Download Natural Selection Review Sheet

Natural Selection Review Sheet
Courtesy of: Pamela J. Shlachtman, Miami Palmetto High School
The Theory
Darwin, after visiting the Galapagos Islands and seeing finches with obvious similar origins doing
different things according to the niches they had taken, came up with his Origin of the Species. A
lot of his work was ridiculed because people immediately jumped on the monkey - man thing and the
"survival of the fittest" idea. There are things that one needs to know about Darwin's theory
before any ideas are worked with. One thing is that all the things you see today are a result of
selection and do NOT come from one another. Today's chimpanzee is a result of millions of years of
selection and has nothing to do with today's Homo sapiens. Both chimpanzee and man have evolved
along separate routes to look like what they are today. Another thing is that survival of the fittest
does not necessarily mean the strongest. The fittest refers to the ability to reproduce. Those
organisms that have 100 % or their young reproduce are the fittest. If strength were a factor,
Tyrannosaurus rex would still be around. Darwin did not have the benefit of DNA. He had no idea
how traits were passed on and this was one of his problems in his theory. Not having the DNA
concept made his work even more phenomenal. What is the Darwinian theory of the Origin of the
Species that has caused so much debate in the world? We still have debate over his theory. Some
people still believe that man and all other creatures were created in 4 days in the year 4004 BC.
Some people believe that a supreme being created everything in 4 days. Of course there is an
argument on how long those for days actually were. Were they 24 hours or 4 million years or 400
million years? Does the Supreme Being decide what organism makes it and what doesn't? Very
speculative. You may believe what you wish to believe. However, this presentation is the most
updated theory of evolution and selection that I could find.
Darwin's Theory of Evolution
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All organisms have the ability to produce more individuals than can survive. A female cod
lays millions of eggs. If all of them survived, the oceans would be crawling with cod. Most of
them never survive.
The environment has things that kill organisms. Too hot, too cold, too dry, storms, floods,
predators all contribute to the death of organisms. Too frequently, there is not enough food
in the ecosystem to sustain the life there or the predators are too many or too good.
Competition occurs for the food and space in the ecosystem.
Not many organisms are exactly like. Individuals vary , some drastically. They may differ in
color, in size, in speed, in resistance to disease and other traits. Some of these traits are
inherited.
Some of the inherited traits allow the organisms to survive better than others in bad times.
Those that have those traits survive. Those that don't. don't'. This is called adaptation.
Some mutations are harmful but many are harmless. Some are advantageous which result in
genetic traits that give that organism better chance of reproduction. Some of the adaptive
traits are protective coatings, gripping mechanisms , and the ability to hibernate in
unfavorable conditions. Those with favorable traits soon mesh with other favorable traits
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and the mutant young are much better off. When the trait is predominant in the population,
natural selection has occurred.
Because those that have more advantageous traits have more offspring, each generation
contains more of those individuals. The number of organisms without the advantageous
traits decreases. This is called evolution.
It isn't a difficult theory but it has implications that are not liked by religious groups and some
non-religious groups. However, today, it is fairly obvious and is VERY difficult to refute with the
fossils that we find. Man's fossils are very different than man today. His weight, height and brain
capacity has changed dramatically since written history has started. The average Egyptian male was
5 ft tall. The average Roman soldier was 5' 4". The average American soldier is 6'. The average
Watusi is 6'6". A person 7 ft tall was unheard of 100 years ago. Today , there are a lot of them,
especially in the NBA. Obviously, height is an advantage. There is NO doubt that tall women are
MUCH more successful in business than short women. Tall men have a better chance of employment
than short men. The average primitive man was less than 4 ft.
Natural Selection
The entire genes of all the organisms in the population are called the gene pool. Any change in the
gene frequencies in a population is called genetic drift. Many are independent variables. A massive
kill-off of a population, such as a disease or weather that allows the individuals to survive will
randomly change the gene pool. Some are density dependent. In large gene pools, the favored traits
tend to hide or eliminate unfavorable ones until they never appear again. Giraffes are a good
example. There used to be tall giraffes and short giraffes, both few from the top and edge of
trees in a savanna. During hard times, the short ones could feed only from the sides. The short gene
was a definite disadvantage and the short gene disappeared from the gene pool. There are 3 types
of selection:
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Stabilizing selection - The population eliminates the "edges" of the population, the not so
normal individual.
