How to Understand Evolutionary Trees
Summary
TLDRThis tutorial elucidates the concept of evolutionary trees, or phylogenies, which illustrate the paths of evolution and relatedness among species. It explains the tree's anatomy, including roots, nodes, and branches, and clarifies misconceptions about relatedness and evolutionary advancement. The video also distinguishes between different types of groups within trees, such as monophyletic, paraphyletic, and polyphyletic, and highlights the importance of cladistics in classifying organisms based on shared characteristics and evolutionary relationships.
Takeaways
- π³ An evolutionary tree, or phylogeny, shows the paths of evolution and relatedness of species, helping us understand evolution on a larger scale.
- π The root of the tree represents the common ancestor of all organisms in the tree, and internal nodes indicate further diversification points.
- π Terminal nodes or tips represent current organisms, illustrating relationships that might not be immediately apparent.
- π Branches on the tree represent sister taxa, groups that share a direct common ancestor.
- π The ingroup in a phylogeny shows species with common characteristics relevant to the specific tree, while the outgroup is less closely related but included for broader context.
- π Trees can be represented in various ways, but the key is the topology, or the order of branching, rather than the direction of branches.
- π In cladistics, branch lengths are not significant, only the order of branching matters, whereas in a phylogram, branch lengths indicate time or divergence.
- π¨βπ©βπ§βπ¦ Monophyletic groups show a common ancestor in all descendants, and the number of clades can be found by counting nodes.
- π« Paraphyletic groups include a recent common ancestor but not all descendants, while polyphyletic groups include distant relatives but no common ancestor.
- β Soft polytomies in a tree indicate unknown patterns of branching, representing relationships that are not fully understood.
- π ββοΈ Common misconceptions include misunderstanding the relatedness indicated by the order of tips, the role of the root and tips in time of divergence, and the evolutionary status of nodes.
- π« It's important to note that species do not evolve based on being hybrids of their ancestors but through natural selection based on heritable traits.
Q & A
What is an evolutionary tree also known as?
-An evolutionary tree is also known as a phylogeny, which shows the paths of evolution and relatedness of species.
What does the root of a phylogenetic tree represent?
-The root of a phylogenetic tree represents the common ancestor of all organisms present in the tree.
What do the internal nodes in a phylogenetic tree indicate?
-The internal nodes in a phylogenetic tree indicate other common ancestors and represent diversification of species.
What are terminal nodes or tips in a phylogenetic tree?
-Terminal nodes or tips in a phylogenetic tree represent current organisms.
What is the significance of sister taxa in an evolutionary tree?
-Sister taxa are groups that come from the same direct common ancestor, indicating a close evolutionary relationship.
What is the role of the ingroup in a phylogenetic tree?
-The ingroup shows the species with common characteristics relevant to the specific tree, highlighting their shared traits.
Why is an outgroup included in a phylogenetic tree?
-An outgroup is included to provide a broader context of evolution, showing that species that may not look similar can still be related.
What is the difference between a cladogram and a phylogenetic tree in terms of branch lengths?
-In a cladogram, branch lengths are not significant and only the topology matters, whereas in a phylogram, branch lengths represent the time or quantity of divergence.
What is a monotypic group in the context of phylogenetic trees?
-A monotypic group, also known as a holonome, shows the common ancestor in all of its descendants within a phylogenetic tree.
What is a paraphyletic group and how is it represented in a phylogenetic tree?
-A paraphyletic group includes a recent common ancestor but not all descendants, showing an incomplete evolutionary lineage.
What does a soft polytomy in a phylogenetic tree indicate?
-A soft polytomy indicates that the pattern of branching is unknown, representing an evolutionary relationship that is not fully understood.
Why is it incorrect to assume that tips beside each other are more related than tips further apart in a phylogenetic tree?
-The order of the tips does not show relatedness; it is the topology that matters. Closeness of tips does not necessarily indicate closer evolutionary relationships.
What misconception about phylogenetic trees is corrected by emphasizing that the root is the ancestor and the tips are the evolved species?
-The misconception that the most recently evolved species are at the tips and the oldest ancestor is at the root is corrected by understanding that the root represents the common ancestor and the tips represent current, evolved species.
