The Evolution of Multicellularity: How Plants, Animals and Fungi Evolved

Millions of years after the first single cells appeared, there now exists various multicellular organisms: plants, animals, fungi, algae, etc. These all consist of multiple cells that collectively form a single being. But how has it all evolved over millions of years?

It's quite amazing how the conglomeration of cells over time has allowed millions of organisms to thrive through the consumption of energy, chemical breakdown and reproduction. Karl Niklas, a plant evolutionary biologist at Cornell University, is focused on the evolution of plants over the past few million years--particularly their size, shape, structure and reproduction. He recently documented his work in an article published in the American Journal of Botany. In the article, he elaborates more upon natural selection, genetics and physical laws: aspects that have heavily influenced the evolution of multicellularity.

But on a more general note, scientists have acknowledged that multicellularity has occurred and evolved multiple times across different clades: once in animals, three times in fungi, six times in algae and multiple times in bacteria.

In order for multicellularity to evolve, many factors must be in congruence. The cells must be genetically compatible to some extent in order to achieve proper functionality, which relies on communication, cooperation, and specialization of functions. There are two stages that the evolution undergoes.

The first is called the "ailment-of-fitness" stage, which requires a unicellular organism (a spore, zygote, or uninucleate asexual propagule) to ensure that all subsequent cells share similar genetic material.

The second is referred to as the "export-of-fitness" stage. This requires that cells work together in order to achieve reproduction of more cohesive units. Once accomplished, a distinct form of organism now exists.

However, these steps differ among plants, animals, fungi, algae and others. Niklas described the process philosophically: "This convergent evolution is well summarized by the saying 'There are many roads to Rome, but Rome is not what it used to be.'" (Found in this article from EurekAlert!)