What is an organism?
Rice evolutionary biologists Queller, Strassmann redefine the meaning of ‘one’

BY MIKE WILLIAMS
Rice News staff

What if your foot refused to work with your leg? Or your heart just wouldn’t play well with your liver? All kinds of bad things could happen, but the fact that all your parts mesh is no accident. The cooperative of cells that makes up our bodies makes us whole.

The central tenet of a new paper by Rice professors David Queller and Joan Strassmann is that a high level of cooperation and low level of conflict between components, from the genetic level on up, give a living thing its “organismality,” whether that thing is an animal, a plant, a bacteria — or a colony.

	JOAN STRASSMANN AND DAVID QUELLER

They also note some of the traits scientists use to describe an organism, such as individuality or even membership in the same species, may not be necessary to achieve organismality. What is necessary is commonality of interests and minimal conflict that, combined, makes this the premier level of adaptation.

Tackling the big issues doesn’t seem to daunt Queller and Strassmann, the Harry C. and Olga K. Wiess Professors of Ecology and Evolutionary Biology, so their ongoing quest to address what they call “the truly central questions about the organization of life” is no surprise.

They gathered decades of accumulated experience and knowledge into a new paper, “Beyond Society: The Evolution of Organismality,” published this month in the Philosophical Transactions of The Royal Society B.

“This is more than a semantic game of deciding that X is an organism and Y is not,” they wrote. “The scientific community could choose any name they want for entities with extensive cooperation and very little conflict, but the existence of such entities is one of the striking features of life, and explaining how they evolve should therefore be an important task.”

The ideas they present have been bubbling just below the surface of the couple’s extensive research into the conflicts and cooperation that drive Dictyostelium amoebas (slime molds) and social insects.

“Adaptation is what makes living things different from nonliving things, to my mind, so the concept of organism is centered on that,” said Queller, sitting with Strassmann in her Rice office. “It seems to make sense.”

Setting themselves the task of defining the essential characteristics of organismality, they decided an organism is not necessarily an individual. A colony of honeybees is an organism, the authors argue, because of its sense of shared purpose. A high degree of cooperation and low level of conflict — even when the potential for conflict is there — is a primary trait of an organism, whether its components share a body or not.

Their grand scheme centers on a set of charts that separate living things into four groups, based on observed levels of cooperation and conflict. “One thing I think is really important about the paper — and it’s fairly simple — is the idea that the opposite of high cooperation is not conflict. It’s absence of cooperation,” Strassmann said. “That allows us to put conflict on a different axis from cooperation and divide the social space into organisms, societies, competitors and simple groups.”

Queller and Strassmann analyzed dozens of species in three distinct classes of groups to determine where they land on the organismal charts, based on their levels of cooperation and conflict.

On the cellular level, whales, mice, redwoods, the malarial parasite Plasmodium in mosquitoes and Dictyostelium rank high on the organismality scale for their levels of cooperation with little conflict.

Humans are obviously organismal, Queller and Strassmann agreed. All the parts of the body, from the macro level (arms and legs) to the micro (cells), work nicely together with very little conflict. But unlike the honeybee colony, a city is not organismal. Though the human colony requires a great deal of cooperation to keep it running, it is, they said, “far too full of conflicts.”

On the level of groups of multicellular individuals, the Portuguese man-of-war is a paragon of organismality. Technically it is a colony of seagoing polyps and each polyp seems to know its place and takes on a specialized duty that contributes to the survival of the whole. “The cooperators have become so close as to blur their boundaries,” they wrote.

In the third grouping of two-species pairings that may seem simply symbiotic, the researchers find close cooperation without conflict is often necessary for the survival of both parties. The relationship between mitochondria and the host cells they power is one example; bobtail squid and the bacteria that allow them to light up in return for sustenance is another. The authors put the relationship between lions and gazelles at the opposite end of the scale for obvious reasons.

Queller and Strassmann wrote that “organisms should be defined by what they actually do” and not by the potential for cooperation or conflict.

“Factors like high-relatedness that select for high cooperation also select for low conflict. But they don’t always go exactly hand in hand in the real world,” Queller said. “We’re trying to say, ‘Look at the real world; look at what things actually do.'”

The couple also put their work into an interesting historical context, noting their ideas are a natural evolution from those of Julian Huxley, a father of modern evolutionary synthesis and Rice’s first professor of biology in 1912. Huxley was the grandson of Thomas Huxley, an English biologist and friend of Charles Darwin who became known as “Darwin’s Bulldog” for his enthusiastic defense of the theory of evolution.

“Huxley, of all the early people, really had an approach that’s the most similar to ours,” Strassmann said. “He would consider a lichen an individual and even a yucca and a (symbiotic) yucca moth an individual. He talked about individuals; we talk about organisms.”

“In a way,” said Queller modestly, “we’re just continuing his work.”

This chart by David Queller and Joan Strassmann scales species of multi-cellular individuals by their levels of cooperation and conflict 
into four classifications: organisms, societies, competitors and simple groups.