Transcript Darwin`s Theory of Evolution

Darwin’s Theory of
Evolution
Chapter 15
The Puzzle of Life’s Diversity


Biological Diversity – the variety of living things
- describes the millions of different shapes, sizes &
habitats on Earth
Evolutionary Theory – a possible answer to
explain the diversity of living things
- a collection of scientific facts, observations, and
hypotheses.
Evolution


Change over time
The process by which modern organisms have
descended from ancient organism
Charles Darwin


Born in England on Feb. 12, 1809
(same day as A. Lincoln)
In 1831, he set sailed on the H.M.S Beagle for a
trip around the world
Darwin’s Observations

Patterns of Diversity:
1. plants and animals seem remarkably well
adapted to whatever environment they
inhabit (live)
2. organisms have many different ways to
survive & produce offspring
3. certain animals were only found on specific
continents, even though other continents
had similar environments .
Darwin’s Observations

Living Organisms and Fossils:
1. Darwin collected many fossils:
- preserved remains of ancient
organisms
2. he realized that some resembled living
organisms and others looked completely
unlike any other creature.
3. These fossils made Darwin wonder how so
many species disappeared & if they were
related to living things now
Charles Darwin
Galapagos Islands





Small group of islands located off S. America
Very different climates even though there are
close together
Darwin used his observations from these islands
to create his Theory of Evolution
He studied land tortoises & marine iguanas and
observed differences between each island
Most importantly he studied birds called a Finch
and observed and analyzed their differences in
their beaks
Land Tortoises of the Galapagos Islands
.
Pinta
Pinta Island
Tower
Marchena
Intermediate shell
Fernandina
James
Santa Cruz
Isabela
Santa Fe
Hood Island
Floreana
Isabela Island
Dome-shaped shell
Hood
Saddle-backed shell
Land Tortoises
Land Iguana
Marine Iguanas
Marine Iguanas
Galapagos Islands from Space
H.M.S. Beagle
Finches
Finches
Finches
The Journey Home

Upon returning to England, Darwin thought about
his observations & asked himself 3 very important
questions:
1. Were the animals living on the different islands
once members of the same species?
2. If they were, how did these species evolve
after being separated onto the different islands?
3. If they did evolve (change) how did they do it?
Ideas that Shaped Darwin’s Thinking



Before Darwin’s time, most Europeans believed
that Earth and all life forms:
1. were created only a few 1000 years ago
2. had not changed since creation
During Darwin’s life, a lot of evidence was
discovered to change this way of thought
This made Darwin dramatically change his way
of thinking.
An Ancient, Changing Earth

During the 18th and 19th centuries, scientists
recognize:
1. Earth is millions of years old
2. processes that changed Earth in the past are the
same processes that are happening today

James Hutton
Charles Lyell
Jean Baptiste Lamarck
Thomas Malthus



James Hutton - 1795

He believed:
1. geological forces have shaped Earth
2. Earth was made of layers of rocks that form very slowly
3. rocks move up by forces beneath the surface & others are
buried & others are pushed up to make mountains
4. outer layer is shaped by natural forces – rain, wind, heat &
cold temperatures
5. All of these processes operate extremely slow – over
millions of years
6. Concluded that Earth is millions of years old
Charles Lyell





Wrote book called “Principles of Ecology”
Darwin read it when on the Beagle
He stressed that scientists must study past events to
understand the events they are observing now
His work explained how geological features could be
build up & broken down over long periods of time
It also helped Darwin understand how important
geological phenomena is on the location and
findings of fossils
Jean Baptiste Lamarck


French scientist who was one of the first to:
1. recognize that living things have
changed over time
2. all species were descended from other
species
3. organisms somehow adapted to their
environments
Lamarck’s work was published in 1809, the
same year Darwin was born
Lamarck’s Evolution Hypothesis

He proposed that by:
1. use or disuse of organs, organisms
gained or lose certain traits during
their lifetime.
2. These traits could then be passed on to
their offspring
3. Over time, this process led to change in a
species
Tendency Toward Perfection

Lamarck proposed that all organisms have an
innate tendency toward complexity &
perfection.

As a result, living things are always changing
& acquiring new traits to help to adapt &
survive
Use and Disuse



Lamarck proposed that organisms could
change the shape and size of certain organs by
using their bodies in new ways
If the organism used a new part of body, it
would develop into a new structure
If the organism disused the part of body, it
would decrease in size and over many
generations disappear.
Inheritance of Acquired Traits



Lamarck thought that acquired
characteristics could be inherited
Acquired Characteristics – traits you gain
from your own experiences and training
Example – if you spent your life lifting
weights to build your muscles, then your
children would inherit big muscles too!
Evaluating Lamarck’s Hypothesis

Incorrect in many ways:
1. He did not know how traits are inherited
2. He did not know that an organism’s
behavior has no effect on its inheritable
characteristics
** Lamarck was the 1st to develop a hypothesis of
evolution & to realize that organisms can adapt
to their environment.**
Thomas Malthus



Important influence on Darwin
In 1798, Malthus published a book that stated:
“If the human population continued to grow
unchecked, sooner or later there would be
insufficient living space & food for
everyone”
He felt that the only forces that could fight
against this were: war, famine, & disease
Darwin’s Thoughts on Malthus



He realized Malthus’ ideas applied to plants and animals
even more
Because animals & plants can reproduce much faster &
more numbers than humans
What Darwin did not realize at this time was:
1. majority of offspring die
2. only a few survive long enough to reproduce themselves
** Trying to figure out why the above occurs was the
central idea behind his explanation of evolutionary
change.**
When Is a Flipper a Wing?
All living things are related. Some
relationships are easy to see—your pet cat
may not roar like a lion, but it clearly
resembles one. Other relationships are less
obvious.

