DESlides Evolution by Natural Selection for Bio

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This powerpoint will help you understand the main points of Darwin’s Theory of

Evolution, the role of mutations in natural selection and evolution of new

species and the difference between micro and macro evolution. We will do this

by examining evolution in humans.

When you hear the word evolution what do you think of? Take a few moments

to jot down your thoughts.

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If your answer contained the words change, time, genes, species…you are on

the right track Evolution is the Genetic change in lines of descent over time.

Evolution occurs in populations of organisms. It begins when the genetic

makeup of a population changes. Evolution explains the diversity of living

organisms we see on earth, and by examining the similarities of diverse

species, it also explains how we diverged from common ancestors.

Evolution is not simply change over time. The top left shows you change

through time as when a deciduous tree loses its leaves over as season

change during the year. That occurs in relatively short period of time. A

mountain eroding is also change but that takes place over very long periods of

time. However neither of these could be called evolution. If the genetic

material doesn’t change, you can’t have evolution. The bottom half shows

examples of evolution through the shuffling of genes through sexual

reproduction over the short term or through speciation over longer periods of

time

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It’s easy to get confused and think evolution is a linear progression because

contemporary diagrams and artwork make it seem that evolution is ladder-like

as depicted in this evolutionary timeline.

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Evolution occurs in a tree like fashion with different branches. In this diagram

we wouldn’t say that A is a more evolved species than D but we can say that at

one time in the past A and D had a common ancestor and we might expect A

and D to share some features in common. Their common ancestor took

different paths. One went on to become A and the other, an ancestor to B, C,

D

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Thus Humans are not more evolved than chimpanzees. We share a common

ancestor that was neither human or chimpanzee. Each species evolved traits

unique to their own lineages

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This chart shows how the different hominoids evolved. Notice where the

common ancestors were. 13 million years ago we shared a common ancestor

with the orangutans. During evolution a population went on to become the

organgutans while a different population became the ancestor to the gorilla,

chimps and humans.

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About 7 million years ago, the ancestors of humans and chimpanzees took

different evolutionary paths. With both ape and human features,

Australopithecus aferensis is somewhere in between and is our direct ancestor

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Click on the link to watch this video. You will need about an hour but it is

extremely engaging and fascinating. By examining the anatomy and

physiology of some of our primate relatives as well as fossil remains, and

genetic evidence, scientist Neil Shubin explains how human hands, vision and

brains evolved. I have listed some questions for you to answer to help tie the

video with the content of chapter 23 in our textbook.

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The video also reinforced the main ways that scientist look for evidence for

Evolution.

Fossil remains of our ancestors allowed scientists to understand when

bipedalism came to be

Comparison of genes for eye color provided evidence for evolution

Biogeography- they looked at fossils of other animals that were around Ardi’s

bones to provide clues to the prevailing conditions for bipedalism to develop

Comparison of the brain development of 3 month old monkey and human

provide clues to evolution as well as looking at the brain of sharks and fish

compared to humans.

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Primates evolved from an ancestral primate (northarctus) that had a divergent

thumb, long fingers and nails (not claws)

This hand structure made it possible to grab hold of narrow branches at the

ends of branches

23 million years ago, one group of primates evolved red/green color vision

through a duplication and mutation in an opsin gene

Bipedalism evolved in Australopithecus (Lucy) 3.2 mya and Ardipithecus 4.4

mya

Ardi was bipedal when the area was a woodland and she had a grasping toe

Walking upright freed our hands to make and use tools.

Our brains have a special region involved with hand-eye coordination (shared

by monkey,ape, human) 40% of our brain is involved in seeing.

Humans have unusually long childhood; gives us longer to learn and pick up

skills.

The genetic roots of our complex brain existed in much simpler creatures

(Amphioxis fish) that first arose over 500 million years ago

Looking at the fossil remains of the jaws and teeth, paleontologists can tell the

type of food eaten by early humans. Moved from insects and leaves to an

omnivorous diet

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The previous diagrams oversimplify the actual evolutionary steps so I show

you this drawing only to stress

that the extinct common ancestor of two living forms should not be expected to

look like a perfect intermediate between them. Rather, it could look more like

one branch or the other branch, or something else entirely. Humans were

becoming distinct from chimps and bonobos around 6-8 million years ago.

Notice when Australopithecus emerges and where Sahelanthropus is on this

chart. The evogram shows the hypothesized order of acquisition of the traits

that emerged during human evolution. Note that each of the Homo species

was unique in its own way, so human evolution should not be seen as a simple

linear progression of improvement toward our own present-day form.

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Here’s a pictorial look at how we are related to other organisms. We are

animals and so our DNA shares common traits with snails, clams, insects and

other animals. A subset of those animals have backbones. Known as the

Chordates. This includes the mammals, fishes, reptiles, birds and amphibians.

