Evolution
1800’s
The Evolution of Evolution
Fossil discovery confounded scholars who held
notion of a single time of creation; species
were perfect and unchanging.
Jean Baptiste Lamarck’s ideas:
• organisms evolve by the use and disuse of body parts
• Inheritance of acquired characteristics
Alfred Wallace and Charles Darwin introduced
the idea of Natural Selection which has been
supported by evidence since the 1850’s.
Darwin’s Voyage on the Beagle
• 1831
• Collected organisms, became the ship’s
naturalist
Influences on Darwin….
• Lyell’s
• Malthus
• Wallace
Evolution explains the unity and
diversity of life
• The history of life, as documented by fossils, is a
saga of a changing Earth
– billions of years old
– inhabited by an evolving cast of life forms.
• Evolution accounts for life’s similarities and
differences! What similarities???
A theory of evolution by natural selection is
an explanation of life’s diversity.
Darwin observed the following:
Populations produce more offspring than survive.
Population size remains relatively stable.
Resources are limited.
Individuals compete for resources and survival.
Individuals of a species have different traits.
The variation of traits was passed from parent to offspring.
The most fit organisms survive. (“survival of the fittest”)
Evolution occurs as favorable traits accumulate in the
population.
Darwin studied examples of artificial selection
A theory of evolution by natural selection is
an explanation of life’s diversity.
The cornerstone of biology….the theory that helps us
understand how life began and continues to succeed…..
Evolution by means of natural selection.
1) Members of a species (population) vary in traits &
pass those traits onto offspring. (VARIATION)
2) Certain forms of traits are better adapted to the
environment than others. (FAVORABLE TRAITS)
3) Individuals with the better adapted traits are more likely to survive & reproduce
than those without such traits (FITNESS & REPRODUCTION)
4) Therefore, the trait better adapted to the environment become more common in
future generations. The traits not well adapted become less common. The
population has evolved. (FAVORABLE GENES PAST ON TO NEXT
GENERATION)
NATURAL SELECTION
Darwin's basic idea of natural selection. The concept is simple; individuals in populations vary
slightly from one another. Some of those variations help the individuals that possess them to
produce more offspring than others. Those offspring, in turn, inherit the successful variations
and produce more offspring themselves.
As generations pass, the population evolves towards the variation that is the more successful
.
There are IMPORTANT points
about evolution by natural selection 1. Individuals do not evolve: populations evolve.
2. Natural selection can amplify or diminish only heritable
traits. Acquired characteristics cannot be passed on to
offspring.
3. Evolution is not goal directed and does not lead to
perfection. Favorable traits vary as environments
change.
4. Organisms do not evolve structures because of want or
need. Instead, evolution is a passive process in which
the environment favors certain traits that exist within a
population. Adaptations evolve in populations.
Organisms do not actively or willingly evolve.
Peppered Moths…
http://www.biologycorner.com/worksheets/pepperedmoth.html
Types of Evidence
• Fossil Record (Paleontology)
fossil remains indicate different organisms than today
• Biogeography
unrelated species, in similar environments look alike
• Comparative Anatomy
structures are similar among different organisms (homologous)
structures with no function (vestigial)
• Embryology
patterns of development similar
• Molecular Biology
same or similar proteins, all organisms have DNA
Fossils
• Mostly found in sedimentary rock
• Unique conditions result in a fossil
molds, casts,
• Fossil record helps to reconstruct patterns
and trend in the history of life
Comparative Morphology:
Homologous Structures
Comparative Morphology:
Vestigial Structures
• In humans
– Wisdom teeth
– Appendix
– Tail bone
• In Snake
– Pelvic girdle
• In Whales
– Pelvis and femur
Comparative Embryology
All vertebrate
embryos go
through the same
early phases.
Comparative Biochemistry
• DNA
• Protein comparisons
– Cytochrome c
Biochemical similarity
is greatest among
closely related species.
• Human & Chimp the same
• 104 amino acids
• 56 different between humans & yeast
– Hemoglobin
Homologies indicate patterns of descent that can
be shown on an evolutionary tree
 Darwin was the first to represent the history of life
as a tree,
– with multiple branchings from a common ancestral trunk
– to the descendant species at the tips of the twigs.
 Today, biologists
– represent these patterns of descent with an
evolutionary tree, but
– often turn the trees sideways.
Lungfishes
Amniotes
Mammals
2
Tetrapod
limbs
Amnion
Lizards
and snakes
3
4
Crocodiles
Ostriches
6
Feathers
Hawks and
other birds
Birds
5
Tetrapods
Amphibians
1
The phylogenetic tree of reptiles shows that crocodilians
are the closest living relatives of birds.
Lizards
and snakes
Crocodilians
Pterosaurs*
Common
ancestor of
crocodilians,
dinosaurs,
and birds
They share numerous features,
including four-chambered hearts,
“singing” to defend territories, and
parental care of eggs within nests.
Ornithischian
dinosaurs*
Saurischian
dinosaurs*
Birds
A cladogram showing the emergence of new traits
Frog
Iguana
Duck-billed
platypus
Amnion
Kangaroo
Hair,
mammary
glands
Gestation
Beaver
Long gestation
Phylogenetic Tree