Evolution

AP Biology

Chapter 17

What is Evolution?

Defined as the accumulation of inherited changes within populations over time.Population – group of individuals of one

species that live in the same areai.e. all organisms have descended from

common ancestors with modifications, over long periods of time

Some questions that can be answered by evolution.

Why are there bones and fossil evidence of creatures that no longer exist? What happened to them?

Why do so many different animals have the same structures?Ex. The arm bones in a human are the same

bones as a flipper in a whale.

Why do organisms have structures they no longer use?Ex. The appendix in humans,

non-functioning wings in penguins, pelvic bones in whales

Why do so many organisms’ morphology and anatomy follow the same plan?

Why is the sequence of DNA very similar in some groups of organisms but not in others?

Why do the embryos of animals look very similar at an early age?

Why do males often develop elaborate traits/characteristics despite the possible effect on their survival?

Evolution is considered a Unifying concept of Biology, because it answers many of these questions and offers an explanation for the data.

Lamarke’s Theory of Acquired Characteristics

Hypothesized that an organism gains or loses features if they were not used.Use/DisuseTendency toward perfection

Then, these traits would be passed on to your offspring.

Inheritance of Acquired CharacteristicsEx. A giraffe stretched its neck to reach higher

leaves, stretched neck would be inherited by offspring.

Darwin’s Theory of Evolution by Natural Selection Charles Darwin –

naturalist He observed many

species on trips to places like Galapagos Islands Particularly interested in

the finches

Wrote “On the Origin of Species”

Animals in the Galapagos Islands

Darwin’s Theory of Natural Selection

1. Variation exists among individuals in a species.

2. Individuals of species will compete for resources (food and space).

3. Some competition would lead to the death of some individuals while others would survive.

4. Individuals that had advantageous variations are more likely to survive and reproduce.

Darwin’s Theory of Natural Selection This process = Natural Selection Favorable variations = Adaptations Example of the Finches:

Looked the same except for the beak size and shape.

Concluded that all the finches were descendents of the same original population.

Shape of the beaks were adaptations for eating a particular type of food.

Artificial Selection

Choosing certain traits and breeding only individuals that display the desired traitsBreeds of dogs Plant varieties

Ex. Cabbage, broccoli, cauliflower, Brussels sprouts, kale, collard greens – all the same species

Occurs in just a few generations

•Different dog breeds are examples of how selection can change the frequency of alleles in a population.

Evidence of Evolution Fossil Evidence

If today’s species came from ancient species, then we should find remains of those species that no longer exist.

There are tons of fossils of creatures that no longer exist but bear striking resemblance to creatures that do exist today.

Carbon-dating: gives an age of a sample based on the amount of radioactive carbon

Fossil Record – creates a geologic time scale

Evidence of Evolution

Evidence of Common Ancestry Homologous Structures – structures that are

embryologically similar, but have different functions (p.378)Ex. Wing of bird and forearm of human

Vestigial organs – functionless partsEx. Snakes have small pelvic and limb bonesEx. Humans have a tail bone

Biochemistry and DNA Observation of species change (wolves/dogs,

peppered moths)

Examples of Evolution

Industrial Melanism Dog Breeds (artificial selection) Bacteria and Antibiotics Elephant Tusks

Evolution – on a small scale Bacterial Resistance

Bacteria life cycle – very short! Bacteria continually evolving – even inside the bodies

of hosts. Bacteria develop genetic resistance through mutations

and from acquiring new genes from plasmids or viruses.

Surviving bacteria that resist antibiotics pass on their genes to future generations.

Poor prescribing practices and poor patient compliance are factors that determine bacteria resistance.

The Synthetic Theory of Evolution

Darwin knew that individuals transmitted traits to the next generation.

What Darwin didn’t know:How or Why individuals vary within a

population. During the 30’s and 40’s, biologists

combined the principles of genetics with Darwin’s theory of Natural Selection

The unified explanation of evolution is known as the synthetic theory of evolution.

The Synthetic Theory of Evolution

Explains Darwin’s observation of variation among offspring in terms of mutation. Mutation provides the genetic variability on

which natural selection acts. Universally accepted and constantly

studied by scientists.

Convergent Evolution

Independent evolution of similar structures in distantly related organismsEx. Aardvarks, anteaters, and pangolins Resemble one another in lifestyle and

structural features Strong, sharp claws to open ant/termite

mounds and long, sticky tongues to catch insects

However, they evolved from 3 distantly related orders of mammals.

aka: analogy

Phylogeny The evolutionary history of a group of related species. Phylogenetic trees can be constructed to show

relationships: Diagrams showing lines of descent

Evolutionary hypotheses can be tested experimentally

Guppy Experiment – Reznick and EndlerObserved that different streams have different

kinds and numbers of fishes that prey on guppiesDifferences in predation are correlated with many

differences in guppies: Male coloration, behavior, age and size at sexual

maturity, number of offspring per litter, size of offspring, and the frequency of reproduction

Sexual Selection

Natural selection that acts on an organism’s ability to mateSelection where organisms go to extreme

lengths to attract a mate.Sometimes results in features that are harmful

to the individuals survival.

http://www.pbs.org/wgbh/nova/evolution/creature-courtship.html

Examples of Sexual Selection

Peacock image courtesy of Rock Maple Farm.Elephant seals image courtesy of Craig’s Homepage.

Review Questions – Chapter 17

Questions p. 388-389Post Test # 1-6, 8-15Review Questions # 1-4, 7YMTC # 5