Chapter 12 Glossary, Summary, and Practice Questions

KEY TERMS

analogous structure a character found in two taxa that looks similar because of convergent evolution, not because of descent from a common ancestor

binomial nomenclature a system of two-part scientific names for an organism, which includes genus and species names

branch point a point on a phylogenetic tree where a single lineage splits to distinct new ones

clade a group of taxa with the same set of shared derived characters, including an ancestral species and all its descendants

cladistics a method used to organize homologous traits to describe phylogenies using common descendent as the primary criterion used to classify organisms

class the category in the taxonomic classification system that falls within phylum and includes orders

domain the highest level category in the classification system and that includes all taxonomic classifications below it; it is the most inclusive taxon

family the category in the taxonomic classification system that falls within order and includes genera

genus the category in the taxonomic classification system that falls within family and includes species; the first part of the scientific name

kingdom the category in the taxonomic classification system that falls within domain and includes phyla maximum parsimony applying the simplest, most obvious way with the least number of steps molecular systematics the methods of using molecular evidence to identify phylogenetic relationships monophyletic group (also, clade) organisms that share a single ancestor

order the category in the taxonomic classification system that falls within class and includes families

phylogenetic tree diagram used to reflect the evolutionary relationships between organisms or groups of organisms

phylogeny evolutionary history and relationship of an organism or group of organisms

phylum the category in the taxonomic classification system that falls within kingdom and includes classes

rooted describing a phylogenetic tree with a single ancestral lineage to which all organisms represented in the diagram relate

shared ancestral character a character on a phylogenetic branch that is shared by a particular clade

shared derived character a character on a phylogenetic tree that is shared only by a certain clade of organisms

sister taxa two lineages that diverged from the same branch point

species the most specific category of classification

systematics the science of determining the evolutionary relationships of organisms

taxon a single level in the taxonomic classification system

taxonomy the science of classifying organisms

CHAPTER SUMMARY

Organizing Life on Earth

Scientists continually obtain new information that helps to understand the evolutionary history of life on Earth. Each group of organisms went through its own evolutionary journey, called its phylogeny. Each organism shares relatedness with

others, and based on morphologic and genetic evidence scientists attempt to map the evolutionary pathways of all life on Earth. Historically, organisms were organized into a taxonomic classification system. However, today many scientists build phylogenetic trees to illustrate evolutionary relationships and the taxonomic classification system is expected to reflect evolutionary relationships.

Determining Evolutionary Relationships

To build phylogenetic trees, scientists must collect character information that allows them to make evolutionary connections between organisms. Using morphologic and molecular data, scientists work to identify homologous characteristics and genes. Similarities between organisms can stem either from shared evolutionary history (homologies) or from separate evolutionary paths (analogies). After homologous information is identified, scientists use cladistics to organize these events as a means to determine an evolutionary timeline. Scientists apply the concept of maximum parsimony, which states that the likeliest order of events is probably the simplest shortest path. For evolutionary events, this would be the path with the least number of major divergences that correlate with the evidence.

ART CONNECTION QUESTIONS

• Figure 12.3 In what levels are cats and dogs considered to be part of the same group?

REVIEW QUESTIONS

• What is a phylogeny a description of?
• mutations
• DNA
• evolutionary history
• organisms on Earth
• What do scientists in the field of systematics accomplish?
• discover new fossil sites
• organize and classify organisms
• name new species
• communicate between field biologists
• Which statement about the taxonomic classification system is correct?
• There are more domains than kingdoms.
• Kingdoms are the top category of classification.
• A phylum may be represented in more than one kingdom.
• Species are the most specific category of classification.
• Which best describes the relationship between chimpanzees and humans?
• chimpanzees evolved from humans
• humans evolved from chimpanzees
• chimpanzees and humans evolved from a common ancestor
• chimpanzees and humans belong to the same species
• Which best describes a branch point in a phylogenetic tree?
• a hypothesis
• new lineage
• hybridization
• a mating
• 
  Figure 12.8 Which animals in this figure belong to a clade that includes animals with hair? Which evolved first: hair or the amniotic egg?

• Which statement about analogies is correct?
• They occur only as errors.
• They are synonymous with homologous traits.
• They are derived by response to similar environmental pressures.
• They are a form of mutation.
• What kind of trait is important to cladistics?
• shared derived traits
• shared ancestral traits
• analogous traits
• parsimonious traits
• What is true about organisms that are a part of the same clade?
• They all share the same basic characteristics.
• They evolved from a shared ancestor.
• They all are on the same tree.
• They have identical phylogenies.
• Which assumption of cladistics is stated incorrectly?

• Living things are related by descent from a common ancestor.
• Speciation can produce one, two, or three new species.
• Traits change from one state to another.
• The polarity of a character state change can be determined.
• A monophyletic group is a .
• phylogenetic tree
• shared derived trait
• character state
• clade

CRITICAL THINKING QUESTIONS

• How does a phylogenetic tree indicate major evolutionary events within a lineage?
• List the different levels of the taxonomic classification system.

• Dolphins and fish have similar body shapes. Is this feature more likely a homologous or analogous trait?
• Describe maximum parsimony.
• How does a biologist determine the polarity of a character change?