Cladograms

Cladograms - Building the Tree of Life

Constructing the Tree of Life using Cladograms

1. To determine the relationship between organisms, it is important to look further than apparent similarity.  While a barnacle and a limpet might appear to be cone-shelled animals, they are distantly related.  A barnacle is more related to shrimp than it is to the limpet which is a mollusk, and so more related to clams and other squishy-bodied critters.

2. Cladistics uses a system of comparing "derived characteristics" to determine relationships over time.  The more organisms have in common (ex. a backbone), the more general the trait and the older that trait is.  On the other hand, the opposable thumb in hominids is shared by very few organisms on our planet.  It's an exclusive characteristic indicating it a recent trait.  In comparing the commonality or rarity of traits, we create decision points on the tree of life that indicate where on the tree organisms reside.  This helps us determine evolutionary relationships.

3. Watch the video lesson on cladistics.  

4. When done, go to the Cladogram Activity