Speakers at AAAS Mull Chance and Necessity in the Origins of Life

Andrew Pohorille The Rev. Walter Shropshire Jr.

In the search for a solution to the puzzle of life’s origin on Earth, scientists and philosophers are exploring whether chemical chance or some more inevitable, deterministic forces were responsible for emergence of the first systems that would eventually evolve into higher life forms.

For astrobiologist Andrew Pohorille, director of the NASA Center for Computational Astrobiology at Ames and professor of Chemistry at the University of California San Francisco, computer simulations of biomolecular pathways as well as modeling of genetic and metabolic networks enable him to design and mimic possible systems that might have originated life.

Speaking recently at AAAS, Pohorille explained that one of the most challenging aspects of studying life is defining it. He notes that for a definition of life to be applicable for scientists, it must be valid for both modern, complex organisms as well as life found during its most simple and basic stages 1 billion years ago.

“Life is a self-replicating chemical system capable of undergoing Darwinian evolution” — that’s one definition that has been proposed, Pohorille says. He goes on to add that hidden in this definition are two more implied characteristics of life — spontaneous organization and interaction with nature. For Pohorille, these two qualifications invoke the most curiosity.

Pohorille and the Rev. Walter Shropshire Jr., a Methodist pastor who served as the respondent, spoke at a 26 January lecture in Washington, D.C., organized by the AAAS Dialogue on Science, Ethics and Religion (DoSER). The forum was part of a series which aims to address issues of life’s origin that have fascinated scientists, theologians and others.

“The origin of life on Earth is one of the great puzzles of the evolutionary sciences,” noted Jim Miller, DoSER senior program associate. “It is also one of the events in the history of nature that many Jews, Christians and Muslims view as the unique domains of divine creation. The discovery of a plausible evolutionary pathway from inanimate chemistry to animate creatures would further reinforce the continuity of nature.”

For many years, the scientific community assumed that for an organism to be considered living, it had to reproduce and create further generations. Scientists surmised that for this to occur there must have been some necessary, specific form of material transferred between individuals, like DNA, that allowed biological information to be passed on. It is commonly believed that existence of this material is necessary for Darwinian evolution. Scientists were puzzled by this assertion because it raises questions about the genesis of the genetic material itself. Pohorille equates this with a chicken and egg paradox — nucleic acids forming genes are needed to transfer information about proteins, which in turn are needed to catalyze the chemical reactions of life, including making nucleic acids.

The discovery that nucleic acids can catalyze chemical reactions led to a possible solution of this paradox, known as the RNA hypothesis, according to which RNA molecules initially played a dual role of information carriers and catalysts. The source of building blocks for making RNA remains, however, unresolved. This leads to the possibility of non-genetic evolution often referred to as a “metabolism first” hypothesis.

Pohorille explained that it is possible for primitive metabolism to create simple proteins that in turn have the potential to create more complex proteins as well as other compounds. The proposed mechanism opens the door for early evolution to progress without genes and eventually lead to the emergence of specific genetic polymers. Pohorille points to a remarkable feature of this mechanism: basic concepts associated with Darwinian evolution, such as species, fitness to the environment and inheritance still apply. They operate, however, not at the level of individual “organisms” but instead at the level of the whole population.

One of the most fascinating aspects of Pohorille’s research is its ability to bridge the gap between chance and deterministic origins of life. Specifically, Pohorille said that while the events at the origins of life involved a great deal of chance, its outcomes were quite deterministic (but not in every respect). These outcomes Pohorille asserts are strongly constrained by physical and chemical principles that are universal and applicable on Earth as well as throughout the universe.

Shropshire, who also holds a Ph.D. in Plant Physiology/Biophysics from George Washington University and served as the lecture’s respondent, contends that while the scientific method may answer many questions regarding life on Earth, it is deficient in its ability to answer others.

Shropshire pointed to the Wesleyan Quadrilateral as a way to understand the world. This process of thought requires that questions about life must be evaluated in relation to four discrete sources of authority — scripture, tradition, experience and reason. The Quadrilateral embraces customary scientific concepts (experience and reason), but includes notions of faith (scripture and tradition). Shropshire rhetorically asks: “Can science alone understand God’s actions?”

While some might expect Shropshire’s line of thinking to lessen the importance of science, he postulates that the best way to study the world is from a standpoint that balances science and religious faith.

AAAS established DoSER in 1995 to facilitate communication between scientific and religious communities. DoSER builds on AAAS’s long-standing commitment to relate scientific knowledge and technological development to the purposes and concerns of a society at large. The objectives of the program are to contribute to the level of scientific understanding in religious communities and to promote multidisciplinary education and scholarship of the ethical and religious implications of advancements in science and technology.

Benjamin Somers

3 February 2006