Cladograms or Phylogenetic Trees

Phylogenetic Trees or Cladograms

• By studying inherited species' characteristics and other historical evidence, we can reconstruct evolutionary relationships and represent

them on a "family tree”, called a phylogeny.

• a branching pattern of evolutionary relationships.

Uses for phylogenetic trees

Biologists use phylogenetic trees for many purposes, including:

•Testing hypotheses about evolution •Learning about the characteristics of extinct species and ancestral lineages •Classifying organisms

Aristotles’s Great Chain of Being

• Idea based on a step ladder• Simplest to most complex

New Classification System• Linnaean system of classification that assigns every

organism a kingdom, phylum, class, order, family, genus, and species.

• This system was created long before scientists understood that organisms evolved.

• Linnaean system is not based on evolution, most biologists are switching to a classification system that reflects the organisms' evolutionary history.

• Linnaean System of Classification Evolutionary Based Classification

3 Keys to remember about phylogenies

1) They are not ladders

• Evolution produces a pattern of relationships among lineages that is tree-like, not ladder-like.

2) Just because we tend to read phylogenies from left to right, there is

no correlation with level of "advancement."

3) For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the

left is irrelavant.

Understanding Phlogenies (Cladograms)

• The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendants of that ancestor. As you move from the root to the tips, you are moving forward in time.

Speciation

• When a lineage splits (speciation), it is represented as branching on a phylogeny. When a speciation event occurs, a single ancestral lineage gives rise to two or more daughter lineages.

Lineages

• Phylogenies trace patterns of shared ancestry between lineages. Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages.

Common Ancestor

• Similarly, each lineage has ancestors that are unique to that lineage and ancestors that are shared with other lineages — common ancestors.

Clades

• A clade is a grouping that includes a common ancestor and all the descendants (living and extinct) of that ancestor

• A clade may include many thousands of species or just a few.

What do we use to “group” organisms into their clades

• Shared-Derived Characteristics (Shared=what they have in common; Derived=what separates them)

– Physical Characteristics (morphology)• Homologous and Analogous Structures

– Genetics Sequences – Behavioral Traits

Using Homologous and Analogous characteristics

• How does this clade show both homologous and analogous characteristics?

Homologous Structure• Tetrapods- “Four Footed”

• Why aren’t bats and birds more closely related?

Analogous structures

• Bat wings and bird wings are analogous due to convergent evolution

• Bat’s wings consist of stretched skin between the bones

• Bird’s wings consist of feathers along the arm

Using DNA technology

• Scientist are using DNA sequences to construct phylogenetic trees

» Construct a possible phylogenetic tree using the information in the table for humans, chimpanzee,

gibbon, rhesus monkey, and galago.

Human

Chimpanzee

Gibbon

Rhesus

Galago

Amniotic Egghttp://youtu.be/Qq0kMEWzdHg

• The significance of the evolution of the amniotic egg is that it afforded greater independence to land animals

• They would no longer have to return to water to lay their eggs as there was no risk of the eggs drying out

What came first….

The Chicken or the Egg?????

http://youtu.be/1a8pI65emDE