November 15, 2006
TBL: What Is Life? Pt. I
It is probably one of the most deceptively simple questions in any scientific field. Defining life becomes a problem of attribution, finding commonalities of matter reliant on energy.
With each new technological breakthrough things get more complicated. Microscopes become successively more powerful, able to penetrate the depths of body, cell and nucleus, revealing new life, different life, unclassifiable by common convention.
This process has repeated itself throughout history, and continues today. We live in a biological world of genes and molecules, far flung from the macro days of limbs and organs.
As a microbiologist, FSU Biology Professor Dr. Scott Fritz studies the boundaries in this world of the infinitesimal.
“It really is a fascinating question,” says Fritz. “We [biologists] have a working definition: something organic that can obtain energy, independently reproduce and have the ability to adapt to its environment.”
But Fritz and other biologists wonder if the definition is adequate.
“It’s all in your perspective,” says Fritz. “Are viruses life? That is still a very controversial question that may or may not ever be resolved.”
Viruses spark controversy because of their inability to independently reproduce. They essentially hijack the host’s reproductive machinery in order to multiply; without the host they cannot survive.
But viruses have all of the other components of life; they feed, they adapt with profound efficiency and they are organic in nature. Viruses possess the same basic components as all other life, nucleic acids (DNA, RNA), amino acids, sugars and lipids, which are each composed of simple, carbon based, organic molecules.
Back in the 1950’s, the decade when DNA was finally pinned down as the genetic blueprint of life, a grad student named Stanley Miller tried to reproduce these organic compounds by replicating the harsh atmospheric conditions of Earth 3,800 million years ago, pulsing electric charges through the hydrogen, methane, ammonia and water vapor soup.
Miller’s experiments produced amino acids, commonly called the building blocks of life. Subsequent experiments by Miller and others in this new field of “abiotic chemistry” would yield purine and pyrimidine, sugars integral to the structure of both RNA and DNA. Miller and company proved that life’s components could be synthesized from an inorganic substrate.
He found the pieces, but how do they fit in the puzzle?
“That’s the real question,” says Fritz. “How do you go from [organic compounds] to life? How do the components of life rise up and coalesce into an organism?”
Certain organic structures, such as bacterial flagella, viral capsids (capsules) and the lipid bilayer of eukaryotes, are able to self-assemble, meaning that if the proteinous components of the structure were to discorporate, they are “programmed” to reform into the original structure.
Fritz suggests that this mechanism might have something to do with the assemblage of early life.
Once life assembled, it was compelled to persist, to survive. In order to survive, it had to be aware of its surroundings on some level; in order to obtain energy, to adapt. That meant an exchange of information. Some would define the acquisition and use of information intelligence. Is intelligence another attribute of life?
“It depends on how you define intelligence,” says Fritz. “Is it the ability to learn or to reason, to draw conclusions? Is it physiological in nature? Does it require a complex neural network, or merely a set of chemoreceptors?”
Recent research has suggested that bacteria are able to draw conclusions and make decisions in some respects. For example, certain bacteria will preferentially use one sugar over another.
“Are they making an intelligent decision?” says Fritz. “If so, then intelligence takes place at the level of the gene. Bacteria have no neural network, no brain.”
As a comparative psychologist, Dr. Erica Kennedy uses some of the most brainy of animals to explore reasoning “analogs” in the animal kingdom: Capuchin monkeys.
“We look for patterns, comparisons and possible ways that these reasoning abilities may have developed under certain circumstances in different organisms,” says Kennedy.
The monkeys explored two-dimensional computer mazes with a simple joystick, and then compared their ability with the abilities of chimpanzees. The capuchins were not as capable as the chimps, but did exhibit the ability to make decisions and draw conclusions.
“The process requires a lot of training,” says Kennedy. “[The monkeys] don’t know the question, so you have to find the clearest way to get across what you want them to do. Researchers also have to be careful to avoid unintentially giving animals cues that could influence their behavior.
“As far as ‘what is life,’ I would have to go with the biological explanation,” she says.
Fritz believes that we will be asking the same question years into the future.
“I’m always amazed by microorganisms in particular,” says Fritz. “Life is all around us, within us and we just take it for granted, forgetting how complex it really is.”
But is life confined to Earth, to the biological carbon base? Can artificial intelligence and software be categorized as life?
Originally printed here.