Charles Darwin & Natural Selection

Darwin’s Theory EVOLUTION – all changes that have transformed life

over immense time.

“Evolution is the biological history

of life on Earth”

Before Darwin people thought:

1. species are fixed

-they do not change

2. Earth is less than 10,000 yrs oldhttps://flic.kr/p/9D76x3Rights Reserved under CC BY 2.0

The Changing of Ideas In the mid 1700’s, his study of fossils caused Georges Buffon

to suggest that the Earth might be much older

He also noticed that some fossils and some living organisms were similar, but not exactly alike

LAMARCKProposed that life evolves/changes

It Adapts Ex: hind legs of a kangaroo

How did massive hind legs of a kangaroo allow them to adapt to the environment?

Macropus giganteus https://commons.wikimedia.org/wiki/File:Macropus_major_hind_legs.pngRights Reserved under CC BY-SA 4.0

Charles DarwinTravels to Galapagos Islands

The Infamous Voyage of Darwin

Charles Darwin voyaged on the H.M.S. Beagle to the Galapagos Islands – saw lots of animals, read lots of books, did lots of thinking – and came up with the following:

Darwin Observed that the Galapagos Islands had many unique

organisms, similar to, but different than those on the mainland

Also noticed that each island had some organisms that were not found on any other islands in the chain

Inferred that mainland species had changed after colonizing the islands, and adapted to their new environments

Mr. Darwin, your thoughts please?

Organisms Change Over TimeHow? Natural Selection!

All organisms can produce more offspring than can surviveThere are variations between the individuals in a populationLimited resources = struggle to surviveIndividuals with the traits that make them the most “fit” have better

chance of surviving and passing their traits to their children

Why is variation important?Variation allows natural selection to happenHow?

Survival of the fittest- The best adaptation (variation) will survive and reproduce

Can you think of any other examples of survival of the fittest? What variation allowed for survival?

Variation Exists within a Species

The Backbone of Evolution Scientists study the fossil record to

compare extinct organisms to modern organismsThe fossil record indicates:

the order in which species emergedHow do we get fossils?

in wet, environments where they can be quickly covered by sediment

How old are fossils?Relative dating -top layer must be younger than

bottom layerRadiometric (absolute) dating -use radioactive

isotopes- decay (half life)

Analyzing the Present to Understand the Past-Evolutionary Support

Comparative Anatomy: Compare body structures

of different speciesHomologous structures:

similar to due to common ancestry

ex: human arm and whale flipper

https://www.flickr.com/photos/bibliodyssey/6245974006/galleries/

Homologous Body Structures

‘Homology Vertebrates Rights Reserved under CC BY-SA 4.0

Vestigial Structures: Remnants of Structures

that may have been useful in the past, but have little

or no importance now.Ex. Appendix

Tail Bone

Biochemistry: Similarities in DNA and protein sequences

https://commons.wikimedia.org/wiki/File:Schematic_relationship_between_biochemistry,_genetics_and_molecular_biology.svgRights Reserved under CC BY-SA 3.0

Natural Selection

Explains resistance of insect

populations to pesticides or

bacteria to antibioticsSpray insecticideThose that aren’t resistant - dieThose that are resistant - live and reproduceThe next generation contains more resistant individuals - the

population is changing

Adaptation Is a variation, not a change!

‘Colorado Potato BeetlePublic Domain

Overuse of antibiotics has lead to strains of bacteria that are resistant to them.

The bacteria adapted and now have a resistant gene.

Antibiotic Resistance

Genetic DriftMovement of genes in or out of a populationGreatly affects small populations

Geographic IsolationA barrier separates one population

into twoThey evolve different

characteristicsThey become different species-

they coevolve