Evolution. Darwin proposed that species had evolved by a process he called, natural selection. Darwin described natural selection as the way in which.

Lesson 3 – Natural Selection

Evolution

The Theory of Evolution by Natural Selection

Darwin proposed that species had evolved by a process he called, natural selection. Darwin described natural selection as the way in which the environment, or nature, favours the reproductive success of certain individuals over others. Evolution was simply the result of natural selection occurring over many generations.

Natural Selection: the way in which nature favours the reproductive success of some individuals within a population over others.

Observations & Inference 1

1. In each generation populations produce more offspring than there are adults.

2. Populations do not continue to grow in size

3. Food and many other resources are limited

Individuals within a population compete for resources

Observation & Inference 2

1. Individuals within all populations vary.

2. Many variations are heritable.

Some individuals will inherit characteristics that give them a better chance of surviving and reproducing.

Inference & Theory

Individuals within a population compete for resources

Some individuals will inherit characteristics that give them a better chance of surviving and reproducing.

Theory of Natural Selection

The Theory of Natural Selection

The Theory of Natural Selection

Over time the population changes as advantageous heritable characteristics become more common generation after generation.

Survival of the Fittest

What does survival of the Fittest mean?

Survival of the Fittest

Survival of the fittest

Survival of the fittest is often to describe the process of natural selection.

The term “fitness” refers to an individual’s ability to pass its genes to the next generation and not how physically fit it is. The key to natural selection lies in its ability to favour reproductive success.

Adaptation

Adaptation: a characteristic or feature of a species that makes it well suited for survival or reproductive success in its environment.

Darwin’s theory of evolution by means of natural selection is able to explain how an adaptation can arise.

Theories?

Think of any time you’ve ever use the word theory

Scientific Theory

Examples of Scientific Theory- All living organisms are made of cells (cell theory)- Earth Orbits the Sun (Heliocentric Theory)- Surface of Earth is made of plates (Theory of Plate Tectonics).

Scientific Theory

A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on knowledge that has been repeatedly confirmed through observation and experimentation.

It must 1. Explain a phenomenon 2. Be used to correctly make predictions 3. Must be testable and falsifiable

Explanatory Power

Darwin’s theory of evolution by means of natural selection is able to explain how an adaptation can arise.

Predictive Power

Darwin’s theory of evolution by means of natural selection can be used to make predictions about the future evolution of species.

 Ex: the theory of evolution predicts that species will evolve in response to climate change because different environmental conditions will favour different traits. Over time, birds species may change the timing of their migration, and plants may adapt to warmer or drier conditions.

Testable

Darwin’s theory of evolution by means of natural selection is a testable scientific theory.

In order to be scientific, a theory must be falsifiable. This means that a scientific theory is testable – there must at least be the possibility of it being wrong. Darwin knew that if evolution had not occurred, if species had not changed over time, it should be easy to find falsifying evidence.