Download the processes of evolution

The central ideas of evolution are that life has
a history — it has changed over time — and
that different species share common
ancestors.
Mechanisms: the processes of evolution
Evolution is the process by which modern organisms have descended from ancient
ancestors. Evolution is responsible for both the remarkable similarities we see across
all life and the amazing diversity of that life — but exactly how does it work?
Fundamental to the process is genetic variation upon which selective forces can act in
order for evolution to occur. This section examines the mechanisms of evolution
focusing on:
Descent and the genetic differences that are heritable and passed on to the next
generation;
Mutation, migration (gene flow), genetic drift, and natural selection as mechanisms of
change;
The importance of genetic variation;
The random nature of genetic drift and the effects of a reduction in genetic variation;
How variation, differential reproduction, and heredity result in evolution by natural
selection; and
How different species can affect each other's evolution through coevolution.
Lamarck’s Ideas
• Theory of acquired characteristics.
• Organisms can change during their lifetime
because they want to “better” themselves.
• These changes acquired during their lifetime
can be passed onto the next generation.
Lamarck
• Lamarck’s ideas don’t work.
• Traits acquired during an organism’s life
cannot be passed onto the next generation.
• Examples: missing limbs etc.
Scientists Contributions
• Cuvier – fossil evidence
• Malthus – population growth
• Lyell – geological features
• Wallace – natural selection as a mechanism
Darwin’s Idea
• 4 Main Ideas
1.Variation within a species
2. Organisms adapt to their environments
3.Variation in characteristics were passed on
to the next generation: Inheritance
4.There is competition to reproduce AND
there this competition to survive. Some
organisms are more successful at both!
Natural Selection
• Darwin realized that nature was selecting
the fittest individuals within a species.
• These fit individuals were most likely to
survive and reproduce.
• Darwin called this “survival of the fittest”.
• Example: Peppered Moths
Summary of Darwin’s Theory
1. Organisms differ; variation is inherited
2. Organisms produce more offspring survive
3. Organisms compete for resources
4. Organisms with advantages survive to pass
those advantages to their offspring
5. Species alive today have descended with
modifications from common ancestors
Other Evidence for Evolution:
Fossil Record
Homologous Structures
Vestigial Organs
Embryological Development
Sources of Variation
• Where does variation
within a species come
from?
1.Mutations: Physical
changes in DNA. Most
have negative effects,
but some may actually
increase an
organism’s fitness.
More variation
1.Sexual reproduction: when meiosis occurs,
homologous pairs of chromosomes are
separated RANDOMLY.
• This results in many combinations of
chromosomes.
• In humans there are 223 (8 million possible
combinations).
Adaptive Radiation
• Also known as divergent evolution.
• Process by which 1 species gives rise to
many species.
Convergent Evolution
• Different species come to look like one
another as they adapt to similar
environments.
• Results in the formation of ANALOGOUS
STRUCTURES look similar, but are of
different origin
• Examples: wings of birds, bats and insects
or penguin, whale and dolphin swimming
structures and streamlining.
Speciation
• The formation of new species.
• In order for 2 species to form from one,
populations must be separated from one
another.
• Over time, the populations will change such
that they will no longer be able to reproduce.
Table 23.1a
Table 23.1b
Genetic Drift
• Sometimes the genetic makeup of a
population can change due to chance rather
than natural selection.
• Example: a natural disaster wipes out a
random portion of a population.
• The survivors may not be the fittest.
Time will tell
1.Gradual change evolution occurs slowly
and steadily.
2.Punctuated Equilibria there are long
periods of equilibrium (no changes in
populations) interrupted by brief periods of
change. May be brought on by mass
extinctions.