Researcher Christoph Adami Describes How Digital “Organisms” Evolve
Using some ingenious computer methods, Christoph Adami and his colleagues have studied how generations of rapidly proliferating digital “organisms” can evolve traits that appear to be irreducibly complex.
The work has been cited as a clear refutation of “intelligent design,” a doctrine which argues that complex features, such as the human eye or the blood clotting system, could not have evolved by gradual accumulation of random mutations over time. Such features, proponents say, are irreducibly complex and could only have resulted from the intervention of an intelligent agent, whether God or some unnamed designer.
But Adami, who discussed his research in a recent lecture at AAAS, said computer analogues of living systems show, in a very concrete way, how simple organisms can acquire complex adaptive traits by standard Darwinian mechanisms of mutation and natural selection.
“We tried to evolve something complex,” Adami said. The researchers succeeded in showing that after 111 mutations, one of the digital organisms developed a complex traitthe ability to compare pairs of binary numbers and determine if each pair of digits is the same. The researchers then demonstrated that the trait is irreducibly complex. Knock out any single component of the digital “equals” gene and the function disappears.
Adami, who until recently headed the California Institute of Technology’s Digital Life Laboratory, has been doing the work in collaboration with biologist Richard Lenski, computer scientist Charles Ofria, and philosopher Robert Pennock, all on the faculty at Michigan State University. Adami is now a professor of applied life sciences at the Keck Graduate Institute in Claremont, Calif. His lecture was sponsored by AAAS’s Dialogue on Science, Ethics and Religion (DoSER).
To accomplish evolution on a computer, the team essentially starts with a domesticated version of a computer virus. The organism, with about 50 computer instructions as its genome, can direct its own replication. Like any organism, the digital critter requires energy to survive. Its principal energy resource is access to time on the computer’s central processing unit or CPU.
Instead of the chemical reactions associated with biological life, the digital organisms thrive by doing calculations, Adami said. “If they do an interesting calculation, we give them extra CPU time,” he said. To do a complex operation, such as adding numbers, a digital organism has to perform simpler steps first. Each time it accomplishes one of those intermediate steps, such as recognizing a number and holding it in its memory, the organism is rewarded.
The organisms “adapt to their world and grow in complexity,” Adami said.
Even before the current debate on whether intelligent design should be discussed in science classrooms, scientists have been seeking better ways to explore the concept of biological complexity. There are questions about how to define the term, complexity, and whether there is an inevitable trend in evolution from simple organisms to the more complex.
Even with simple, rapidly proliferating organisms such as bacteria, tracking genetic changes over 10,000 generations or more is a formidable challenge. Efforts to mimic evolution on a computer provide a way to carry out experiments in a reasonable time frame, Adami said.
In defining complexity, biologists can choose to look at structural complexity, such as the number of limb pairs an organism develops over time. Or they can look at how many different functions an organism can perform. They also can analyze the organism’s genetic blueprint or genome, a measure called sequence complexity. That is the approach Adami and his colleagues took with their digital organism.
Why not just look at the length of an organism’s genome, the number of base pairs in its DNA? Because there is no necessary correlation between genome length and species complexity, Adami said. “Certain types of amphibians have more than 10 times as much DNA sequence as humans,” he noted. Instead, he said, biologists look for regularity and randomness within an organism’s DNA, trying to determine whether complex chunks of sequence can give rise to complex structural features.
In the digital world, the research team was able to watch the mutations and selective pressures at work on millions of digital organisms as they evolved through thousands of generations.
By studying evolution of digital critters on a computer, Adami said, the team has been learning more general lessons about biological complexity as well. Is there a trend? “Overall, the complexity must increase as an organism adapts to its environment and learns more about it,” Adami said. But there are exceptions.
If the environment changes drastically over time, whether on a computer or in the real world, the genes that might have been beneficial in the previous era are unlikely to be sufficiently robust in the new circumstances. There can be “complexity crashes” that result in major extinctions of species, Adami said.
AAAS established DoSER in 1995 to promote 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 society at large.
Jim Miller, senior program associate for DoSER, was the respondent at Adami’s 20 October lecture. He spoke of evolution and complexity from a theological perspective. If organismswhether biological or digitalcan evolve in complex ways through random mutations and natural selection, where is there room for God?
“If you have what Christoph described, how is it we can talk of divine action?” Miller asked. Augustine of Hippo (354-430 AD) offers one answer, Miller said. He held that God had created “rationes seminales,” or seed principles, that were present in matter from the moment of creation and contained the necessary information for the growth and development of all creatures. But, Miller noted, this implies a deterministic world, very different from a contingent evolutionary world.
More recently, proponents of intelligent design would answer that God or an unnamed intelligent agent intervenes in nature to bring about the appearance of complex structures. But that view, like Augustine’s, assumes a theologically grounded form of determinism, Miller said, that is not supported by scientific investigation of the history of nature, a history that scientists say is deeply indeterminate.
Miller, an ordained Presbyterian minister, said there is no inherent conflict between science and religion though each bears on the other. He proposed there is a realm of what he called “graded potentiality” in the cosmos, in relation to which novel or complex structures can emerge. God does not determine the outcomes, he said, but gives them an initial direction.
28 October 2005