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Biological Classification (1)

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Biological Classification
time
Our
species
This chart shows one idea of how
1
Biological Classification
Carl Linnaeus
• Organisms are classified into
groups called taxa (singular:
taxon) based on their shared
characteristics
• Carl Linnaeus (1707–1778), a
Swedish scientist, is
considered the father of
modern biological
classification (AKA taxonomy)
• His “Linnaean” system is still
used today
2
Characteristics/Traits
• A characteristic or trait is an observed
structure or behavior
• Example: Humans have large brains for their
size (structure) and adults walk on two legs
(behavior)
Problem: Which traits
are the most important
when assigning taxa?
For example, should
whales be grouped
Convergence is when two
species evolve similar traits
independently due to
Phylogenetics
• Phylogenetics is the evolutionary relationship
between organisms
• DNA analysis is
the most
important tool in
phylogenetics
• If all the
members of a
group share an
exclusive
common
ancestor, then
the group is
This sort of diagram is called a
4
Which of these
groups is a clade?
5
“Ontogeny Recapitulates Phylogeny”
• Before they are born, developing
organisms of different species look
similar
• This similarity lasts longer in species
which split from each other rather
recently in evolutionary history
Human embryos
• Before they are born, developing
have tails and
organisms may have traits which they
pharyngeal pouches
do not have when born, but which
(structures similar to
the organisms that they evolved from
gills in fish) shown
had when they were adults
here with red arrows.
This tells us that
6
Similarities in Development
Egg
Adult
7
Taxonomic Levels
• There are many different sizes/levels
of taxa
• These are often based on
phylogenetics, but not always
• The biggest taxon is “domain” and the
smallest is “species”
• Small groups are within larger groups
• For example, all members of the
family “mammalia” must be members
of the phylum “chordata”
Biggest
group
Smallest
In this diagram, the length of the lines repre
9
Taxonomy and Phylogeny
• Taxonomy is based on traits that someone thinks are
the most important traits to look at, so it’s more
subjective
• Phylogeny, however, is about evolutionary
relationships, so it’s more objective
• No organism or species currently living is “more
evolved” in general than any other. Why is this?
Bacteria
• Bacteria are single-celled (each organism is
only one cell)
• They don’t have organelles
• Some bacteria cause human diseases, but
others help us
• Bacteria can live in many places, including
inside animals, like you!
This animation
shows bacteria
reproducing
Archaea
• Archaea are like bacteria in that they are
single-celled and don’t have organelles
• They can live in extreme places where, until
recently, it was thought life cannot exist
• Archaea can live in hot springs, underwater
volcanoes, and sewage treatment plants
• A lot is still being learned about Archaea
Archaea can
live in
hydrothermal
vents, which are
A new group
of archaea was
recently
discovered in
Eukaryota
• Eukaryote cells have organelles
and are bigger and more
complex than bacteria or
archaea
• Eukaryota is the only domain
containing multicellular
organisms, however, not all
eukaryotes are multicellular
• Which domain are humans in?
Domain Eukaryota’s 4 Kingdoms
14
Fungi
• Single- or multicellular
• Fungi digest food
outside their body
and then absorb it
• They help break down
dead things and
recycle nutrients
• Mushrooms, molds,
and yeasts are fungi
This peach is being
broken down by
mold over 6 days
Protists
• Protists are small and can be single- or
multicellular
• Some protists are like plants and make food
from sunlight, while others are more like
animals and get their food from other living
things
• Live in liquid water
Here is a
multicellular
Protists: Not a Clade
• The group “Protist” is
really just a category for
eukaryotes that aren’t
plants, animals, or fungi
• Protists are an example
of how a taxonomic
group can be very
different than a
The groups in yellow are
phylogenetic
group
called protists. However, they
are not a clade because they
do not have an exclusive
Human Taxonomy
• Domain: Eukaryota (cells have organelles)
• Kingdom: Animalia (fixed body plan and eat other
organisms)
• Phylum: Chordata (have a spinal cord)
• Class: Mammalia (have hair, mammary glands)
• Order: Primates (forward-facing eyes and nails
instead of claws)
• Family: Hominidae (large, no tail)
• Genus: Homo (larger brain, walk on two legs)
• Species: sapiens (even larger brain, small teeth)
18
Human Evolution
• Humans share a common ancestor with our closest living
relatives, chimpanzees, from about 7 million years ago
• Modern humans originated in Africa about 200,000 years
ago
• Much is still being learned about human evolution from
fossils and DNA evidence
19
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