Why is it incorrect to view nodes in a phylogenetic tree as indicators of levels of advancement or primitiveness?
-Nodes simply indicate the number of common ancestors and do not represent levels of advancement or primitiveness, as evolution is driven by natural selection, not a linear progression of advancement.
What is the misconception about outgroups undergoing no evolutionary change in a phylogenetic tree?
-The misconception is that outgroups, being less closely related to other taxa, do not undergo evolutionary change. In reality, their changes are not shown in the specific tree because they do not fit the characteristics of that tree.
Why is it incorrect to assume that species arising from nodes are hybrids of their ancestors?
-Species evolve based on natural selection, which is non-random and based on heritable traits that confer survival advantages. New species are not simply combinations of their ancestors but evolve independently.
Outlines
π³ Understanding Evolutionary Trees
This paragraph introduces the concept of evolutionary trees, also known as phylogenies, which illustrate the evolutionary relationships and paths among species. It explains the structure of a phylogenetic tree, including the root as the common ancestor, internal nodes representing other common ancestors, and terminal nodes representing current species. The paragraph also discusses the significance of branches, sister taxa, ingroup and outgroup, and clarifies that the direction of branches is irrelevant, but the topology is crucial. It introduces the concept of cladistics, distinguishing between different types of groups like monophyletic, paraphyletic, and polyphyletic, and explains the concept of soft polytomy. The paragraph concludes by addressing misconceptions about the interpretation of phylogenetic trees.
π Common Misconceptions About Evolutionary Trees
The second paragraph focuses on debunking common misconceptions related to evolutionary trees. It clarifies that the proximity of tips does not indicate relatedness, and that the order of branching (topology) is what matters, not the physical distance on the tree. It also corrects the misunderstanding that the root represents the most primitive species and the tips the most advanced, emphasizing that evolution is not a ladder of progress but a process of natural selection. The paragraph further explains that outgroups are not static but part of the broader evolutionary picture, and refutes the idea that new species are hybrids of their ancestors, instead highlighting the role of natural selection in species formation. The paragraph ends by encouraging viewers to explore more resources for a deeper understanding of evolutionary trees.
Mindmap
Keywords
π‘Phylogeny
π‘Common Ancestor
π‘Diversification
π‘Terminal Nodes
π‘Branch
π‘Sister Taxa
π‘Ingroup
π‘Outgroup
π‘Cladistics
π‘Monophyletic Group
π‘Paraphyletic Group
π‘Polyphyletic Group
π‘Soft Polytomy
π‘Misconceptions
Highlights
Understanding evolutionary trees, also known as phylogenies, helps to comprehend the paths of evolution and relatedness of species.
The root of a phylogeny represents the common ancestor of all organisms in the tree.
Internal nodes in a phylogeny signify common ancestors and diversification of species.
Terminal nodes or tips represent current organisms and their relationships.
Branches in a phylogenetic tree are part of sister taxa, sharing a direct common ancestor.
The ingroup in a phylogeny shows species with common characteristics relevant to the tree.
The outgroup in a phylogeny is a species included for broader evolutionary context but not fitting the specific classification.
Cladistics is a method of classifying organisms based on shared characteristics and evolutionary relatedness.
In a cladogram, branch lengths are not significant; only the order of branching matters.
A phylogram shows branch lengths that are significant, indicating time or quantity of divergence.
Monotypic groups in phylogenies show a common ancestor in all of their descendants.
Paraphyletic groups include a recent common ancestor but not all descendants.
Polyphyletic groups include distant relatives but do not include a common ancestor.
Soft polytomies in phylogenies indicate unknown patterns of branching and relationships.
Common misconceptions about phylogenies include misunderstanding the relatedness indicated by the order of tips.
In phylogenetic trees, the root represents the common ancestor, and the tips represent evolved species.
Evolutionary trees do not indicate levels of advancement or primitiveness; they show common ancestry and divergence.
Outgroups in phylogenies undergo evolutionary changes, though they may not be depicted in the specific tree.
New species evolve through natural selection, not as hybrids of their ancestors.
