EVOLUTION2015 - TOPIC 4

EVOLUTIONThings to coverHistory of the theory of evolutionNatural selection

◦ Variation◦ Isolation◦ Selection pressure◦ Selection

EvolutionArtificial selection

EVOLUTION

Source: C.Williamson (2010)

EVOLUTION The female loggerhead turtle lays up to 150 eggs during

the breeding season. Of these, only one or two will survive to an age where

they can reproduce. Heat will influence whether these

eggs produce female or male turtles.

Why do so many turtles that hatch successfully, die?

EVOLUTION In nature, many more

animals are born than will survive to reproduce.

This is because there is a struggle for survival.

EVOLUTION Factors that affect the

survival of the loggerhead turtles, and of all animals include:

PredatorsLack of food

Lack of living spaceClimateDisease

EVOLUTION It is the struggle for

survival that allows us to evolve.

And it has been happening for millions and millions of years!

The Lion King

HISTORY OF

EVOLUTION

HISTORY OF EVOLUTION The Book of Genesis

states that the world was created by a divine being in six days.

Still a widely held Theory of Evolution known as “special creation”.

HISTORY OF EVOLUTION The Greek philosopher

Aristotle perceived a “ladder of life” where simple organisms gradually change to more elaborate forms.

HISTORY OF EVOLUTION1785 James Hutton believed

that the earth was formed by an ancient progression of natural events, including erosion, disruption, and uplift.

HISTORY OF EVOLUTION1798 Thomas Malthus Proposed idea that

populations produce more offspring than they can survive

HISTORY OF EVOLUTION1798 Georges Cuvier

suggested that the earth was 6,000 years old.

He is well known for establishing extinction as a fact.

HISTORY OF EVOLUTION1809 Jean B. Lamarck proposed

the Theory of Acquired Characteristics

This states that traits acquired in an organism’s life time are passed to offspring.

For example, the neck of the giraffe stretched as it reached for food and its offspring would retain this longer neck.

HISTORY OF EVOLUTION1830 Charles Lyell published

evidence suggesting the age of the earth was several million years.

HISTORY OF EVOLUTION1844 Charles Darwin

Established that all species of life have descended over time from common ancestry.

He proposed that this branching pattern of evolution resulted from a process that he called natural selection.

HISTORY OF EVOLUTION1859 Alfred Wallace

Developed a concept of evolution similar to Darwin's.

Independently proposed a theory of evolution due to natural selection that prompted Charles Darwin to publish his own theory.

HISTORY OF EVOLUTION1915 Alfred Wegener

Proposed a theory of continental drift, which hypothesized that the continents were slowly drifting around the Earth.

WHAT IS EVOLUTION

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WHAT IS EVOLUTION?Evolution involves changes which are inherited

(ie. involves DNA & genetics!)

Evolutionary change is usually gradual and may take generations to show up, especially for organisms of long generation time (eg. humans).

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WHAT IS EVOLUTION?For evolution to happen, 2 things need to occur:

1. A source of variation between individuals of one species.

◦ resulting from mutations, cell division and fertilisation

2. A change in the frequency (occurrence) of the genes in the gene pool of a population.

◦ caused by natural selection

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WHAT IS NATURAL SELECTION

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WHAT IS NATURAL SELECTION?Charles Darwin’s theory

He suggested that, within a species, the individuals with variations that best suit their environment survive to reproduce and pass on their variation to their offspring.

Another way of saying this is that they are selected for survival by their environment.

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WHAT IS NATURAL SELECTION?

Individuals with unadapted variations are said to be selected against.

These either fail to survive, or, if they do survive, do not reproduce as successfully.

Overtime, they will become extinct.

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WHAT IS NATURAL SELECTION?

In the following generations:

◦ there will be an increase in the proportion of adapted individuals

◦ and a decrease in proportion of unadapted individuals

The result is the survival of the fittest.

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WHAT IS NATURAL SELECTION?

Over many generations, populations become more and more different from each other so that eventually, new species develop.

The new species will no longer be able to mate successfully with the old species.

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NATURAL SELECTION – QUICK GUIDE –

1. Overproduction of offspring occurs

2. Variation exists in a population

3. Environment changes

4. Selects for one variant and against another

5. Most adapted variant survives to reproduce

6. Adaptation becomes more common in population

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THE ENVIRONMENT &

EVOLUTION

THE ENVIRONMENT & EVOLUTION

A major driving force behind evolution is the environment in which the species lives.

Selection pressures in the environment influence the survival chances of an individual in that environment

Selection pressures may be:

◦ Biotic = living

eg. predators, disease, prey, competition, mates

◦ Abiotic = non-living

eg. temperature, shelter, sunlight, water, nutrients

The result of this selection is adaptation.29

THE ENVIRONMENT & EVOLUTION

If a species is somehow separated into two groups by an isolation mechanism or barrier, one species could potentially diverge into two.

If the environments on either side of the barrier are different, each environment will select for a different set of features.

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THE ENVIRONMENT & EVOLUTION

The two isolated groups cannot interbreed, so there is no gene flow between them.

After a long period, the groups on either side of the barrier may become so different that they can no longer interbreed even when put together.

One species has evolved into two = speciation!

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THE ENVIRONMENT & EVOLUTION

Two examples of evolution in response to environmental change include:

1. Biston betularia the peppered moth

2. Multiple antibiotic resistance in bacteria

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THE ENVIRONMENT & EVOLUTIONThe peppered moth

One of the earliest and best documented cases of natural selection.

Up until mid 19th century, most peppered moths were light in colour.

This allowed them to be well camouflaged on the light coloured lichens on the trees and rocks.

A black mutant form did exist, but numbers were small because they were easily seen by predators.

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THE ENVIRONMENT & EVOLUTIONThe peppered moth

As industrialisation spread, soot and pollution increased the number of lichens being killed off and also resulted in the tree trunks being much darker.

The numbers of the dark mutantincreased and the numbers of the light form decreased because the light form now became more visible to predators.

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ARTIFICIAL SELECTION

ARTIFICIAL SELECTION Dogs are a great example of evolution in action.

All dogs are members of the exact same species: Canis lupus familiaris

All dogs, whether Chihuahua or Great Dane, are capable of interbreeding and producing fertile offspring — but there may be some logistical complications involved here.

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ARTIFICIAL SELECTION

Artificial selection works like natural selection, in that only individuals with certain traits get to have offspring.

The main difference is that in artificial selection, humans are selecting certain traits, and with natural selection, individuals with traits allowing survival and reproductive success do the best.

Artificial selection in dogs has occurred over thousands of years, a relatively small time interval in the grand scheme of evolutionary time.

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http://www.youtube.com/watch?v=aTftyFboC_M&list=PL3EED4C1D684D3ADF