Evolution Unit: What is Evolution?

Evolution is,

– a change (in the genetic composition) of a population over time.

– on a larger scale, the entire biological history, from the earliest life forms to the enormous diversity of organisms that live on Earth today.

– an explanation for the diversity of life we see today.

– A body of evidence that supports the idea that all living things are related and share an ancient common ancestor.

What is The Theory of Evolution?

What is a Theory?

• A widely accepted explanation that is supported by a large body of evidence.

– Examples

– Big Bang Theory

– Newton's Laws of Motion

– Universal Law of Gravitation

– Kepler's Laws of Planetary Motion

– Law of Relativatey

Who Was Darwin?

• Born February 12, 1809 in England

• Consumed by his interest in nature.

• He was 22 years old when he set sail on a 5 year voyage around the world on the HMS Beagle (the voyage of the Beagle).

The Voyage of the Beagle

The Voyage of the Beagle

On his journey on the Beagle, Darwin

• collected thousands of specimens.• observed an incredible amount of diversity.• observed that organisms are well suited to the

environments they live in.• found fossils -the preserved remains of ancient

organisms.• Darwin observed that some fossils look similar

to modern organisms, while others look completely different!

Galapagos Islands

Galapagos Islands

Galapagos Islands

Darwin’s Conclusions

On November 24, 1859, nearly 23 years after the voyage of the Beagle, Charles Darwin published On the Origin of Species by Means of Natural Selection, an assemblage of facts about the natural world.

“Descent with Modification”

Darwin’s Conclusions

Darwin made 2 main points in The Origin of Species.

1. Organisms inhabiting Earth today descended from ancestral species.

a) species is defined as a group of organisms with the same anatomical characteristics that can breed and produce fertile offspring.

2. Natural selection is the mechanism for evolution.

• Natural selection is a process in which organisms with certain inherited characteristics are more likely to survive and reproduce than are individuals with other characteristics.

What is Natural Selection?

Natural selection leads to evolutionary adaptation.

– an adaptation is an inherited trait that leads to an increased fitness.

– fitness is the ability to survive and reproduce!!!

Survival of the Fittest!!

Natural Selection can be broken down into 4 processes

1. Genetic Variation – individuals in a population vary in many heritable traits.

2. Overproduction of Offspring – populations of most species have the potential to produce more offspring than the environment can support.

How Does Natural Selection Work?

3. Struggle for Existence - Organisms compete for resources.

4. Unequal reproductive success – individuals with better suited traits will leave more offspring.

• As a result of natural selection, a population, a group of individuals of the same species living in the same place at the same time, changes over generations.

Evolution through the Process of Natural Selection

Examples of Natural Selection

WARM UP QUESTIONS

1. Define evolution.

2. In your own words, explain the process of natural selection.

3. In order for natural selection to work, what 4 processes must be present in a population?

4. Can an individual organism evolve? Explain your answer.

5. In any given natural population, natural selection is constantly exerting a selective pressure on individuals in that population. What changes in the population due to natural selection?

Natural Selection on Single-Gene Traits

Leads to changes in allele frequency and thus to

EVOLUTION!

Natural Selection on Polygenic Traits

Natural selection can affect the distribution of phenotypes in three ways

1. Directional Selection

2. Stabilizing Selection

3. Disruptive Selection

• Directional Selection: When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end

Stabilizing Selection: When individuals at the center of the curve have higher fitness than individuals at the extremes

Disruptive Selection: When individuals at either end of the curve have higher fitness than those at the center.

WARM UP

Using your knowledge of the Rock Pocket Mouse, explain how natural selection works as a mechanism of evolution.

Include the following vocabulary words in your explanation: evolution, fitness, genetic mutation, population, natural selection.

EVIDENCE OF EVOLUTION

• Evolution leaves observable signs.

• We will examine three of the many lines of evidence in support of evolution:

1. the fossil record

2. comparative anatomy

1. embryology

3. molecular biology (DNA).

The Fossil Record

• Fossils are

– imprints or remains of organisms that lived in the past

– often found in sedimentary rocks.

• The fossil record

– is the ordered sequence of fossils as they appear in rock layers

– reveals the appearance of organisms in a historical sequence

• Paleontologists (scientists who study fossils) have discovered many transitional forms that link past and present.

• Transitional fossils include evidence that

– birds descended from one branch of dinosaurs

– whales descended from four-legged land mammals.

The Fossil Record

Figure 13.7-3

Transitional Fossils

Evolution of Tetrapods(four-limbed creatures)

Whale Evolution

Comparative Anatomy

• Comparative anatomy

– is the comparison of body structure between different species

– Shows us that evolution is a remodeling process in which ancestral structures become modified as they take on new functions.

Comparative Anatomy

• Homologous Body Structures

– structures that have different mature forms and functions, but develop from the same embryonic tissue.

Analogous Structures

Evolved to fulfill the same function in unrelated

species, not because they were inherited from a

common ancestor.

• Vestigial structures

– structures found in living animals that are greatly reduced in size and serve no obvious function

Comparative Anatomy

WARM UP

Look at the image below. Explain how evolutionary biologists can conclude that the organisms below share a common ancestor.

WARM UPExamine the picture below and explain what

evidence is present that supports the Theory of Evolution. .

Molecular Biology (DNA)

• The hereditary background of an organism is documented in

– its DNA

– The (amino acids) proteins encoded by the DNA.

• Evolutionary relationships among species can be determined by comparing

– genes

– proteins of different organisms.

Speciation

Speciation is the formation of new species.

The biological species concept defines a species as “A group of populations whose members have the potential to interbreed with one another in nature to produce fertile

offspring.”

So….what must happen for a species to evolve into two or more new species???

And…how does this happen?????

Speciation-Separation of Gene Pools

For a species to evolve into two or more new species the gene pools of

two populations must become separated.

As new species evolve, populations become reproductively isolated

from each other which means they can no longer interbreed and

produce fertile offspring.

Reproductive Isolation

As new species evolve, populations become reproductively isolated from one another.

Reproductive isolation - members of two populations that cannot interbreed and produce fertile offspring.

Geographic Isolation

Two or more populations separated by geographic barriers such as rivers, mountains or bodies of water.

Geographic isolation can then lead to changes in the genetic diversity of a population, which lead to physical and behavioral changes. If the physical and behavioral changes are big enough, they can lead to reproductive isolation and the formation of a new species = SPECIATION!!!!

Behavioral changes within a population can also lead to speciation!!!

Meet the Eurasian Blackcap

Sylvia atricapilla