Explaining Evolution. Darwin published “On the Origin of Species” in 1859 He had spent 20...
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Transcript of Explaining Evolution. Darwin published “On the Origin of Species” in 1859 He had spent 20...
NATURAL SELECTION Explaining Evolution
THE ORIGIN OF SPECIES
Darwin published “On the Origin of Species” in 1859
He had spent 20 years amassing evidence and developing his theory of NATURAL SELECTION
NATURAL SELECTION The way in which nature favours the
reproductive success of some individuals within a population over others
Over time the population changes as advantageous heritable characteristics become more common generation after generation
Evolution is the result of natural selection occurring over many generations
“SURVIVAL OF THE FITTEST”
A term coined by Herbert Spencer to describe the process of natural selection
The key to natural selection is an individual’s REPRODUCTIVE SUCCESS and its ability to ADAPT
ADAPTATION: a characteristic or feature of a species that makes it well suited for reproductive success and survival
EVALUATING A THEORY
Darwin’s theory of evolution by means of natural selection is able to: Explain how adaptation can arise in a species
Make predictions about the future evolution of a species
Be a testable scientific theory
MODERN THEORY OF EVOLUTION
Evolutionary biology has made tremendous advances since Darwin because of the following: RADIOMETRIC DATING MODERN EVOLUTIONARY SYNTHESIS
PALEONTOLOGY
RADIOMETRIC DATING
Involves the use of radioisotopes to obtain precise estimates of the ages of rocks
RADIOISOTOPE: an atom with an unstable nucleus that is capable of undergoing radioactive decay
HALF-LIFE: the time required for half the quantity of a radioactive substance to undergo decay; the half-life is constant for any isotope
MODERN EVOLUTIONARY SYNTHESIS
The modern theory of evolution that takes into account all branches of Biology
Involves changes in the GENE POOL of a species over time
GENE POOL: the complete set of all alleles contained within a species or a population
RECALL: genetic mutations provide a continuous supply of new heritable information and variation within a species
PSEUDOGENES Vestigial genes that no
longer code for functioning proteins
Are found in virtually all species EXAMPLE: Dolphins
have genes that code for smell however they have no need for a sense of smell
MODERN PALEONTOLOGY
We have made many important discoveries over the last 100 years: Fossils of early human ancestors in
Pakistan Feathered dinosaurs in China
PLATE TECTONICS: the scientific theory that describes the large scale movements and features of Earth’s crust
Explains species distributions
TYPES OF SELECTION There are FOUR types of
selection:1. DIRECTIONAL2. STABILIZING3. DISRUPTIVE4. SEXUAL
DIRECTIONAL SELECTION
A selection that favours an increase or decrease in the value of a trait from the current population average
Common in artificial selection where individuals with an enhanced trait are selected
EXAMPLE: A habitat with long flowers will favour hummingbirds with longer bills, and thus create future generations of birds with longer bills
STABILIZING SELECTION
A selection against individuals exhibiting traits that deviate from the current population average
EXAMPLE: An environment with medium length flowers will select against long billed or short billed hummingbirds
DISRUPTIVE SELECTION
A selection that favours two or more variations of a trait that differ from the current population average
EXAMPLE: An environment with long and short flowers will select against hummingbirds with medium sized bills
SEXUAL SELECTION The favouring of
any trait that specifically enhances the mating success of an individual
Results in males and females of a species differing in behaviour and appearance
SELECTION AT WORK EXAMPLE: Polar bears and white fur
Ability to sneak up on seals on snow covered ice
EXAMPLE: Wolves keen sense of smell Ability to locate and track the
movements of prey EXAMPLE: A human’s large brain
Ability to reason and communicate
GENETIC DRIFT Changes to allele frequency as a result
of chance Such changes are much more
pronounced in small populations Can result in the allele becoming very
common or disappearing entirely over a number of generations
GENETIC BOTTLE NECK
A dramatic, often temporary reduction in population size
Usually results in significant genetic drift and a loss of genetic diversity
EXAMPLE: Cheetahs
HARDY-WEINBERG PRINCIPLE
In large populations in which only random chance is at work, allele frequencies are expected to remain constant from generation to generation
Evolution occurs: If natural selection occurs In a small population If there is a mutation There is immigration or emigration If there is a gaining of new alleles from a
different species
HUMAN INFLUENCE EXAMPLE: Commercial fishing
The alleles that code for large adult sized cod are being lost
EXAMPLE: Insecticide use Bedbugs are becoming resistant to
pesticides EXAMPLE: Antibiotic and antimicrobial use
Many infectious bacteria (MRSA) are becoming resistant to a variety of antibiotics