The Role of Fungi in the Evolution of Land Life

Although fungi are often associated with disease and madness (LSD is a derivative of ergot, a fungus infecting rye grass), they played a major role in the evolution of life. They were one of the first lineages of eukaryotic cells (cells with nuclei) to evolve multicellularity after diverging from the protoctists; plants and animals were the others. The best guess is that they either were the first colonizers of more or less dry land, or partners with photo-synthetic settlers of the land—algae on the way to becoming plants. One strong clue is that the earliest known plant fossils, from the Rhynie chert of the Devonian Period, more than 350 million years ago, bear fossils of fungi along with plants. The terrestrial preference of mem bers of this kingdom is attested to by the existence of only a very few marine forms of fungi. Without the cell whips known as undulipodia, fungal cells are poorly adapted to an aqueous environment: the very few marine forms (such as underwater mushrooms) probably evolved secondarily to a water habitat, just as marine mammals such as seals and walruses (whose ancestors had already moved onto the land) evolved blubber and other adaptations to go back to the water. The mycelial and hyphal networks of fungi help create soil and digest the hard parts of organisms requiring rigidity to move to land. Skin, cotton, feathers, wood, hair, caulking, refrigerator liner, camera lens mounting compound, and other refractory materials are digested by these tenacious life forms. Their injection of enzymes into the environment and subsequent absorption could have played a role in paving the way for the arrival of animals, who came to land after (not before, as is commonly thought) plants and fungi.

The fact that lichens (fungi-algae and fungi-photosynthetic bacteria alliances) are among the first to break down solid rock suggests the soil-making powers of these beings. Another indicator of the role of fungi in making land inhabitable by the rest of life is the existence of mycorhizae root symbioses in many important plants. Of course, although their cells do not swim, as we all know from personal experience, fungi tend to like moist and damp environments. Thus, from a perspective of global evolution, one can argue that watery life moved to land by extending the domain of the original wet, cycling processes of marine life to land. This process, which we traditionally picture as the conquering of the land, can also be regarded as the extension of the original marine ecosystem to include land in its wet fold; life did not come to land so much as re-form it according to the original template of a marine ecosystem. In either perspective, fungi were crucial.

—Lynn Margulis and Dorion Sagan

See also: Adaptation; Arthropods, Terrestrial; Evolution; Five Kingdoms of Nature; Lichens; Microbiology; Protoctists; Soil; Topsoil Formation

Bibliography

Barnes, R. S. K., ed. 1998. The Diversity of Living Organisms. Oxford, UK: Blackwell Science; Kendrick, Bryce. 1992. The Fifth Kingdom. Sidney, British Columbia: Mycologue Publications; Margulis, Lynn, and Karlene Schwartz. 1998. Five Kingdoms: An Illus-trated Guide to the Phyla of Life on Earth, 3d ed. New York: W. H. Freeman; Margulis, Lynn, Karlene V. Schwartz, and Michael Dolan. 1999. Diversity of Life: The Illustrated Guide to the Five Kingdoms. Sudbury, MA: Jones and Bartlett; Sagan, Dorion, and Lynn Margulis. 1993. Garden of Microbial Delights: A Practical Guide to the Subvisible World. Dubuque, IA: Kendall/Hunt.

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