Download Theory of Evolution by Natural Selection

Theory of Evolution by Natural Selection
_________________________ is the way in which nature favours the reproductive success of
some individuals within a population over others
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During Darwin’s voyage he collected significant physical evidence that helped him to make
specific inferences that help form his theory of evolution by natural selection
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Healthy populations produced far more offspring than could survive and reproduce. These
individuals had heritable variability.
As a result of these conditions as well as competition, some individuals would have a
better chance of survival
________________________ is a term used to describe the process of natural selection
(Herbert Spencer, a contemporary of Darwin coined this term). An individual that is
considered fit, has adaptations that allow it to survive longer and favour reproduce
success.
_________________________ is a result of a characteristic or feature of a species that
makes it well suited for survival or reproductive success in its environment
o Examples:
o A ______________ coat of a polar bear provide an adaptation for camouflage
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o The long snout of an anteater provides it with an adaptation to better __________
its food source
o The thick blubber of a seal provides it with an adaptation to survive ____________
temperatures of its habitat
o The size and shape of a ground-finch’s _____________ determines which food
sources it can access and provide an adaptation that makes them suitable for
specific niches ( a habitat suitable for its behaviour and food preferences)
Darwin’s Prediction:
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The theory of evolution predicts that species evolve over time in response to _______
changes, competition and different environmental conditions that favour specific traits.
Observations:
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Darwin’s finches provide us with evidence of a mechanism for the evolution of largebilled finches
An ancestral population of ___________________ billed ground finches are amongst
the first seed eating birds to arrive on the Galapagos Islands.
These birds had access to all types of seeds ( mostly large and some medium) and had
little to no competition
Over time, the finch population grew to it maximum ______________________. New
born finches born with variability (some slightly lager bills and some slightly smaller
than average sized bills) were exposed to competition within the species
Most of the birds had to compete for the medium sized seeds, while those with the
larger bills were able to utilize the ________________________ as a food source
Generation after generation, the average bill size continues to increase.
In a different situation, how might the evolution of beak size been different?
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Darwin’s theory was designed to be testable. He knew that if evolution had not occurred
then it would be easy to falsify his theory.
His theory was strengthened by the complete lack of evidence t falsify his theory.
Natural Selection:
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Evolution occurs when natural selection acts on __________________ within populations.
Genetic variation occurs by chance through genetic _______________ and recombination.
The process of natural selection does __________ occur by chance. The environment
selects individuals that are better suited to their environment.
Types of selection:
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_____________________:
o Selection that occurs when selection favours individuals with a more __________
variation of a trait. The result is a shift in the average condition
o Example: The beak size of the ground finches was a result of directional selection
toward the larger beak size.
o Example: Strawberries as a result of artificial selection, have been selected for
larger and sweeter fruits
o Example: Hummingbirds exposed to a new habitat with longer flowers. Individuals
with slightly longer bills will be more successful or “fit” in comparison to those with
small or medium bills as the environmental pressures favour long bills.
______________________:
o Occurs when the _______________ phenotype within a population is favoured by
the environment. Selection against individuals exhibiting traits that deviate from
the current population average occurs.
o Example: Human babies with an average birth rate have a higher survival rate at
birth than very small or very large babies
o Example: Hummingbirds in an unchanging environment with medium flowers, the
most common medium-sized bills would be favoured as longer bills may require
more energy to grow and carry around and short bills limit access to food.
_______________________:
o Selection that favours individuals with ________________________ of a trait over
the individuals with the intermediate variations.
o Example: If a habitat exists where flowers can be found with both small and large
flowers, then hummingbirds with either long or short bills. Neither plant is ideal for
the medium-sized bill, decreasing their survival and ability of reproduction
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Sexual selection:
Differential reproductive success caused by variation in the ability to obtain ____________,
resulting in sexual dimorphism (males and females evolving distinct appearances and
behaviour) and mating and courtship behaviours.
Most common examples of sexual selection are ____________________________ and
_________________________________________.
Examples include different colourings, body sizes, physical attributes and different mating
behaviours.
o _________________: Male peacocks have brighter plumage than female
counterparts in order to attract them as a mate
o _________________: Male deer are larger than females so as to better compete
during mating rituals
o _________________: the horns of male big-horn sheep are substantially larger than
the females. Males require big horns to compete head-to-head clashes.
o _________________: the male bower bird creates elaborate nesting areas or
“bowers” to attract a female. The most impressive bowers are those that are
largest and with the most trinkets (often blue). Disadvantages include decreased
longevity as a result of the brighter colours or risky behaviour
Natural Selection in Action:
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Directional selection in a human population. Tibetan people have inhabited the Himalayan
Mountains for thousands of years. Oxygen levels average at 40% of that found at sea level.
Short term adaptation of people from the lowlands results in increased red blood
production. This over time can be harmful as it makes the blood more viscous, causing
extra stress on the heart, reduced infertility and higher child mortality.
Tibetans do not exhibit high red blood cell counts, but do not have issues coping at these
high altitudes. Geneticists have discovered a genetic mutation that increases the oxygencarrying capacity in their blood, which has been selected for.
Other examples:
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o Antibiotic resistance means that bacteria can survive
in the presence of an antibiotic
o Upon discovery, penicillin was used to treat a wide
variety (not all) of bacterial pathogens afflicting
humans
o Since the Second World War, many disease causing
bacteria have developed resistance to
____________________________
o This resistance has been noted in several other
instances with more newly developed antibiotics.
Some strains of tuberculosis are resistant to ALL
known antibiotics. Treating cholera has now been
reduced to a single effective antibiotic.
o Resistance is thought to be a result of an existing
____________. This mutation allows the mutated
bacteria to survive and then reproduce, thus creating
a population resistant to the antibiotic
____________________________:
o Evolution of this moth (the onset of ________, darker
colour) is thought to be a result of an ___________________________.
o Before 1848, trees within their habitat were covered in off-white lichens, which
allowed for the peppered moths to camouflage.
o Due to coal mining in surrounding areas, the trees became covered in soot, and the
peppered moths became easy targets for prey. The black form became common.