Download Part 1: Evidence of Evolution

Part 1:
Evidence of Evolution
*notes in red are for teacher version/answer key
Artificial Selection
Humans have a long history of breeding plants and animals. It is typically done to
increase the efficiency of an animal (e.g. horses, livestock, dogs) or to maximize the
output in agriculture (e.g. food crops, ornamentals).
1) http://t2.gstatic.com
2) http://web.idrc.ca/openebooks
3) http://www.bulbsonline.org
Can you describe how a human might intervene with breeding to artificially select for the
desired characteristics in a plant or animal?
Natural Selection
While humans can apply selective pressure to plants and animals, so can the
environment. Charles Darwin published On the Origin of Species by Means of Natural
Selection. Natural selection explains how evolution can occur.
There are four main principles to the theory of natural selection: variation,
overproduction, adaptation, and descent with modification.
Variation-The heritable differences, or variations, that exist in every population are the
basis for natural selection. The differences among individuals result from diffrences in
the genetic material of the organism, whether inherited from a parent or resulting from a
genetic mutation
Overproduction- While having many offspring raises the chance that some will survive, it
also results in competition between offspring for resources.
Adaptation- Sometimes a certain variation allows an individual to survive better than
other individuals it competes against in its environment. More successful individuals are
“naturally selected” to live longer and to produce more offspring that share those
adaptations for their environment.
Descent with modification- Over time, natural selection will result in species with
adaptations that are well suited for survival and reproduction in an environment. More
individuals will have the trait in every following generation, as long as the environmental
conditions continue to remain beneficial for that trait.
In order for selection to occur (artificial or natural) a trait must be heritable. In addition, a
population must contain genetic variability. Individuals with favorable traits are more
likely to leave more offspring better suited for their environment, increasing their fitness.
Genetic traits that increase their survival will likely be passed onto their offspring-natural selection
Explain why the phrase “survival of the fittest” does not accurately reflect Darwin’s
concept of evolutionary fitness. Answer: Because it takes more than merely “surviving”
for a creature to increase their fitness. For natural selection to occur that individuals
must also successfully reproduce. Therefore, perhaps a better phrase to describe the
concept would be “survivals of the survivals”!
Structural Adaptations
African Rock Rat
Mole Rat
http://photos.mongabay.com http://www.newswise.com
Look at the above images. The terrestrial ancestral African rock rat and the
subterranean mole-rat have some very distinct differences. Some of their differences
proved to be beneficial to survival, while other characteristics played no role in their
survival.
Can you name some of these structural adaptations and describe how these
adaptations may have helped the animals to better survive and to inhabit their new
subterranean habitat?
Hints: eyes, claws, teeth, loss of hair
Mimicry
Coral snakes (venomous) and king snakes (non-venomous)
The harmless king snake mimics the poisonous coral snake, causing would-bepredators to avoid them.
http://3.bp.blogspot.com
Monarchs (toxic to predators) and viceroys (non-toxic)
The viceroys mimics the coloration and pattern of the unpalatable monarch, also
avoiding would-be-predators.
http://fish.mongabay.com
Camouflage:
A flounder will be less conspicuous to predators and to would-be prey if it blends in with
its environment.
http://conservationreport.files.wordpress.com
Compare/contrast mimicry and camouflage.
Pick an organism and explain the benefit of that animal or plant mimicking
another. Purpose how this leads to natural selection in that organism.
Let’s put it all together with Peppered moths
The peppered moth population in England has had wide variability over the past two
hundred years. The original population composed of light colored moths with some
speckling, typically perched upon trees with lichen covered trees. During the Industrial
Evolution, pollution decreased the lichen covering and deposited soot on the tree
trunks. Therefore the light colored moths were no longer camouflaged against the light
colored bark. Slowly the peppered moth population transitioned from one of a light color,
to one of a dark color. With the increase in environmental awareness and the
implementation of standards, the pollution decreased and the light colored moths have
again increased in number.
http://iamyouasheisme.files.wordpress.com/2008/03/moths.jpg
Look at the diagram above. Explain why the peppered moth population transitioned
from light to dark colored moths during the Industrial Revolution? And how did cleaning
up the environment allow for a reversal in this trend.
Peppered moth (website resource) http://www.techapps.net/interactives/pepperMoths.swf
Physiological adaptations
Antibiotic resistance
Can you name any other types of physiological adaptations that could become a
problem for humans? Hint: think pests
Fossils
Archeopteryx- The “Missing Link” between reptiles and birds
1) http://www.ucmp.berkeley.edu
2) http://www.search4dinosaurs.com
Anatomy
homologous structures
The similarities in the bone structure of the forelimbs of mammals demonstrate
evidence for evolution: comparative anatomy and common ancestry.
http://www.indiana.edu
analogous structures
Show similarities in function, but are not evidence of a common ancestor--an example
of convergent evolution.
http://209.68.138.57/lc/archive/biology/PublishingImages/0345l.jpg
vestigial structures
The relic pelvic bones of a whale indicate that an ancestor may have walked on land
with legs.
http://www.kirksville.k12.mo.us
Evolution can be described as a change in allelic frequencies of a gene pool over time.
Natural selection can place pressure on specific phenotypes and cause a change in the
frequency of the alleles that produce the phenotypes. For example, traits of prey
species that either make them more difficult to detect/identify or to catch may be
selected for within that prey population. Think about the peppered moth example.
What would happen to the allelic frequency within a prey population if the predator
population declined? Exploded?
Embryology
It is easy to distinguish between an adult fish, adult reptile, or an adult mammal. But can
you do so for their respective embryos? Take a look below.
http://nitro.biosci.arizona.edu
The embryos of fish, reptiles and mammals all have a tail and pharyngeal pouches. In
fish, these pouches develop into the supports for the gills, while in the mammals and
reptiles (birds too), they develop into parts of ears, jaws, and throat.
