BILD 3: week 2_history of evolutionary thought

Prevailing 1800s view of species

Species were thought to be individually created by God (special creation)

1800s view of Earth’s age

Earth was believed to be older than 6,000 years, but its exact age was unclear and thought to be only a few million years

Fossil evidence in the 1800s

Fossils showed that species had changed over time and that extinction occurred

Missing element in early evolutionary thought

There was no known mechanism explaining how evolution occurred

Gradual and consistent geologic change hypothesis

The idea that slow, observable geological processes can produce large-scale changes over long periods of time

Proponent of gradual geologic change

Charles Lyell

Lyell’s prediction about Earth’s age

Earth must be extremely old to allow slow processes to create major geological features

Darwin’s Andes evidence

Fossil marine shells found at 12,000 feet showed land had risen over time

Darwin’s observed geologic events

Earthquake and volcanic eruption that raised the coastline by eight feet

Darwin’s conclusion about Earth

Earth is very old, providing time for descent with modification and the tree of life

Principle of succession

Modern species in a region resemble ancient fossil species from the same region

Biogeography pattern across time

Similarity between modern and fossil species within the same geographic area

Example of succession pattern

South American sloths and armadillos resemble fossil species from South America

Match between organism and environment

Traits of organisms correspond closely to their local environment

Galapagos tortoise pattern

Different islands had tortoises with different body shapes matched to vegetation

Evolutionary support from biogeography

Species descend with modification from local ancestors and adapt to local conditions

Evidence for descent with modification

Modern species resemble ancient species because they evolved from them

Dispersal definition

The movement of organisms to new habitats where they establish populations

Galapagos dispersal example

Ancestors of finches and tortoises arrived from the mainland and colonized the islands

Other dispersal examples

Sticklebacks and cichlid fishes undergoing adaptive radiation

Adaptive radiation definition

Diversification of a single ancestral species into many species adapted to different niches

Galapagos finch radiation

One ancestral species diversified into many species with specialized beaks

Local adaptation

Populations adapt to specific environments due to different selection pressures

Local adaptation and divergence

Adaptation to different environments increases differences between populations and leads to speciation

Descent with modification and divergence

All organisms evolved from a common ancestor through lineage splitting over time

Natural selection

A non-random process where heritable traits affecting survival and reproduction become more common

Biogeography’s influence on Darwin

Showed that species distributions are related to environment and ancestry

Biogeographical succession

Lineages persist in regions over time while undergoing modification

Dispersal’s role in evolution

Allows species to reach new and isolated environments

Selection’s role in evolution

Favors traits suited to local environmental conditions

Divergence outcome

Populations branch off from ancestors and each other, forming the tree of life

Darwin’s variation observation

Individuals in a population vary in their inherited traits

Overproduction of offspring

Species produce more offspring than the environment can support

Struggle for existence

Many offspring fail to survive and reproduce due to limited resources

Differential survival and reproduction

Individuals with advantageous traits leave more offspring

Sloths and armadillos observation

Modern species resemble ancient species from the same region

Interpretation of succession

Species descend with modification from local ancestors and extinction occurs

Seashells in the Andes

Evidence that Earth changes slowly and is very old

Rising coastline evidence

Geological change occurs gradually over long periods of time

Time for divergence

Earth’s age allows extensive branching to create biodiversity

Galapagos tortoise conclusion

Different environments led to different adaptations via natural selection