Artificial and Natural Selection Angela Gula & Audrelyn Watkins

Artificial Selection Human intervention in animal or plant reproduction to ensure that certain desirable traits are represented in successive generations. Human intervention in animal or plant reproduction to ensure that certain desirable traits are represented in successive generations. Examples? Examples?

The Theory of Natural Selection Originally presented in The Origin of Species in Originally presented in The Origin of Species in The theory of natural selection was not accepted by the scientific community until 60 years later. The theory of natural selection was not accepted by the scientific community until 60 years later. Today, natural selection is considered one of the most important causes of evolution. Today, natural selection is considered one of the most important causes of evolution.

What leads to natural selection? 1. Variation of individuals in the population 2. Inheritance of variation 3. Overproduction 4. Non-random Survival and Reproduction

Variation Take a look around—individuals within populations vary. Take a look around—individuals within populations vary. Similar variations occur in plant populations Similar variations occur in plant populations Some plants bloom sooner than other Some plants bloom sooner than other The amount of caffeine produced in the seeds of a coffee bean varies The amount of caffeine produced in the seeds of a coffee bean varies Each different type of individual in a population is termed a variant. Each different type of individual in a population is termed a variant.

Inheritance of Variation When The Origin of Species was written, Darwin did not understand the process of inheritance. When The Origin of Species was written, Darwin did not understand the process of inheritance. Darwin hypothesized that offspring tend to have the same characteristics as their parents. Darwin hypothesized that offspring tend to have the same characteristics as their parents. Until Gregor Mendel’s work on inheritance was accepted, there was controversy over this component of natural selection. Until Gregor Mendel’s work on inheritance was accepted, there was controversy over this component of natural selection. Now understood, natural selection operates on genetic variation that can be passed from one generation to the next. Now understood, natural selection operates on genetic variation that can be passed from one generation to the next.

Overproduction The capacity for reproduction outstrips the resources of the environment. The capacity for reproduction outstrips the resources of the environment. Therefore, many individuals do not survive to reproductive maturity. Therefore, many individuals do not survive to reproductive maturity.

Non-random Survival and Reproduction The subset of individuals that survive long enough to reproduce is not arbitrary. The subset of individuals that survive long enough to reproduce is not arbitrary. Some variants in a population have a better likelihood of survival and reproduction. Some variants in a population have a better likelihood of survival and reproduction. This is known as fitness. This is known as fitness. Traits that increase an individuals fitness in that particular environment are adaptations. Traits that increase an individuals fitness in that particular environment are adaptations.

So….What does it mean? If the four underlying observations Darwin made are true, what can we infer? If the four underlying observations Darwin made are true, what can we infer?

Types of Natural Selection Directional Selection—when an extreme phenotype is favored and the distribution shifts in that direction. (peppered moth, bacteria resistance, pesticide resistance) Directional Selection—when an extreme phenotype is favored and the distribution shifts in that direction. (peppered moth, bacteria resistance, pesticide resistance) Stabilizing Selection—occurs when an intermediate phenotype is favored. (birth weight in humans) Stabilizing Selection—occurs when an intermediate phenotype is favored. (birth weight in humans) Diversifying Selection—two or more phenotypes are favored over any intermediate phenotype. (Sickle-cell anemia) Diversifying Selection—two or more phenotypes are favored over any intermediate phenotype. (Sickle-cell anemia)

Graphic Representation of Selection Types A. ________________B. ________________C. ________________

Addressing Misconceptions

Three dreaded words…Try Individuals or populations can try to evolve, but it won’t work! Individuals or populations can try to evolve, but it won’t work!

Three dreaded words…Need Natural selection cannot provide what an organism needs. Natural selection cannot provide what an organism needs.

Three dreaded words…Want Individuals or populations cannot control what they want. Individuals or populations cannot control what they want.

The lifetime problem… Natural selection acts on the inherited traits. Natural selection acts on the inherited traits. Individuals cannot change within their lifetime in order to survive environmental changes. Individuals cannot change within their lifetime in order to survive environmental changes.

Good, Better, Best… Natural selection does cause populations to become better fit to the environment, BUT… Natural selection does cause populations to become better fit to the environment, BUT… The result of that process is not necessarily a “better” organism. The result of that process is not necessarily a “better” organism.

The Predetermined Goal Natural selection does not occur with a goal in mind; instead, it is situational. Natural selection does not occur with a goal in mind; instead, it is situational. Consider: Consider: Environmental conditions—drought, temperature change, food availability, etc. Environmental conditions—drought, temperature change, food availability, etc.