Natural selection
1 / 23

Natural Selection - PowerPoint PPT Presentation

  • Uploaded on

Natural Selection. The Theory of …. VARIATION WITHIN POPULATIONS. Consider individuals from the same species. Within a giraffe population some giraffe’s will be born with longer necks than others. For example consider two different giraffes, one with a longer neck than the other.

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' - melvyn

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 Theory of …..

Variation within populations

  • Consider individuals from the same species. Within a giraffe population some giraffe’s will be born with longer necks than others. For example consider two different giraffes, one with a longer neck than the other.

Environmental pressure

  • Now consider if a drought occurred leaving only a few trees and plants with edible foliage…


  • Now consider all the different animals that rely on plants for food in order to survive. These animals compete with one another for whatever food remains


Who will survive?

  • The giraffe with a short neck that can only reach limited branches or the giraffe with a longer neck?

Survivors reproduce

  • The giraffe with the longer neck will have a better chance of survival as it will be able to reach leaves at a higher point on the tree and will therefore have access to more of the limited food.

    Those that survive can go on to reproduce

    What type of neck will be likely to be passed on?

End result evolution by natural selection
END RESULT: Evolution by Natural Selection

  • The more advantageous trait, longer necks, which allows the giraffe to survive and have more offspring, will become more common in the population.

  • If this process continues, eventually, all individuals in the population will have longer necks.

Natural selection1
Natural Selection

  • Natural selection is the way in which nature favours the reproductive success of some individuals within a population over others

Process of natural selection
Process of Natural Selection

  • variation - individuals in a population vary from one another

  • inheritance - parents pass on their traits to their offspring genetically

  • selection - some variants reproduce more than others (as a result of competition, environmental change or other selection processes)

  • time - successful variations accumulate over many generations


  • On his voyage Darwin collected many pieces of physical evidence and observations that he compiled to come up with his theory of natural selection

Darwin s finches
Darwin’s Finches

  • Darwin noted that there were many different variations of the finch.

  • He also noted that each of the Galapagos islands contained a different assortment of finches

  • He hypothesized that depending on the food available on the island, different traits became more common as it helped survival

Survival of the fittest
Survival of the Fittest…

Coined by Herbert Spencer

  • An individual that is considered fit, has adaptations that allow it to survive longer and favour reproduce success.

  • Adaptation is a result of a feature of a species that makes it well suited for survival or reproductive success in its environment (White coat of a polar bear in the Arctic)

Types of selection
Types of Selection…

  • Directional Selection- favours an EXTREME variation of a trait. E.g a large beak or a small beak

    • Stabilizing Selection: the AVERAGE phenotype is selected for. E.g. a medium beak

    • Disruptive Selection: OPPOSITE EXTREMES are selected for E.g. A small beak and large beak

Sexual selection
Sexual Selection…

  • Differential reproductive success caused by variation in the ability to obtain mates, resulting in sexual dimorphism (males and females evolving distinct appearances and behaviour) and mating and courtship behaviours. –bower bird

Female selection

  • Colouring: Male peacocks have brighter plumage than female counterparts in order to attract them as a mate

  • Mating behaviour: elaborate mating calls, rituals or dances are used to attract individuals of the opposite gender. (E.g. bower birds, bird of paradise)

  • – bird of paradise

  • –dancing bird

  • Male vs male competition
    Male vs. Male competition

    • Body size: Male deer are larger than females so as to better compete during mating rituals

    • Physical attributes: the horns of male big-horn sheep are substantially larger than the females. Males require big horns to compete head-to-head clashes.

    Can you think of any
    Can you think of any?

    • The water boatman may be the loudest animal on earth for its size because females prefer to mate with the loudest male

    • Lyre Bird-can copy the sounds of any sounds and females are attracted to the most songs


    • Many plants have flowers that are pretty and brightly colored. This is because the brightest colors attract bees, butterflies, and other pollinators, which enable the plant to reproduce.

    Directional selection in tibetan population
    Directional selection in Tibetan population

    • Tibetans live at an altitude where oxygen levels are at 40% of that found at sea level

    • Normal adaptation would include an increase in EPO production (recall EPO results in more RBC production)

    • Long term exposure to increased EPO results in blood beoming more viscous, causing extra stress on the heart, reduced infertility and higher child mortality

    Antibiotic resistance
    Antibiotic Resistance…

    • Antibiotic resistance means that bacteria can survive in the presence of an antibiotic

    The peppered moth industrial melanism
    The peppered moth…(Industrial melanism)

    • The peppered moth has two types of colouring possible (Black and peppered)

    • Prior to the industrial revolution the white morph was dominant ( least visible to predators)

    • With the onset of the industrial revolution, soot was produced because of processing coal and this soot coated surrounding trees

    • The black morph became more predominant because the black moth could better camouflage in the soot covered trees.

    Follow up
    Follow up:

    • 1. What are the 4 steps in the process of natural selection?

    • 2. What are 4 types of selection?

    • 3. Describe 1 example of natural selection in action.