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Transcript of Evolution
Nothing mutates with a purpose. Environmental changes do not make organisms mutate, and organisms can't choose how to mutate.
*CHANGE IN POPULATION OVER TIME*
in the population.
1. Change in the
So... evolution requires:
Process called *Natural Selection*: Those with the traits that best help them win competitions will reproduce more and pass on these traits.
L e a d s t o
Produced through random mutations of the DNA of an individual. Must be inheritable!
Natural selection is also known as *Survival of the Fittest*:
Organisms that are the most fit (well adapted), survive. The rest die.
BUT... It's not always the "fittest" that survive:
Sometimes, they're unlucky and die before reproducing.
Sometimes, the other gender does not find them attractive
Therefore, Survival of the Fittest isn't a great name for this phenomenon.
Natural selection always refers to CURRENT environment.
Example: Antibiotic-Resistant Bacteria
Antibiotics interfere with specific proteins required for cell respiration. Some bacteria have a mutated protein, that doesn't work so well, but the antibiotic doesn't recognize it. In a ^normal^ environment, these bacteria are not "evolutionarily fit" (they get outcompeted by the rest of the bacteria), but when antibiotics are present, all other bacteria die, and these mutant bacteria have the advantage.
This is another reason why "survival of the fittest" isn't a great term.
Natural selection over time leads to organisms with specific *niches* (roles in the ecosystem) which reduces competition between species.
Can lead to...
*Speciation*: Formation of a new species
The end :-)
If a mutation that allows some organisms to adapt is not present,
extinction of the species occurs
Factors that help
A population of trees
Time passes, some die, some are born. Population size doesn't change much.
Time passes, a mutation occurs and suddenly there is variation!
May mean one trait (example: being tall) is
better at winning competitions than others
(example: being short)
Lots more time passes, more mutations occur.
selective processes or unselective processes
Certain traits allow an individual greater reproductive success, so their frequency increases in the population: Some loss of variation may occur, if the trait decreases reproductive success
Outside forces select "best" traits
Individuals within the population select "best" traits
Random Loss of Variation
Natural disaster destroys
large portion of population
A portion of the population leaves
and colonizes a new area
Through these processes, populations that survive and are isolated from each other can become
so different that they cannot reproduce together. This is:
Species don't always have the
traits needed to survive: they
** They cannot mutate to avoid
Once this variation exists, evolution can occur through