. " . . surely we should realize, like the amateur, that the organic world is also an inexhaustible source of spiritual and aesthetic delight. And especially in the college we are unfaithful to our trust if we allow biology to become a colorless, aridly scientific discipline, devoid of living contact with the humanities."
William Morton Wheeler Address as President of the American Society of Naturalists December 29, 1922
Chapter 26
The Tree of Life
Overview
Life is a continuum extending from the earliest organisms to the great variety that exist today
Geological events that alter environments change the course of biological evolution Conversely, living things change the planet they inhabit
Figure 26.1
Geologic history and biological history have been episodic and marked by what were in essence revolutions that opened many new ways of life
Concept 26.2
The fossil record chronicles life on Earth The study of fossils opens a window into the lives of organisms that existed long ago and provides information about the evolution of life over billions of years
Stratigraphy
Trapping dead organisms in sediment freezes fossils in time Fossils in each stratum of sediment are a local sample of the organisms that existed when the sediment was deposited Reveal the relative ages of fossils
The strata of one location can be correlated with strata at another location by the presence of similar fossils, known as index fossils
Figure 26.6
The absolute ages of fossils can be determined by radiometric dating
Figure 26.7
Concept 26.3
The oldest known fossils are stromatolites
Rocklike structures composed of many layers of bacteria and sediment Existed 3.5 billion years ago
Prokaryotes were Earth's sole inhabitants from at least 2 3.5 billion years ago When oxygen began to accumulate in the atmosphere about 2.7 billion years ago it posed a challenge for life and provided organisms opportunity an to exploit new ecosystems
Concept 26.6
Early classification systems had only two Kingdoms
Plants Animals
In recent years, molecular data have provided new insights into the tree of life
Robert Whittaker proposed a system with five Kingdoms
Figure 26.21
More recently, a three Domain system has replaced the five Kingdom system
Domain Bacteria Domain Archaea Domain Eukarya
Figure 26.22a
Figure 26.22b
Chapter 25
Phylogeny and Systematics
Overview
Biologists use phylogeny to trace the evolutionary history of a species or group of species Biologists also use systematics, which is an analytical approach to understanding the diversity and relationships of organisms
Recently, systematists have been using molecular systematics
Figure 25.2
Concept 25.2
Taxonomy is an ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences Carolus Linnaeus developed a taxonomic system based on binomial nomenclature
Binomial nomenclature is the two-part format of the scientific name of an organism
First part: Genus Second part: specific epithet (species) First letter of the genus is capitalized and the entire binomial is italicized
Scientific names
Humans: Homo sapiens Corn: Zea mays House fly: Musca domestica Lone star tick: Amblyomma americanum
Common names
Can be handy, but can also be confusing "Maples"; "mosquitoes", "gnats" Some organisms have numerous common names while others have no common name
Name This Insect
Linnaeus also introduced a system for grouping species in increasingly broad categories
Figure 25.8
Systematists use phylogenetic trees to depict evolutionary relationships
Figure 25.9
In a phylogenetic tree each branch represents a divergence of two species
Deeper branch points represent progressively greater amounts of divergence