Disruptive selection - The common traits disappear leaving the edges of the population. This
is very common on islands. Many finches living on an island with many niches are in danger of
a disease that would wipe out many flowering plants. If a change in the flowers occurred,
only the finches with longer beaks could feed. Seeds of plants that are very small and thin
to the extreme of being very large and thick that only a large bird could break, the large
bird would ignore the small seeds. The bigger than average bird may do away with the
center section of the seeds leaving only the large and small ones. This is disruptive.
Directional selection - One end of the tolerance chart starts to disappear. The pepper moth
of England is a perfect example.
Limits to Adaptation
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A change in the environmental conditions can lead to a change in the genes only if that gene
was there in the first place
Adaptation of that gene is limited by the population's reproductive power. R-strategist
populations will adapt quickly but K strategists can take millions of years.
Even though a favorable gene is in the populations, it may take a lot of the population to die
to allow the favorable gene to advance
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Coevolution - two species that have interactions cause changes within their respective
species. The Arctic fox and Arctic hare both have white coats in the winter and brown in
the spring.
Theories of Beginnings
If natural selection results in gradual incremental changes in the genetic composition of populations,
why isn't there one continuous spectrum of organisms all the way back to the origin of life? We
believe there is but there are a lot of organisms (parts) missing simply because they no longer exist.
We know that saber toothed tigers existed but they no longer do. Why not? Where did their niche
go? Why couldn't they make it and the lynx did? How did one organism show up and the other
disappear? First, look at the idea of a species. A species is a reproductively isolated individual. Lions
and tigers can breed with one another to produce a tiger or a lion but they don't. Why not? Because
there is a serious desert and several mountain ranges between the groups. They are reproductively
isolated. What would happen if a species were to be split by a river shift and they could not swim.
Suppose the system on one side of the river all of a sudden became very different. The individuals
in the population of the East Side may have a trait that allows them to survive on the East Side.
This trait would be passed on and the number of individuals in that area would increase drastically.
All of a sudden, the river shifts again and the two types are mixed again. They may or may not be
able to reproduce with one another. This is called speciation and one species is, presto, two. How did
the Earth generate and how did life actually appear. It is thought that the Earth with all the
components of our universe were created at one time, the Big Bang Theory about 6 billion years ago.
This is a result of finding nothing from outer space over 6 billion years old. The Earth would have
condensed about 5 billion years ago. It would have been too hot to have water but gradually
developed it. The atmosphere was methane and nitrogen. If you were to stand on the spot where
you are now, if there would have been land there (and there wasn't) 4 billion years ago, you would
die of asphyxiation in about 4 minutes. It is thought that about 4 billion years ago , the oceans had
about 1 % organic matter and the amino acids and polypeptides formed the first life. The first life
is referred to as phototrophs and they produced oxygen. In the Cambrian period, the atmospheric
level of oxygen was probably 1 %. By the end of the Silurian period, about 400 million years ago, it
had reached about 2 %. Huge numbers of phototrophs dumped massive amounts of oxygen into the
atmosphere that set the stage for animals. Oxygen was converted to ozone and the ultra violet
light, deadly to animals was reduced. 2-300 million years ago, in the late Silurian period, massive
amounts of plants occurred and the plant niches abounded. The Permian period provided foods for
the reptiles and the huge reptiles that followed but the end of the Mesozoic era found most of the
huge plant growth gone and the large reptiles gone. Mammals began to dominate the scene and we
have modern changes to look at. What happened to the animals that are not there.? Extinction.99%
of all species are extinct.
