Biological Classification
time
Our
species
This chart shows one idea of how humans are related to
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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
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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 closer to fish (both swim)
or humans (both breathe air)?
Convergence is when two species evolve
similar traits independently due to
having similar lifestyles
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
“monophyletic”
•This is also called a
“clade”
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This sort of diagram is called a phylogenetic tree
Which of these groups is a
clade?
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“Ontogeny Recapitulates Phylogeny”
Human embryos have tails
and pharyngeal pouches
(structures similar to gills in
fish) shown here with red
arrows. This tells us that
human ancestors probably
had tails and gills
• 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
• Before they are born, developing
organisms may have traits which they
do not have when born, but which
the organisms that they evolved from
had when they were adults
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Similarities in Development
Egg
Adult
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Taxonomic Levels
Biggest group
• 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”
Smallest group
In this diagram, the length of the lines represent time/change
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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
asexually
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 parts of an
underwater volcano
A new group of
archaea was recently
discovered in
poisonous water
from mines
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?
Some eukaryotes
Domain Eukaryota’s 4 Kingdoms
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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
protist
Protists: Not a Clade
The groups in yellow are called protists.
However, they are not a clade because
they do not have an exclusive common
ancestor
• 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
phylogenetic group
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)
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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
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