Classification Processes – Organisms

Cladistics

This categorises organisms into groups based on their most recent common ancestor.

Syllabus statement: recall that common assumptions of cladistics include a common ancestry, bifurcation and physical change.

  1. Any group of organisms are related by descent from a common ancestor.
  2. There is a bifurcating pattern of cladogenesis.
  3. Change in physical characteristics occurs in lineages over time.

The first assumption is a general assumption that states that all life arose on earth only once. This means all organisms are related and all life has been produced through the reproduction of existing organisms.

The second assumption is that there is a bifurcating, or branching, pattern of lineage-splitting, essentially meaning that when a lineage splits, it divides into exactly two groups. Please note that there are some situations which may violate this assumption, such as in adaptive radiation, but they’re rare, so this assumption generally stands true.

The third assumption states that there is a change in physical characteristics occurring in lineages over time.

State a common assumption of cladistics.

1. Any group of organisms are related by descent from a common ancestor.

2. There is a bifurcating pattern of cladogenesis/bifurcation.

3. Change in physical characteristics occurs in lineages over time.