Transcripts
welcome to a video tutorial on how to
understand evolutionary
trees an evolutionary tree is called a
philogyny phogy show Paths of evolution
and relatedness of species which makes
them helpful because they allow us to
understand Evolution on a larger
scale this is the anatomy of a
philogyny the root is at the very bottom
and this is where the rest of the trees
stems from the root is the common
ancestor of all organisms present in the
tree the internal nodes represent other
common ancestors present in the tree
nodes also indicate diversification of
species in this tree the heart and the
circle both share two common ancestors
in addition to the
root the terminal nodes or the tips
represent current organisms all although
they may not seem related they show
relationships between species that you
may not have even thought
of a branch is also part of an
evolutionary
tree these groups are sister taxa they
come from the same direct common
ancestor the ingroup shows the species
with common characteristics relevant to
this specific
tree the outgroup is a species that is
included in the philogyny but does not
fit in well with the tree specific
classification however they are all
related note that the outgroup does not
have any branching occurring this does
not mean that the outgroup doesn't
undergo any evolutionary change
branching is just not shown in the
outgroup because the out group itself
does not fit in with the common
characteristics of the tree as a whole
in this way the out group acts as a
reminder to biologists of the grand
scheme of evolution and that species
that may not look similar can still be
related
it's important to note that trees can be
represented in many ways however they
still tell us the same information
remember the direction of the branch is
irrelevant but rather the topology or
the order of the branches urrent is what
matters nodes can be rotated so the
order of the tips can be changed do not
read across the tips
moving on to cladistics cladistics is a
term used for classifying organisms
based on evolutionary relatedness or
shared characteristics in a cladogram
the branch lengths are not significant
only the topology the order of branching
matters in a phram the branch lengths
are significant they show the time or
quantity of
Divergence within an evolutionary tree
there are different groups this is a
monoptic group it can also be called a
CLA monoptic groups and clayes show the
common ancestor in all of their
descendants as a helpful tip to find the
number of clayes count the number of
nodes remember each node and the root
are common ancestor so the number of
nodes is equal to the number of clayes
this is a paraphyletic
group the recent common ancestor is
shown but not all descendants are
included this is a polyphilic
group The Reason common ancestor is not
included but distant relatives are
included a tree that looks like this is
called a soft polytomy soft polytomy
indicates that the pattern of branching
is unknown so this is an evolutionary
relationship that is not fully
understood congratulations you just got
through tree thinking 101 we're going to
end things off by addressing some common
misconceptions misconception number one
tips beside each other are more related
than tips further
apart
wrong the order of the tips do not show
relatedness topology does it is
important to remember to not read across
the tips
as an example let's look at this tree
the blue circle is more closely related
to the red heart than it is to the green
triangle even though the circle and the
triangle are right next to each other
this is because the circle and the Heart
share a more recent common
ancestor again do not read across the
tips misconception number two looking at
this
phram the yellow star is the ancestor
and the green triangle is the most
recently evolved
species wrong
in the PHR tree the root is the ancestor
and the tips are the evolved species
read from root to tip to determine the
time of Divergence in a
phog let's try another example looking
at this tree the swirl is more evolved
and advance than the smiley
face
wrong nodes simply indicate the number
of common ancestor they do not indicate
levels of advancement or show
primitiveness remember Evolution occurs
by means of natural selection so the
odds of survival are higher for
organisms that have traits that work for
them in that specific environment at
that specific time a trait that led to
survival previously may not do so now
and a trait that leads to survival now
may not later advancement and
primitiveness are Concepts that are
irrelevant to tree thinking
misconception number three looking at
this tree the outgroup in this case s
under goes no evolutionary change
wrong Oak groups are less closely
related to other taxa in the tree out
groups are meant to show the bigger
picture of evolution their evolutionary
changes exist but aren't shown in the
specific tree because they do not fit in
with the characteristics of that tree
one more to go misconception number four
species that arise from no are hybrids
of their ancestors so for example in
this tree the circle is a hybrid of the
flower the X and the
diamond
wrong again species evolve based on
natural selection which is non-random
differences in survival and or
reproduction among individuals on the
basis of hereditable traits new species
are not accommodation of
ancestors congratulations you now know
the basics of evolutionary trees and the
common misconceptions associated with
them good job looking for more check out
some of our resources used for this
video for more in-depth material
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