DAY 1Topic 8 – Natural Selection

Natural Selection: A Mechanism of Change

THEORY OF EVOLUTION

WHAT ARE WE LEARNING TODAY?Benchmarks

SC.912.L.15.13 – Describe the conditions required for natural selection, including: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success.

Learning Objectives

I will analyze the reasoning in Darwin’s theory of evolution by natural selection.

I will relate the concepts of adaptation and differential reproductive success to the theory of natural selection.

“It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is most adaptable to change.”

Charles DarwinAfter reading the quote above and learning about Darwin’s theory of natural selection, what do you think he meant by it?

WHAT IS THE ESSENTIAL QUESTION?

WHO IS CHARLES DARWIN?

Greatest contributor to our understanding of evolution.

Evolution is:

the change of allele frequencies in a population over time.

process by which modern organisms have descended from ancient organisms.

DARWIN’S TRAVELS TO THE GALAPAGOS ISLANDS

• 1831: voyage on the HMS Beagle

• 5 year voyage around the world to Australia, S. America, Galapagos Islands, and Africa

• Made several observations on the different species he found

• He noticed 3 patterns of biodiversity1. Species vary Globally

2. Species vary locally

3. Species Vary over time

OTHER SCIENTISTS THINKING ABOUT EVOLUTION

Jean-Baptiste Lamarck

• Suggested organisms change during their lifetime

• Suggested individuals pass on acquired traits to offspring

• Recognized a link to an organism’s environment and its body structures

Where did Lamarck go wrong in is theory?

• We now know individuals do not evolve in their own life time

• We also know that acquired traits cannot be passed on to offspring.

ACQUIRED TRAIT VS. INHERITED TRAIT

Acquired traits

• are obtained by the individual in their life time

If you were to get a tattoo, that would be an acquired trait

Inherited Traits

• Are passed on from the genes of parents to offspring

Will affect the traits of future generations of offspring

OTHER SCIENTISTS THINKING ABOUT EVOLUTION

James Hutton and Charles Lyell

• Concluded that earth was extremely old

• Processes that changed earth in the past are the same ones changing the earth now

• Principles of Geology

Thomas Malthus

• English Economist

• Reasoned that is populations grew unchecked, there would not be enough space, food, resources for everyone

An adaptation is any inherited characteristic that increases an organism’s chance of survival.

WHAT IS AN ADAPTATION?Stripes to help them hide

Long, retractable claws to grab prey

Long, sturdy tail to help with balance

Razor sharp teeth with muscular jaws

to kill prey

Eyes with light reflective retina to

see in the dark Loose abdomen skin to reduce injury when

kicked

WHAT ADAPTATIONS IMPROVE THIS ORGANISM’S ABILITY TO SURVIVE?

DARWIN’S 4 TENETS OF NATURAL SELECTION

• Natural Selection: process by which organisms with variations most suited to their environments survive and leave more offspring

• Natural selection is the driving force, the mechanism, of evolution

• Darwin proposed that in order for evolution to occur by natural selection, 4 conditions must be met (4 tenets)

1. Overproduction of Offspring

2. Inherited variation within the population

3. Struggle for existence

4. Differential reproduction

What is taking place in this picture? o Grasshoppers can

lay over 200 eggs at a time.

o Only a small fraction of these offspring survive to reproduce.

Organisms produce more offspring than can survive.

WHAT IS OVERPRODUCTION OF OFFSPRING?

What are some of the differences you see in the population of grasshoppers?

What do you think causes these variations?

Inherited variations are the heritable differences that exists in every population.

Mutations Recombination

WHAT IS INHERITED VARIATION?

Where this variation comes from

How would you describe the environmentin which the grasshopper lives?

Which grasshopper is better adapted to survive in this environment?

What would happen to this population if a drought causedthe grass to turn brown?

WHAT IS THE STRUGGLE TO SURVIVE?

Certain heritable variations, called adaptations, increase an individual’s chance of surviving and reproducing.o Heritable variation

includes brown and green body color.

o Green coloration is an adaptation that allows grasshoppers to blend into their environment to be less visible to their predators.

WHAT IS THE STRUGGLE TO SURVIVE?

What do you think it means that “green grasshoppers have a greater differential reproductive success than brown grasshoppers?”

Green grasshoppers survive and reproduce more often than do brown grasshoppers in this environment.

WHAT IS DIFFERENTIAL REPRODUCTIVE SUCCESS?

Organisms whose traits are best suited to the environment experience better reproductive success and become more common1) more grasshoppers are

born than can survive,2) individuals vary in color, a

heritable trait, and 3) green individuals have a

higher differential reproductive success in the current environment

DIFFERENTIAL REPRODUCTIVE SUCCESS

SUMMARY OF DARWIN’S THEORY (NATURAL SELECTION) Individuals organisms within a species are different. Some of these differences are passed down from parent to

offspring, or heritable. Individuals produce more offspring that can survive due to

limited resources creating a struggle for existence. Individuals best suited, or adapted, to their environment

survive to experience higher differential reproductive success.