Lecture #3 Evidence of Evolution

Unit 6: Evolution

Evidence of Evolution

Based on a large amount of evidence, most

scientists agree on the following three major

points

–Earth is about 4.5 billion years old.

–Organisms have inhabited the Earth for most of its history

–All organisms living today evolved from earlier, simpler life forms.

There are 4 major areas of evidence that exist for evolution

1. Fossil Evidence• Fossils provide an actual record of Earth’s past life

forms. Change over time (evolution) can be seen in the fossil record.

Fossils - Remains or traces of a once-living organism • Fossil specimens found in older rocks are different

from those found in newer rocks.

Evidence for Evolution – The Fossil Record

• Darwin predicted that intermediate forms between the great groups of organisms would eventually be found.

• Since Darwin’s time, many of these links have been found.

Ex: Archaeopteryxlinks birds andreptiles

• The fossil record is far from complete. Finding fossils is no easy task. Not all organisms lived in areas where fossils form.

Paleontologists - scientists who study fossils. • They can determine the age of fossils using

different techniques.

Radiometic dating is used to get an actual age (absolute age)

You can also compare a fossils position in the rock strata to the position of another fossil (relative age).

How does this help us? When fossils are

organized from

oldest to youngest,

orderly patterns of

evolution can be

seen.

Example

• Evolution of the horse

Evolution of the Whale

2. Molecular Evidence (Comparative biochemistry) Darwin could only study traits that could beseen but molecular genetics supports histheory• All living organisms have the same molecular

code• Many organisms have homologous genes

Example: Hox gene directs growth of limbs; theprotein hemoglobin carries oxygen

Prediction: A species that descended from a

common ancestor in the distant past should

have more differences in the amino acid

sequences of the same protein than do

species that shared a common ancestor

more recently.

Common ancestor - species from which

two or more species have diverged.

Comparing Proteins This predication was

tested by analyzing

the amino acid

sequences of

hemoglobin in

humans and several

other species.

The data supported the prediction. Humans and gorillas have fewer differences than do humans and chickens.

Comparing DNAScientists cancompare the# of nucleotidechanges in agiven gene aswell.

Closely relatedorganisms =fewer basedifferences inthe same gene

Phylogenetic tree

Phylogenetic trees branching diagram whichshows how organisms are related throughevolution.

These provide strong evidence supportingevolution because they show the samerelationships indicated by the fossil record.

Cladogram- a diagram used in which shows ancestral relations among organisms. It is based on sharedcharacteristics.

Humans and Chimpanzees are 97% genetically identical.

• This supports the claim that chimpanzees and humans have a common ancestor

3. HomologyHomologous Structures Structures found in organisms that share a commonancestry but have since evolved for differentfunctions.

Example The forelimbs of ALL vertebrates are made from the samebasic groups of bones, hooked up in the same way.

‘Same structure, different function’

Analogous structures –Similar features oforganisms that evolveindependently.

Example - Wings of afly and the wing of a bird

‘Same function, different structure’

Vestigial Structures – Structures that are reduced in size and function.

• They are considered to be evidence or an organism’s evolutionary past.

• These structures have no apparent function. (evolutionary leftovers)

Examples- human appendix, wisdom teeth, tailbone

Example- internal hind-leg bones in whales

4. Early Embryological Evidence

Early on in development,vertebrate embryosare strikingly similar.

Each has• A tail• Pharyngeal pouches (develop into gills inamphibians and fish)• Buds that become limbs

Structures develop at different rates indifferent groups of vertebrates, and arecalled homologous structures when its all saidand done.

Take 2 minutes to summarize what you havelearned regarding the different sources of

evidence of evolution that exist.