Processes of Evolution
Individuals of a population are selected for because of the genetic phenotype
Populations evolve because of the individual phenotypes that are selected for.
Only the members of the same species can produce viable, fertile offspring in the next
generation. This is a method of establishing if individuals are of the same species.
Natural Selection: Genetic phenotypes interact with the environment around them,
either; surviving and producing viable, fertile offspring in the next generation or not.
Natural selection guides which genes will be passed on and therefore, bottlenecks
genetic variation.
Reproductive Isolation: (Genetic drift, founder effect, sampling error): Is an isolated
population that as no in flowing genetic contributions. Genetic traits tend to be passed
through the population quickly. Limits variation in the gene pool.
Genetic recombination: Members of the same species, but opposite sex combine
genetic material. Yes in a word ‘sex’. Adds variation to the gene pool.
Gene Migration: The flow into or out of a population. A split off population given enough
time for natural selection to work can become another species. Adds variation to the
gene pool.
Gene Mutation: Change in the genetic code resulting in a mutated phenotype. The
majority of mutations are not viable and do not survive. Blindness, Missing limbs, other
physical and mental abnormalities are negative mutations. Not all mutations are
negative, but most do not survive without cultural assistance. Not to be confused with
variation. Adds variation to the gene pool.
Sexual Selection: Within a species one sex (usually female) act as a limiting force for
the other. Competition for the limiting sex results in sexual selection
Indirect effect
Genetic Drift
Sexual selection
Genetic
Recombination
Migration
Mutation
G
E
N
E
P
O
O
L
D
I
R
E
C
T
A
F
F
E
C
T
P
H
E
N
O
T
Selection
Natural
Cultural
Artificial
Y
P
E
Decrease gene variability
Increase gene variability
The above diagram illustrates how the five basic processes of evolution: interact to produce a genetic
change in the population, which keep certain beneficial traits that allow adaptation to the changing
environment.
Chart by Lisa Rodriguez
Geological Time Scale
ERA
PERIOD
EPOCH
MILLIONS OF
YEARS AGO
FORMS OF LIFE
Quaternary
Holocene
(recent)
10,000 B.P.
Dominance of Homo sapiens. (Domestication)
Pleistocene
1.8-2
Numerous fossil types of human appear: Homo
habilis; Homo erectus: four glacial periods.
(Tool use and use of fire)
Pliocene
5
Australopithecines (bipedality)
7-6
Sahelanthropus (genus)
Miocene
25
True anthropoid apes
Oligocene
35
Anthropoidea and appearance of Hominoidea
Eocene
53
Spread of modern mammalian forms;
prosimians flourish.
Paleocene
65
Appearance of Prosimii.
Cretaceous
136
Rise of archaic mammals and birds. Extinction
of dinosaurs, pterodactyls, toothed birds.
Insectivores appear.
Jurassic
190
Spread of primitive mammals, pterodactyls first
toothed birds. Great age of dinosaurs.
Triassic
225
Rise of primitive mammals; pterodactyls;
dinosaurs appear; reptiles dominant
Permian
280
Spread of amphibians and insects. Reptilian
radiation. Mammal-like reptiles.
Carboniferous
345
Primitive reptiles, insects; fern and moss forests.
Devonian
395
Rise of fishes and amphibians; spread of forests.
Silurian
430
Rise of Ostracoderms. First land plants.
Ordovician
500
Earliest fishes. Possible land plants.
Cambrian
570
Trilobites, mollusks, brachiopods and other
invertebrates. No land life yet.
PRECAMBRIAN
PALEOZOIC
(Age of Ancient Life)
MESOZIC
(Age of Reptiles)
CENOZOIC
(Age of mammals)
Tertiary
Periods difficult
to define
A few soft multicellular invertebrates.
First known fossils- 3.8 b.y.a.
Life begins?
Formation of the Earth? 5.0 b.y.a.