CHAPTER12 : PROCESSES OF EVOLUTIONPart 3

Macroevolution• Macroevolution: evolutionary patterns on a large scale

(over millions of years)• Such as: • animals with four legs evolved from fish• Birds evolved from dinosaurs

Stasis• Simplest macroevolutionary pattern• Lineages exist for millions of years with little or no change• Example

• The coelacanth: modern coelacanth is very similar to fossils hundreds of millions years old

Modern coelacanth Coelacanth fossil

Coevolution• Process by which close interaction in the same environment

between two species cause them to evolve together• Each species acts to select for the other one and each

adapt to changes in the other one• Can to lead to such interdependent between the two that

one can’t survive without the other one• Examples:• Flowers and pollinators(mutualism)• Predator and prey• Host and parasite• Commmensals

Exaptation• Also called preadaptation• Adaptation of an existing structure for a completely

different purpose• Such as feathers: birds use them for flight but the first

dinosaurs that had feathers used them for insulation

Extinction• More than 99% of all species that have ever lived ar enow

extinct (irrevocably lost from Earth).• Small scale extinctions are ongoing on Earth.• There have more than twenty mass extinctions in Earth’s

history.• A mass extinction is a simultaneous loss of many

different lineages of organisms.• Such as the event that caused the impact crater of the

coast of the Yucatan Peninsula that wiped out the dinosaurs

Adaptive Radiation• A lineage rapidly diverges into several new species• Occurs when a lineages of animals encounters a set of new niches (or ways

of life).• New niches may be used when mutation allows an existing population to

find new opportunities to survive in their existing habitat.• New niches may also become available due to geologic or climatic events

changing the existing habitat of the population so that it becomes very different or when these events make a new habitat available to the population.

• An example would be finches on the Hawaiian Islands.

Evolutionary Theory• Genetic change is at the root of all evolution, whether it is

microevolution or macroevolution.

Organizing Information About Species• Taxonomy: the science of naming and classifying species• Because many different explorers were discovering the same

species in different areas in the 18th century, they were giving many different names to these same species and some of the scientific names given to different species were very long and complicated.

• Carolus Linnaeus devised a simpler naming system.• In his system, every species is given a two part scientific name:

Genus species• Each category (or taxon) is a group of organisms.• The taxa are Kingdom, Phylum, Class, Order, Family, Genus,

species• Species are assigned to higher taxa based upon similar shared

traits.

Ranking Versus Group: Taxonomy Versus Phylogeny

• Linnaeus devised his system before anyone knew about evolution.

• Because species change in ongoing, organisms don’t always fit neatly into Linnaeus’ taxa.

• Also, Linnaeus’ ranking do not show evolutionary relationships.

• Phylogeny is the evolutionary history of a spcies or group of them.

• It is a genealogy that follows a lineage’s evolutionary relationships.

• Concerned with the central question,” Who is related to who?”

Phylogeny• Cladistics: groups species on the basis of shared characters (or

quantifiable, inheritable characteristics).• A character can be physical, behavioral, physiological, or molecular.• This can result in cladistic classifications of organisms being different

depending upon which character is used to do the classifying.• The result of cladistic classification is a cladogram, which is a diagram

that shows evolutionary relationships.• Each line in a cladogram is a lineage, which may branch at a node.• The node represents a common ancestor.• At the end of a branch is a clade, or a group of species that share a

set of characters.• Two lineages that branch from the same node are called sister

groups.

Phylogeny

node

clade

sister groups

Homework• Explain the difference between taxonomy and phylogeny.

Homework: Complete the following.