Evidences of EvolutionEvidences of Evolution

EvolutionEvolution

Genetic change in a Genetic change in a population over timepopulation over timeGenetic change in a Genetic change in a population over timepopulation over time

Charles DarwinOn his journey around the world, Darwin found evidence of gradual change (evolution).

Darwin cited evidences he found in fossil records, homologous structures, and geographic distribution.

Evidences of Evolution

Today most evidences for evolution are grouped into five main categories:

Fossil Record

Biochemical

Comparative Anatomy

Biogeography

Observable Events

Fossil Record

• Paleontology- the study of fossils

• Fossils – remains or traces of organisms that lived long ago

• Remains: ex. bones, teeth, or shells

• Traces: ex. burrows, footprints, or imprints

Most fossils are found in layeredsedimentary rock

Oldest fossils areon the lowest layer

Fossil Record

• The fossil record is incomplete– Some environments are less likely to cause

fossil formation– Bodies of some organisms decay faster than

others

• The fossils that have formed present strong evidence that evolution has taken place– Relative and radiometric dating

Fossil Record

Comparing fossils from different layersshows:

Life on Earth has changed

Increased number of life forms

Fossil Record

Biochemical Evidence• Universal Genetic Code

– Triplets of DNA nitrogen-base sequences that code for specific amino acids

The similarity of triplet DNA codes making-up amino acids shows:a probable common ancestor for all life on Earth

Biochemical Evidence• Amino Acid Sequencing

The amino acidsequence in aparticular protein iscompared betweenorganisms. Species that have fewdifferences are thought tohave shared a commonancestor more recently. Number of differences

from human hemoglobin

45

167

8

27

125

Species Difference

Gorilla 1

Rhesus Monkey 8

Mouse 27

Chicken 45

Frog 67

Lamprey 125

Amino Acid Difference in Hemoglobin

Compared with Human

Human hemoglobin has 146 amino acids

Amino Acid Sequencing is probably

the STRONGEST evidence for relationships

among organisms.

Biochemical Evidence

What organism belongs at

each branch?

• Cladogram: diagram that shows the evolutionary relationship among a group of organisms.

Species Difference

Gorilla 1

Monkey 8

Mouse 27

Chicken 45

Frog 67

Lamprey 125

Amino Acid Difference in Hemoglobin

Compared with Human

Number of Amino Acid Differences150

10050

040 2030 10

G

FE

DCBA

Common ancestor

Where would the common ancestor be?

Biochemical Evidence

Comparative Anatomy• Homologous structures- structures that share

a common ancestry; similar structures with different functions

TurtleAlligator

Bird

Mammal

Ancient lobe-finned fish Homologous structures show:an organism’s evolutionary pastand common ancestry

Comparative Anatomy

• Vestigial structures- structures that are present but diminished in size or function

Vestigial structures show:• an organism’s evolutionary

past• a common ancestor with

species that have similar structures that are still functioning

Examples: Human tailbone, snake pelvic bones and limb bones, and some cave-dwelling salamanders have eyes even though members of the species are completely blind.

Comparative Anatomy

• Embryology- embryos of different species may appear similar in early stages of development

Example: vertebrate development– Tail buds and

pharyngeal pouches

Comparative Anatomy

• Comparison of similarities in embryos can show:

relationships to a common ancestor

Biogeography• Geographic Distribution of Organisms

• Organisms living widely apart (even different continents) may be similar because they share a common ancestor

Beaver

Muskrat

Beaver andMuskrat

Coypu

Capybara

Coypu andCapybara

Observable Events• Observable events show that evolution is an ongoing

process• Some changes in species have been observed and

studied:

Peter & Rosemary Grant’s Study of Beak Size Shift in Darwin’s

Finches

H. Kettlewell’s Study of Peppered Moth Color

Shifts