Emergence of Evolutionary Thought
Evolution: Change in populations of organisms over time
Early Explanation of life’s diversity
Species individually created at one time and one place
Questions arising from such thoughts
Why were organisms different in different regions of earth?
Why are current organisms different from ancient organisms?
If each species is different, why are there the same fundamental
structures (bone plans) that do different things in animals?
New Ideas
Scientists thought that species changed over time
Both animals, though very different,
exhibit similar wing structures
Extinction, fossil record, and Carbon-14 dating
suggest that organisms arose (and became
extinct) at different time periods
Dinosaurs- Arise ~ 200 myaExtinct 65 mya
Chimps- Arose on earth ~6 million years ago
Woolly Mammoth- Extinct
4500 years ago
Different regions of planet have animals
with unique traits that help them survive
New Ideas
Scientists thought that species changed over time
Lamarck’s Disproven Theory of Evolution
Jean Baptiste Lamarck
Believed that an animal’s physical
needs determine its development and genes
Exp. Giraffe
Early Giraffes stretched their necks to feed
Long neck was then passed off to offspring
WRONG!!!
Charles Darwin 1809-1882
Putting the Picture Together
Darwin Travels to the Galapagos Islands
Witnessed tremendous diversity of animal life
Fascinated by differences among beaks on finches
Becomes convinced that species change over time
Young bull
Old bull
Thomas Malthus & Charles Darwin
Malthus
Populations tend to grow faster than the
food supply needed to feed it
Charles Lyell & Charles Darwin
Lyell
Changes occur over time in geology; land
formations move and topography changes
Darwn’s Descent with Modification
Evolutionary pathway resembled a branched tree
NOT a ladder from lower forms to higher forms
No species that exists today was an ancestor to another living species
Darwin’s Observations
•Individuals in a population vary, some of these variations are
inheritable
•Populations produce more offspring than the environment’s food,
space, and other assets.
•Therefore, species compete for resources
Lions and cheetahs compete for food
Dolphins compete for baitfish
The Mechanism of Natural Selection
Natural Selection greater reproductive success displayed by
individuals with favorable traits
Nature selects that are passed on to the next generation
Variation differences within a population
Adaptations traits that are selected for because they help an
organism survive and reproduce
Evolution occurs when genes in a population change shift to enhance
survival and reproduction
Exp. Giraffe
How Do Variations Arise?
•Natural selection IS NOT the cause of variation
•Mutation-> Random changes in DNA sequences in the parents genome
•Gene Shuffling mixing of parental chromosomes can create new
genetic combinations
•Variation arises randomly. Variations are then selected on by nature.
•Variations which are selected for are called adaptations
Adaptations and Speciation
Types of Adaptations
Structural Adaptations  Involve structure or anatomy
Bird’s beak, Anteaters sticky tongue
Physiological Adaptations  Functions in organisms
Poison Venom in a snake, ink of an octopus
Behavioral Adaptations  Behavior aids in survival and reproduction
Wildabeasts/ Caribou/ Bird Migration
Wolves Hunt in Packs
Fish swim in schools
Types of Adaptations
Structural
Physiological
Wolf Pack
Herd of African Gazelles
Species & Speciation
Species  group of organisms that can interbreed and produce fertile
offspring
Horses + Donkey = Mule…Not the same species
Human male + human female = human baby…same species!
Speciation  Organisms which are separated by distance + gene pool
will no longer interbreed. Each group becomes new species
Horse
Donkey
Mule
Types of Natural Selection
Directional Selection  shifts a population toward one extreme form of
a trait
Example: 4 million years ago; heavy cheetahs
Over time, light, fast animals reproduced more successfully
Natural selection favored the genes that pushed the cheetah’s weight in
one direction…lighter
Types of Natural Selection
Stabilizing Selection shifts a population toward intermediate
(medium) traits
Example: Most human babies weight ~ 7pounds
Disruptive Selection  Extreme phenotypes are more common
Example: African butterflies appear as either bright orange or bright
blue
These colors mimic other butterflies that are foul-tasting; less likely to
be eaten
Intermediate butterflies look like neither, and are more likely to be eaten
Patterns of Evolution
Species become dissimilar or more alike over time
Gradual Change  Genetic changes occur slowly over many
generations
Divergent Evolution  Single population is split into 2 or more
populations.
Exp. Ground squirrels in the Grand Canyon were split into 2 populations
after canyon widened
Patterns of Evolution
Adaptive Radiation  Organisms occupy different niches in an
environment and diverge from one another
Exp. Darwin’s Finches
Convergent Evolution  2 dissimilar species evolve in ways to make
them LOOK more similar
Exp. Sugar Gliders winged marsupials in Australia
Flying Squirrels  Winged squirrels in Northern Hemisphere
Sugar Glider
Flying Squirrel
Pace of Evolution
Gradualism  Over time, new species arise as environment change
If true, we should see intermediate species in fossil record…not always
true
Punctuated Equilibrium  Species exist for long periods of time without
changes, then large changes occur over short periods of time
Populations & Evolution
• Larger populations tend to have more genetic variation
• Smaller populations tend to have less genetic variation
• Genetic Drift/Founder Effect Loss of genetic variation
due small population sizes. Extinction more likely
• 10,000 years ago, almost all cheetahs go extinct due to
climate changes. Resulting cheetahs have little genetic
diversity
Evidence for Evolution
Fossil  trail of animal that is preserved in rock
Found in Sedimentary Rock
Fossils show overall structural scheme of how living things evolved
Body scheme
Feeding behavior
Mobility
Society?
New fossils in upper layers, older fossils in lower layers
Examples
Burgess Shale
Location : British Columbia, Canada
Development: Foot of continental shelf
Organisms: Early Marine worms (Hallucigenia)
Badlands, SD
Development: Shallow ocean
Organisms: Early Squid, octopus
Badlands
Importance
Land masses move
Were once covered under oceanic water
Species adapt and go extinct
Comparative Anatomy
Homologous structures Similar structures in related organisms
Suggests that organism arose from a common ancestor
Exp. Cheetah forelimb = human hand
Wing = Whale flipper
Vestigial Organs
Organs with no apparent use, but resemble functional structures in
ancestors
Whale Pelvis
Whale femur
Wisdom Teeth
Appendix
Comparative Embryology
Organisms with common descent have similar organs
Vertebrates breathe though lungs
As embryos, vertebrates have gills (turns into Eustachian tube)
Biochemistry
Common ancestors have similar fundamental body chemistry
Most organisms have:
Same 4 bases in DNA
Same 20 AA
Biogeography
Study of species distribution on Galapagos Islands look similar to
South American species
Each island would have to had it own special creation event for each
species; more likely migrated from South America
Direct Evidence
Bacteria & Antibiotics
Fruit Flies (Drosophila)
Artificial Selection
Artificial selection (or selective breeding) describes
intentional breeding for certain traits, or combination of traits
Dogs are a prime example.
Bulldogs selectively bred for increasingly large heads. Most
bulldogs delivered via Caesarian Section. Trait not favored
in nature, but selected for by humans