Transcript Evolution Powerpoint

Evolution
What We Now Know
Creationism
The traditional Judeo-Christian version of
creationism was strongly reinforced by
James Ussher , a 17th century Anglican
archbishop of Armagh in Northern Ireland. By
counting the generations of the Bible and
adding them to modern history, he fixed the
date of creation at October 23, 4004 B.C.
Evolution
The Creation of
Adam is a section of
Michelangelo’s
fresco on the ceiling
of the Sistine Chapel
painted in 1511.
 Evolution is the process in which significant changes in
the inheritable traits (genetic makeup) of a species
occur over time.
 What evidence supports this change of thinking?
1. Fossil Evidence
- Shows a record of the diversification of species
- It also shows the record of the extinction of many
others.
Mass Extinctions
 Why are mass extinctions important?
 They stimulate new biodiversity!
 No competition.
 geographic distribution of living species gave scientists
clues to the patterns of evolution
1. Fossil Evidence
- Shows a record of the diversification of species
 What exactly is a fossil:
- Any preserved remains or traces of an organism or its
activity.
- In 1669 Nicholas Steno detailed an impressive analysis
of fossils showing that they were the remains of living
organisms
- fossils form in sedimentary rocks
How does a fossil form?

Organisms must die and then be rapidly buried to prevent scavengers or rapid
decomposition (if there are only soft parts).
There are two types of
fossils:
 Body Fossils which are actual remains:
Includes actual bones, shark’s tooth, petrified wood,
frozen mammoth, insects in amber.
 Trace Fossils which include: Mold or Cast formed by
replacement
Or footprints, worm trails, coproliths, or
stomach stones
Ages of Rocks

Relative Age – age of rocks and the relative age of fossils can be determined by
the chronology of the rock layers. Oldest on bottom, youngest on top.

Absolute Age – determined by radioactive decay (radioactive dating using half
lives)

C14 has a half life of 5730 y

K 40 has a half life of 1.3 b.y.
Charles Lyell
 Proposed that the earth’s surface has changed and
continues to change through similar gradual processes.
 1851 visited Joggins
Index Fossils
 Used to determine ages of rock layers
Examples of index fossils:
 Short lived, easy to identify
2. Structures – Homologous
and Analogous
 Homologous- structures that share a common origin
but may serve different functions in modern species
Long bone
Two short bones
 Example of Homology:
the tetrapod limb
 The wing of a dragonfly and the wing of a butterfly are
homologous — they were both inherited from an
ancient flying insect.
 Not all homologies are obvious if they have been
adapted for different roles. For example, the chomping
front teeth of a beaver look quite different than the
tusks of an elephant. Each is a modification of the basic
incisor tooth structure
 Homologies show that Divergent Evolution takes
place
Divergent Evolution:
A common ancestor evolves into new species, which
continue to evolve and become less and less alike over
time due to differences in the demands driven by the
environment.
 Brown Bears and Polar Bears illustrate divergent
evolution.
 Scientists think that a long time ago a group of Brown Bears became
geographically separated from the rest. This isolated group acquired new
characteristics, such as the ability to eat meat, blubber to keep warm in
snowy weather, and a white coat for camouflage. They slowly evolved into
Polar Bears
 Analogous – structures similar in function but not in
origin
So what about ANALOGY??
 Consider the following example....
 Both are extinct animals and both of them have saberteeth...but are they
homologous??
(Consider that Australia had separated from the Supercontinent a
loooooong time ago)
Thylacosmilus,
a marsupial mammal
Smilodon, the saber-toothed cat,
which is a placental mammal
They are Analogous!
analogy
similarity due to convergent evolution not common ancestry
CONVERGENT Evolution: When two separate groups of
animals evolve to have similar structures
How do analogies evolve?
Often, two species face a similar problem or challenge.
Evolution may then shape both of them in similar ways —
resulting in analogous structures.....like the saber teeth.
Another good example of Analogous structures......
While sugar
gliders
(marsupials)
superficially
resemble the
placental flying
squirrels of
North America,
the ability to
glide through
the air evolved
independently
in these
unrelated
mammals.
So there you have it.....
HOMOLOGY vs.
ANALOGY
 Embryonic Development – Embryos of different
organisms can have homologous features
 Human embryos have a tail
 Vestigial Features- Structures which serve no useful
function in a living organism
 Digits (dogs)
 Hipbones (whales)
Now the evidence continues
 Lamarck – each species gradually became more complex
and that new simple species were created by spontaneous
generation (He did not believe that a single species could
give rise to additional species (no common ancestor)).
- He believed in the inheritance of acquired traits (changes in
an individual resulting from interaction with the
environment) Giraffe’s with longer necks (acquired trait
inherited by the offspring)
- -now know that acquired traits cannot be inherited
- -he does deserve credit for his recognition of the role of the
environment in driving evolutionary change
“Use and Disuse” –
CHARACTERISTICS
that were in constant
use developed (were
ACQUIRED) and those
that were not used
were LOST.
Wallace Vs. Darwin
 Darwin always put the emphasis on selection acting on
individuals whereas Wallace (the letter writer)
apparently thought selection acted on groups or
species. That selection acts on the individual, due to
competition between individuals of the same species, is
one of the key points in Darwin’s theory.
 Another apparent difference is that Darwin emphasised
competition within populations as the driving force for
evolution wheres Wallace put more emphasis on the
species meeting the demands of a change in their
environment.
Darwin…..
 Set sail in 1831 on the HMS Beagle
 Voyage lasted 5 years
 He recorded and collected specimens in South America
 Reached the Galapagos Islands and noted that the flora and
fauna although similar to South America, also had unique
traits
 Darwin came to the conclusion that perhaps a single
ancestral species transported from a single nearby island
might give rise to a number of similar but distinct new
species
 Adaptive Radiation is an example of Divergent
evolution (remember the bears) but happens more
quickly

