1. Evolution—The Theory and Its Supporting Evidence

2. Darwin & the Galápagos Charles Darwin’s five-year voyage
( ) on the HMS Beagle
Visited the Galapagos Islands & observed similarities & differences among many organisms

3. Darwin’s Theory Darwin’s observations:
Fossil mammals in S. America were similar het different from present-day llamas, sloths, & armadillos
Finches & tortoises living on the Galapagos Islands vary from island to island
Yet resembled ones from S. America
Observations convinced Darwin that organisms descended with modification
Central claim of the Theory of Evolution

4. Galápagos Finches Darwin’s finches from the Galápagos Islands
arranged to show evolutionary relationships
Notice that beak shape
varies depending on diet
Berry eater
Insect eaters
Seed eaters
Cactus eaters

5. Why Study Evolution? Evolution Evolution is a unifying theory
involving inheritable changes in organisms through time
is fundamental to biology and paleontology
Paleontology is the study of life history as revealed by fossils
Evolution is a unifying theory
explains an otherwise encyclopedic collection of facts
Evolution provides a framework for discussion of life history

6. Misconceptions about Evolution
Many people have a poor understanding of the theory of evolution
Misconceptions include:
evolution proceeds strictly by chance
there are no transitional fossils
so-called missing links
connecting ancestors and descendants
humans evolved from monkeys
so monkeys should no longer exist

7. Evolution: Historical Background
Theory usually attributed solely to Charles Darwin
But it was considered long before by some ancient Greeks, philosophers & theologians during the Middle Ages.
Jean-Baptiste de Lamarck ( )
Remembered for his theory of inheritance of acquired characteristics
New traits arise in organisms
because of their needs &
somehow passed on.
Refuted decades later with
the discovery of genes

8. Lamarck’s Giraffes
According to Lamarck’s theory of inheritance of acquired characteristics
ancestral short-necked giraffes
stretched their necks
to reach leaves high on trees.
Their offspring were born
with longer necks

9. Darwin In 1859, Charles Robert Darwin (1809-1882) in which he detailed
published On the Origin of Species
in which he detailed
his ideas on evolution formulated 20 years earlier
proposed a mechanism for evolution

10. Natural Selection Plant and animal breeders
practice artificial selection
selecting those traits they deem desirable and then breed plants and animals with those traits
Observing artificial selection
gave Darwin the idea that a process of selection among variant types in nature could also bring about change
Natural Selection
Natural process of selecting only a few individuals for survival

11. Natural Selection—Main Points
Organisms in all populations
possess heritable variations
size, speed, agility, color, etc.
Some variations are more favorable than others
some have a competitive edge in acquiring resources and/or avoiding predators
Not all young survive to reproductive maturity
Those with favorable variations are more likely to survive and pass on their favorable variations

12. Naturally Selected Giraffes
Example: giraffe’s long neck evolved
because ancestors with longer necks had an advantage and reproduced more often

13. Natural Selection Sometimes expressed as “survival of the fittest”
One misconception about natural selection
is that among animals only the biggest, strongest, and fastest are likely to survive
These characteristics might provide an advantage
but natural selection may favor
the smallest if resources are limited
the most easily concealed
those that adapt most readily to a new food source
those having the ability to detoxify some substance
and so on...
Survival of the Fittest comic

17. Modern View of Evolution
During the 1930s and 1940s,
paleontologists, population biologists, geneticists, and others developed ideas that merged to form a modern synthesis
neo-Darwinian view of evolution
They incorporated
chromosome theory of inheritance into evolutionary thinking
seeing changes in genes (mutations) as one source of variation

18. What Brings about Variation?
Reshuffling of genes from generation to generation
During sexual reproduction
potential for variation is enormous
with thousands of genes, each with several alleles, and with offspring receiving 1/2 of their genes from each parent
New variations arise by mutations
change in the chromosomes or genes
Mutations that take place in the gametes are inheritable
May be beneficial, neutral, or harmful

19. What Causes Mutations? Some mutations are induced by mutagens
agents that bring about higher mutations rates such as
some chemicals
ultraviolet radiation
X-rays
extreme temperature changes
Some mutations are spontaneous
occurring without any known mutagen

20. Styles of Evolution Divergent evolution occurs
when an ancestral species gives rise to diverse descendants adapted to various aspects of the environment
Divergent evolution leads to descendants
that differ markedly from their ancestors
Convergent evolution involves the development
of similar characteristics
in distantly related organisms

21. Divergent evolution

22. Convergent Evolution

23. Convergent Evolution

24. Cladistics and Cladograms
Traditionally, scientists have
depicted evolutionary relationships
with phylogenetic trees
in which the horizontal axis represents
anatomical differences
vertical axis denotes time
In contrast, a cladogram shows
the relationships among members of a clade
a group of organisms including its most recent common ancestor
Cladistics focus on derived characteristics
method of grouping animals that makes use of lines of descent rather than structural similarities

25. Cladogram A cladogram showing inferred relationships
Some of the characteristics used to construct this cladogram are indicated

26. Two Steps in Natural Selection
Evolution by natural selection
is a 2 step process
Only the first step involves chance
Variation must be present
or arise in a population
Whether a mutation is favorable
is a matter of chance
The natural selection of favorable variations
is not by chance

27. Evidence in Support of Evolution
Darwin cited supporting evidence
for evolutionary theory such as
classification
embryology
comparative anatomy
geographic distribution
fossil record, to a limited extent
He had little knowledge
of the mechanism of inheritance,
and biochemistry and molecular biology
were unknown at his time

28. Biological Evidence Supporting Evolution
If all existing organisms descended with modification
from ancestors that lived during the past,
all life forms should have fundamental similarities:
all living things consist mainly of carbon, nitrogen hydrogen and oxygen
their chromosomes consist of DNA
all cells synthesize proteins
in essentially the same way

29. Structures with Similarities
Homologous structures
are basically similar structures
that have been modified for different functions
They indicate derivation from a common ancestor.
Analogous structures are structures
with similarities unrelated
to evolutionary relationships
that serve the same function
but are quite dissimilar
in both structure and development

30. Homologous Structures
Forelimbs of humans, whales, dogs, and birds
are superficially dissimilar,
yet all are made up of the same bones,
have similar arrangement
of muscles, nerves and blood vessels,
are similarly arranged with respect to other structures,
have similar pattern of embryonic development

31. Analogous Structures Wings of insects, birds and bats
serve the same function but differ in structure and embryological development
Are any of these wings
both analogous and homologous?
Yes, bird and bat wings

32. Evolution in Living Organisms
Small-scale evolution can be observed today.
For example
adaptations of some plants to contaminated soils
insects and rodents developing resistance to new insecticides and pesticides
development of antibiotic-resistant strains of bacteria
Variations in these populations
allowed some variant types
to live and reproduce,
bringing about a genetic change

33. What do We Learn from Fossils?
The fossil record consists
of first appearances of various organisms through time
One-celled organisms appeared
before multicelled ones plants appeared before animals invertebrates before vertebrates
Fish appeared first followed
in succession by amphibians, reptiles, mammals, and birds