Transcript File - Down the Rabbit Hole

Why Classify?
Why Classify?

Organization is necessary when
dealing with large numbers of
something

It’s easier to work if there is a system of
how to keep track of things

If you have a specific place for
something, then you don’t spend time
hunting around trying to find it

There are some 10-30 million organisms
on Earth!

Biologists organize according to
similarities and proposed relationships
Tacitus bellus
Erithacus rubicula
Robin
Turdus migratorius
Robin
A common name can be used by
more than one species
A scientific name must be unique
A group of organisms that
can reproduce only
among themselves and
that are usually contained
in a geographic region
African Elephant
Loxodonta africana
Asian Elephant
Elephas maximus
Taxonomy, the ordered
division of organisms into
categories based on
similarities and differences
Systematic Taxonomy,
commonly called
systematics, is the study of
the evolution of biological
diversity.
Populus tremuloides
Quaking Aspen

Phylogeny is the evolutionary
history of a species or group of
related species
› classifies organisms and their
evolutionary relationships using
 fossils
 morphology
 embryology
 molecular evidence
Black Swan nesting
Cygnus atratus
Planet Earth is
about 4.6 billion
years old.
 Oldest known
rocks are about
3.8 billion years
old.
 Oldest fossils
(prokaryotes) are
about 3.5 billion
years old.

All living organisms on
this planet share a
common ancestor.
 What is the
evidence?
 The tree of life reflects
the branching pattern
of speciation
 A phylogenetic history
of life that has
occurred since the
origin of life.

• Swedish biologist
considered the father of
modern taxonomy.
• Science of Systematics
dates to Linnaeus in the
18th century who devised
the basic systems of
binomial nomenclature and
hierarchical classification
• All organisms have a
unique binomial name
• Humans are Homo sapiens


The arrangement of
organisms in a series of
nested groups, in which
similar or related groups
at one level are
combined into larger
and more general
groups at the next higher
level.
Biological classification is
based on shared
descent from the nearest
common ancestor
Each categorization at any level is called a taxon.

Phylogenetic trees are
constructed by studying
features of organisms
formally called
characters.

Characters may be
morphological or
molecular.

Character similarity
resulting from shared
ancestry is called
homology.

In a phylogenetic
tree the tips of the
branches specify
particular species
and the branching
points represent
common
ancestors.
The aim is to figure out
the evolutionary
relationships among
species.
 Branching diagrams
called phylogenetic
trees hypothesize
evolutionary
relationships thought
to exist among groups
of organisms.
 Why a hypothesis?

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Cladograms are also
diagrams that display
patterns of shared
characteristics.
Within a tree a clade is
defined as a group that
includes an ancestral
species and all of its
descendants.
Cladistics is the science of
how species may be
grouped into clades.

A cladogram and a phylogenetic tree are similar,
but not identical.

Traditional evolutionary taxonomy is subjective and
therefore more prone to bias. A phylogenetic
tree’s branches put more emphasis on certain
characters rather than others. . It is thought that
evolutionary success is dependent on high-impact
events.

Cladistics treats each character equally. It is more
objective by ignoring how some characters have a
higher impact on evolution
Mammals
Turtles
Phylogenetic
Tree


Lizards and
Snakes
Crocodiles
Birds
Mammals
Turtles
Lizards and
Snakes
Crocodiles
Birds
Cladogram
What’s the difference?
Essentially CLADISTICS and PHYLOGENY are the same
Phylogenetic trees and Cladograms are
usually based on a combination of these
lines of evidence:
Fossil record
Morphology
Embryological patterns of
development
Chromosomes and DNA

The fossil record refers to the order in which fossils
appear within layers of rock that mark the passing
of geologic time.

Comparing physical structural
characteristics
Similarities due to shared ancestry
Convergent Evolution and
Analogous Structures
These animals have evolved
similar adaptations because they
occupy similar environments.
Analogous Structures
Analogous Structures
Traits that are
morphologically and
functionally similar even
though there is no
common ancestor.
Convergent Evolution
Similar solutions to similar problems
Chromosomes and DNA

An organism’s evolutionary history is documented
in its genome

The rate of evolution of DNA sequences varies from
one part of the genome to another

Comparing the different sequences helps us to
investigate relationships between groups of
organisms that diverged long ago

DNA that codes for ribosomal RNA and
mitochondrial DNA are both used
Amount of genetic difference between
sequences is a function of time since
separation.
 Rate of molecular change is constant
(enough) to predict times of divergence

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
The more alike the DNA
sequences of two organisms,
the more closely related
they are evolutionarily.
Early phylogenetic tree of
amniotes based on
cytochrome c gene by Fitch
and Margoliash (1967).
Note numbers on branches.
These represent estimated
numbers of mutational
changes in gene.

Ancestral:
 Trait of the
ancestor

Derived:
 Trait that is present in
the organism, but not
in the common
ancestor of the group
A dichotomous key is a written set
of choices that leads to the name
of an organism.
 "Dichotomous" means "divided into
two parts". Therefore, dichotomous
keys always give two choices in
each step.
 After each description, the key
directs the user to another pair of
descriptions or identifies the
organism.

Example:
1 a) Is the leaf simple? Go to 2
b) Is the leaf compound? Go to 3
2.a) Are margins of the leaf jagged? Go to 4
b) Are margins of the leaf smooth? Go to 5
A bee
Osmia ribifloris
on a barberry flower


When the authors of
your text book were in
high school they were
taught two kingdoms:
plants and animals.
When your teacher was
in high school she was
taught five kingdoms:
Monera, Protista,
Plantae, Fungi and
Animalia

Now biologists have
adopted a threedomain system
› Discovery that there
are two distinct
lineages of prokaryotes
Characteristic
Bacteria Archaea
Eukarya
Nuclear envelope
No
No
Yes
Membrane-enclosed
organelles
No
No
Yes
Introns
No
Yes
Yes
Histone proteins
associated with DNA
No
Yes
Yes
Circular chromosome Yes
Yes
No