Human beings are great big conglomerates of millions upon millions of cells. In this respect, we are very similar to other animals, as well as land plants, algae and filamentous fungi — we are multicellular.
Multicellularity is thought to have evolved independently several times throughout history. Traditional thinking was that the ancestors of land plants evolved multicellularity separately to the ancestors of animals, who evolved multicellularity separately to the brown algae forebears. It was thought to have evolved multiple times in fungi, red algae and slime molds. Even some bacteria — the blue-green cyanobacteria — figured out the secret to multicellularity somewhere along the line
Phylogenetic trees illustrates how different organisms on the tree of life relate to each other. The example on the left is best imagined as a tree lying on its side with the trunk at the far left and smaller, more recently formed branches toward the right. As you can see, the metazoans (animals) branched away from fungi and the amoebazoa (which includes slime molds) fairly close to the trunk of the tree. All of the branches within the metazoan block — separating worms and crustaceans and jellyfish — are more recent evolutionary divergences. Continue reading “On multicellularity and slime molds”