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I N T E R P R E T I N G C L A D O G R A M S
B I G I D E A : P H Y L O G E N I E S D E P I C T A N C E S T O R A N D D E S C E N D E N T R E L A T I O N S H I P S A M O N G O R G A N I S M S B A S E D O N H O M O L O G Y
T H E S E E V O L U T I O N A R Y R E L A T I O N S H I P S A R E R E P R E S E N T E D B Y D I A G R A M S C A L L E D C L A D O G R A M S ( B R A N C H I N G D I A G R A M S T H A T O R G A N I Z E R E L A T I O N S H I P S )
CompZoo QQ #2: Interpreting
cladograms
Reading Cladograms
- When an ancestral lineage splits: speciation is indicated due to the “arrival” of some new trait.
Each lineage has unique traits to itself alone and traits that are shared with other lineages.
each lineage has ancestors that are unique to that lineage and ancestors that are shared with other lineages — common ancestors.
Read like a family tree: show patterns of shared ancestry between lineages.
Reading Cladogram: Identifying Clades
Using a cladogram, it is easy to tell if a group of lineages forms a clade. Imagine clipping a single branch off the phylogeny all of the organisms on that pruned branch make up a clade So everything in the pink circle is a clade (common ancestor and all descendants)
Quick Question #
Looking at the image to the right:
Is the green box a clade?
The blue?
The pink?
The orange?
Interpreting Cladograms
it's easy to misinterpret cladograms as implying that some organisms are more "advanced" than others
however, cladograms don't imply this at all.
when reading a cladogram, it is important to keep three things in mind
(mis)Interpreting Cladograms: One
Evolution produces a pattern of relationships among lineages that is tree-like, not ladder-like.
(mis)Interpreting Cladograms: Three
For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left is arbitrary. The following phylogenies are equivalent:
Interpreting Phylogenies: Human Example
The points described above cause the most problems when it comes to human evolution.
It is important to remember that: Humans did not evolve from chimpanzees. Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human. Humans are not "higher" or "more evolved" than other living lineages. Since our lineages split, humans and chimpanzees have each evolved traits unique to their own lineages.