1. In your notebook, construct a table that has 5 columns & 6 rows.
In the columns, write the following headings:
Animal Group, Example, Legs, Fins, and Tail.
Then, place the following animal groups in their own row:
Mammal, Bird, Fish, Amphibian, Reptile, and Insect.

2. Give one example for each group, and then fill in the
information for that example.
For Legs, write in the number of legs that each animal has.
Do animals with fins have legs?
Do animals with wings have legs? If so, how many?

3. Can you tell from your table if a fish is more closely related to a
bird or to an amphibian? Explain your answer.
Animal
Mammal
Bird
Fish
Amphibian
Reptile
Insect
Example
Legs
Fins
Tail
Animal
Example
Legs
Fins
Tail
Mammal
elephant
4
No
Yes
Bird
Seagull
2
No
Yes
Fish
Shark
No
Yes
Yes
Amphibian
Frog
4
No
Yes/no
Reptile
Turtle
4
No
Yes
Insect
Ant
6
No
No
Darwin Presents His Case



It took 25 years for Darwin to present his
Theory of Evolution
1859 – “On the Origin of Species”
This book proposed:
1. a mechanism for Evolution called
Natural Selection
2. Evolution has been taking place for millions
of years & continues today
Details of the Origin of Species

Inherited Variations – differences that are
passed from parents to offspring
- Darwin had no idea how it happened
- We now know it is caused by variations in genes
- variations are found in both wild and
domesticated living things
Artificial Selection



When nature provides the variations and
humans select specific variations that they
find useful
Produces many diverse domestic animals &
plants
Example – breeding only the fastest horses
The Struggle for Existence


Darwin was convinced that Artificial Selection worked in
nature.
He knew that:
↑ birth rates & ↓ of basic needs = competition of resources
Struggle For Existence:
Members of each species regularly compete for the
necessities of life
Ex. Faster, bigger predators catch more prey
Faster, camouflaged, & protected prey will not be eaten
The Struggle for Existence (cont.)

Key Factor – how well suited an organism to its
environment

Fitness – ability of an individual to survive &
reproduce in its own environment
**the ability to ADAPT = ↑ FITNESS**
Adaptations


Any inherited characteristics that increases an
organisms chance of survival
3 types:
1. Anatomical – porcupine develops sharp quills
2. Physiological – plants being able to make
own food
3. Behavioral – living in groups & hunting
Survival of the Fittest



Individuals with traits that are not well suited to
their environment (low levels of fitness) will die
or leave few offspring
Individuals with traits that are well suited to their
environment (adaptations that enable fitness)
will survive & reproduce successfully
Darwin referred to Survival of the Fittest as
NATURAL SELECTION because it has
similarities to Artificial Selection.
Natural Selection





Traits being selected increase over time
Contribute to an organism’s fitness in its
environment
Over time, it results in changes in the
inherited traits of a population
Can only be observed as changes in a
population over many successive generations
Cannot be seen directly
Descent with Modification




Each living thing has descended with changes from other
species over time
Species today look different from their ancestors
Natural selection over long periods of time, produce
organisms with:
1. different structures
2. occupy different habitats
3. establish different niches
(place on the food web)
Also implies that all living organisms are related to one
another
Common Descent

All species – living and extinct – are from
common ancestors

A single “Tree of Life” links all living things
Evidence of Evolution


Darwin argued that living things have been
evolving on Earth for millions of years.
Evidence for this process could be found in the:
1. fossil record
2. the geographical distribution of living species
3. homologous structures of living organisms
4. similarities in early development, or
embryology
Fossils Record




Darwin saw fossils as a record of the history of
life
By comparing fossils in older layers with ones
from younger layers, we can document the indeed
life has changed over time
Transitional Fossils (between modern & ancient
species) have shorten the gap between the two
Gaps in the fossil record point out uncertainties
in our understanding of exactly how some species
evolved.
Geographical Distribution
of Living Things



Similar animals in different locations were the
product of different lines of evolutionary descent
However, because some animals on each
continent were living under similar ecological
conditions, they were exposed to similar
pressures of natural selection
Because of this, different animals ended up
evolving certain common features.
Figure 15–14 Geographic Distribution
of Living Species
Section 15-3
Beaver
Beaver
NORTH
AMERICA
Muskrat
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Capybara
SOUTH
AMERICA
Coypu
Coypu and
Capybara
Homologous Body Structures




Structures that have different mature forms but
develop from the same embryonic tissue
Evidence of evolution can also be found in living
animals
This provides strong evidence that all 4-limbed
vertebrates (has a backbone) have descended, with
modifications, from common ancestors
Vestigial Organs – homologous organs that have
been reduced in size – resemble miniature legs,
tails, or other structures. Does not effect the
organisms ability to survive or reproduce.
Figure 15–15 Homologous
Body Structures
Turtle
Alligator
Typical primitive fish
Bird
Mammals
Similarities in Embryology




Embryos of many animals with backbones are
very similar
Embryos look especially similar during early
stages of development
The same group of embryonic cells develop in the
same order and in similar patterns to produce
tissues and organs
These common cells & tissues, growing in similar
ways, produce the Homologous Structures
Strengths & Weaknesses of
Evolutionary Theory



Scientific advances in biology, geology and
physics, have confirmed and expanded most
of Darwin’s hypotheses.
Today, evolutionary theory offers great
information to all biological and biomedical
science.
Evolution is known as the “great unifying
theory of the life sciences”
Strengths & Weaknesses of
Evolutionary Theory


Like any theory, it continues to change as new
data is gathered & new ways of thinking come
about.
Researchers still debate:
1. how new species arise
2. why species become extinct
3. how life began
Summary of Darwin’s Theory

Page 386 – copy the 5 main points into your
notebook.