The meaning of “life”David BaumProfessor University Wisconsin, Madison

Life as we know itLAWKI shares many features

Life as we know itA reflection of common ancestry

Last universal common ancestor

Life in general?Focus on generic features

LIFE

..but which?

A “working definition”

Life is a self-propagating chemical system capable of undergoing adaptive evolution(Modified from Joyce, 1994)

Focus on generic features..but which?

A “working definition”“Self-propagating” includes growth and cellular

reproduction

A “working definition”“Adaptive evolution” entails the potential to

complexify and become more out-of-equilibrium

Fitness/Co

mplex

ity

Time

MutationSelection

Chan

ce o

rigin

of p

roto

cell

Protocell

First cell

Towards modern cells

Chance origin of surface protoplasm

Metabolizingpropagule

Growingpropagule

Dividingpropagule

Adaptive evolution explains how more complex structures can arise over time

Baum (2015)

Origin of life cares about LAWKI and life in general

Self-propagation and evolution are key

MutationSelection

ReferencesBaum D.A. 2015. Selection and the origin of cells.

Bioscience. 65:678-84Joyce, G., 1994. Foreword: In Origins of life: The central

concepts, ed. DW Deamer and GR Fleischaker. Jones and Bartlett, Boston.