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