Charles Darwin and Charles Darwin and Natural SelectionNatural Selection

Darwin’s ideas were influenced by:

• Jean Baptiste Lamarck, who hypothesized that acquired traits were passed onto offspring

•Charles Lyell, a geologist, who suggested that the Earth was much older than 6000 yrs•Thomas Malthus, who wrote that human populations grow much faster than their food supply

•Alfred Wallace, who suggested natural selection after studying wildlife in the Malay Archipelago.

Darwin journeyed on the HMS Beagle as a naturalist

• 5 year journey• studied and collected many biological specimens• on Galapagos Islands, off coast of Ecuador, observed

animals such as finches, tortoises, and iguanas • Thirteen different but similar species of finches, each

with a distinctive bill that is specialized for a particular food source.

• Suggested that these birds migrated from Ecuador

and changed after they arrived.

Darwin observed differences among island species.

Marine iguana

Land iguana

Thirteen different but similar species of finches, each with a

distinctive bill that is specialized for a particular food.

Suggested that these birds migrated from South America and changed after they arrived

Principles of Natural Selection1. Overproduction. What are pros and cons

of overproduction? 2. Variation. What can cause variation in a

population?3. Selection. Having a particular trait can

make individuals more or less likely to survive and have offspring.

4. Adaptation. Over time, those traits that improve survival and reproduction will become more common.

Adaptation or Variation?

• A feature that allows an organism to better survive in its environment

• The difference in the physical traits of various members of a population

• One bird in a population has a slightly thicker beak than its relatives

• A tortoise population lives in an area with high grass. These tortoises have longer necks than tortoises that live in other areas.

Elephants in Queen Elizabeth National Park, Uganda, Africa

Normally, nearly all African elephants, male and female, have tusks. In 1930, only one percent of the elephant population in Queen Elizabeth Park was tuskless because of a rare genetic mutation. Food was plentiful, and by 1963 there were 3,500 elephants in the park.

In the 1970’s, a civil war began in Uganda. Much of the wildlife was killed for food, and poachers killed elephants for their ivory tusks. By 1992, the elephant population had dropped to about 200. But by 1998, the population had increased to 1,200. A survey in 1998 revealed that as many as 30 percent of the adult elephants did not have tusks. Ugandan wildlife officials also noted a decline in poaching.

Natural selection acts on distributions of traits. • A normal distribution graphs as a bell-shaped curve.

• Traits not undergoing natural selection have a normal distribution.

– highest frequency near

mean value– frequencies decrease toward each extreme value

Types of Natural Selection

• Stabilizing selection – favors the average

• Small spiders have a hard time capturing prey

• Large spiders easily spotted by birds

• Medium sized spiders are best suited to survive in their environment, reproduce more often, leave more offspring.

Directional selection – favors one of the extreme variations

• Woodpeckers with long beaks capture the most insects, as they can reach the insects deep in the tree trunk.

Disruptive selection - favors both extremes

• On light colored rocks, the light limpets are camouflaged and survive the best

• On dark rocks, the dark limpets are most successful

• Tan (intermediate) limpets are visible on both the light rocks and dark rocks, and their numbers decline due to predation

Evidence of Evolution

A. Fossils Fossil links found between • fish and amphibians• reptiles and birds• reptiles and mammals

http://www.pbs.org/wgbh/evolution/library/11/2/e_s_3.html

Fossil linking fish and amphibians

• 365 million years old

• arm bone with fish fin characteristics

• found in Pennsylvania

• thought to be from a lobed-finned fish

Archaeopteryx – links reptiles and birds

                                                                                                                                         

A fossil of Archaeopteryx was discovered at about the same time Darwin published On the Origin of Species. This pigeon-size creature had a dinosaur like shape, complete with a long bony tail, heavy jaws with serrated teeth, and three long fingers. It also had feathers like those of modern birds.

Hind leg bones in whales

An amphibious reptile found in Texas, 2005

Diarthognathus, an animal with reptile and mammal characteristics

Early mammals may have looked like this

Evolution of the horse

B. Biological Molecules• Differences in amino acid sequences

and DNA are greater between species that are distantly related than between species that are closely related

• phylogenetic trees show how organisms are related through evolution

http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html

C. Homologous structures – similar in structure, with different functions

D. Vestigial Structures

• Structures that are reduced in size and either have no use or a less

important use than they do in other, related organisms.

• Examples: wings on flightless birds, Human ear muscles, human wisdom teeth human appendix , hind leg bones in whales

The cassowary, a flightless bird with wings

Wisdom teeth in human

Human appendix

E. Vertebrate Embryos

• Early in development, vertebrate embryos have similar characteristics such as a tail, buds that become limbs, and pharyngeal pouches that hold the gills of fish and amphibians.

http://www.pbs.org/wgbh/evolution/library/04/2/l_042_02.html

Examples of EvolutionA. Tuskless elephants becoming more common in

Africa

B. Antibiotic resistance in bacteria such as those that cause

pneumonia and tuberculosis

C. Pesticide resistance in insects• Tobacco plants are sprayed with

pesticides as many as 16 times in 3 months.

• The pesticides kill many insects, but not all.

• Only those insects that can resist the pesticides survive to lay eggs.

• These insects pass their ability to resist pesticides to future generations of insects through their genes.

The result is insects that are not affected by pesticides.

D. Industrial Melanism

• Example is the peppered moth.• Explained by the concealment hypothesis.

E. Beaks of finches

•

Adaptation

• the changing of a species that results in its being better suited to its environment.

• Examples: camouflage, mimicry, echolocation, migration, dormancy

Camouflage

Mimicry: one species resembles another

Snake mimicry: which is harmful?

Eastern Coral snake Highly venomous

King snake

Non-venomous

Echolocation in bats.

Hibernation

Migration

Dormancy: cacti embryos coming out of dormancy

Patterns of Evolution

A. Divergence – Darwin’s finches.

Dogs evolving from wolves. Can lead to formation of new species (speciation)

B. Convergent evolution

• distantly related organisms evolve similar traits.

• Example is seen in the streamlined, finned bodies of dolphins and sharks.

• The fins would be an example of analogous structures.

1. Natural Selection: certain traits might be an advantage for survival

2. Mutation: creates new genetic variation

3. Sexual selection: certain traits may improve mating success; alleles for these traits increase in frequency

Five Evolutionary forces

4. Gene flow: movement of individuals to or from a population (also known as migration). Immigrants add alleles, emigrants take alleles away.

Example: troops of baboons in eastern Africa. Females remain with the troop, but younger or less dominant males leave their birth troop, eventually joining another troop. This ensures gene flow.

5. Genetic drift: random change in allele frequency in a population. Causes a loss in diversity.

Example: In the 1800’s, northern elephant seals were overhunted. The population was reduced to about 20 individuals. Hunting has ended, and there are now about 100,000 seals. However, the population has little genetic variation.

Genetic drift

Fitness

the genetic contribution of an individual to the next generation's gene pool relative to the average for the population, usually measured by the number of offspring that survive to reproductive age

Microevolution• a change in gene frequency in a population —

such as all the individuals of one beetle species living on a particular mountaintop.

Macroevolution

• generally refers to evolution above the species level

Evolution of whales from land-dwelling mammals

Evidence

• transitional fossils between land mammals and whales

• vestigial structures such as pelvic and leg bones, and external ear muscles

• nostrils at end of snout in embryos; nostrils travel to top of head before birth

• DNA for milk protein very similar in hippos and whales