 Consider Darwin’s finches...each evolved a new
beak to fill a wide range of ecological niches...or
ADAPT.
How did one species of finch become so many species?
http://www.youtube.com/watch?v=l25MBq8T77w&feature=related
 Darwin’s finches had differences in their beaks.
 Beaks are associated with eating different foods.
 Darwin’s conclusions:
 Small populations of original South American finches land on
islands. The variations in the beaks allowed individuals to gather
food successfully in different environments.
 Over
the population of finches changed both
anatomically and behaviorially.
emerged
The most recognized symbol of the Galapagos is the tortoise. When
Charles Darwin visited the Galapagos Islands, the vice-governor of
the Islands told him that he could identify what island the tortoise was
from simply by looking at him.
Artificial Selection Vs. Natural
Selection
 Darwin believed that there must be a mechanism of
inheritance that would provide the key to the
evolutionary process.
 He studied the structures, functions and behavior of
species.
 He also looked for evidence of changes in populations
of organisms that were reproducing.
 Humans have been improving domesticated plants and animals species for
thousand of years.
 Offspring are selected with desirable traits as breeding stock of the next
generation
 Selective breeding techniques have led to these genetically superior
beef cattle that have incredible muscles and strength known as “Belgian
Blue”. Modern breeds of Belgian Blue cattle are the creation of genetic
engineering, with the specific goal of expanding the muscular content of the
animals as much as possible.
 http://www.youtube.com/watch?v=Nmkj5gq1cQU&feature=related
Useful Selective Breeding
Artificial selection has been used in modern farming to
get:
- The best beef cattle – taste and texture
- The best milking cows – yield and disease resistance
- Wheat – better yields and disease resistance
- Flowers – bigger and more colourful
- Chickens – egg size and number
Natural Selection
 Thomas Malthus – postulated that in nature, plants and
animals produce far more offspring than are able to
survive.
 Darwin realized that if far more offspring are born than
can survive and reproduce, there must be intense
competition among the individuals to survive. “Survival
of the Fittest”.
 The mechanism causing evolution was natural
selection. All species exhibit inheritable variations that
are selected through the struggle by individuals for
survival within their populations.
 Individuals with more favourable traits produce more
offspring that survive than others and pass along those
favourable traits. Over many generations this process
results in change in the inheritable traits of the population.
 On November 24, 1859
Darwin published “On the
Origin of Species”
(prompted by a letter
from Alfred Russel Wallace who
had come up with the
same idea).
A Summary of Darwin’s Ideas (Steps of Natural
Selection)
 1. Many more offspring are born each season than can possibly survive to
maturity. As a result, there is a struggle for existence- competition.
 2.Individual variation exists in natural populations.
 3. Individuals with advantageous variations survive and pass on their
variation to the next generation.
 4. Characteristics beneficial in the struggle for existence will tend to become
more common in the population, changing the average characteristics of the
population (adaptations).
Over long periods of time, and given a steady input of new variations into a
population, these processes lead to the emergence of new species.