Chapter Two: 

How did evolution get started?

Why study the origin of life?

To explain how evolution started on earth, we need to be able to describe how a population of replicators could emerge from naturally occurring molecules. Thinking about the origin of life is a good way to get to grips with the concept of evolution by natural selection (origins of microevolution). It also provides a platform for considering ways that the complexity of information coded for and passed between generations can increase over evolutionary time through a series of major transitions in evolutionary complexity (origins of macroevolution). This chapter explores how we generate hypotheses, building explanations for events in the distant past that we cannot ever witness directly. Because we can’t directly observe the origin of life, we need to use a range of scientific tools to study it, so origin of life provides an opportunity for us to think about the roles of experiments, models and comparative tests in macroevolution.

What are the main points?

• For evolution to occur, there must be a population of replicators able to copy themselves with near-perfect accuracy, with occasional variations that provide the potential for natural selection to improve copying ability
• The capacity for heritable information can be increased by combining previously independent replicators into co-ordinated systems that rely on each other for replication.
• The Major Transitions in evolution are macroevolutionary events that led increases in informational capacity, permitting the evolution of diversity and complexity over time.

What techniques are covered?

• Experiments: simple systems manipulated to explore outcomes of particular conditions and processes (such as Miller’s spark experiment and Spiegelman’s RNA “monster”)
• Models: idealised representations for testing the implications of processes and conditions (such as the “prebiotic pizza” and hypercycles)
• Comparative analyses: comparing living species to reconstruct ancestral states and histories of change (such as the reconstruction of the last common ancestor, LUCA)

What case studies will be included?

• Using homology to reconstruct history: the common ancestor of all living species (LUCA)