Extinction
Extinction means the disappearance of a species form the face of the earth. If extinction is bad,
then things have been bad for millions of years as practically all the species that have ever been
alive are now extinct. The background rate for marine organisms is abut 3-5 families or 180 -300
species per million years. Most of the losses have been due to predation, competition, habitat
change, and reproductive rates. There have been periods of abrupt changes which may or may not
have been the result of cataclysmic events such as the collision of earth with an asteroid. Fossil
records indicate at least 6 periods of mass disruption on land and 4 in the oceans. During the last
disruption, 20 families and up to 1200 species disappeared in the oceans. Most mass disruptions
have occurred in the late Ordovician, Permian, Triassic and Cretaceous Periods. It seems to average
about every 26 million years and coincided with meteor showers. The biggest disruption was 65
million years age during the Cretaceous Period. A very high amount of phytoplankton disappeared,
drastically reducing the oxygen and the rest of the dinosaurs. Because of the high amount of
iridium deposited in layers of that period, and the fact that iridium is rare on Earth but VERY
abundant in asteroids, it is thought that a large asteroid collided with the earth causing a decline in
the solar radiation reaching the earth, depletion of the ozone and otherwise messed the earth up
for thousands of years. Extinction is a natural process in evolution of the species. Man has
interfered with the extinction process. Instead of killing off 1 per hundred years, we are killing off
many per hundred years. We are killing off a lot of animals. The latest biggie kill was the Dusky
Seaside Sparrow that lived in Cape Canaveral. Because the mosquitoes were so numerous in this salt
water marsh, NASA sprayed the marsh continually. It killed the mosquitoes, the birds, the fish and
all the rest of the life in the marsh. Along with the pressure of housing, NASA draining and cement,
the removal of its habitat and foods, the Dusky died out a few years ago. Knowing that we could not
possibly kill off the passenger pigeon because the flocks darkened the sky, we shot and trapped
millions of them. One hunter alone trapped over 10,000. They died off rather rapidly. The Dodo, the
Stellar's Sea Cow, hundreds of Tropical Rainforest Animals, small fishes of rivers and streams that
could not take reservoirs, simply too many to list have disappeared. Some are just about gone. The
Hawaiian Monk Seal is dying out at about 100 per year. There are currently 550 left. The
Guadeloupe Seal is disappearing as rapidly - less than 300 left. The California Condor stays alive
only because man keeps them alive. The Whooping Crane is coming back but could not make it if man
didn't help it. Zoos, parks and preserves are the only place species diversity is going to find refuge.
Wildernesses, constantly under attack in every government, are not going to withstand the pressure
of hunger and greed. Loggers and miners look at a wilderness and find a "waste of land and
resources" whereas environmentalists look at a wilderness as the last possible species diversity
areas in the world. The environmentalists are not winning. It is only a matter of time until the
extinction level is massive again, not because of a catastrophe but because of people.
Natural Selection/Planned
Natural selection has found a place in the breeders of the world. New species have been made all
over the world to provide new foods and new species to look at. New orchids, new lilies, new miracle
grains and all found in our society. Our new wheat is now planted all over the world. It is a result of
the new hybrids crossed with the original Jerico wheat to produce a wheat rust resistant wheat. It
produces far more wheat per acre than the old wheat. The miracle rice produces 4-5 times the
amount of rice on the same acres. The new hybrid corn produces 100 bushels per acre compared to
the 40 in the 1950s. We are breeding new animals. We are beginning to engineer changes in DNA
which will drastically affect selection. Our breeding has developed cattle that are so fat they could
not survive the natural range. Horses that could not tolerate the natural world, hairless dogs that
would die out immediately in China where they originated and so on. We are "selecting" what we
want, not what is naturally selected. It may be good, it may be a disaster. Who knows? Will
genetically engineered people be the next step in our evolution? Will the world outside go away
leaving only the methane breathers of the vents alive to start a new evolutionary process. Only time
will tell but we are doing what we can to destroy the species of Homo sapiens and there is only one
species left.
Human's Effect on Natural Selection
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We simplify ecosystems. We eliminate some wildlife by plowing clearing forests, filling in
wetlands and use one crop, monoculture. This eliminates many species in the system. We
spend fortunes trying to keep that monoculture alive
We strengthen some populations of pests and bacteria by treating them with pesticides and
antibiotics making them resistant and thereby stronger than their competitors.
We eliminate some predators. We eliminate prairie dogs, wolves, coyotes, lions, tigers,
eagles, etc because they prey upon tamed species.
We introduce competition or predators into ecosystems Dutch Elm Disease, Lampreys into
the Great Lakes, carp, walking catfish, Melaleuca.
We over harvest species. Cod, Anchovies, Salmon, overgrazing 6. Interfering with the
normal chemical cycling and energy flows monoculture reduces nitrogen cycling, CFC's, PCBs,
heavy metals additional CO2 , rapid transmission of sulfur and carbon into the system.