was the first to propose a feasible mechanism for evolution. It is called natural selection.

2 Evolution 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.

3 Natural Selection- differential success in survival and reproduction of individuals with different phenotypes (physical characteristics) resulting from interactions with their environments

4 Conditions Needed for Natural Selection: VISTA 1.Variation There are a variety of forms of traits or phenotypes.

5 Conditions Needed for Natural Selection: VISTA 2. Inheritance ● Only 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.

6 What 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.

7 Remember natural selection can only act on the heritable variation that EXISTS in a population.

8 Conditions Needed for Natural Selection: VISTA 4. Survival and Reproduction ● Individuals 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

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11 Conditions Needed for Natural Selection: VISTA 4) Time ● Evolution occurs over generations.

12 Conditions Needed for Natural Selection: VISTA 5) Adaptations- an inherited characteristic that increases an organism’s chance of surviving and reproducing Over time, natural selections causes adaptations to become more common in a population.

13 Drug 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.

14 Natural selection can lead to a variety of changes within a population. These changes can be roughly grouped into three categories: 1.Stabilizing Selection: natural selection that favors an intermediate phenotype Example: Birth weight, Human height

15 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 curve Example: Birth weight, Human height

16 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

17 Since 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.

18 Since Darwin’s time, several other forces of selection have been explained: 2. Artificial Selection: adaptive changes in organisms that occur because of human forces.


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