The Theory of …..

Natural Selection

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.

VARIATION WITHIN POPULATIONS

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

ENVIRONMENTAL PRESSURE

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

COMPETITION

Who will survive?The giraffe with a short neck that can only

reach limited branches or the giraffe with a longer neck?

SURVIVAL…

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?

SURVIVORS REPRODUCE

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.

END RESULT: Evolution by Natural Selection

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

Natural Selection

1. variation - individuals in a population vary from one another

2. inheritance - parents pass on their traits to their offspring genetically

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

4. time - successful variations accumulate over many generations

Process of Natural Selection

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

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

Darwin’s Finches

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)

Survival of the Fittest…Coined by Herbert Spencer

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

Types of 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.

Sexual Selection…

http://www.youtube.com/watch?v=tJ32_ijdmLo –bower bird

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)

http://www.youtube.com/watch?v=CYcs73oeFkc – bird of paradise

http://www.youtube.com/watch?v=FlIRv6fJ3nU –dancing bird

FEMALE SELECTION

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.

Male vs. Male competition

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 songshttp://www.youtube.com/watch?v=VjE0Kdfos4Y

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.

Can you think of any?

Natural Selection in action…

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

Directional selection in Tibetan population

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

Antibiotic Resistance…

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.

The peppered moth…(Industrial melanism)

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.

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