Download Natural Selection Darwin*s Ideas

Natural Selection
Darwin’s Ideas
Objectives
• Be able to explain Darwin’s journey to an
idea.
• Be able to explain how populations of
organisms can adapt to their environment
through natural selection.
What happens?
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Natural selection
• the consequence of certain individual organisms in
a population being born with characteristics that
enable them to survive better and reproduce more
than the offspring of other individuals in the
population
• Able to reproduce because they were still ALIVE!
Evolution
• A genetic change in the population
• Surviving organisms were better able to do
something than others
Darwin’s journey
• Before Darwin, most people believed
that all species had been created
separately and were unchanging.
1831 voyage of H.M.S. Beagle
Took 5 years
Was seasick for much of the time
Important and unexpected patterns:
Island species resembled mainland species
 Finches more variable
than he had seen
elsewhere
 Collected specimens and
sent them back to
London to be catalogued
 He thought they were
same species, just
different varieties
 Not reproductively
compatible so they were
separate species
 One for each of the 13
islands
 Still closely resembled
the mainland finches
 Evolution is a change in the allele
frequencies of a population over time
 Proportions of the alleles change
 Alleles determine the characteristics of
the individuals in a population
 Cumulative characteristics of all the
individuals determines the
characteristics of the population
 Doesn’t involve changing the genetics or
features of an individual
Let’s Break down Darwin
Three simple conditions are necessary:
1. There must be variation for the particular
trait within a population.
2. That variation must be inheritable.
3. Individuals with one version of the trait
must produce more offspring than those
with a different version of the trait.
 Fitness depends on the specific environment in which
the organism lives.
Fitness is not fixed in stone and changes over time and
in different habitats
What happened with Darwin’s
Finches?