Chapter 16
Ancestral trait: traits that two species share because of common ancestry
Binomial nomenclature: A taxonomic naming system in which each species is given
two names (a genus name followed by a species name).
Clade: A monophyletic group made up of an ancestor and all of its descendants.
Class: A taxonomic rank.
Convergent evolution: Independent evolution of similar features from different
ancestral traits.
Derived trait: A trait that differs from the ancestral trait.
Evolutionary Reversal: The reappearance of an ancestral trait in a group that had
previously acquired a derived trait.
Family: A taxonomic rank.
Genus: A group of related, similar species recognized by taxonomists with a distinct
name used in binomial nomenclature.
Homologous: A similarity between two or more features that is due to inheritance from a
common ancestor. The structures are said to be homologous, and each is a homolog of the
others.
Homoplasies: The presence in multiple groups of a trait that is not inherited from the
common ancestor of those groups. Can result from convergent evolution, evolutionary
reversal, or parallel evolution.
Ingroup: In a phylogenetic study, the group of organisms of primary interest.
Kingdom: A taxonomic rank.
Lineage: A series of populations, species, or genes descended from a single ancestor
over evolutionary time.
Maximum Likelihood: A statistical method of determining which of two or more
hypotheses (such as phylogenetic trees) best fit the observed data, given an explicit model
of how the data were generated.
Molecular clock: The approximately constant rate of divergence of macromolecules
from one another over evolutionary time; used to date past events in evolutionary history.
Monophyletic: Pertaining to a group that consists of an ancestor and all of its
descendants
Orders: A taxonomic rank.
Outgroup: In phylogenetics, a group of organisms used as a point of reference for
comparison with the groups of primary interest (the ingroup).
Paraphyletic: Pertaining to a group that consists of an ancestor and some, but not all, of
its descendants.
Parsimony Principle: Preferring the simplest among a set of plausible explanations of
any phenomenon
Phyla: A taxonomic rank.
Phylogenetic tree: A graphic representation of lines of descent among organisms or their
genes.
Phylogeny: The evolutionary history of a particular group of organisms or their genes.
Polyphyletic: Pertaining to a group that consists of multiple distantly related organisms,
and does not include the common ancestor of the group.
Sister Clade: Two phylogenetic groups that are each other's closest relatives.
Sister species: Two species that are each other's closest relatives.
Synapomorphies: A trait that arose in the ancestor of a phylogenetic group and is
present (sometimes in modified form) in all of its members, thus helping to limit and
identify that group. Also called a shared derived trait.
Systematics: The scientific study of the diversity and relationships among organisms.
Taxon: A biological group (typically a species or a clade) that is given a name.
Questions
1. Shared derived traits or synapomorphies are trait that appeared in ancestor of a
phylogenetic group and is present in all of its members. They come about through a
mutation in the genome, and are passed on to all descendants.
2. A phylogenetic tree shows a timeline of descendants of organisms or their genes,
created by comparing and grouping living things based on adaptations and evolutionary
history.
3. A clade is a taxa that share the same common ancestor and sister clades are those that
are close to each other on the evolutionary tree.
4. Both the new and old methods of classification classify by behavior, morphology, and
genes, but the clades also focus on time and from which species each one came from.
5. The Linnaean system simply splits species into groups based on behavior, morphology,
and genes, while a phylogenic tree also records how species are related.
6. Convergent evolution is independent evolution of similar features in unrelated animals,
not from one ancestor.
7. Evolutionary reversal occurs when the environment puts certain pressures on animals,
usually similar to pressures from past environments.
8. Homoplasy is presence in multiple groups of a trait that is not inherited from the
common ancestor of those groups, so it simply developed due to environmental pressure.
Homology, however, is a similarity between two or more features due to inheritance from
a common ancestor.
9. Bat and birds are unrelated, yet they have a similar feature: wings. Because this trait is
not inherited from a common ancestor, it is an example of homoplasy. However, the
bones of the wings are similar, and have come from a common ancestor, so it is an
example of homology as well.
10. In a phylogenetic tree, the outgroup contains the differing trait compared to the other
species, and therefore splits off from the tree. The ingroup contains the common traits is
defined by the outgroup.
11. The parsimony principle states that the simplest explanation or representation must be
the explanation. It makes creating a phylogentic tree simpler, as one should always first
assume that the trait is homologous rather than an example of homoplasy.
12. These sources (including morphology, development, behavior and molecular data) are
used as defining characteristics in deciding what species will be in the outgroup and the
ingroup. For example, if a species barks, it will be separated from the main group and
become an outgroup.
13. Studying a phylogenetic tree provides useful information for scientists today, for
example, it helped them map the origin of HIV in humans.
14. Monophyletic is a group that consists of its ancestor and all its descendants,
polyphyletic is a group that consists of multiple distantly related organisms and doesn’t
include the ancestor of the group, and paraphyletic is a group that consist of an ancestors
and some, but not all of its descendants. Because monophyletic contains the most
information it is the best of the three.
Practice: Constructing a Phylogenetic Tree
1.
2.
3.
4.
The sunflower and the pine tree are the most closely related.
The sister group to the seed plants are the megaphylis or the true leaf plants.
Having true leaves and vascular cells evolved.
Yes, traits such as a stomata developed independently.