Objectives:1. Explain what a theory is and a law and

explain the difference between them. 2. Identify Darwin’s observations and their

role to conclude that species evolve. 3. Identify ideas that Darwin evolved from his

Voyage on the HMS Beagle4. Explain natural selection.

Theory of Evolution

Guess or hunch Science: set of statements that explain the natural

world. Science is controlled by experiments, data collection,

and theories to explain what has been observed.

Definition:

A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. A theory is valid as long as there is no evidence to dispute it. Therefore, theories can be disproven. Basically, if evidence accumulates to support a hypothesis, then the hypothesis can become accepted as a good explanation of a phenomenon. One definition of a theory is to say it's an accepted hypothesis (about.com)

What is a Theory?

LawA law generalizes a body of observations. At the time it is made, no exceptions have been found to a law. Scientific laws explain things, but they do not describe them. One way to tell a law and a theory apart is to ask if the description gives you a means to explain 'why'.

Example: Consider Newton's Law of Gravity. Newton could use this law to predict the behavior of a dropped object, but he couldn't explain why it

(about.com)

What is a Law?

A change in the genetic characteristics of a population over time

Well-supported based on a variety of evidence including fossil records, diversity of organisms, and similarity across species of anatomy and development.

Refers to common descent of organisms from shared ancestors.

What is Evolution?

1. Roman Philosopher, (Lucretius)lived 1,900 years before theory of evolution existed, believed organisms could not continue their species unless they were able to survive and produce offspring.

- this was not even looked at until 18th and 19th century2. Used to be that everyone believed that species were unchanging. 3. 1809: Jean Baptise Lamarck proposed a process in which evolution happened. a. Use and disuse of physical features: increase in size if used and decrease in size if not used.

b. Thought linked to environmental conditions

Charles Darwina. Studied medicine but did not like surgery. b. Father sent him to Cambridge Univ. To study ministry

where he completed degree in theology.

Theory of Evolution: Other people’s contributions.

4. Charles Darwin, went on a 5 year voyage on the ship HMS Beagle. (See route)

a. Found fossils in South America of armadillos. They were

closely related to the armadillos but not exactly the same

as the armadillos in that area.

b. Galapagos Islands: found plants and animals that

were found on the nearby coast of South America.

- explanation that the ancestors on the Galapagos

latter changed. (descent with modification)

The longest part of his voyage: 5 weeks He collected specimens of finches from 3

islands All in all he collected 9 distinct species all similar to each other

except their bills

1. fruit eater

2. cactus eater

3. large bills crush seeds

4. narrow bill eats insects

5. sharp beak feeds on

blood of sea birds

One ancestral finch evolved to

adapt to different food sources

Galapagos Islands

It was found that beak size was an adaptation to weather. A. Wet year: smaller, slender beaks food was more abundant. b. Dry years, larger, longer beaks. Few seeds produced so they

had to work harder Number of bird with different beak shapes are changed by natural selection in response to food supply.

We've defined evolution as descent with modification from a common ancestor, but exactly what has been modified? Evolution only occurs when there is a change in gene frequency within a population over time. These genetic differences are heritable and can be passed on to the next generation — which is what really matters in evolution: long term change.

Compare these two examples of change in beetle populations. Which one is an example of evolution1. Beetles on a dietImagine a year or two of drought in which there are few plants that these beetles can eat.

All the beetles have the same chances of survival and reproduction, but because of food restrictions, the beetles in the population are a little smaller than the preceding generation of beetles.

2. Beetles of a different colorMost of the beetles in the population (say 90%) have the genes for bright green coloration and a few of them (10%) have a gene that makes them more brown.

Some number of generations later, things have changed: brown beetles are more common than they used to be and make up 70% of the population.

http://evolution.berkeley.edu/evolibrary/article/evo_15

Which example illustrates descent with modification — a change in gene frequency over time?

The difference in weight in example 1 came about because of environmental influences — the low food supply — not because of a change in the frequency of genes. Therefore, example 1 is not evolution. Because the small body size in this population was not genetically determined, this generation of small-bodied beetles will produce beetles that will grow to normal size if they have a normal food supply.

The changing color in example 2 is definitely evolution: these two generations of the same population are genetically different. But how did it happen?

1. Thomas Malthus: wrote an essay in 1798 how human populations increase faster than food supply.

2. He said that humans should cover the earth in a very short time however this is not what happens because of death due to disease, war, and famine. This slows population growth.

3. Population definition: all individuals of a species that live together in one place at one time.

Thomas Malthus

1. Darwin took Malthus’s information in his essay and said that this

could apply to all species. All species can reproduce many

offspring in its lifetime however, only a few offspring survive.

2. Incorporating Malthus’s information and what he found on his

voyage he came up with this

a. Individuals that have physical or behavioral traits that better

suit their environment are more likely to survive and

reproduce than those that do not have such traits.

3. Darwin suggested that species that survive long enough to reproduce pass on favorable traits to their offspring, in time these favorable characteristics will increase in population and the population will gradually change over time.

4. NATURAL SELECTION: process by which populations change in response to their environment.

Natural Selection

Natural selectionNatural selection is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift.Darwin's grand idea of evolution by natural selection is relatively simple but often misunderstood. To find out how it works, imagine a population of beetles:

1.There is variation in traits.For example, some beetles are green and some are brown.

2.There is differential reproduction.Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.

3.There is heredity.The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

4.End result:The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.

University of California Museum of Paleontology's Understanding Evolution (http://evolution.berkeley.edu).

1. Darwin suggested that organisms differ from place to place because habitats are different. This presents both challenges and opportunities survival reproduction.

2. ADAPTATION: Changing of a species that results in betterment for survival in their environment.

3. He also determined that organisms closely resembled species in a nearby geographic region than those living in similar yet widely separated parts of the world

4. Conclusion: species evolved from a species that previously lived there or migrated from nearby areas.

5. Darwin published his findings in 1859. Book was called

“On the Origin of Species by Means of Natural Selection”

Adaptation

Earth changed slowly over many yearsDarwin found extinct armadillo fossils that

closely resembled – living armadillos

In other words: Natural Selection - Populations change in response to their environment

1. All species have genetic variation

2. The environment presents many different challenges to an individual’s ability to reproduce.

3. Organisms tend to produce more offspring than their environment can support; thus, individuals of a species often compete with one another to survive.

4. Individuals within a population that are better able to cope with the challenges of their environment tend to leave more offspring than those less suited to the environment.

5. The traits of the individuals best suited to a particular

environment tend to increase in a population over time.

Summary of important points of Natural Selection

1. Scientists know that genes are responsible for inherited traits.

2. Certain traits become more common in a population because more individuals in the population carry the alleles for those traits.

3. In other words, natural selection causes the frequency of certain alleles in a population to increase or decrease over time.

4. Populations of the same species living in different locations tend to evolve differently

5. Extinct: May have species that are better suited replace the ones that become extinct (natural disaster, climate changes etc..)

Darwin’s ideas Updated

Populations of the same species living in different locations tend to evolve in different directions.

Isolation: two populations of the same species cannot breed with one another.

In other words. 2 species were the same but as they evolved through time they have become so different that biologists consider them 2 different species.

Darwin’s ideas Updated

1. Variation exists within the genes of every population or species (resulting from random mutations).2. In a particular environment, some individuals of a population or species are better suited to survive (as a result of variation) and have more offspring (Natural selection).3. Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population.4. There is clear proof from fossils and many other sources that living species evolved from organisms that are extinct.

Theory of Evolution (4 Major Points)