misconceptions of natural selection. 2 charles darwin charles darwin was a scientist who was very...

Misconceptions of Natural Selection

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Charles Darwin

Charles Darwin was a scientist who was very interested in the study of nature.

He introduced the idea of Natural Selection, however it is often misunderstood.

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While natural selection is widely accepted, some have problems understanding it.

There are three major ways that Darwin has been misunderstood.

That survival of the fittest means only thestrongest and fastest survive.

That Natural Selection is random.

That an organism can evolve over thecourse of its own lifetime.

Misconception 1

“Survival of the Fittest” means only the strongest and fastest survive.

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Lizards Living on the Island

Long Tongue Medium Tongue Short Tongue

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Lizard Data

Phenotype

Long Tongue

Medium Tongue

Short Tongue

Number of

Lizards on May

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10 10 10

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Lizard Data

Phenotype

Long Tongue

Medium Tongue

Short Tongue

Number of

Lizards on

May 6

10 10 10

Number of

Lizards on

May 13

10 9 8

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Lizard Data

Phenotype

Long Tongue

Medium Tongue

Short Tongue

Number of

Lizards on

May 6

10 10 10

Number of

Lizards on

May 13

10 9 8

Number of

Lizards on

May 20

10 7 5

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Lizard DataPhenoty

peLong

TongueMedium Tongue

Short Tongue

Number of

Lizards on

May 6

10 10 10

Number of

Lizards on

May 13

10 9 8

Number of

Lizards on

May 20

10 7 5

Number of

Lizards on

May 23

10 + 120 =130

7 + 63 =70

5 + 15 = 20

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What is “fit”?

Sometimes you hear the phrase, “survival of the fittest”, but what does that mean?

How would you define a “FIT” individual?

In other words, what two things must an individual do in order to be considered FIT?

SURVIVE and REPRODUCE!SURVIVE and REPRODUCE!

Think about the lizards… what two things did the Long Tongue lizards do?

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What is “fit”?

“Survival of the Fittest” really means that some individuals survive AND reproduce better than others in their population.

Why? Because they have traits that allow them to do so, they have an advantage over others without these traits.

Misconception 2

Natural Selection is random.

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Natural Selection is not Random!

There are thousands of reasons why “fitness” varies between individuals, but they fall into two main categories.

In the first category, some individuals lose out simply because of bad luck.

This is random.

In the second category, some individuals don’t have the right physical or behavioral traits it takes to survive in their environment (phenotypes).

Selection based on phenotypes is NOT random.

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Natural Selection is not Random!

How about a couple of examples…

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Wyoming, USA

Bison

Here we see a herd of bison.

Last night as they were crossing a ridge during a thunderstorm, 3 of the 227 were struck by lightning and killed.

Does the bison’s phenotype affect its ability to reproduce in this situation?

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Wyoming, USA

BisonNot at all. The bison that were struck and killed just happened to be in the wrong place at the wrong time.

Does the bison’s phenotype affect its ability to reproduce in this situation?

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Cambodia

DamselflyMale damselflies establish territories along stream or pond edges. Females choose a good territory for raising their young, then mate with the male holding that territory.

In the competition for good territories, some males lose out and are forced to less desirable territories.

This less desirable location attracts fewer mates and therefore they produce fewer offspring.

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Cambodia

DamselflyDoes the male damselflies’ phenotype affect its ability to reproduce in this situation?

Some males are more capable than others of fighting to hold a good territory, and these differences are part of their phenotype.

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Review

In ONE of the populations we saw, the ability to reproduce was based upon phenotype, not luck. Which one was it?

A) Bison in Wyoming

B) Damselflies in Cambodia

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Natural Selection is not Random

Natural Selection ISN’T random.

Unlike lightning (random), selective pressure removes individuals whose phenotypes give them lower “fitness”.

All individuals don’t have an equal chance.

Misconception 3

That an organism can evolve over the course of its own lifetime.

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Natural Selection Doesn’t Create Variation!

Many people have misunderstood the variation idea. They thought that natural selection creates variation.

Really…Natural Selection acts on/uses the variation that is already present in populations (what is already there).

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Remember the lizards?

Why were the long tongued individuals able to reproduce successfully more than the others?

Phenotype

Long Tongue

Medium Tongue

Short Tongue

May 6 10 10 10

May 13 10 9 8

May 20 10 7 5

May 23 10 + 120 =130

7 + 63 =70 5 + 15 = 20

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Remember the lizards?

What was the selective pressure for the lizards?

Could any of the lizards have grown a longer tongue in order to catch more flies?

What phenotype varied in this population of lizards?So, natural selection acts on/uses existing variation, it doesn’t create/make new variation.

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Recap

Fitness is a measure of reproductive success, not physical ability.

Natural Selection isn’t random. Selective pressure removes those individuals whose phenotypes give them lower fitness.

Natural Selection doesn’t create variation, it acts on/uses variation already present in a population.

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