Author: Stephen Caesar
Subject: Biology
Date: 2/16/2005

Traditional theory holds that animal and plant species improve over time via beneficial mutations that cause the species to become better able to fend off attackers and flourish in a hostile environment. A common example of this would be fungal attacks on plants: a fungus such as the potato blight that caused the Irish Potato Famine attacks a certain plant species; through random mutations, some of the individuals within this species develop the ability to fend off the fungal attacker. Being fitter than their non-mutated peers, these individuals survive the fungal onslaught to pass their genes on to the next generation. The non-mutated individuals succumb to the lethal fungus and die off, leaving only the fittest to survive and perpetuate the improved species.

Recent studies have shown that this is not necessarily the case. Plants are able to fend off assaults by lethal fungi not by undergoing chance, random mutations, but, ironically, by sharing their physiology with non-lethal fungi. Scientists have found “tons of fungi inside healthy plants, squeezed into nooks and crannies between cells,” according to the science journal Discover (Gadsby 2004: 16). In the words of evolutionary ecologist Allen Herre, “What we call a plant isn’t just a plant. It’s usually a mosaic of plant and fungal tissues” (Ibid.).

Herre and his colleague Elizabeth Arnold, along with other biologists at the Smithsonian Tropical Research Institute in Panama, studied the plant Theobroma cacao, the source of chocolate. In the wild, these plants are saturated with a wide array of harmless fungus species, collectively known as endophytes. Herre, Arnold, et al. grew isolated cacao specimens in a greenhouse, with the result that the new plants were devoid of any endophytes. They injected half the leaves of these newly grown plants with endophytes and left the other half untouched. They then exposed the entire batch of greenhouse specimens to black pod, a lethal fungus that destroys cacao plants. Leaves without the endophytes were three times more likely to die, demonstrating that somehow the endophytes fended off the black pod fungal assault (Ibid.).

In a phenomenon that has not yet been explained, at some point in time the endophytes entered the cacao plant and struck up a symbiotic relationship: the harmless endophyte fungi got a safe place to live, while the cacao plant got a brand-new, life-saving suit of internal armor. “You can think of these fungi as an environmentally acquired immune system,” commented Herre (Ibid.).

This shows that the standard Darwinian model of survival of the fittest through random mutations is not automatically the correct one. There are other mechanisms that explain how a species can become more fit over time. Only further research will uncover how many other species of plants and animals have increased their ability to fend off natural attacks via this symbiotic arrangement.

 

References:

Gadsby, P. 2004. “It Takes a Fungus to Make a Plant.” Discover, vol. 25, no. 10.

 

Stephen Caesar holds his master’s degree in anthropology/archaeology from Harvard. He is a staff member at Associates for Biblical Research and the author of the e-book The Bible Encounters Modern Science, available at www.authorhouse.com.