Evolution: Evidence,Evolution: Evidence,Selection and AdaptationSelection and Adaptation
One of the key words of our modern time is Evolution
OutlineOutlineu 1. Key concepts
u 2. Early Beliefs, and New Discoveries
u 3. Darwin developed the theory of evolution
u based on his observations and other evidence
a. Darwin’s observations
b. Factors that influenced Darwin’s thinking
u 4. Natural selection: A mechanism of evolution
u 5. Conclusions
Key Concepts:Key Concepts:
Evolutionary theories gave early scholars new
ways to interpret the occurrences in the world
Today, biological evolution is interpreted as
heritable changes
Darwin and Wallace explained evolution on the
basis of Natural Selection
The traits that characterize a population can
change over time
Early Beliefs, and New DiscoveriesEarly Beliefs, and New DiscoveriesAristotle – believed that each kind of organism was
distinct from all the rest
“Chain of Being”- fourteenth century (A chain of Being
was seen to extend from the “lowest” forms of life to
humans.
Biogeography – until the fifteenth century, naturalists
were not aware that the world is much bigger than
Europe, a few scholars began to examine the world
distribution of organisms
Comparative Anatomy – eighteenth
Fossils – from the late 1600s on geologists added to the
growing confusion.
Chain of Chain of BeingBeing(1579)(1579)
A Flurry of New TheoriesA Flurry of New Theories
Lamarck
Theory of Inheritance of Acquired
Characteristic
Darwin
Voyage of the Beagle - 1831
LamarckLamarck’’ss TheoriesTheories
According to Lamarck's theory, life created long
ago in a simple state gradually improved.
For example, the ancestor of giraffes could have
been a short-necked animal. Pressed by the
need to find food, the animal stretched its neck,
which permanently lengthened. This acquired
characteristic (a long neck) was then passed on
to the giraffe's offspring.
Lamarck inferred, correctly, that environment is a
factor in evolution.
LamarckLamarck’’ssTheoriesTheories
Charles Darwin
[1809-1882] called evolution “Descent with modification”
DarwinDarwin’’s Voyages VoyageAt age 22, Charles Darwin began a five-year,
round-the-world voyage aboard the Beagle
He collected and examined the species that inhabited the regions the ship visited
EQUATOR
Galapagos
Islands
DarwinDarwin’’s observationss observations
Prevailing ideas about species: they did not change or interbreed
Darwin’s evidence for change came from:1. his observations of living organisms
2. geologic evidence and fossil record
3. theories of population growth
DarwinDarwin’’s observationss observationsWhat the evidence showed:
• Relationship between living and fossil organisms (distinct yet similar)
• Among living organisms: distinct yet similar organisms occur in
� Similar climates – S. Africa, Chile, Australia
� Isolated populations of same species –species often change slightly due to geographical isolation
� Island v. mainland populations – Island species often resembles to mainland species
DarwinDarwin’’s Theory Takes Forms Theory Takes Form
Armadillo – 10 pounds
Glyptodont – fossil from S. A. (2 tons!)
Three Species Native to Three Three Species Native to Three Geographic RealmsGeographic Realms
Ostrich
of Africa
Rhea of
S. America
Emu of
Australia
DarwinDarwin’’s Theory Takes Forms Theory Takes Form
Variations in traits
Survival
Reproduction
Four finch
species from the
Galapagos
Islands
Galapagos Islands todayGalapagos Islands today
Factors that influenced Factors that influenced DarwinDarwin’’s thinkings thinking
• Geology: as Earth changed, so did types of fossil organisms in rock strata
• Population studies: many organisms are produced; only a few survive to reproduce [Thomas Malthus (1766-1834) Essay on Disease, Famine, and Population Size]
• Artificial breeding experiments: humans “select” desirable traits in plants and animals; so does “nature”
Natural selection: A Natural selection: A mechanism of evolutionmechanism of evolution
Darwin’s explanation for species diversity:
Nature “selects” organisms which have inheritable traits (adaptations) suited to their environment which allow them to survive to reproductive age
Survivors then breed and pass on these characteristics to their offspring
Variation in a Snail SpeciesVariation in a Snail Species
Shell color and
banding patterns
differ due to
different alleles
for the genes for
that trait
Adaptation and Natural Adaptation and Natural SelectionSelection
Mutation (Lethal mutation, Neutral mutation,
Good mutation) – no purpose, no direction
Fitness
Adaptation to the environment
Natural Selection
Result of differences in survival and reproduction
among individuals that differ in heritable traits
An example of natural An example of natural selection: Darwinselection: Darwin’’s finchess finches
Showed relatively rapid evolution:
• Ancestral finches from mainland reached islands, underwent adaptive radiation and populated many diverse habitats
• Ancestral species became groups of closely related yet diverse populations
An example of natural An example of natural selection: Darwinselection: Darwin’’s finchess finches
Natural SelectionNatural Selection
Selection can increase the frequency of a trait in a
population
Environment may favor a trait over another
Alfred Wallace
Developed same theory as Darwin
Origin of Species
1859 - Darwin
Evidence for the Theory of Evolution
In ConclusionIn Conclusion
The Theory of Evolution by Natural Selection
states
More offspring are produces than the environment can
support
Variant forms of a trait may be more or less adaptive
under environmental conditions
An adaptive trait allowed organisms to survive and
reproduce more frequently. The frequency of that
adaptive trait increases in a population
In ConclusionIn Conclusion
Comparative anatomy, biogeography,
fossils, and a lot of other evidence showed
changes in lines of descent
Natural Selection results in modification of
traits and can bring about the evolution of
a new species