Download Models of evolution

Process of Evolution
1. Development of the theory of evolution
a. Lyell (1833)
 wrote Principles of Geology and explained that natural
processes occurring now have shaped Earth’s geological
features over long periods of time;

helped Darwin understand the importance of geological
processes he had observed (volcanic eruption and an
earthquake); also

gave Darwin the idea of long periods of time
b. Lamarck (1809)
 creatures have an inner need to change towards complexity
and perfection

parts of the body that are used will develop and parts that
aren’t used will wither
traits that are gained over a lifetime are passed onto the

next generation
first to realize that organism are adapted to their

environment
c. Malthus (1798)

if human populations continued to grow unchecked, sooner or
later there would be insufficient living space and food for

everyone;
not enough food so those best suited survive

Darwin thought that this was even more true for plants and
animals since they had way more offspring
d. Darwin (1859)
 individuals differ within a species and this variation is
heritable:

organisms produce more offspring than needed and many
don’t reproduce or survive;


individuals compete for resources (survival of the fittest);
each individual has different advantages and disadvantages

that help them survive or not survive;
successful individuals pass on their traits to offspring

(natural selection causes species to change over time)
species alive today are descended with modification from
common ancestors
2. Evolutionary change
-
Variation is studied in populations (same species that can breed)
-
Populations share a common collection of genes called a gene pool
-
which consists of different alleles
Scientists look at the alleles relative frequency of times the allele
-
occurs compared to the number of times other alleles for the same
gene
Genetically speaking, evolution is any change in the relative
frequency of alleles in a population
a. Role of DNA in evolution as a hereditary material
o Deoxyribonucleic acid transmits info from parent to offspring
o Nucleotides consist of a phosphate and sugar backbone and one
of four nitrogen bases (adenine, guanine, cytosine and thymine)
coiled into a double helix
o The ability to transmit info lies in the arrangement of the
bases
o During DNA replication, the sequence of the bases is
maintained
o Inheritance refers to the DNA that offspring receive from
each parent
b. Agents of change:
i. Mutation

a change in the base sequence of DNA that may result
in a change in the genotype and phenotype (visible) of

the offspring
can occur due to mistakes in replication because of
mutagens (environmental agents that harm DNA such

as radiation or chemicals)
although usually minor, a mutation may result in an
organism being more adapted to its environment (or
not!)
ii.
Genetic drift
 in small populations, individuals that carry a particular
allele may have more descendants than others

(chance/accidents);
over time, a series of chances like this can cause an
allele to become more common or extinct in a
population
iii. Gene flow
 movement of alleles from one population to another
due to migration of individuals
iv. Non random mating

proximity, dominant males, picky females; certain
genotypes become more common
v. Natural selection
 all organism produce more offspring than the


environment can support;
individuals of a given species vary in their traits
(random inheritance);
every organism struggles to survive and competes for
food, water, space and mates;

individuals best adapted to the environment live
(survival of the fittest);

organisms that survive will reproduce and pass on
“good” traits
3. Models of evolution
a. Gradual change model
 gradual changes in a species over time

Hard to notice over a short period of time

Small variations that fit an organism slightly better to
its environment are selected for

A few more individuals with more of helpful
trait survive
A few more individuals with less of the helpful
trait die
Over a long period of time, the population changes


b. Punctuated equilibrium model

species have long stable periods of equilibrium (no

change) interrupted by short rapid bursts of change
Can be a result of:


Mutation in the genes of a few individuals
Sudden changes in the environment that results
in harsher selection

Isolation of a small population (restricting the
gene pool)

A mass extinction event opening up a variety of
niches
4. Speciation – formation of a new species
a. Divergent evolution (adaptive radiation) –
 start with one species and eventually become two

can be caused by isolation mechanisms (behavioural – I
don’t want to mate with you, geographic – I can’t mate
with you, temporal- sorry, wrong time)
b. Convergent evolution
 A process where unrelated organisms come to
resemble one another


Analogous structures develop based on how the
organism interacts with its environment
Structures with similar functions but have different
origins (wings in a bird or wings in a bat or wings in a
moth)
c. Co-evolution

two species evolve in response to changes in each
other over time (ie. Flowers and pollinators)