WHAT FACTORS PROMOTE THE EMERGENCE OF BIOCOMPLEXITY?

WHAT FACTORS PROMOTE THE EMERGENCE OF BIOCOMPLEXITY? Robert M. Hazen, Carnegie Institution Kavli Futures Symposium – Bio & Nano June 13, 2007

Four Objectives • Identify emergent steps in life’s origins. • Define a system’s complexity in terms of its function. • Identify factors that promote complexification.

PART I: ORIGINSCentral Assumptions The first life forms were carbon-based. Life’s origin was a chemical process that relied on water, air, and rock. The origin of life required a sequence of emergent chemical steps of increasing complexity.

What is Emergent Complexity? Emergent phenomena arise from interactions among numerous individual particles, or “agents.”

Emergent Phenomena – Life

Life’s Origins:Four Emergent Steps • Emergence of biomolecules • Emergence of organized molecular systems • Emergence of self-replicating molecular systems • Emergence of natural selection

Why Is It Difficult to Quantify Complexity? Genomic Structural X Behavioral X X

Functional Information Hazen et al. (2007) defined functional information (I) as related to the fraction of configurations of a system [F(E)] that achieves a specified degree of function (E): I(E) = -log2[F(E)] where I(E) is measured in bits.

PART III: How to Increase I(E) 1. Increase the number of interacting agents. 2. Increase the diversity of interacting agents. 3. Increase selective pressures by environmental cycling

Implications of I = -log2[F(E)]:System Size and Diversity Sand Grains Galaxies Ant Colonies The Brain

Implications of I = -log2[F(E)]:Cycling and Complexification Cycling of environmental conditions (day-night, wet-dry, high-low tide, hot-cold, freeze-thaw) enhances selection processes and therefore increases both E and I. Kessler & Werner (2003) Science 299, 354.

Implications of I = -log2[F(E)]:Cycling and Complexification Each cycle has the potential to add information to the system (e.g., waves, aptamers, reproduction).

FUNCTIONAL INFORMATION Jack Szostak, Harvard University Experiments in Molecular Evolution

Aptamer Evolution • Create a random RNA pool *1

Aptamer Evolution • Random RNA pool • Initiate in vitro selection process *1 *2

Aptamer Evolution • Random RNA pool • In vitro process • Wash 15 times to remove nonbinding • strands *1 *2 *3

Aptamer Evolution • Random RNA pool • In vitro process • Remove nonbinding • strands • Collect bound RNA strands *1 *2 *3 *4

Aptamer Evolution • Random RNA pool • In vitro process • Remove nonbinding • strands • Collect bound RNA • Reverse (RNADNA) transcriptase to copy bound sequences *1 *2 *5 *3 *4

Aptamer Evolution • Random RNA pool • In vitro process • Remove nonbinding • strands • Collect bound RNA • Reverse transcriptase • Use PCR to amplify bound sequences with errors. *1 *6 *2 *5 *3 *4

Aptamer Evolution • Random RNA pool • In vitro process • Remove nonbinding • strands • Collect bound RNA • Reverse transcriptase • PCR amplify with errors • Transcribe DNA to new RNA strands *1 *7 *6 *2 *5 *3 *4

Aptamer Evolution • Random RNA pool • In vitro process • Remove nonbinding • strands • Collect bound RNA • Reverse transcriptase • PCR amplify with errors • Transcribe DNA to new RNA strands • Repeat 1 thru 7 *1 *7 *6 *2 *5 *3 *4

Results: An RNA molecule which can: • Self replicate • Bind to a non-nucleic acid substrate (BIE) • Perform a chemical reaction ( N-C bonding; i.e.: N-alkylation) • Closely resembles tRNA

“ISLANDS OF FITNESS” We propose that the gaps are the result of “islands” of solutions in configuration space.

CONCLUSIONS 1. The origin of life required a sequence of emergent steps. 2. Complexity only has meaning in the context of function. 3. We can achieve complexity through design or selection.

With thanks to: NASA Astrobiology Institute National Science Foundation Carnegie Institution of Washington

WHAT FACTORS PROMOTE THE EMERGENCE OF BIOCOMPLEXITY?