Transcript Natural Selection - kestrelteambiology

Evolution
Darwin and Natural Selection
Charles Darwin

On the Origin of Species

Sailed with the HMS Beagle

Observations made in the Galapagos Islands

These observations helped him form the
theory of how species change
What is Natural Selection?
Within every species or population,
there is diversity (variation).
 Organisms with variations that are
favorable survive and pass their genes
onto their offspring.
 The next generation has the favorable
variations.

Types of Adaptations

Protective Coloring
– Camouflage
– Mimicry

Physiological Adaptations
– Reproductive Changes
– Other changes

Behavioral Adaptations
– Using tools
Evidence for Evolution
Fossil record
 Anatomy

– Homologous structures
– Analogous structures
Vestigial structures
 Embryology
 Molecular biology (DNA differences)

Evidence for Evolution

A. The fossil record
1. Geological time scale - major events
2. The history of the Earth is divided into
Eons, Eras, Periods , and Epochs.
3. Think…….Jurassic Park
4. Radioactive Isotopes are used to find
the age of rocks.
Darwin’s Evidence for Evolution
 Fossils
 ossils
– Extinct species resemble living ones for same
region
– Species found in successive layers of rock
show progressive changes in characteristics
Darwin’s Evidence for Evolution

Geographical Distribution
– Distant regions with similar climates have
unrelated plants/animals
– Plants/animals of a region or continent are
distinctive, and many/all are often related to a
single group
Darwin’s Evidence for Evolution

Oceanic Islands
– Although islands generally have few species,
those they have are often unique and show
relatedness to one another
– Species on islands often show relatedness to
nearest continent, and not to species on
similar islands in other oceans
Darwin’s Evidence for Evolution

Artificial selection
– Plant and animal breeders
– Breeders select who survives/breeds next
generation
– Many widely different breeds/cultivars
produced from same original stocks
– Could nature act similarly?
Darwin Influenced by Others
Malthus
– “Essay of the Principle of Population” (1798)
– Populations of plants/animals can increase
geometrically
– Populations of plants/animals remain relatively
constant
– Death limits populations

Darwin hypothesized natural selection as a
means by which selective survival of
individuals with superior attributes gradually
changes the average characters of the
population as a whole over many generations

B. Evidence from Comparative Anatomy
– Comparative Anatomy- the study of structural similarities
and differences between living things
• 1. Homologous Structures- parts of different organisms
that have similar structure, but different forms and
functions
– human arm and hand, whale flipper, cat leg, bat
wing, bird wing
• 2. Analogous Structures- parts of different organisms
that have similar forms and functions, but different
internal structure (example: wing of a bird, wing of an
insect)
• 3. Vestigial Structures- remnants of structures that
were once functional in an ancestral form
» -appendix, wisdom teeth, coccyx (tailbone)
Homologous Structures- same
structure: different function
Analogous structures

Insect wing
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decompressor
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Bird Wing
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are needed to see this picture.
 C. Comparative Embryology
– Structurally different species show
common patterns in embryological
development
• presence of gill slits, 2-chambered
hearts, tails
• the longer the embryos show
similarities, the more closely related the
species

D. Evidence from DNA
– - Each individual organism has its
own specific DNA structure (DNA
fingerprint)
– The closer the structure of DNA
between organisms (species), the
closer the evolutionary relationship
What is a Population?

Population:groups of interbreeding
individuals that live in the same place at the
same time

Populations evolve over many generations,
individuals don’t

Individuals in a population compete for
resources with each other
How Does Evolution Work?
Populations produce more offspring
than the environment can support
 The unequal ability of individuals to
survive and reproduce leads to the
gradual change in a population over
many generations

Mechanism for change in a
population of organisms
Animals who have greater fitness
survive in environment and live to
reproduce
 Random changes (mutations) can lead
to greater or less fitness
 Adaptations allow an organism to
survive better in their environment

Adaptations

Can arise in response to environmental
pressures
– Temperature
– Antibiotic resistance in bacteria
– Pesticide resistance
– Morphological changes in peppered moths
Types of Selection

Directional
– Extreme form favored by natural selection

Stabilizing
– Middle form most successful

Disruptive
– Two extreme forms successful in separate
environments
Stabilizing Selection
Disruptive Selection
Directional Selection
How fast does evolution occur?

Gradualism
– Darwin
– Species change slowly over time

Punctuated Equilibrium
– Steven Jay Gould
– Species can make rapid “leaps” in
evolution

Modern Synthesis
– Parts of both are correct
Types of Evolution
• Convergent Evolution
•
Species may resemble each other but not
be related - happens when environment
selects for phenotypes (sharks and
dolphins)
• Divergent Evolution
•
Two or more related populations becoming
more and more different - response to
differing habitats
Adaptive radiation is one type
Darwin’s Finches are an example
How do you define a species?
Species: a group of individuals that actually
or potentially interbreed in nature.
In this sense, a species is the biggest gene
pool possible under natural conditions.
- Biological Species Concept: Ernst Mayr
Speciation -making new species or adaptive
radiation
Go to:
http://evolution.berkeley.edu/evosite/evo101/VADefining
Species.shtml
How are new species created?
•Geographic Isolation
physical separation of members of
a population
•Change in chromosome number
•Polyploidy in plants
•Adaptive Radiation
What is Biodiversity? - The diversity of living things on this
planet.
"In a Darwinian sense," Professor E.O. Wilson wrote, "the
organism does not live for itself. Its primary function is not
even to reproduce other organisms; it reproduces genes,
and it serves as their temporary carrier.”
All the living things on this planet contribute to the
Biodiversity of Earth.
Biodiversity studies determine endangered species and
endangered habitats.