Evidence for EvolutionReview what we know

so far: Mutations provide variability within species

Some traits give individuals within a species an advantage and those organisms live longer and/or reproduce more = natural selection

Over time, the population shifts so the all (or most) individuals have this trait = adaptation

Evolution of a whole new species (speciation) takes long periods of time

Main evidence for evolution

1. Fossils

2. Global geographic distribution of organisms

3. Comparitive Anatomy

4. Embryology

5. DNA and Proteins: Molecular Biology

Title

The Fossil Record

Fossils

The bulk of our understanding about ancient life

Bacterial cells to complete T-Rex skeletons

How are fossils formed? (Short video)

Fossil Questions#1 How are fossils formed?

Organism covered by sediments (mud, sand, silt, clay, ash)

Calcium replaced by minerals in the sediments over time.

Sometimes imprints can also be preserved (tracks, leaf impressions, etc.)

Fossil Questions#2 Why do most living things not leave fossils behind?

Organism was eaten

Didn’t die in correct environment to be preserved

Body has no ‘hard parts’ (shell, skeleton) Virtually absent from fossil record: amoebae, flatworms,

jellyfish, sea slugs, etc.)

Fossil Questions#3 How are fossils uncovered?

Erosion brings fossils back to surface

Humans dig to find fossils• Determine specific locations that are likely spots to hold fossils

Fossil Questions#4 How do scientists determine the age of fossils?

Technique 1: Relative dating

Compare fossils position in rock layer with placement of other known fossils in that layer, or layers just above and below

Youngest Layer

Oldest Layer

Fossil Questions#4 How do scientists determine the age of fossils?

Technique 2: Radioactive Dating:

- Calculate amount of remaining radioactive isotopes the rock contains = age of rock

http://www.teachersdomain.org/6-8/sci/life/div/radiodating/index.html

Transitional Fossils

Intermediate fossils

Provide a link between past forms of an organism

Transitional Fossils: fossilized remains of intermediate forms of life that shows a transition from

one species to another.

Whale evolution: evidence indicates whales descended from land animals rather than evolving

in the water. Evidence: transitional fossils homologous structures,

and anatomy for swimming fundamentally different from fish.

Geographic Distribution of Organisms

Beaver

NORTH AMERICA Muskrat

Capybara SOUTH AMERICA

Coypu

Beaver

Muskrat

Beaver and Muskrat

Coypu

Capybara

Coypu and Capybara

GEOGRAPHIC DISTRIBUTION ORGANISMS

Different organisms may show similar adaptations because they inhabit similar ecological environments.

Geographic Distribution Organisms from a

common ancestor will change in structure and function to adapt to a new, specific environment

Prime example: islands! the more isolated the

island, the more distinct its organisms

GEOGRAPHIC DISTRIBUTION OF ORGANSIMSOrganisms on isolated islands show distinct characteristics.

Example: almost all mammals in Australia are marsupials- but there are few marsupials found elsewhere.

Comparative Anatomy

A) Homologous Structures:

B) Vestigial Structures

Homologous Structures:

Forelimbs of humans, cats, whales, and bats all have similar parts/bones but different shapes.

Provides evidence they evolved from a common ancestor and became adapted to their particular environment.

Vestigial Structures

Structures or organs that were once important in an ancestor, but are no longer

essential in the modern day species.

Python has “hip bones”

Blind Cave Fish still has eyes, but they can no longer see and have no need for vision.

Human examples: tail bone, appendix, “goose bumps”

Comparative Embryology

Using the pieces in your envelope, arrange each species according to the age of the embryos.

Base your arrangement on the physical characteristics of each embryo (how they appear).

TitleComparative Embryology

Early stages of vertebrate (animals with backbones) are very similar an indication that vertebrates descended from a common ancestor.

Example: gills, tails, limb buds, and eye spots

Comparative Embryology

Molecular Biology

Evidence from DNA and proteins

Molecular Biology The more closely related two species are, the

more similar the DNA and protein profiles.

Darwin had no knowledge of genes and DNA. However, modern molecular biology evidence strongly supports his theory of evolution by natural selection.