The Human Place in the Organic World
Chapter 5 PROCESSES OF MACROEVOLUTION
The Human Place in the Organic World
Humans have a great need to answer questions about who we are and where we belong in the greater story
Classification is sciences way of handling the diversity of life on the planet in an organized way
Classification
•Organizes diversity into categories
•Indicates evolutionary and genetic relationships
•The kingdom Animalia includes 20 major phyla
• Chordata are all animals with a nerve cord, gill slits (at some point) and supporting cord along the back. (This is us)
Human Classification
• Kingdom: Animalia
• Phylum: Chordata
• Subphylum: Vertebrata
• Class: Mammalia
• Subclass: Eutheria
• Order: Primates
• Family: Hominidae
• Genus: Homo
• Species: sapiens
Principles of Classification
The field that establishes the rules of classification is taxonomy.
Organisms are classified first on the basis of physical similarities.
• Basic physical similarities must reflect evolutionary descent in order for them to be useful.
Principles of Classification
Homologies ◦ Similarities based on a common ancestor.
Analogies ◦ Similarities based on common function, with no assumed
common evolutionary descent.
Homologies
• The foot bones of these animals can be most easily explained by descent from a common ancestor.
• Small mutations in Hox genes can lead to huge differentiation over time
Analogies
•Wings have evolved for flight, but birds bats and butterflies do not share common ancestry
•Homoplasy is the process of evolutionary development of similar characteristics in different groups of organisms that leads to analogies.
Classification and Evolutionary Relationships
Evolutionary systematics ◦ Traditional approach in which presumed ancestors and descendants
are traced in time by analysis of homologous characters (ancestral).
Cladistics ◦ Newer approach uses only certain traits (derived) to try to make more
relevant evolutionary connections
◦ Predominant method used by anthropologists
Ancestral and Derived (Modified) Characters
Ancestral Characters inherited by a group of organisms from a remote ancestor and not diagnostic of groups that diverged after the character appeared; also called primitive.
Derived (Modified) Characteristics are modified from the ancestral condition and thus are diagnostic of particular evolutionary lineages.
Clade
A distinct evolutionary lineage that shares a “recent” common ancestor
• Shares derived traits that allow for the distinction of groups
• This group distinction allows for more relevant and informative evolutionary analysis
• i.e. forelimb bones in land vertebrates vs. hooves, flippers and wings
Traditional Interpretation of Birds and Dinosaurs
Traditional view, no close relationship.
Cladistic Interpretation of Birds and Dinosaurs
Revised view, common ancestry of birds and dinosaurs.
Phylogenetic Tree
• A chart showing evolutionary
relationships as determined by
evolutionary systematics.
• It contains a time component and
implies ancestor descendant
relationships.
Cladogram
•A chart showing evolutionary
relationships as determined by
cladistic analysis.
•It’s based solely on interpretation
of shared derived characters.
•It contains no time component
and does not imply ancestor-
descendant relationships.
Types of variation
Intraspecific: Variation accounted for by individual, age, and sex differences seen within every biological species • Sexual Dimorphism
Interspecific: Variation representing differences between reproductively isolated groups
Understanding “Genus” •A genus is a group of species composed of members more
closely related to each other than to species from any other genus. • Genus Equus
•Species that are members of the same genus share the same broad adaptive zone. • Horses, donkeys, zebras are grazing herbivores that live on open
plains
•Members of the same genus should all share derived characters not seen in members of other genera. • Single toe (hoof)
Interpreting the Fossil Record
The goal is to make meaningful biological statements about the variation represented in groups of organisms.
Identifying individual variation, age changes, variation due to sex (sexual dimorphism)
Fossil species are understood based on observations of living animals
Fossils
Traces of ancient organisms and formed in several ways
•Mineralization occurs very slowly as water carrying minerals, such as silica or iron, seeps into the tiny spaces within a bone. In some cases, the original minerals within the bone or tooth can be completely replaced.
•Traces of life forms that include insects trapped in tree sap, leaf imprints, footprints, skeletal remains and remains of digestive tracts
•Taphonomy is the study of how bones and other materials come to be buried in the earth and preserved as fossils
Archaeopteryx
150 million
years ago
Homo heidelbergensis 700 to 200,000 years ago
Laetoli
Footprints
3.5 million
years ago
99 million year old lizard in amber
Geological Time Scale
The organization of earth history into eras, periods, and epochs;
commonly used by geologists and paleoanthropologists.
Geological Eras Paleozoic ◦ Vertebrates appeared 500 mya.
Mesozoic ◦ Reptiles were dominant land vertebrate, placental
mammals appeared 70 mya.
Cenozoic ◦ Divided into Tertiary and Quaternary periods and 7
epochs.
◦ The Age of Mammals
Epochs
Smaller more defined categories of the geological time scale.
In the Cenozoic, epochs include ◦ Paleocene ◦ Eocene ◦ Oligocene ◦ Miocene ◦ Pliocene ◦ Pleistocene ◦ Holocene
Where we are today We are currently living in the Holocene Epoch (The Age of Civilization), which is part of the Quaternary Period (The Age of Man), within the Cenozoic Era (The Age of Mammals) ◦ * It was recently decided that we have entered a new
epoch. The name Anthropocene, or “New Man” has been proposed for it, as well as a start date at the beginning of the atomic era
Continental Drift The movement of continents on sliding plates of the earth’s surface.
As a result, the positions of large landmasses have shifted drastically during the earth’s history.
Why does this matter?
Continental Drift
The positions of the continents during the Mesozoic (c. 125 mya.).
Pangea is breaking up into a northern landmass (Laurasia) and a southern landmass (Gondwanaland).
Continental Drift
The positions of the continents at the beginning of the Cenozoic (c. 65 mya).
Mammalian Evolution
The Cenozoic era, the Age of Mammals.
The enlargement of the cerebrum, especially the neocortex, which controls higher brain functions, resulting in more nerve cells
A longer, more intense period of growth in utero
Distinctive dentition, termed a heterodont dentition, with 3 incisors, 1 canine, 4 premolars, and 3 molars in each quarter of mouth
Maintenance of constant internal body temperature, warm- bloodedness, and endothermic
Lateral View of the Brain
Lateral view of the brain in fishes, reptiles, dogs, and primates.
Note the increased size of the cerebral cortex of the primate brain.
Reptilian and Mammalian Teeth
Reptilian teeth (top) are homodont.
Mammals are heterodont, they have different kinds of teeth; incisors, canines, premolars, and molars.
Body temperature regulation Endothermic: Able to maintain internal body temperature by producing energy through metabolic processes within cells; mammals, birds, and perhaps some dinosaurs.
Ectothermic: Internal body temperature is
controlled through exposure to the sun;
reptiles
Major Mammalian Groups
Monotremes: Egg laying mammals
Marsupials: Pouched mammals
Placental: Longer in utero time
Adaptive Radiation A process that takes place when a life form rapidly takes advantage of the many newly available ecological niches.
A species, or group of species, will diverge into as many variations as two factors allow: 1. Its adaptive potential. 2. The adaptive opportunities of the available niches.
Generalized and Specialized Characteristics
Refer to the adaptive potential of a particular trait
Generalized if a trait is adapted for many functions: a mammalian limb with five fairly flexible digits, adapted for many possible functions
Specialized if a trait is limited to a narrow set of functions: hand or foot suited for specialized function of stable weight support in an upright posture
