natural selection n.
Skip this Video
Download Presentation
Natural Selection

Loading in 2 Seconds...

play fullscreen
1 / 18

Natural Selection - PowerPoint PPT Presentation

  • Uploaded on

Natural Selection. The Key Mechanism of Evolution. Natural Selection (film page) (copy the following at the top of the page). the process by which characteristics become either more or less common in a population

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about 'Natural Selection' - diata

Download Now An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
natural selection

Natural Selection

The Key Mechanism of Evolution

natural selection film page copy the following at the top of the page
Natural Selection (film page)(copy the following at the top of the page)
  • the process by which characteristics become either more or less common in a population
  • Characteristics will become more common if they enhance survival or reproduction
  • It is a key mechanism of evolution
film natural selection notes
Film Natural Selection (notes)

1. Distinguish between Genotype & Phenotype

Genotype: the genetic makeup.

Phenotype: the physical expression of the genes; traits (not necessarily a trait which is visable)


2. Survival of the FITTER???

So called “FIT” organisms are those with characteristics which allow them to survive and reproduce…..they don’t necessarily have to have the very BEST of the characteristics…just “good enough”…or “fit enough” - not necessarily the“fittest”.

3. Does selection have to cause death?

No – not necessarily. A selection pressure just has to prevent reproduction.


4. Explain the evolution of the giraffes long neck.

Long ago both short and long necked giraffes existed. Then, food for short necked giraffes declined, but lots of food in tall trees for long necked giraffes. Long necked giraffes reproduced more long necked offspring while short necked giraffes starved and did not reproduce.

Nature selected long necks over short.


5. Why plants good to study Natural Selection?

Plants can be easily cloned. Because of this, scientists can place genetically identical plants in different environments to prove that evolution in fact occurs by natural selection….that environmental pressures actually force and direct evolution to occur through adaptation to the different environments


6. Role of Mutation and Genetic Recombination?

They provide the variation upon which Natural Selection can act. No variation means that nature has nothing to choose.


7. Does Natural Selection occur at the zoo?

Only somewhat. Many natural selection pressures are gone (ex. Food and water are plentiful and there are no predators), but some new pressures exist that can prevent reproduction (stress, boredom)

8. How has man interfered with Natural Selection?

Cures for disease, habitat destruction, pollution, genetic modification, artificial (human) selection…

famous examples
Famous Examples

of Natural Selection

antibiotic resistance
Antibiotic Resistance
  • (Why Does Evolution Matter now - Seagate 6 min)
pesticide insecticide resistance
Pesticide (Insecticide) Resistance
  • When pests (usually bugs) evolve to resist the chemical that was designed to kill them
  • (3:11)
industrial melanism peppered moths
Industrial Melanism/Peppered Moths
  • The Industrial Revolution resulted in huge amounts of coal smoke being emitted into the atmosphere, causing lichens that grew on tree bark to die and soot to adhere to the trunks, thus changing the bark from a light to a dark color.
  • As a result, peppered moths shifted from being predominantly light to being predominantly dark in color, to blend in with their resting places on tree trunks.
  • (2:05)

ddt selection

Population of non-resistant survivors

DDT Selection

Wild Type – original population

Low % Survival of low levels of DDT

Population surviving low levels of DDT

Mortality (death rate)

Population surviving high levels of DDT


ddt selection questions
DDT Selection Questions

1. What does it mean that there is no apparent difference between R and NR mosquitos?

You can not tell by looking at mosquitos which ones are R and which are NR

2. What change did DDT bring about?

It brought about evolution through adaptation/Natural Selection

3. If no heterozygositywas present, would R have evolved?

No. The gene for the R trait had to have existed in two heterozygous parents in order for offspring to show the R trait. Heterozygosity provides raw material upon which Natural Selection can act

4. What was the role of DDT?

It was the selective agent. It played the role of Natural Selection, selecting the R mosquitos to live and the NR ones to die

peppered moths
Peppered Moths

Polluted Forest

Unpolluted Forest

Original Gene Pool consisting of both dark and light moths

Birds are Selective Agents

peppered moths questions
Peppered Moths Questions

1. Causative agent of change in phenotypes?

The Industrial Revolution was the cause, with factories emitting high amounts of coal smoke and soot adhering to tree bark, blackening the moths environment

2. Part played by the soot?

It changed/blackened the environment – the soot became the camoflage for the dark colored moths

3. Part played by the birds?

They were the selective agents – in the dark environment, the birds could see and thus chose white moths to eat, leaving more dark moths alive.