The Theory of Evolution

Chapter 13 – Sect. 1: Natural Selection

Charles Darwin - 1859

Published convincing evidence that species evolve

Proposed a reasonable mechanism to explain how evolution occurs

Darwin’s Voyage on the HMS Beagle

Darwin’s Voyage on the HMS Beagle

1831-1836 (5 year voyage) Darwin was 22 years old at the start Naturalist – someone who studies nature Ships purpose was to survey the coast of

South America

Darwin’s FinchesDarwin observed that many

of the plants and animals of the Galapagos Islands resembled but were not the same as those on the nearby coast of South America

Population – all the individuals of a species that live in a specific geographical area and that can interbreed

Natural Selection

Individuals that have physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully than those that do not have such traits These advantageous traits are adaptations

As a result, the nature of the population will gradually change – evolution!

Harsh Criticism

Darwin wrote down his ideas about evolution and natural selection in 1844

He did not try to publish his work until 1858

The theory of evolution goes against religious beliefs and was not accepted by the public in general

On the Origin of Speciespublished in 1859 (pg. 280 1-4)

Inherited variation exists within the genes of every population or species (the result of random mutation or translation errors)

In a particular environment, some individuals of a population or species are better suited to survive and have more offspring

Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population

There is overwhelming evidence from fossils and many other sources that living species evolved from organisms that are extinct

Reproductive Isolation

Two populations of the same species do not breed with one another because of geographic separation, a difference in mating periods, or other barrier to reproduction

These isolated populations will become more different over time until they are no longer able to breed with one another

The Tempo of Evolution

The Theory of Evolution

Chapter 13 – Sect. 2: Evidence of Evolution

Most Scientists Agree on the Following:

Earth is about 4.5 billion years old. Organisms inhabited Earth for most of its

history. All organisms living today share common

ancestry with earlier, simpler life forms.

The Fossil Record

The preserved or mineralized remains or imprint of an organism that lived long ago.

Provide a record of Earth’s past life forms

Evidence of evolution can be seen in the fossil record.

Formation of Fossils

The fossil record is not complete. Fossils do not form in all environments

Most fossils form when organisms are rapidly buried in fine sediments Bodies may decay too quickly or be eaten or

scattered Fossils are most likely to form in:

Wet lowlands, slow-moving streams, lakes, shallow seas, and areas near active volcanoes

Anatomy & Development

Comparisons of the anatomy of different types of organisms reveal basic similarities in body structures The structures may have different functions

in different organisms Ex.) bones may be present in both organisms but

are reduced in size and have no use or less important function

Vestigial Structures

Reduced in size or function, but may have been complete in an ancestor Ex.) hind limbs of

whales

Homologous Structures

Structures that share a common ancestry ex.) forelimbs of

vertebrates

Changes in DNA

Mutation – a change in the nucleotide-base sequence of a gene or DNA molecule If species have changed over time, then the

genes that determine the species’ characteristics should also have changed by mutation

The Theory of EvolutionChapter 13 – Sect. 3: Examples of

Evolution

Natural Selection at Work Environment dictates

the direction and amount of change in evolution

If the environment changes in the future, the set of characteristics that most help an individual reproduce successfully may change

Factors in Natural Selection(pg. 288 1-4)

All populations have genetic variations. The environment presents challenges to

successful reproduction. Individuals tend to produce more offspring than

the environment can support. Individuals that are better able to cope with the

challenges presented by their environment tend to leave more offspring.

Examples of Natural Selection

Strains of lung disease tuberculosis (TB) becoming resistant to certain antibiotics DNA in each strain is different = evolution &

natural selection Darwin’s finches developed different size

and shape beaks based on food sources Finches with proper beak for food survive =

evolution & natural selection

Formation of New Species

Divergence – accumulation of differences between groups Leads to the formation of new species

Subspecies – populations of the same species that differ genetically because of adaptations to different living conditions Can become so different that can no longer

interbreed successfully Speciation – the process by which new species

form