• Identify how natural selection can create new species.

Today’s Objective:

Can be found in the book: Pg. 404 - 413

• Stabilizing selection is a natural selection that favors average individuals in a population.

• There are three different types of natural selection: stabilizing, directional, and disruptive.

NATURAL SELECTION

Middle sized Siberian Huskies are selected for

Evolution will not occur

Stabilizing Stabilizing SelectionSelection

• Example: human birth weight. Babies of low weight lose heat more quickly and get ill from infectious disease more easily, whereas babies of large body weight are more difficult to deliver through the pelvis

• Directional selection occurs when natural selection favors one of the extreme variations of a trait.

NATURAL SELECTION

• This type of selection can lead to rapid evolution of a population.

Examples: Directional Selection

• Peppered Moths: as the environment changes, so do the traits that are fit for the new environment.

• In the case of the moths, the forests changed from light to dark and selection moved in the direction of darker moths

• Antibiotic Resistance

• Pesticide Resistance

• In disruptive selection, individuals with either extreme of a trait’s variation are selected for.

NATURAL SELECTION

• This results in eventually having no intermediate form of a trait, and leading to two separate species.

What type of selection?• Tortoise neck length

– Short grasses, for short-necked tortoises– Tall grasses, for long-necked tortoises– No grasses for average-necked tortoises, so

over time, they are selected against

Disruptive Selection

What type of selection?• Lizard body size:

– Large lizards are easily seen by predators, but smaller lizards cannot run as fast to escape the predators

– Mid sized lizards are most fit in the environment, so they survive and reproduce more often, changing the allele frequencies in the population

What type of selection?• Anteater tongue length:

– Anteaters with long tongues are most fit because of the depth of the nests of the termites they eat.

So…what is a species?

– A population whose members can interbreed & produce viable, fertile offspring

– Being reproductively compatible is a key component

Western Meadowlark

Sturnella magna

Eastern Meadowlark

Sturnella neglecta

Distinct species:songs & behaviors are different enough to prevent interbreeding

Distinct species:songs & behaviors are different enough to prevent interbreeding

• The evolution of new species, a process called

speciation.

• This occurs when members of similar populations change so

much from each other that they no longer interbreed to produce

fertile offspring.

SPECIATION

• In nature, physical barriers can break large populations into smaller ones.

• Geographic isolation occurs whenever a physical barrier divides a population and over time

they change and become two different species.

SPECIATION

SPECIATION

SPECIATION

SPECIATION

• Most of the evidence for evolution is indirect, coming from sources such as fossils and studies of anatomy, embryology, and biochemistry.

EVIDENCE

Scientists believe that the fact that ALL LIVING THINGS have A,T,C, and G in their DNA and all use

the same coding for proteins means we are all related in some way.

BIOCHEMISTRY

Anatomical evidenceOne form of evidence in the unity of life…..

Science sees structural similarities as evidence that organisms evolved from a common ancestor.

Structural features with a common evolutionary origin are called homologous structures.

Homologous parts are similar in structure, but

may be very different in

specific function.Whale forelimb

Crocodileforelimb

Birdwing

The body parts of organisms that do not have a common evolutionary origin but are similar in function are called

analogous structures.

Analogous parts are very different in

structure, but perform similar

functions.

• Vestigial structure—a body structure in a present-day organism that no longer serves its original purpose, but was probably useful to an ancestor.

ANATOMY

Video clip

• An embryo is the earliest stage of growth and development of both plants and animals.

• Embryos of different species have similar pharyngeal pouches and tails.

EMBRYOLOGY

• Scientists believe the shared features in the young embryos of different species suggest evolution from a distant, common ancestor.

Fish Reptile Bird Mammal

Pharyngealpouches

Pharyngealpouches

Tail Tail

EMBRYOLOGY

Chicken Turtle

Rat