Chapter 22 Part 1: Overview of Darwinian Evolution

The Origin of Species

Charles Darwin 1859 - focused biologists' attention on great diversity of organisms

Main principle of Darwin

current species are descendants of ancestral species

Evolution

defined by Darwin's phrase "descent with modification"

Can be viewed as both a pattern and a process

Concept 22.1

The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species

Scala Naturae

all living organisms arranged in a linear order from simple to complex - Greek Philosopher Aristotle viewed species as fixed

Carolus Linnaeus

interpreted organismal adaptations as evidence that Creator designed each species for specific purpose

- developed binomial format for naming species

Taxonomy

Founded by Linnaeus - branch of biology concerned w classifying organisms

What helped lay groundwork for Darwin's ideas?

Study of fossils

Fossils

remains/traces of organisms from past

usually found in sedimentary rock

Strata

layers of sedimentary rock

Paleontology

study of fossils, developed by French Georges Cuvier

What did Cuvier speculate about strata

Boundaries between strata represent catastrophic events

Difference between Darwin and Cuvier ideas about change

Darwin: populations change over time

Cuvier: catastrophe at each layer

James Hutton and Charles Lyell views

Changes in Earth's surface can result from slow continuous actions still operating today, at same rate

Lamarck's Hypothesis of Evolution

Species evolve through use and disuse of body parts and the inheritance of acquired characteristics - but mechanisms are unsupported by evidence

Concept 22.2

Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life

During travels on Beagle, Darwin collected what specimens

South American plants and animals

What did he observe about fossils

Fossils resembled living species from same region, living species resembled other species from nearby regions

What did Darwin hypothesize about the Galapagos Islands?

Species from South America had colonized the Galapagos and speciated on the islands

After reassessing his observations, what did Darwin perceive?

Adaptation to the environment and the origin of new species are closely related processes

Natural Selection

process in which individuals with favorable inherited traits are more likely to survive and reproduce

What is the mechanism of descent with modification

Natural Selection

What 3 broad observations did Darwin explain

1. Unity of Life

2. Diversity of Life

3. Match between organisms and their environment

Descent with modification meaning

all organisms are related through descent from an ancestor that lived in the remote past

Darwinian view of history of life

Like a tree with branches representing life's diversity

What is explained by branching process of diversity of life and past extinction events?

Large morphological gaps between related groups

Evolutionary Tree aka

Phylogenetic Tree

Artificial Selection

Humans modifying other species by selecting and breeding individuals with desired traits

Darwin Observation #1

Members of a population often vary in their inherited traits

ex: sizes of dots on ladybug

Darwin Observation #2

All species can produce more offspring than the environment can support, many fail to survive and reproduce ex: releasing spores

Darwin Inference #1

Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals

Darwin Inference #2

Unequal ability of individuals to survive and reproduce will lead to accumulation of favorable traits in the population over generations

Thomas Malthus

Noted potential for human population to increase faster than food supplies and other resources

Describe process that explains the match between organisms and their environment

If some heritable traits are advantageous, > will accumulate over time > will increase frequency of individuals with these traits

Summarize Natural Selection

1. indivs w certain heritable traits survive and reproduce at higher rate than other indivs

2. increases match between organisms and their environment over time

3. if envir change over time, may result in adaptation to new conditions + give rise to new species

Do individuals evolve?

No, only populations evolve over time

Natural Selection can only

increase or decrease heritable traits that vary in a population

Adaptations vary with

different environments