Download Evolution by Natural Selection

Evolution by
Natural Selection
Scientific Theory
An explanation of natural phenomenon supported
by a large body of scientific evidence obtained
from many different investigations and
observations
Evolution
A gradual change in a
species (populations)
through adaptations
over time
Charles Darwin
“Theory of Evolution by Natural Selection”
Proposed that new
species could
develop by a
process of natural
selection.
Charles Darwin
• Natural selection: When better adapted
organisms survive to produce a greater
number of viable offspring.
• This has the effect of increasing their
proportion in the population so they
become more common
Darwin’s studies
• Studied animal species in the Galapagos
Islands and found they each had unique
adaptations
– Galapagos finches demonstrate different
adaptations to eat different foods
– Galapagos turtles are the largest on earth
Natural Selection
• A mechanism for change in a population
• Natural Selection (N.S.) is responsible for
most evolutionary change by selectively
changing genetic variation through
differentiated survival and reproduction
• Goal – To be fit “enough” to survive and
reproduce
How does natural
selection produce change
in a population?
3 types of natural selection
1. Stabilizing Selection
• Favors average individuals in a population
• Those individuals have a “selective advantage”
• Reduces variation in a population
2. Directional Selection
• Favors one of the extreme variations of a
trait
• Can lead to rapid evolution of a population
3. Disruptive Selection
• Favors both extreme variations of a trait
• Leads to evolution of two new species
Speciation
• A process of producing two
individual species from one
– Members of the 2 species no
longer interbreed within their
natural environment
Evidence for Evolution
1. Structural Adaptations
•
Methods of protection
•
•
•
Teeth, claws, thorns
Mimicry
Camouflage
2. Physiological Adaptations:
• Changes in an organism’s metabolic
processes
•
Resistance to antibiotics or chemicals
3. Fossils:
• Provide a record of early life and
evolutionary history
4. Anatomy:
•
•
•
Structural features with a common evolutionary
origin are called homologous structures.
The body parts of organisms that do not have
common evolutionary origins but are similar in
function are called analogous structures.
A vestigial structure does not have current function
but may have been useful to an ancestor
5. Embryology:
• Similarities among the young embryos
suggest evolution from a distant, common
ancestor
6. Biochemistry:
• Comparing DNA and RNA
How do we know what happened
when?
1. Radiometric dating relies on half-life decay
of radioactive elements to allow scientists to
date rocks and materials directly.
2. Stratigraphy provides a sequence of events
from which relative dates can be
extrapolated.
3. Molecular clocks allow scientists to use the
amount of genetic divergence between
organisms to extrapolate backwards to
estimate dates.
What’s important from all these
notes?
V
I
S
T
= variation
= inheritance
= selection
= time