Chapter 27: Phylogenic Trees
Hybrid zone: an evolutionary neutral area where hybrids co-exist.
Be able to estimate phylogenies.
-Phylogenic trees document the evolutionary relationships among organisms and are
estimated form data.
-Adaptive radiations are a major pattern in the history of life. They are instances od rapid
diversification associated with new ecological opportunities and new morphological
- We have to infer or estimate phylogenies. Computers measure “distance between
species”. The statistical analysis estimates the separation of taxon’s.Adistance matrix
compares how different the sequence the individuals are.
- A branch represents a population through time.
- Apoint where two branches diverge is called a node. This is where a species diverges.
- a tip or terminal node is the end point of a branch, which represents groups (a species or
larger taxon) that is living today or ended in extinction.
How do researchers estimate phylogenies?
-Phylogenetic trees are effective way of summarizing data on the evolutionary history of
a group of organisms.
-The genealogical relationships of a species cannot be definitively known.
-To infer historical relationships between organisms, researchers analyze morphological
or genetic characteristics of species. Researchers do this be looking at fossil records and
-Researcher use two approaches when constructing the actual phylogenic tree:
1. Phenetic approach: estimating trees using statistical summaries of overall
similarities of organisms. Look t differences or similarities.
2. Cladistic approach: inferring trees based on synapomorphies (two or more
organisms have a trait), recognizing shared characteristics that re derived from
previous species, allowing researchers to analyze monopyholetic groups. (the
simplest is best), The phylogeny is constructed with the least amount of changes
possible. You choose the phylogeny that occurs the least amount of changes.
Synaptomorphy is an evolutionary innovation ex nipples. It is a newly derived feature of
How can Biologists distinguish Homology from Homoplasy?
The issue that traits can be similar in two species not because those traits were
present in a common ancestor but because similar traits evolved independently in
two distinct groups. Homology translates to “same source”. Similar traits are inherited from a common
ancestor. Similarity due to shared ancestry. Ex: the Hox genes are present in fruit flies
and humans due to common ancestry and are involved in the development of the
embroyo. They are strings in specific order horizontally and transcribed from head of
the embryo to the end o the body. This set of genes were then inherited by descendant
populations. Homology is more frequent than Homoplasy.
Homoplasy “same form” occurs when two traits are similar for reasons other than
common ancestry. The flying structure of wings ex insects and birds. The homoplasy
is that they are not related but both have wings. The have the similar bones.
(Similarities not derived from ancestry). Key to look for is their ancestors share the
traits. Even though species look alike they may not be closely related at all.
Convergent evolution occurs when natural selection favours similar solutions to
the environment (homoplasy). Convergent traits are also called analogous traits.
These trait do not occur in a common ancestor of the similar species. When for
example dolphins and fish both evolved gills but do not share ancestral history.
The researchers use a “parsimony” to better understand the true meaning of the
data. Under a parsimony, the most likely explanation that implicates the least
amount of change is thought of as true.
Phylogenies can also be based on transposable elements due to the fact that they
are unique to each organism but related in species.
Even though bone structure is the same, bats and birds evolved independently of
Fossils: direct evidence of past living organisms, physically preserved. It tells us about
mass extinctions and phylogenies.
Limitations of fossilization records
Habitat Bias: Organisms that live in certain areas where sediments are actively being
deposited including beaches, swamps ect. That are much more likely to form fossils.
Some fossils will preserve better in different area proposing a bias in what species are
Taxomic and tissue bias: Slow decay is almost always essential to fossilization, so
organisms with hard part such as bones or shells are most likely to leave fossil
Temporal Bias: Recent fossils are much more common than ancient fossils. This
causes a temporal bias in the record, only having recently made fossils. Strata more
close to the surface are more often found.
Abundance bias: Organisms that are most abundant, and widespread leave much more
evidence more often than other species that are not as widespread. Life’s time line
Precambrian Period: (4.6 biollion-542 million) Includes: Hadean,Achaean,
Life was exclusively unicellular for most of Earth’s history and oxygen was
absent form the oceans and atmosphere.
Phanerzioc eon: The interval between 542 mya and the present is called the Phanerzoic
eon. This eon has divided into three eras. Each of these eras is subdivided into periods.
1. Paleozoic: (ancient life era) The Paleozoi