Big Surprises in the Tree of Life
Has the explosion of phylogenetic research confirmed or overturned our ideas on relationships? The answer is: both!
This research has provided overwhelming support for many long-recognized groups, among them insects, mammals and birds, as well as seed plants and flowering plants. It has also confirmed earlier suspicions that some groups do not form a single branch of the Tree of Life. Brown algae, for example, are only very distantly related to the red algae, and crocodiles and dinosaurs are more closely related to birds than they are to lizards or turtles.
Phylogenetic studies are also uncovering totally unexpected relationships. This is especially true for microorganisms, where little visible structural evidence is available. Here, DNA sequences are providing data that are fundamentally changing our understanding of relationships.
Only over the last few decades have we realized that there are three major branches of the Tree of Life — the Bacteria, the Archaea and the Eukaryotes. The Archaea, single-celled organisms that often live in extreme environments, had been put together with the Bacteria, but molecular evidence reveals that they are widely separated. The Archaea are probably more closely related to the Eukaryotes, the branch that includes humans and most other familiar organisms.
We have also discovered that fungi are more closely related to animals than to plants, and that within the animals the segmented worms (annelids) are more closely related to the unsegmented molluscs (snails, clams and squids) than they are to segmented arthropods (spiders, lobsters, millipedes and insects).
Major new discoveries are being made even in the best-known organisms, including mammals and flowering plants. In this exhibit we feature two totally unexpected results, both showing that really big organisms can be very closely related to really small ones — the Afrotheria lineage within mammals, connecting elephant shrews with elephants, and the story of Rafflesia, the plants that produce the world’s largest flowers.