These shared features in young embryos suggest evolution from a distant, common
ancestor.
Hypothesize the strengths and weaknesses of embryology as evidence for evolution
Part 2:
Mechanisms of Evolution
Natural selection is a mechanism of evolution.
Different types of natural selection act over the range of a trait’s variation. In the
following graphs, the dotted, bell-shaped curve indicates a trait’s variation in a
population. The solid blue, bell-shaped curve indicates the effect of a natural selection.
Stabilizing Selection
The intermediate phenotype is favored and becomes more common in the population.
Example: Consider a population of spiders in which the average size is a survival
advantage: larger spiders are easily spotted and preyed upon by birds and smaller
spiders have more difficulty located resources. Therefore, the average sized spider has
a selective advantage---and is “selected for”, while the extremes are “selected against”.
Number of individuals with trait
http://img.sparknotes.com/
Small  medium  large
Degree of trait (e.g. spider size)
To interpret this graph, you should be able to say that the majority of individuals has
approximately the mean (i.e. average) trait (i.e. intermediate spider size). There are few
individuals at the “tails” of the curve representing small or large spiders.
Hypothesize what might happen to the spider population if the bird population had a
catastrophic decline due to invasion of a parasitic, invasive species such as a cowbird?
Answer: Hard to tell. Might return to original population but might not if cowbirds eat
them too!
Divergent or Directional Selection
One extreme variation of a trait is favored and becomes more common in the
population.
Example: The peppered moth is a good example of directional selection as the
changing environment selected for a relatively rare trait (conversely selecting against
the more common trait) causing that trait to increase within the population.
Number of individuals with trait
http://img.sparknotes.com
White with little speckling

mostly dark
Degree of trait (e.g. amount of pigmentation)
To interpret this graph, you could say the majority of the population has had a increase
in the mean amount of pigmentation.
If a fishery only harvests large fish from the population, how might that affect the
population over time? Answer: It may select for smaller body size and slower growing
individuals in the population.
Disruptive Selection
Both extreme variations of a trait are favored and become more common in a
population.
Example: Consider a population of lazuli buntings. Males plumage ranges from bright
blue, to a mix of blue and brown, to dullish brown. Adult dominant males are those with
the brightest blue feathers on their heads and backs. These birds are more attractive to
potential mates and therefore are typically more reproductively successful than say a
male with a combination of brown and blue plumage (intermediate). The dominant
males are very aggressive towards the intermediate plumage type, but not so of the
dullish brown plumage type. Therefore, the dullish brown plumage birds can affectively
attract a mate due to less competition and harassment. In this example, the
intermediate plumage type is selected against, favoring individuals with either the
brightest blue or the dullest brown plumage. This is also an example of sexual selection,
where one sex favors a specific phenotype/trait in the other sex, leading to differential
reproductive success.
Number of individuals with trait
http://img.sparknotes.com
Dullish brown  brown and blue  bright blue
Degree of trait (e.g. plumage variation and color)
Interpret this graph. What does it illustrate about the number of individuals within the
populations with different degrees of this trait (i.e. plumage variation and color).
Other mechanisms of evolution are mutations, migration, and genetic
drift.
A population without selection pressure of a changing environment, no mutations, a
gene pool that does not change due to movement of genes into or out of the population,
and not experiencing genetic drift due to changes in allelic frequency are said to be in
genetic equilibrium. These populations are not undergoing any form of evolution.
Mutations
In the case of Down Syndrome,
additional genetic material on
Chromosome 21 has detrimental
effects on the individual carrying it.
http://www.thetech.org
What can cause mutations?
Are mutations good, bad, or neither for the organisms/populations in which they occur?
Migration (gene flow)
Blue fin tuna are known to migrate
across the entire Atlantic Ocean! Mainly
from east to west. Understanding gene
flow in highly migratory species is a key
concept in fisheries biology and
management.
http://www.flmnh.ufl.edu
An animal may actually move from one location to another or it may be relocated due to
human activity. Give examples. An animal may leave an area to find a mate, to find food
or other resources; it may be relocated due to a tropical storm; it may stow away on a
ship to be transported to another geographical area; humans may introduce an animal
to a new geographical area.
What about plants? Can you name some ways that gene flow occurs in plants? Seed
dispersal by wind or by animals (sticking to fur or defication), importing/exporting by
humans
Genetic drift
Founder Effect:
When a small portion of a population becomes isolated, whether it be due to
geographical or social/religious reasons, genetic drift can occur.
http://upload.wikimedia.org
In Lancaster, PA there is a community of approximately 12,000 Amish citizens. They
have a particular lifestyle and marry/reproduce only within that group. A recessive allele
resulting in a trait where the individual has shortened limbs and an extra digit on hands
and feet has increased over time due to the small gene pool. Today the frequency of
this allele is much higher in the Amish community than it is in the US population as a
whole.
Describe how the founder effect may occur in plants.
Seed dispersal
Bottleneck Effect
When a catastrophic event drastically reduces the size of the population, whether it be
natural disaster, overharvesting/overhunting, or disease, genetic drift can occur.
http://www.britannica.com/
The northern elephant seal was nearly hunted to extinction in the 1800s. By the turn of
the century there were only 20 individuals remaining. Since then, the population has
grown to over 30,000 individuals, but their genetic variability is still quite reduced—it is
much less variable than their counterpart, the southern elephant seal, that was not so
intensely hunted.
Do you know any other examples of the bottleneck effect? How can scientists identify
species that have gone through such a bottleneck? Giant panda & Galapagos Islands
Giant tortoises, cheetahs, Genetic research and comparison studies
How is genetic drift different from natural selection?