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5.4 - EVOLUTION
“Nothing in biology makes sense
except in the light of evolution.”
Theodosius Dobzhansky, 1973
IB Biology
Stephen Hawking

“A good theory will describe a large range of
phenomena on the basis of a few simple
postulates and will make definite predictions
that can be tested. If the predictions agree with
the observations, the theory survives that test,
though it can never be proved to be correct.
On the other hand, if the observations disagree
with the predictions, one has to discard or
modify the theory.”
Source: The Universe In A Nutshell
Just a theory –
http://www.youtube.com/watch?v=85diEXbJBIk
What is Evolution?

Evolution is
the cumulative change in
the heritable characteristics of
populations
that occurs over
successive generations
Who can evolve?


Individuals cannot evolve!
◦ Individuals cannot change their genes.
Populations are the smallest unit that can evolve.
◦ Populations can have a shift in their gene pool.
Why would populations evolve?
•So that a population becomes better suited
to its habitats.
•Increased survival
•Better chance of passing on
characteristics to offspring.
•Takes place over many generations.
How does a population evolve?
A shift in the gene pool so that a higher
ratio of individuals have a particular
adaptation.
 Adaptation

◦ a particular structure, physiology or behaviour
that helps an organism survive and reproduce
in a particular environment.
 e.g. camouflage, superb sense of smell, bill shape
Lamark
Theory of acquired characteristics

Lamark said
organisms acquired
traits by using their
bodies in new ways

These new
characteristics were
passed to offspring

Lamark was totally
wrong!
What did
Darwin’s Travels
reveal?
Origin of the Species
“can we doubt (remembering that
many more individuals are born
than can possibly survive) that
individuals having any advantage,
however slight, over others, would
have the best chance of surviving
and of procreating their kind? On the
other hand, we may feel sure that any
variation in the least degree
injurious would be rigidly
destroyed. This preservation of
favourable variations and the
rejection of injurious variations, I call
Natural Selection.”

The diversity of living
species was far greater
than anyone had
previously known!!

These observations led
him to develop the
theory of evolution by
Natural Selection!!
Who was Darwin?
Charles Darwin
http://www.youtube.com/watch?v=vmphl
bRhLu8&list=PL0DE312300D53EB93
How did tortoises and birds differ
among the islands of the Galapagos?

Each island
had its own
type of
tortoises and
birds that
were clearly
different
from other
islands
How 1 finch became 13 distinct species?




Darwin's finches share similar size, coloration, and
habits. Their salient difference is in the size and shape of
their beak.
Once on the islands, the various species established
themselves and determined territories. Evolution then
set in and many unique species, of finches, resulted.
These finches probably descended from one type of
ancestor and then, due to isolation and through chance,
different climates and natural forces such as food
availability and type, they evolved into thirteen different
types of finches.
The process of their evolution would probably have
begun with immigrants from the mainland. As they
dispersed to different islands, new populations would be
formed. Every time these satellite populations dispersed,
there would be greater difference between the
individual species.
Natural Selection & Descent with Modification

The traits that help
an organism survive
in a particular
environment are
“selected” in
natural selection

Each living species
has descended with
changes from other
species over time
Natural Selection and Species Fitness



Overtime, natural
selection results in
changes in the
inherited
characteristics of a
population.
These changes
increase a species
fitness (survival rate)
Those that survive,
reproduce and pass on
their genes. These are
the genes that persist
in the population.
How does evolution really
happen?
http://www.youtube.com/watch?
v=xkwRTIKXaxg
Summary of Natural Selection







Individuals within a species vary in many ways
Some of this variability is heritable
Every generation produces far more offspring than can
survive
Members of the same species compete
Individuals with favourable variations are more likely to
survive
As these individuals contribute proportionately more
offspring to succeeding generations, the favourable variations
will become more common.
Species alive today are descended with modifications from
common ancestors
Example of a population that evolved:
Industrial Melanism in Peppered
moths in England
Evolution is a Theory – Just like
Gravity!
Evolution is a well
supported
explanation of
phenomena that
have occurred in
the natural world
• A theory in science
is a well tested
hypothesis, not just
a guess
•
How do we know evolution happens?
http://www.youtube.com/watch?v=ewtw
_nZUIDQ
Evidence of
Evolution
Fossil Record
provides evidence
that living things
have evolved
Fossils show the
history of life on
earth and how
different groups of
organisms have
changed over time
Whales evolved from landdwelling mammals
(Whales Evolution)
http://www.youtube.com/watch?v=8cn0kf8mhS4
Evolution - giant whales - BBC science
http://www.youtube.com/watch?v=xCx-nwkj8fU
Carbon-14 Dating http://www.youtube.com/watch?v=phZeE7Att_s
Homologous Body
Structures
◦
◦
◦
◦
Structures that have
different mature forms
but develop from the
same embryonic tissues
Homology = Same
structure, different
function
e.g. Wing of bat, human arm,
leg of horse
Analogy = Different
structural origin, same
function
E.g. Wing of bat, wing of bird
Turtle
Alligator
Bird
Homologous Body Structures
Vestigial Organs


traces of homologous organs
in other species
Organ that serves no useful
function
◦ e.g. Appendix, wisdom teeth, and
tailbone in Humans
◦ Pelvic Bones in whales
◦ Hind leg bones in snakes
◦ Dew claw in dogs
Embryology
Similarities in
Embryology
In their early stages
of development,
chickens, turtles and
rats look similar,
providing evidence
that they shared a
common ancestry.
Artificial Selection and Selective Breeding



nature provides variation,
humans select variations that are
useful.
Example - a farmer breeds only
his best livestock
Most domesticated animals are
selectively bread
Review
Crash course – Natural Selection
http://www.youtube.com/watch?v=aTftyFboC_M
Crash course – evolulution
http://www.youtube.com/watch?v=P3GagfbA2vo