Evidence for
Biological
Evolution
Evolution results from 4 factors:
 Potential
for a species to increase in number
 Heritable
genetic variation
 Due
to mutations and sexual reproduction
 Competition
for limited resources
 Reproduction
of organisms better able to
survive in the environment
Inherited variation & Artificial selection
 Individuals
of each species vary.
 Darwin argued that variation was important.
 In artificial selection, humans select from the
naturally occurring genetic variations in a species.
 Example: Dogs: all descended from wolves
 Selective breeding
for color, hair, size,
behavior
 Interbreeding reduces
genetic variation
Artificial Selection
 Wheat,
corn, for
resistance to rust,
fungi, etc.

USDA spends $ to breed
new resistant varieties.
 Unintentional
 Antibiotic
artificial selection
resistance in bacteria
 Penicillin, Streptomycin, Tetracycline, etc.
 “Multidrug resistant” tuberculosis
 Pesticide resistance in insect pests
 DDT, Chlordane, etc.
Remember…
 Adaptation
= any inherited characteristic that
increases an organism’s chance of survival
 Anatomical,
physiological, behavioral
 Successful adaptations enable organisms to
become better suited to their environment.
 Fitness
= the ability of an individual to survive
and reproduce in its specific environment.
 Result
 Survival
of adaptation.
of the fittest = individuals with
adaptations that make them better suited to
their environment survive and reproduce.
Natural Selection
 Natural
selection = the traits
being selected, and
increasing over time,
contribute to an organism’s
fitness in its environment.
 Results in changes in the
inherited characteristics of a
population, which increase
a species’ fitness in its
environment.
Evolution by Natural Selection
 Darwin
proposed that a type of artificial selection
occurred in nature.
 Members of each species compete regularly to
obtain food, living space, and other resources.


Selection removes (some) individuals with
unfavorable traits.
Selection preserves (some) individuals with favorable
traits.
 The
struggle for existence was central to Darwin’s
theory of evolution.
Common Ancestry
 Homologous

“same” structures, different fucntions
Comparing the anatomy of fossils and living organisms
All tetrapods have similar limb bones
Common Ancestry examples:
 All
primates have 5 fingers
 Apes and humans lack a tail
Common Ancestry
 Embryological

evidence suggests common ancestry
Homologous structures develop different functions
Common Ancestry
 The
early embryonic stages of a (a) lemur,
(b) pig, and (c) human show strikingly
similar anatomical features.
Common Ancestry:
Fossil Record
 The
only record that
species changed over time
Darwin’s Concept: Natural Selection
 Genetic
variation exists within a population due to
mutations and sexual recombination
 Competition
for resources yields the survival of the
fittest for a certain environmental condition
 Adaptations
 Natural
are changes in genetic traits over time
selection favors traits (variations) that make
an organism more fit for its environment, leading to
adaptations in a population over many generations.
Darwin’s Finches
 Galapagos
Islands:
14 species of finches
with one common
ancestor
 Variety of beak
adaptations due to
isolation of
populations on
different islands
 Ongoing
competition for
resources