Evolution Cont’d

7th Grade BiologyMr. Joanides

http://www.buildamovement.com/blog/wp-content/uploads/2009/09/evolution.jpg

The Fossil Record

• Fossil – Preserved remains or markings left by organisms that live in the past.– Most fossils are found in sedimentary rock– Others can be buried under volcanic ash and dust

• Sedimentary rock – eroded particles of sand, silt, etc that flow down river to seas and swamps and settle at the bottom. Over time, they are cemented together under pressure and heat to form rock.

Sedimentary Rock Being Formed

http://geoscape.nrcan.gc.ca/

nsask/images/rocks1_e.jpg

The Fossil Record

• Provides evidence of Earth’s changing life. • Ex. Timelines from class

• Earth is 4.6 billion years old (byo)• Oldest known fossil is 3.8 byo. • Fossils of prokaryotes [bacteria and archaea]

3.5 byo (oldest form of life)• Fossils in younger rock show evidence of

evolution

Evolution of the Whale

• Modern whales evolved 50 million years ago…• But from where?

– Fossils of extinct species can help put the puzzle together.

– Basilosaurus

http://upload.wikimedia.org/wikipedia/commons/archive/4/4e/20080706155500!Basilosaurus.jpg

Geographic Distribution• Differences and similarities between

organisms around the world– Evolved from ancestral forms

TOPIC FOR DISCUSSION• Why do S. American tropical species have

more in common with S. American desert species than they do with African desert species?

Australia…Unique Plants and Animals

• Numerous pouched mammals (marsupials)• Few placental mammals

• Why did this happen?

• Also…a good case study for introduced animals…economic and ecologic nuisances

http://www.camelotbears.com/images/koala_baby_pic.jpg

Homologous Structures• Forelimbs of animals & goose bumps

http://www.thisviewoflife.org/evolution/forelimb%20homologies.jpg

Vestigial Structures• Modern whales have no hind limbs, but still

have remnant hipbones

http://www.answersingenesis.org/home/area/magazines/tj/images/v14n2_vestigial_structures.gif

Definitions

• Homologous structures – structural similarities species share from a common ancestor

• Vestigial structures – are remnants of structures that may have had important functions in an ancestral species, but have no clear function in modern descendant.

Similarities in Development• Embryos of closely related organisms have similar

states in development.

http://home.honolulu.hawaii.edu/~pine/book1qts/embryo-compare.jpg

Genetics

• DNA & Protein analysis are new tools for testing evolution

• DNA passed from parents to offspring, so should show evolution (i.e. ancestry)

• Darwin hypothesized that all life forms are related. He was right and it is proven in the fact that DNA is the common language in which traits are passed.

Hemoglobin Comparisons

http://www.txtwriter.com/Backgrounders/graphics/evolution/page13.jpg

Answer these in your notes (5 min)

• Why are older fossils generally in deeper rock layers than younger fossils?

• How can evolutionary theory explain why Australia is home to relatively few native placental mammals?

• What are homologous and vestigial structures?• What can you infer about species that differ

significantly in their DNA sequences?

Natural Selection

• Population – a group of individuals of the same species living in the same area.

• “Survival of the Fittest”

http://www.truthinscience.org.uk/site/images/stories/peppered%20moth.jpg

Artificial Selection

• Definition – Selective breeding of domesticated plants and animals to produce offspring with genetic traits that humans value. – Chickens that weigh too much– Dogs with aggression– Dogs with keen sense of smell and longing to

retrieve– Plants that are not susceptible to pesticides

Pesticides – Natural Selection in Action

• Pesticides are poisons used to kill pests– Insecticides– Rodenticides– Etc

• A little poison will kill 99% of “pests” the first time

• Second time it’s not as successful. Why?

Inherited Resistance

http://upload.wikimedia.org/wikipedia/commons/thumb/8/85/Pesticide_resistance.svg/573px-Pesticide_resistance.svg.png

Affects of Pesticides

• Birth Defects

• Cancer• Stronger

Resistance• Affects

Native Species

http://water.usgs.gov/nawqa/pnsp/pubs/fs152-95/atmos1.gif

Gene Pools• Consist of all the alleles (genes) in all the

individuals that make up a population.

http://www.visschervisions.com/Dogs/group_pic.jpg

Changes in Gene Pools

• Mutations• Sexual recombination

– Promotes survival and reproductive success– Some alleles become more common

• Ex. Peppered Moth

• Microevolution – A generation-to-generation change (over a short time)

Genetic Drift

• A change in the gene pool of a population due to chance.– Occurs more drastically in smaller populations

• Ex. Coin toss• 10 x’s vs 1,000 x’s

• The Bottleneck Effect – Disasters such as earthquakes, floods, droughts and fires may drastically reduce the size of a population, which reduces the size of its gene pool.

Bottleneck Effect

http://www.kminot.com/art/charts/bottleneck_effect.jpg

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Mutations

• Change in the DNA of an individual, which in turn can change a population over great time.

• Influenced by natural selection or genetic drift.

• Darwinian fitness = the contribution that an individual makes to the gene pool of the next generation.

Interesting Mutations• Sickle cell disease• Antibiotics and Bacterial Resistance

– Tuberculosis

http://www.biojobblog.com/Bacteria.jpg

Interesting Mutations cont’d

http://news.softpedia.com/images/news2/Researchers-discover-how-to-detect-mutations-2.jpg

http://blog.media-freaks.com/wp-content/uploads/2009/04/teenage-mutant-ninja-turtles.jpg