ANT101H5 Chapter Notes - Chapter 5: Evolutionary Taxonomy, Species Problem, Cladistics

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6 Feb 2013
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CHAPTER 5: MACROEVOLUTION: PROCESSES OF VERTEBRATE AND MAMMALIAN EVOLUTION (PGS. 95-114)
Learning Objectives
Compare microevolution and macroevolution and explain how they are similar and how
they differ
Describe how animals are classified and explain how humans fit into such classification as
vertebrates and as mammals
Explain why evolutionary relationships are the basis for all scientific biological
classifications
Explain what a fossil is and describe how different kinds of fossils are formed
Define the major characteristics of mammals, especially placental mammals
Explain how species are defined by biologists and how they originate from prior species
Introduction
The bits and pieces of fossils are the remains of once living, breathing animals
We are primates, which in turn is one type of mammal and mammals are one of the major
groups of vertebrates
How We Connect: Discovering the Human Place in the Organic World
Classification in biology, the ordering of organisms into categories, such as orders,
families, and genera, to show evolutionary relationships
Multicellular organisms that move about and ingest food are called animals
Chordata the phylum of the animal kingdom that includes vertebrates
o Animals with nerve cord, fill slits and a supporting cord along the back
Vertebrates animals with segmented, bony spinal columns; includes fishes, amphibians,
reptiles (including birds) and mammals
Vertebrates are divided into five classes: cartilaginous fishes, bony fishes, amphibians,
reptiles/birds, and mammals
Principles of Classification
Taxonomy is the field that specialized in establishing the rules of classification
For physical similarities to be useful, they must reflect evolutionary descendants
Evolutionary modification in structure occur with only relatively minor genetic changes
o A few mutations in certain Hox genes in early vertebrates led to the basic limb plan
seen in all subsequent vertebrates, including humans
Large anatomical modifications don’t always require major genetic rearrangements
o Shows how we connect biologically with other life-forms, how our evolutionary
history and thesis are part of the same grand story of life on earth
Homologies similarities between organisms based on descent from a common ancestor
Both birds and butterflies have wings, but they shouldn’t be grouped together on the basis of
this single characteristics
From quite distance ancestors, both butterflies and birds have developed wings
independently
Analogies similarities between organisms based strictly on common function, with no
assumed common evolutionary descent
Homoplasy the separate evolutionary development of similar characteristics in different
groups of organisms
o “Homo” = same and “plasy” = growth
Constructing Classifications and Interpreting Evolutionary Relationships
Two major approaches when interpreting evolutionary relationships with the goal of
producing classifications
(1) Evolutionary systematics is the more traditional
o A traditional approach to classification (and evolutionary interpretation) in which
presumed ancestors and descendants are traced in time by analysis of homologous
characters
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Notes From Reading
CHAPTER 5: MACROEVOLUTION: PROCESSES OF VERTEBRATE AND MAMMALIAN EVOLUTION (PGS. 95-114)
(2) Cladistics emerged primarily in the last three decades
o An approach to classification that attempts to make rigorous evolutionary
interpretations based solely on analysis of certain types of homologous characters
(those considered to be derive characters)
In recent years cladistics methodologies have predominated among anthropologists
Comparing Evolutionary Systematics with Cladistics
Similarities between cladistics and evolutionary systematics
o Both approaches are interested in tracing evolutionary relationships and
constructing classifications that reflect these relationships
o Both approaches recognize that organisms must be compared using specific
features and that some of these characters are more informative than others
o Both approaches focus exclusively on homologies
Differences between cladistics and evolutionary systematics
o How characters are chosen
o Which groups are compared
o How the results are interpreted and incorporated into evolutionary schemas and
classifications
o Cladistics more explicitly and more rigorously defines the kinds of homologies that
yield the most useful information
Some homologous characters are much more informative than other
Ancestral referring to characters inherited by a group of organisms from a remote
ancestor and thus not diagnostic of groups (lineages) that diverged after the character first
appeared; also call primitive
In biological anthropology, the term primitive or ancestral simply means that a character
seen in two organisms is inherited in both of them from a distant ancestor
Misinterpretation of ancestral characters can easily lead to inaccurate evolutionary
conclusions
Cladistics focuses on traits that distinguish particular evolutionary lineages; such traits are
far more informative than ancestral traits
Clade a group of organisms sharing a common ancestor. The group includes the common
ancestor and all descendants
Derived (Modified) referring to characters that are modified from the ancestral condition
and thus diagnostic of particular evolutionary lineages
An Example of Cladistic Analysis: The Evolutionary History of Cars and Trucks
All “descendant” vehicles share a common ancestor prototype passenger vehicle
The first major division differentiates passenger cars from trucks
Second split is between luxury cars and sports cars
Modified (derived) traits that distinguish trucks from cars might include type of frame,
suspension, wheel size and in some forms, an open cargo bed
Derived characters that might distinguish sports cars from luxury cars could include engine
size and type, wheel base size and a decorative racing stripe SUVs are basically trucks; the
presence of a racing stripe could be seen as a homoplasy with sports cars
We need to be careful, looking at several traits, later deciding which are ancestral and which
are derived and finally try to recognize the complexity introduced by homoplasy
Any modification in any species is constrained by that species’ evolutionary legacy what
species starts out with
Using Cladistics to Interpret Real Organisms
Looking at the relationship of dinosaurs to birds
Traditionally it was thought that birds were a distinct group from reptiles and not especially
closely related to any of them (including extinct forms)
The first fossil evidence of a very primitive bird was discovered in 1861 (two years after
Darwin’s publication of Origin of Species)
The last two decades have supported the hypothesis that birds are closely related to some
dinosaurs
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