Download Natural Selection

The Theory of …..
 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.
 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?
 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?
 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 selection is the
way in which nature favours
the reproductive success of
some individuals within a
population over others
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
1.
 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 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
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)
 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
 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.
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
 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.
 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
 http://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.
 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 means that bacteria can survive in the
presence of an antibiotic
 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.
 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.