Ch 14 - Evolution (2) How change occurs. History: Jean Baptiste de Lamark first noticed that living...

Ch 14 - Evolution (2)

How change occurs

History:Jean Baptiste de Lamark first noticed that living things have changed over time.

He proposed an evolutionary theory based on 3 reasons for change.

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1. An INNATE urge to BETTER THEMSELVES.

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2. “Use and Disuse” - CHARACTERISTICS that were in constant use developed (were AQUIRED) and those that were not used were LOST.

3. Inherited Acquired traits

- traits developed by extra “use” were then passed on to the OFFSPRING

Lamarck himself conducted experiments where he cut the tails off of mice hoping to eventually produce a generation without any tails. He was not amused, the joke goes, when a colleague noted that the some doctors had been performing that same experiment on infant boys for thousands of years.

Unfortunately, Lamarck was INCORRECT on all three points, and his evolutionary theory was DISPROVED.

Charles DARWIN first

published the more modern theory of EVOLUTION.

His ideas were INFLUENCED by several other scientists’ work:

I have called this principle, by whicheach slight variation, if useful, is preserved,

by the term Natural Selection.

http://evolution.berkeley.edu/evolibrary/home.php

www.darwinday.org/englishL/life/beagle.htUsed by permission of Darwin Day Celebration (at DarwinDay.org), 2006

www.darwinday.org/englishL/life/beagle.html

http://evolution.berkeley.edu/evolibrary/home.php

1. Charles LYELL A GEOLOGIST who

published “PRINCIPLES OF GEOLOGY “

In this book, Lyell proposed the NEW idea that the Earth was VERY OLD and that it had CHANGED greatly over time. Darwin used this information to formulate his THEORY.

2. Farmers and ARTIFICIAL selection.

Through SELECTIVE breeding, farmers were able to change their crops and livestock. Darwin first realised that natural VARIATION in the species was the basis for change.

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ARTIFICIAL SELECTION

Teosinte (left) and its modern descendent, corn, a product of artificial selection

Individuals with UNDESIRABLE traits were not allowed to BREED, so their specific combination of genes did not get PASSED ON. Those that had DESIRABLE traits were breed - therefore the desirable traits were INHERITED by their offspring. Darwin termed this process ARTIFICIAL SELECTION.

Link for artificial selection super cow http://www.youtube.com/watch?v=Nmkj5gq1cQU:

3. Thomas Malthus An ECONOMIST. First noted that the BIRTHRATE was greater than the DEATHRATE in humans. He hypothesized that the only things that would stop the EXPONENTIAL growth of humans would be FAMINE, DISEASE AND WAR.

They called this the MALTHUSIAN DOCTRINE.

Darwin noticed that other species also have LIMITING FACTORS that control their population. He wondered what determined which individuals would SURVIVE AND REPRODUCE and which would DIE.

14.2 - Evolution by Natural Selection

Using these concepts, Darwin developed the idea of NATURAL SELECTION.

“Survival of the Fittest”

If you are “FIT” you live and reproduce.

If you are not as “FIT”, you do not live or you do not reproduce AS WELL.

Peppered Moth Example

Before Industrial revolution in England

After Industrial revolution

(they started burning coal which turned all the tree’s black from the soot)

NATURAL SELECTION SCENARIO

1. There is variation in traits

2. There is environmental pressure (birds Like the green ones!)

3. There is heredity

4. End result

Variation + differential feeding + Heredity = Natural selection

Natural selection

14.3 - Genetics and Evolutionary Theory

MUTATIONS: The RAW MATERIAL for

natural variation.

Changes in our GENES create the initial VARIATION in species.

(don’t forget to study DNA STRUCTURE,

“de-coding DNA” and MUTATIONS in DNA)

Gene Pool

Total # OF GENES genes in a POPULATION at any one time

SEXUAL REPRODUCTION continues to mix up the gene combinations in GENE POOLs, so there is even more

NATURAL VARIATION in the species.

Evolution: any change in the relative frequencies of alleles in the gene pool of a population.E.g. Field mouse population in back yardBefore grass After sod was laid downSandy brown 45 Sandy brown 10

Black 4 Black 4

Specked brown 29 Specked brown 29

WHAT HAPPENED?The specked brown mice had an advantage over the other colours of mice after the sod was laid.

WHY?Though the specked brown population did not increase, the number of the “specked brown” allele changed as compared to the others. The RELATIVE FREQUENCY of the “specked brown” allele changed. Therefore, according to the new definition, evolution has occurred.

WHICH ONE IS AN EXAMPLE OF EVOLUTION?

Beetles on a dietThere was a year or two of drought, there wereless plants that these beetles can eat. All the beetleshave the same chance of survival and reproduction, but because of food restrictions the beetles are a littlesmaller than the previous generation.

Beetles of a different colour90% of the beetles in the population have the gene for green coloration.A few generations later 70% of the population have the gene for brown coloration.

