Download Intro to MicroEvolution and Natural Selection File

A. The Earth orbits the sun.
For EACH of
these
scientific
explanations
(A-E)
decide if they
are a theory or
a law.
C. Living things are made of cells
D. Matter is comprised of atoms
In everyday usage:
"theory" often refers to a hunch or a speculation.
The word, “theory” is often used when drawing
a conclusion based on inconclusive evidence.
The National Academy of Sciences
The formal scientific definition of theory:
a comprehensive explanation of some aspect of
nature that is supported by a vast body of
evidence.
National Academy of Sciences
“Scientific theories are so well-established
that no new evidence is likely to alter them
substantially.”
• No New Evidence is expected to contradict:
– that the Earth orbits around the sun (heliocentric theory)
– that in nature organisms that are best fit for the environment are the ones
that survive and reproduce (natural selection/ evolutionary theory)
– that living things are made of cells (cell theory)
– that matter is composed of atoms (atomic theory)
– that the surface of the Earth is divided into solid plates that have moved
over geological timescales (the theory of plate tectonics)
Theory vs. Law
In common:
-
BOTH were originally based on hypothesis
BOTH are largely supported by scientific evidence
BOTH are widely accepted by the scientific community
Laws are not viewed as ‘better’ or ‘more complete’ than theories.
-
Laws are descriptions of a phenomenon in nature.
Theories are explanations of ‘why’ and ‘how’ these phenomenon occur.
-
It is a misconception that theories become laws through enough research.
-
In science, laws are a starting place. Once a law is determined, scientists
then ask ‘why’ and ‘how’?
Quickly discuss the definitions of the following words with your group:
Vocabulary From the Past
1. Population:
2. Genes:
3. Alleles:
4. Phenotype:
1.
• Population – a group of individuals belonging to the
same species, occupying the same area at a given
time (therefore sharing resources).
2.
• Genes – are portions of DNA with specific nucleotide
sequences that code for a trait.
3.
Alleles – Any of the alternative versions of a
gene.
4.
Phenotype – The observable physical trait of
an organism that is determined by its genetic
makeup.
Picture all of the alleles of a population as being together
in a large pool called a gene pool.
The percentage of any specific
allele in the gene pool is called
the allelic frequency.
Look around the room….
What is the gene pool for hair
color???
What is the allelic frequency
of people with blonde hair?
Evolution is simply a change in allelic
frequency within a population’s gene
pool over time.
• Individual organisms DO NOT evolve.
Populations Do!
Two ways to study evolution:
Micro-evolution:
Evolution on a small scale.
Looking at how gene frequencies change
over time in a population (How prominent
are certain genes in a population)
Literally microscopic
Macro-evolution:
Evolution on a broad scale.
Looking at the effects of microevolution at
or above the species level (separation of
species, origins of adaptations, impacts of
extinctions, etc)
Mechanisms of Evolution
• These are the factors that cause changes in gene
frequency in populations,
and therefore are the driving forces behind evolution.
• Natural Selection
best adapted contribute most to the gene pool
• Genetic Drift
random events that cause changes in the gene pool
• Gene Flow
migration into and out of populations, changing the gene pool
• Charles Darwin (1809-1882)
• An English scientist
• It took him years of observation and study to
develop his theory of natural selection.
• He began in 1831 at age 22 when he took a job as a naturalist
on the English ship HMS Beagle, which sailed around the world
on a five-year scientific journey.
• Darwin studied and collected biological and fossil
specimens at every port along the route.
• He became curious about possible relationships
among species because of similarities he saw.
• One of Darwin’s
observations is that in
nature, the traits of
individuals vary in
populations.
• Give some examples of
variations in populations
of one species.
• Darwin hypothesized that there was a force in nature that
determined which traits/variations are better for the survival in a
population.
Natural Selection
• When organisms with the most beneficial traits in a
population are the ones that survive and reproduce,
and pass those traits on…
Darwin’s
argument forIdeas
natural
Essence
of Darwin’s
selection was based on two main
observations and two inferences from
those observations…..
1. In any population, individuals
have variations.
2. Many more offspring are born
than can possibly survive to
maturity.
3. The individuals whose traits give them a higher
probability of surviving….tend to leave more
offspring than others, contributing more to the
gene pool…
The individuals with those beneficial traits will be the
ones that survive, reproduce, and pass those favorable
variations on to the next generation.
Individuals without those favorable traits are less
likely to survive and reproduce.
4. After generations, organisms with the favorable
variation make up most of the population.
-The allele for the unfavorable traits may eventually
cease to exist.
Why do you think more and more bad bacteria
(like the kind that cause sinus infections) are becoming
resistant to anti-biotics?
How do you think natural
selection will affect this species
of moth?
(both the same species, just
have a body color variation)
• There are three different ways natural selection can
alter allelic frequencies in a gene pool…
• Stabilizing selection is a natural selection that
favors average individuals in a population.
Very little
evolution will
occur.
Middle sized Siberian Huskies
are selected for
• Directional selection occurs when natural selection
favors one of the extreme variations of a trait.
• This type of selection can lead to rapid evolution of
a population.
Examples: Directional Selection
• Peppered Moths: as the environment changes,
so do the traits that are fit for the new
environment.
• In the case of the moths, the forests changed
from light to dark and selection moved in the
direction of darker moths
• Antibiotic Resistance
• Pesticide Resistance
Disruptive Selection
• Extreme phenotypes are favored
• Intermediate forms are selected against
• In disruptive selection, individuals with either
extreme of a trait’s variation are selected for.
• This results in eventually having no intermediate
form of a trait, and leading to two separate species.
Disruptive Selection
• Hunting and Rabbit Populations
Sexual selection
What is sexual selection?
Selection based on attraction.
This could be based on physical
appearance or mating rituals.
Why a theory of sexual selection?
Darwin needed a theory to explain the many
extravagant traits that CAN reduce survival
e.g. the peacock’s tail
Sexual selection
Is sexual selection different from natural
selection?
Darwin saw them as distinct - only sexual selection
could produce traits that could possibly compromise survival
The basic principles are identical – selection favors
whatever gets more genes into the next generation
https://www.youtube.com/watch?v=W7QZnwKqopo