Download Concepts of Evolution Outline

Concepts of Evolution
Isn’t Evolution Just A Theory?
• How does the scientific meaning of a term like theory differ from the way it is
used in everyday life?
•
Can the “facts” of science change over time? If so, how?
Evolution
• Scientific theories
– Concepts based on the
– Reserved for a conceptual scheme supported by a large number of
observations and not yet found lacking.
Evolution
Cell
Biogenesis
Gene
Evolution
All organisms are composed of
cells.
Life comes only from life.
Organisms contain coded
information that dictates their
form, function, and behavior.
All living things have a common
ancestor. Genetic changes in a
population or species over
generations have led to the
diversity of life on Earth.
How Do We Know Evolution Happens
• How do fossils give us a picture of change over time?
•
What distinguishing feature of the fossil Pakicetus skull identified it as related
to a whale? Why was this surprising?
•
Why do scientists seek fossils that are intermediate in form and time between
modern forms and their probable earliest ancestors?
Fossil Called Missing Link from Sea to Land Animals
• What evidence from the fossil fish skeleton suggests it is an intermediate form
between fish and land animals?
How Does Evolution Really Work?
• What are the 4 components of natural selection?
•
What determines an individual hummingbird’s beak length?
•
What factors in the environment might select for beak length and shape within
the hummingbird population?
•
How can hummingbird DNA help Dr. Schindler determine the evolutionary
history of hummingbirds?
Natural selection
• The process by which
•
The process that results in evolution.
Natural selection is based on variation:
• Individuals in a population differ from one another
• Many of these differences are genetic
– Genetic variation occurs because of
•
•
•
Some variations may
– help individuals in a population to survive
– Increase the amount of offspring the individuals have
These traits if inherited would be passed on to the offspring
Over time,
• Examples:
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–
–
–
–
Peppered moths of England
Snails in England
Flat-tailed horned lizard
Pesticide/antibiotic resistance
Sickle cell disease
• Example of heterozygous advantage – individuals who are heterozygous
for sickle cell disease are resistant to malaria.
2 key points about natural selection
• Natural selection is more of an
– A pesticide does not create resistant individuals, but selects for resistant
insects that were already present in the population
•
Natural selection depends on time and place
– It favors those characteristics in a varying population that fit the current,
local environment.
– Environmental factors vary from place to place and time to time
Microevolution
Gene pool
• The total collection of genes in a population at any one time.
• Occurs when the frequency of the alleles in a population change over a
number of generations.
Hardy-Weinberg Equilibrium
• States what conditions must exist in a population so that it doesn’t change
• The population must be very large
• Individuals do not migrate into or out of the population.
• Mutations do not alter the gene pool
• Mating is random
• Natural selection does not occur
One of the possible causes of microevolution is
Genetic drift
•
Bottleneck effect – an event drastically reduces the number of individuals in
the population. The surviving individuals do not have the same genetic
makeup of the orginal population
Figure 13.23
•
Founder Effect –
Figure 13.28
Natural selection can alter variation in a population in three ways
– Stabilizing selection:
– Directional selection: acts against individuals at one of the phenotypic
extremes
– Disruptive selection: favors individuals at both extremes of the phenotypic
range
Speciation
Species
A population or group of populations whose members can breed and produce
fertile offspring.
Speciation
Causes of speciation include
• Reproductive isolation
• Prezygotic barriers
•
•
Postzygotic barriers prevent the development of offspring that can survive
and reproduce
Geographical Isolation
• Allopatric speciation
•
•
Gene flow is blocked.
Physical separation – mountain range, river.
Figure 14.8
•
Speciation occurs when
•
Example: White-tailed antelope squirrel and Harris’s antelope squirrel
separated by the Grand Canyon
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•
The fossil record shows how speciation has occurred over geological time.
There are four eras (Precambrian, Paleozic, Mesozoic, and Cenozoic) in which
mass extinctions were followed by rapid speciation.
This evidence demonstrates punctuated equilibrium – the concept that
speciation occurs
•
Figure 14.12a
The gradualist model of species formation
• Populations evolve differences gradually as they become adapted to their local
environments
• Speciation occurs by
Figure 14.12b