From there all the mammals are grouped, then all the primates which includes

the great apes like chimps, gorillas and monkeys and lesser apes such as the

lemurs, tarsiers. This is shown in the picture in our textbook. There can be

confusion over the terms hominoids, hominids and hominins but don’t get too

caught up on the terminology. It’s better to know by looking at a tree like the

one in our textbook, and understand who is more closely related to who.

Modern day humans or homo sapiens (which translates to thinking man) are

the only remaining species of the genus homo.

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Evolution is not about the perfecting of species. Each species on this chart

has traits specific for its survival.

One form of a trait may be ancestral to another more derived form, but to say

that one is primitive and the other advanced implies that evolution entails

progress — which is not the case.

an organism’s position on a phylogeny only indicates its relationship to other

organisms, not how adaptive or specialized or extreme its traits are.

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Before getting into the mechanisms of evolution let’s distinguish two terms:

micro and macro evolution. The suffix micro as in microbiology means small

and macro means big. So microevolution is genetic change that occurs at or

below the level of the species. It MAY give rise to new species. Macro

evolution occurs on level greater than the species as what occurred when the

different mammals evolved.

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Recall we said that Evolution was the change in the genetic composition of a

population over time. Here are 4 processes that could possibly account for that

change

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This is the most well studied mechanism of evolution and the one most

students learn about. It is also the one of the most misunderstood and

students frequently hold many misconceptions which I want to address. So we

are going to focus on this mechanism of evolutionary change.

Evolution by the mechanism of Natural Selection cannot happen unless there

is genetic variation within a population.

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It is obvious when looking around at our own species that the traits of

individuals in a population vary.

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These differences can arise from mutations or random changes in the DNA,

recombination of genetic material during sexual reproduction, or through gene

flow where there is movement of genes from one population into another

population. For instance, The U.S. population is much more diverse today

than it was 200 years ago due to humans’ ability to fly anywhere in the world

and this mixes our gene pool.

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DNA is mutating all the time. Sometimes those mutations can have a harmful

effect as we learned about in some genetic diseases we studied in Module 7

and sometimes they can have a beneficial effect. In the exploring your Inner

Monkey video, recall that there was a mutation in the opsin gene that lead to

the development for red/green color vision which was beneficial for ancestral

humans. A neutral trait such as attached earlobes doesn’t help or hurt survival

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The second ingredient for evolution by natural selection is an increase in the

frequency of those particular genes that provide a survival advantage to those

who have it. Individuals better adapted to prevailing environmental conditions

survive and reproduce. Watch the movie about the Pocket mouse. It is a very

simple yet elegant example of how the frequency of certain genes for black fur

increase over a very short period of time when environmental conditions

change. Note what acts as the selection pressure. The gene involved in the

origin of melanism in [some] rock pocket mice is called melanocortin receptor

1, or MC1R for short. That is not a very interesting nugget of information, until I

tell you that the melanic forms of jaguars, snow geese, arctic fox, fairy wrens,

banaquits, golden lion tamarins, arctic skua, two kinds of lizards, and of

domestic cows, sheep, and chickens are caused by mutations in this very

same gene. In some species, precisely the same mutations have occurred

independently in the origin of their dark forms. These discoveries reveal that

the evolution of melanism is not some incredibly rare accident, but a common,

repeatable process. Evolution can and does repeat itself. “ (Carroll, Sean B.

Evolution in Black and White. Smithsonian.com, February 10, 2009).

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To review… Evolution requires Variation in a population, Selection of certain

alleles for a gene, and Time.

So how do these 3 ingredients: variation, selection and time explain the

evolution of skin color? Watch this video. Jot down notes to these guiding

questions as you watch. Then come back to the powerpoint to learn about the

misconceptions that people sometimes have when learning about evolution.

Did you notice that we also have the MCR1 receptor gene that is involved in

melanin production? Just like the pocket mice. We are afterall evolved from a

common ancestor so we DO share many genes.

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There are 3 myths or misconceptions about evolution that I want to clarify

which I will do by means of cartoons

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What is wrong with this picture? Darwin Said it is Survival of the Fittest. When

he referred to fitness this meant reproductive fitness not physical fitness or

who Is strongest.

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It’s all about how successful you are at passing along genes to the next

generation

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Why doesn’t this accurately describe how evolution works?

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Organisms don’t develop traits because they need them

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Can these penguins adapt to global warming?

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Individuals cannot suddenly change their behaviors, or physical traits to

“adapt” to sudden changes in their environment. And there is no plan for

perfecting the species. As you saw in the video, Humans evolved to have

color vision which provided an advantage to distinguish food sources in their

environment but at the same time they also lost the keen sense of smell that

their canine relatives retained.

Here is your review question. If you chose A you are correct! On a quick

reading C might appear correct but remember that populations, not individuals

evolve.

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