1. The Theory of Evolution
Chapter 15
The Theory of Evolution

2. & Evidence for Evolution
15-1 Natural Selection
& Evidence for Evolution
The idea that life evolves was first
Proposed by Lucretius 1900 years ago!

3. His idea was not fully considered until The middle of the 1800’s.
In 1859, the English naturalist
Charles Darwin published convincing
Evidence that species evolve, and
He proposed a reasonable mechanism
Explaining how evolution occurs.

4. Like all scientific theories, the theory
Of evolution has developed over
Decades of experimental data.
Today almost all scientists accept
That evolution is the basis for the
Diversity of life on Earth.

5. The theory of evolution has 4 parts:
Variation exists with the genes of
Every population of species
(the results of mutation)
2) In a particular environment, some
Individuals of a population or species
Are better suited to survive and
Have more offspring than others.

6. 3) Over time, the traits that make Certain individuals of a population
Able to survive and reproduce
Tend to spread in that population.
4) There is clear proof from fossils
And many other sources that living
Species evolved from organisms
That are extinct.

7. Naturalist for the naval voyage of The HMS Beagle.
In 1831, Darwin became the
Naturalist for the naval voyage of
The HMS Beagle.
The purpose of the voyage was to
Survey the coast of South America.

8. During his voyage on the Beagle, Darwin found evidence that challenged
The traditional belief that species
Are unchanging.
As Darwin visited the many places
On his voyage, he saw things that
Seemed as if they could only be
Explained by a process of
gradual change.

9. On the Galapagos Islands, Darwin Discovered different varieties of
Finches that had different beaks.
The birds looked similar, but had
Evolved beaks that suited the
Environment where they ate.

11. When Darwin returned from his Voyage, he continued his lifelong
Study of plants, animals, and geology.
He didn’t report his findings called
“evolution” until much later.

12. After reading an essay by Thomas
Malthus, Darwin made a key association,
Individuals that have physical or
Behavioral traits that better suit
Their environmental are more likely
To survive and reproduce than those
That do not have such traits.

13. Darwin called this process by which Populations change in response
To their environment, natural selection.
The changing of a species that results
In its being better suited to its
Environment is called adaptation.

14. In 1859, Darwin finally wrote down His ideas of evolution and natural
Selection in a book called
“On the Origin of Species by
Means of Natural Selection”
Many people were deeply disturbed by
It, including the church because it
Hints that humans may have evolved from apes.

15. Darwin’s ideas have been updated…
Natural selection causes change
Within population.
Such as, broccoli, cauliflower,
Brussels sprouts, and cabbage all
Come from the same plant!

16. In other words, natural selection Causes the frequency of certain
Alleles in a population to increase
Or decrease over time.
Isolation leads to species formation.

17. Isolation is the condition in which 2 populations of the same species
Cannon breed with one another.
This happens all the time, and is why
There are many different types of
Squirrels, and is the reason that
Darwin saw different types of
The same bird!

19. Extinction leads to species replacement.
Over long periods of time, events such
As climate changes and natural
Disasters result in some species
Becoming extinct, which means
That they disappear permanently.

20. 15-2 Mechanisms of Evolution

21. Fossils provide an objective record Of evolution.
A fossil is the preserved or
Mineralized remains or imprint
Of an organism that lived long ago.

22. Today Darwin’s theory is almost Universally accepted, based on a
Large body of supporting evidence,
Most scientists agree on the
Following 3 points…
1) Earth is about 4.5 billion years old.
2) Organisms have inhabited Earth for
Most of its history.
3) All organisms living today evolved
From earlier, simpler life-forms.

23. Although the fossil record will never Be complete, it presents strong
Evidence that evolution has
Taken place.
Paleontologists, scientists that study
Fossils, can determine that age of
Fossils fairly accurately by using
Radiometric dating.

24. Biological molecules contain a record Of evolution.
A common ancestor is a species
From which 2 or more species
Have diverged.
A phylogenetic tree shows how
organisms are related
through evolution.

25. Anatomy and development Suggest common ancestry.
Comparisons of the anatomy of
Different types of organisms often
Reveal basic similarities in
Body structures.

26. For example, sometimes bones (or other structures) are present
In an organism but are reduced in
Size and either have no use or
Have a less important function.
Such structures are considered to be
Evidence of an organism’s
Evolutionary past.

27. These structures are called
Vestigial structures.

28. Does evolution occur in spurts?
The model of evolution in which
Gradual change over a long period of
Time leads to species formation
Is called gradualism.
The model of evolution in which periods
Of rapid change in species is separated
By periods of no change is called
Punctuated equilibrium.

29. Darwin wrote: “Can we doubt… that Individuals having any advantage,
However slight, over others, would
Have the best chance of surviving
And of procreating their kind?”

30. There are 5 main elements to Natural Selection…
1) All species have genetic variation.
2) The environment presents many
Different challenges to an individual’s
Ability to reproduce.

31. 3) Organisms tend to produce more Offspring than their environment
Can support; thus, individuals of a
Species often compete with
One another to survive.
4) Individuals within a population that
Are better able to cope with the
Challenges of their environment tend
To leave more offspring than those
Less suited to the environment.

32. 5) The traits of the individuals Best suited to a particular
Environment tend to increase
In a population over time.

34. The key lesson scientists have learned About evolution is that the
Environment dictates the direction
And amount of change.
A well studied example of natural
Selection in action is
Industrial melanism.

35. Industrial melanism is the darkening Of populations of organisms over
Time in response to industrial pollution.
The best known case is the
European Peppered Moth.

36. The formation of new species Begins with small changes.
The accumulation of differences
Between groups is called divergence.
Biologists call the process by which
New species form speciation.

37. Overtime, populations of the same Species that differ genetically
Because of adaptations to different
Living conditions become what
Biologists call ecological races.
Eventually races may become so
Different that they can no longer
Interbreed successfully, biologists
Then consider them a new species.

38. What keeps a new species separate?
Reproductive isolation is the inability
Of formerly interbreeding groups
To mate or produce fertile offspring.
This may happen due to geographical
Reasons, or environmental reasons.

39. THE END