Transcript 10. Darwin and more

_____. Darwin
“Nothing in biology makes sense except in the light
of evolution.”
Biologist (1900 – 1975)
Charles Darwin at age 31
Charles Darwin in later years
What is Evolution?
Evolution - the gradual change in a
species over time.
Darwin at age 31 in 1840
(4 years AFTER his voyage)
Darwin’s Voyage of Discovery
A reconstruction of the HMS Beagle sailing off Patagonia (South America).
The Voyage of the Beagle
The Galapagos
Islands
Darwin’s
Finches
Observe the
different feather
colors, and
different size and
shape of the beaks.
AdaptationA trait that helps an organism survive and
reproduce.
Ex. The Finch’s Beak helps it to obtain
food.
Draw this table with only the column headings.
Make this table VERY LARGE!
Darwin’s
Observations
1
2
3
4
Darwin’s
Conclusions
In your own
words!
Darwin’s Observations and Conclusions
Observation 1: Species over-produce
(reproduce in excess). Many more are
produced than can ever survive to adulthood.
Observation 2: Environmental
resources (food, water, habitat) are
limited.
Conclusion #1: When the environment cannot support the number
of individuals, it leads to a struggle for existence (competition)
among individuals, with only some of offspring surviving in each
generation.
Over-production + limited resources  competition
In other words….
When there are too many organisms in one
place, they have to compete for:
– Food
– Living Space
– Water
»They do not all survive.
Darwin’s Observations and Conclusions
Observation 3: There is variation in characteristics of individuals in
a population - no two individuals are exactly alike.
Observation 4: Much of this variation between individuals is
inheritable (passed from parents to offspring).
Variation in Birds
Variation in Dogs
Variation in Humans
Darwin’s Observations and Conclusions
Conclusion 2: Survival in
the struggle for existence
depends partly on the
inherited characteristics of
individuals.
Individuals who inherit
characteristics best fitted
to their environment are
more likely to survive and
reproduce than less fit
individuals.
Inherited Variations + Competition  Natural Selection
In other words….
Survival of the Fittest!
Organisms that are best suited (adapted) to their
environment will survive and reproduce!
Their offspring will inherit this helpful
adaptation and will survive and reproduce.
 Their offspring will inherit this helpful
adaptation and will survive and reproduce.
And so on…..
Example Page 143
Example Page 144
Darwin’s Observations and Conclusions
Conclusion 3: The unequal ability of individuals to survive and
reproduce leads to a gradual change in a population, with favorable
characteristics accumulating over generations.
Natural Selection + Time  Evolution
Taken together, these three conclusions are a statement of Darwin’s
Theory of Evolution.
Darwin’s Points
• Species over-produce (reproduce in excess). Many more
offspring are produced than can ever survive to adulthood.
• Limited resources (food, water, shelter) lead to
competition for these resources.
• There is variation within the population. Some of these
variations have an advantage over others.
• Those species members with an advantage will be
selected to survive and reproduce, and their offspring will
inherit this advantageous trait.
• As a consequence the species will change over time.
V*I*S*T
V
V = Variation: All life forms have variations (differences in
I
I = Inheritance: Genetic traits are inherited from parents
S
T
traits between members of a species). Some examples in
humans: height, skin color, eye color
and are passed on to offspring.
S = Selection: Organisms with traits that are favorable to
their survival get to live and pass on their genes to the next
generation.
T = Time: Evolution takes time; usually, millions of years.
Evolution can happen in a few generations (for example, in
bacteria and viruses), but major changes take long periods of
time.
Evolution “Equations”
O
Overproduction
+
LR
C
Limited
Resources
Competition
Evolution “Equations”
IV
Inherited
Variations
C
+ Competition
NS
Natural
Selection
Evolution “Equations”
NS
Natural
Selection
+
T
E
Time
Evolution
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
mutation!
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
Generation 4: 0.12 not resistant
0.88 resistant
Evolution’s Core Principle
Natural Selection
“I have called this principle, by
which each slight variation, if
useful, is preserved, by the
term Natural Selection.”
—Charles Darwin from "The
Origin of Species"
Mutation
= random, inheritable changes in DNA
sequences that introduce new alleles into a
species’ gene pool.
•members.tripod.com/~Alphacentaur/ X-men.JPG
The Missing Link: HOW does Evolution occur?
A major problem in Darwin’s theory was the lack
of a mechanism to explain natural selection.
How were favorable variations (adaptations)
passed on to later generations?
With the rediscovery of Mendel’s work in the
first half of the 20th century, the missing link in
evolutionary theory was forged.
Darwin’s theory supported by genetics is
known as the modern synthesis.
Darwin
Is evolution progressive?
This is not an easy question to answer. From a plant's perspective, the best
measure of progress might be photosynthetic ability; from a spider's it might be
the efficiency of its web in catching insects.
The problem is that we humans think it’s
“all about us”! We often define progress
by how it affects our species. But that
definition is anthropocentric.
It is tempting to see evolution as a grand
progressive ladder with Homo sapiens
emerging at the top. But evolution
produces a tree, not a ladder — and we
are just one of many leaves on the tree.
The “Tree of Life”
•Animals are the newcomers in the evolution of life on Earth.
•All living things are “cousins”; some more distant than others.
Plant Evolution
Cone-bearing
plants
Ferns and
their relatives
Flowers; Seeds
Enclosed in Fruit
Mosses and
their relatives
Seeds
Water-Conducting
(Vascular) Tissue
Green algae
ancestor
Flowering
plants
Evolution links
Evolution Exploratour
Understanding Evolution
Univ. Calif. Museum of Paleontology
Evolution: PBS