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Evolution
Evolution- the theory that species change over time
Charles Darwin- 1859 published On The Origin of Species
Darwin’s Theory of Natural Selection
Overproduction- in nature there is a tendency for organisms to produce more
offspring than can survive
Most of the young do not survive to reproduce.
Variation
All populations contain heritable variations - size, speed, agility, coloration
Some variations are more favorable
Natural Selection
Those with favorable variations are more likely to survive and pass on their
favorable variations
Natural Selection and Adaptations
Natural Selection can be applied to explain the evolution of adaptations in
organisms
Mimicry - copies the appearance of another species
Camouflage - blends in
Evidence For Evolution
Fossils can show evolutionary changes over time but can give an incomplete
picture
What fossil evidence is missing?
If all animal species evolved from common ancestors, there should be fossils of
the intermediate species found.
The only “intermediate” fossils found have been of the birds.
Examples: Archaeopteryx & Microraptor gui
This fossil was discovered in late 2002 in China. It appears to be a 4-winged bird
and a possible link between the reptiles and birds.
Biological Evidence for Evolution
All living things are made of the same chemical elements- C, N, H, & O
Chromosomes are all made of DNA
Proteins are synthesized in essentially the same way
Biochemical, Embryological, Anatomical similarities
Biochemical Evidence
Comparison of nucleotide sequences in the DNA of species
Embryological Development
Some organisms are similar to one another until late in embryonic development
One theory hypothesizes that during its embryological development, an organism
retraces its entire evolutionary history.
For example, humans begin life as a single cell, then grow into a multicellular
organism in water.
Early in fetal development, humans, like other vertebrates have what appear
to be “gill slits” on the side of the neck area.
"The throat (or pharyngeal) grooves and pouches, falsely called "gill slits" are not
mistakes in human development. Far from being useless evolutionary vestiges,
then, these so-called "gill slits" are quite essential for distinctively human
development."
Homologous Structures
Similar arrangement in structure, vary in function, but are derived from the same
structures in the embryo
Analogous Structures
Serve the same function but differ in structure
represents convergence - a similar solution to an adaptive problem
Vestigial Structures
Nonfunctional or partially functioning remnants of organs that were functional in
their ancestors
Patterns of Evolution
Divergent Evolution - two or more related species become more dissimilar.
Involves an adaptive radiation when species of related ancestry exploit different
aspects of the environment
Convergent Evolution - Unrelated species become more and more similar as
they adapt to the same kind of environment
What Causes Variations in Traits?
Gene Pool - collection of genes for all the traits in a population
Allele Frequency - percentage of a specific allele of a gene in the gene pool
A population in which allele frequencies do not change is in “genetic equilibrium.”
Genetic Equilibrium - A state of evolutionary stability. No mutations occur
Individuals neither enter or leave the population through migration
The population is large and remains relatively stable.
Individuals mate randomly & natural selection does not occur.
Disruption of Genetic Equilibrium
Mutation - physical change in a gene or chromosome, will produce new alleles
for a trait
Migration - movement of individuals into or out of a population
Genetic Drift
Allele frequencies in a population change as a result of random events or
chance, occurs in small to medium-sized populations
Formation of Species
Natural selection causes the most significant genetic changes in a population.
These changes do not necessarily lead to speciation- formation of a new
species.
Isolated Populations
Geographic Isolation - physical separation of members of a population
Reproductive Isolation - inability of formerly interbreeding organisms to produce
offspring
Gradualism
Species originate through a gradual buildup of new adaptations
Punctuated Equilibrium
Speciation occurs in rapid bursts with long periods of stability in between
Extinction
Species die off
Many extinctions are due to human destruction of habitats