THEORIES AND PATTERNS
OF EVOLUTION
Chapter 15
Theories of Evolution
Biological Evolution: the change of
populations of organisms over time
 New
life forms are really modified versions
of older ones in same geographic area
 2 Explanations:
 Lamarck’s
 Darwin’s
Jean Baptiste Lamarck
Thought acquired
traits (learned, not
inherited) could be
passed to offspring
 Not True!!

Charles Darwin
Spent 5 years aboard
H.M.S. Beagle traveling
world & recording
observations
 Animal adaptations and
geographic changes
required VERY LONG
periods of time to occur
Modern Evolutionary Thought

Natural Selection: organisms best suited
to their environments will reproduce more
successfully
 Over
time, # organisms with favorable traits
increases within a population
Artificial Selection:
Breeding organisms with
specific traits to produce
desired offspring
Modification by Natural Selection
The Process:
 1)
Organisms better
equipped to survive
environment will produce
more offspring
 2) Eventually, popltn made
up of only successful
members
 3) Over time, an entirely
new species may form!!
Descent with Modification

“Newer forms appearing in fossil record are
actually modified descendants of older species”
 Implies
that ALL species descended from only a few
ancient organisms
Adaptation

Populations adapt as their # of favorable traits
increases
 The
types of traits that are favorable depends on the
environment
 Examples:
 Mimicry:
a harmless species resembles a dangerous one;
both are avoided by predators

Penicillin-resistant bacteria, rose thorns, etc.
 Camouflage:

enables species to blend with surroundings
As genetic makeup of popltn changes, evolution
occurs
Patterns of Evolution
The pattern & speed with which
organisms adapt is dependent upon their
environment
 3 Patterns:

 1)
Coevolution
 2) Convergent Evolution
 3) Divergent Evolution
Coevolution

Coevolution: the
change of 2 or
more species in
close association
 i.e.
predator/prey;
parasite/host;
plants/herbivores
Convergent Evolution

Convergent
Evolution: occurs
when environment
selects phenotype
 Results
in similar
phenotypes of
different organisms
 i.e.: body shape of
dolphin (mammal) &
shark (fish)
Divergent Evolution

Divergent Evolution:
when 2 related
species become more
dissimilar
 Adaptive
Radiation:
when different species
evolve from common
ancestor
 i.e.: Galapagos
finches