14.4 Notes: SPECIATIONhow new SPECIES develops from old ones

usually due to ISOLATION. (they aren’t able to get to each other, so they are not able to BREED. )

GEOGRAPHIC ISOLATION often leads to REPRODUCTIVE isolation; they are no longer able to produce FERTILE offspring.

This might even be due to differences in MATING rituals – they might not recognize the “signs”!

BIRD OF PARADISE MATING RITUALS - FROM PLANET EARTH

SEXY? --->

Once reproductive ISOLATION occurs, the DIFFERENCES between the two new species often increases.

5 Steps to SPECIATION

1. FOUNDING Fathers and Mothers.

An original POPULATION is established in it’s environment and fills a particular NICHE.

2. Separation of the Populations.

- (=GEOGRAPHIC ISOLATION)

- a few individuals move away from the original POPULATION and don’t RETURN.

3. Changes in the GENE POOL

the two locations have different environments. The populations slowly “ADAPT” to the environment.

**Remember that adaptation does not occur because the populations WANT to change.

Change occurs because NATURAL VARIATION is present in the population.

Some traits will give an individual an ADVANTAGE over others, making them more FIT to the ENVIRONMENT.

Greater FITNESS means more OFFSPRING. Those genes will be passed on, while those that are not as FIT to the environment will not be PASSED ON..***

4. REPRODUCTIVE IsolationThe changes in the GENE POOL make it impossible for them to BREED.

They might not RECOGNIZE each other any more, or they might have different MATING

rituals. Their “REPRODUCTIVE MACHINERY” might not fit together anymore! There could be many reasons why they can no longer produce FERTILE offspring.

A niche refers to the “PROFESSION” of the species, as well as the RESOURSES the species utilizes for LIVING.

If, after SPECIATION has occurred, the two populations still fill the same NICHE, they will be in direct COMPETITION with each other for RESOURSES when they try to share the same space.

One species may OUTCOMPETE the other and cause its EXTINCTION. However, the competition may cause the species to further ADAPT to fill separate NICHES so that they might live in HARMONY!

How do we define a SPECIES? They look different, but they can interbreed, so

they are still the same species

The Western meadowlark (left) and the Eastern meadowlark (right) appear to be identical, and their ranges overlap, but their distinct songs prevent interbreeding.

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But these two ants ARE the same species - they are sisters, actually! (they have different jobs)

Adaptive Radiation (DIVERGENT Evolution) vs. CONVERGENT Evolution

ADAPTIVE Radiation – many different species evolve from one COMMON ANCESTOR.

(like the SPOKES on a wheel that RADIATE from the centre)

CONVERGENT EvolutionMany different species will evolve with similar SOLUTIONS to environmental

CHALLENGES..

Different sorts of anteatersThough not closely related, they all

INDEPENDENTLY evolved the "tools" necessary to subsist on an ant diet: a long, sticky tongue, few teeth, a rugged stomach, and large salivary glands.

However, unless the species evolved from a common ANCESTOR, the structures formed are often very DIFFERENT in form. Convergent evolution produces ANALOGOUS structures.

Eg. Birds, BATS, squirrels, flying fish and INSECTS all have

“WINGS” so that they can FLY, but the INTERNAL structure of the wings is very different.

14.5 – Genetic DRIFTOccasionally, NATURAL SELECTION is not responsible for evolutionary changes. Genetic drift is known as evolution “BY CHANCE.”

There are some traits that have evolved despite the fact that they do not give an ADVANTAGE over another.

Example: Indian Rhinoceros –

ONE horn African Rhinoceros –

TWO horns – but there is no

ADVANTAGE to having a second horn, or to having only one.

In many cases, genetic drift occurs due to a NATURAL DISASTER

Example: A FLOOD wipes out the most of the mouse population in that area.

By chance, a few of the black mice were AWAY FROM THE AREA.

When the water drained away, they were left to REPRODUCE. Now the area has a mostly BLACK mouse population. It wasn’t that the black color was an ADVANTAGEOUS trait; the black mice were just LUCKY!

GRADUALISM vs Punctuated EQUILIBRIUM

Darwin’s theory of evolution supports a GRADUALISM theory of change. That is, Darwin believed that species change SLOWLY AND STEADILY over a very long period of time, and that they are always changing due to ENVIRONMENTAL PRESSURES.

However, the FOSSIL RECORD seems to suggest that there were species that experienced PERIODS of change followed by periods of NO CHANGE AT ALL..

It has been suggested that species experience a type of EQUILIBRIUM with the environment until something in the environment CHANGES. Then the species have to ADAPT, so they undergo RAPID PERIODS of evolution. These periods are followed by equilibrium, and the CYCLE REPEATS.

This relatively new and controversial theory is called PUNCTUATED EQUILIBRIUM.

# of species

Living Fossils

Ex: the horseshoe crab Limulus. This species of crab has not changed in hundreds of millions of years. Could it really have such a great design that it didn’t need to CHANGE?

Ch 14 - Evolution (2) How change occurs. History: Jean Baptiste de Lamark first noticed that living...

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