Post on 18-Jan-2018
description
Natural selection
Charles Darwin• Born February 12, 1809 Shrewsbury England• Medical School (1825-1827)
– Darwin is 16 Years Old
• Cambridge (1827-1831) Clergyman • Naturalist of H.M.S. Beagle• Beagle Departs from Plymouth, England
on December 27, 1831– Darwin is 22 Years Old
H.M.S. Beagle
Route of the H.M.S. BEAGLE
timeline• January 1832 Santiago, Cape Verde Islands “Seashells”• April 1832 Rio de Janeiro, Brazil “Entomological Specimens”• August 1832 Patagonia Coastline “Useless Junk (Fossils)”• March 1833 Falkland Island, Port Louis “Comparing Fossils”• September 1835 Galapagos Islands, “Discovering Diversity”• October 1836 Falmouth England, “Journey Ends” 4Y9M5D• March 1837 London Zoo “Discovery of Darwin’s Finches”• November 1859 Published “Origin of the Species”• 1930’s-1940’s Evolutionary Synthesis “Mendel and Darwin”
Theory of Natural Selection
1. Organisms produce more offspring than can survive.
2. In any given population, variations exist.
3. Individuals with certain “useful” or beneficial variations survive and pass on their variations to the next generation.
4. Over time, offspring with “beneficial” variations will make up most of the population.
Natural Selection
Darwin used his collections and observations to identify a mechanism for change in populations.
Darwin called this mechanism:NATURAL SELECTION
Natural SelectionScience’s “best
guess” on how populations change over time.
Natural Selection is based on the following scientific evidence.
Structural Adaptations
Physiological Adaptations
Fossils
Anatomy
Embryology
Biochemistry
Structural Adaptations
Structural adaptations are changes in an organism’s appearance
Structural Adaptations
usually develop over a long period
of time
• Defensive Adaptations
• Large Teeth and Claws, Speed and agility, chemical
• Protective Adaptations
• Camouflage, Mimicry, Speed, Chemical, Quills, Spines
• Specialized• Height, Strength,
“Specialized Anatomy”
Physiological Adaptations
Changes in an organism’s metabolic processes.
Can occur over a relatively short period of time.
• Examples– Bacteria– Pesticides– Herbicides– Symbiotic
Relationships (Clown Fish and Sea Anemone)
FOSSILSFOSSIL EVIDENCE:• Provide record of
early life
• Show how changes occurred within most populations and species.
• FOSSIL SHORT COMINGS– Incomplete for many
species – Inferences [However, DNA
can support these inferences]
ANATOMYCONVERGENT
EVOLUTION
Organisms share same function, but not the same form, come from different ancestral lineages.
• Analogous Structures– Similar structural functions but
do not share a common evolutionary origin.
• Similar in function but not arrangement
– Insects vs. Birds
ANATOMYDIVERGENT EVOLUTION
Species that were once similar
• Homologous Structures– Structural features with a common
evolutionary origin• Can be similar in arrangement and
function.– Forelimbs of human, cat, whale, bat
• Vestigial Structure– Body structure in a present day
organism that no longer serves its original purpose.
• Feature is still inherited, although it no longer serves it’s purpose.
– Eye balls present in blind cave salamander
Embryology• Early Embryonic development, all
embryo’s have a tail and pharyngeal pouches.
Biochemistry• Organisms share same
biochemical molecules
– DNA, ATP, ENZYMES, AMINO ACID SEQUENCE
• Organisms that are biochemical similar have fewer differences in their amino acid sequence and are believed to be more closely related or share a common ancestor.
• Phylogeny: Construction of “family trees” using DNA and RNA
THE EVIDENCE• Scientist use:
– Adaptations• Structural• Physiological
– Fossils– Anatomy
• Micro and Macro– Embryology – Biochemistry
• DNA, RNA, Amino Acids
Applying Natural Selection• SPECIATION: Process in which a new species arises
from a formerly interbreeding population.– Cause
•Geographic Isolation•Reproductive Isolation
– Rate•Fast—Punctuated Equilibrium
» Periods of speciation occurs quickly within a long period of genetic equilibrium.
•Slow—Gradualism» Species originate through a gradual change of
adaptations.
Applying Natural Selection• Populations, Not Individuals, Evolve
– Variations arise from mutations– Alleles represent the genetic variation in a
population– The Gene Pool is the all of the different
alleles in a given population.– The percentage of any one allele in the
gene pool is called the Allelic Frequency.– If the frequency of an allele remains
constant we refer to that as Genetic Equilibrium.
Applying Natural Selection:Directional
SelectionNatural Selection Favors OneExtreme Variation of a Trait
Example:Birds with varying sizes of beaks, after a drought, the large beak birds have selective advantage
Applying Natural Selection:Disruptive SelectionIndividuals with either extreme traitare selected for.
Example:Tourists in the desert like to pick up a souvenir from their travels, they pick up the medium spine cactus.
Leaving the “homelier” low spine and avoiding the “prickly” high spine cactus, both of which have the selective advantage.
Applying Natural Selection:Stabilizing SelectionNatural Selection Favors averageindividuals in a population.
Example:Birth weight in humans is highly variable, however, a child that is of average weight has a higher chance of being born and of good health, as to mature and reproduce. Nature selects against the extreme phenotypes.
Natural Selection is currently the best theory scientists have to explain the vast diversity of life on Earth and how populations change over time. In science, nothing can ever be proven as fact, there are no facts in science, only “best guesses”. These best guesses are based on current, verifiable, and testable evidence. We call a collection of evidence that fails to disprove a hypothesis—a theory. In fact, science can only be used to disprove not prove anything.