Download The Theory of Evolution

EVOLUTION (Ch 16 & 17)
Since formation of Earth (4.5 bya) there has been:
Geologic
evolution
Organic
Evolution
The fossil record shows the order of which organisms were
present on Earth (p 2 in packet)
Practice Question:
Organism X appeared on Earth much earlier than organism Y.
Many scientists believe organism X appeared between 3 and 4
billion years ago, and organism Y appeared approximately 1
billion years ago. Which row in the chart below most likely
describes organisms X and Y?
Row
1
2
3
4
Organism X
Simple multicellular
Complex multicellular
Unicellular
Complex multicellular
Organism Y
Unicellular
Simple multicellular
Simple multicellular
unicellular
The Theory of Evolution: the process by which species have
changed over time; resulting in the diversity on Earth today
Evidence of the theory:
1) studying the fossil record
 Fossil: remains or traces of an organism that has been
preserved (ice/mud)
 Most commonly found in sedimentary rock because they
have been formed by layers over time (bottom
layers=older)
 Paleontologists study fossils
 Comparing fossils to present day organisms we can see
changes that have occurred…evolution
2) Comparative Studies: observations of similarities between
various organisms; (structural = physical features; molecular =
chemical makeup)
a. anatomy: similarities in skeletal structure
homologous structures: parts of different organisms
that are similar in structure , but different in function
vestigial structures: remnants of structures that were
functional in ancestral form, showing there has been
change over time ex: appendix
b. biochemistry: studying molecules among species (ex: amino
acid sequences in proteins)
c. cytology: studying cell structures among species
d. embryology: studying stages of development among species
*Comparisons look for common ancestry between species*
History of the Theory
Lamarck (1809) – his 2 principles
1. law of use and disuse: the more an animal utilizes a
structure, the better adapted it will become
2. inheritance of acquired characteristics: traits developed will
also be passed on to offspring
Charles Darwin: Evolution by Natural Selection
His book: The Origin of species (1859)
His theory:
Natural Selection: process by which
organisms having the best adaptive
traits for a given environment are more
likely to survive, reproduce, and pass
their traits on to next generation; those
not successful will die
5 main ideas of his theory:
1. overproduction – more born than will survive
2. competition for resources
3. survival of the fittest (those best adapted will survive)
4. reproduction – pass genes on to next generation
5. speciation: eventually evolution of a new species
“descent with modification”
Weakness of his theory: he couldn’t explain HOW the favorable
variations arose
Modern theory of Evolution = Darwin’s theory + genetics
**the 2 sources of variations in a population:
1. mutations
2. Sexual reproduction
Population genetics
The frequency of alleles can change within gene pool of a
population…
o The alleles of favorable variations will increase over
time
o The alleles of unfavorable variations will decrease
Can an individual evolve????
Practice Question:
When is extinction of a species most likely to occur?
(1) when environmental conditions remain the same and the
proportion of individuals within the species that lack adaptive
traits increases
(2) when environmental conditions remain the same and the
proportions of individuals within the species that possess
adaptive traits increases
(3) when environmental conditions change and the adaptive
traits of the species favor the survival and reproduction of
some of its members
(4) when environmental conditions change and the members of
the species lack adaptive traits to survive and reproduce