What Darwin won't tell you about evolution - with Jonathan Pettitt

The speaker begins by expressing gratitude for the award and clarifies that the talk will not solely focus on their research. They emphasize the complexity of life, drawing attention to biological systems that range from molecular to societal levels. The speaker challenges the immediate attribution of complexity in biology to Darwinian selection, highlighting the need to understand the reasons behind the complexity of organisms. They introduce the concept of natural selection and its dependency on population size, setting the stage for a deeper dive into population genetics.

The speaker delves into population genetics, explaining its fundamental role in evolution. They discuss the impact of population size on the fate of genetic mutations, using the concept of genetic drift to illustrate how random sampling can lead to the loss or fixation of certain traits. The speaker uses visual aids to demonstrate how a small population can lead to the extinction of a beneficial trait due to chance, while a larger population can maintain genetic diversity. They underscore the importance of understanding genetic drift and selection in the context of population size.

The speaker further explores the role of genetic drift in evolution, emphasizing that the fate of genetic variants is influenced by population size. They conduct a simulation to show how different population sizes affect the persistence of genetic traits, even when those traits confer a reproductive disadvantage. The speaker highlights the profound impact of population genetics on the survival and spread of genetic variants, challenging the assumption that all biological complexity is the result of natural selection.

The speaker discusses the evolutionary history of introns, non-coding regions of DNA that interrupt genes. They explain the puzzling presence of introns, which require removal during RNA processing, and propose that introns originated from prokaryotes and became widespread in eukaryotes due to a union between two types of prokaryotes. The speaker suggests that the proliferation of Group II introns in early eukaryotes was a problem, leading to 'mutational fragility' and the need for a mechanism to remove introns. They argue that population genetics played a role in how eukaryotes dealt with this challenge.

The speaker continues the discussion on introns, describing their initial detrimental impact on early eukaryotes and the subsequent development of a complex machinery to manage them. They explain that while introns initially seemed useless, they later became essential for genetic diversity and gene regulation. The speaker also touches on the differences in intron numbers across species, suggesting that population genetics has influenced the retention or loss of introns in various organisms.

The speaker introduces trans-splicing, a process where separate RNA molecules are joined together, and its role in the evolution of eukaryotes. They explain that trans-splicing likely evolved multiple times in eukaryotic cells and discuss its significance in organisms such as C. elegans and trypanosomes. The speaker suggests that trans-splicing allows for the creation of long arrays of genes, which can be efficiently translated, and that this complexity initially evolved through neutral evolution before becoming essential for certain organisms.

The speaker discusses the broader implications of trans-splicing, highlighting its prevalence in harmful organisms and its potential as a target for therapeutic intervention. They explain that trans-splicing's complexity can arise through neutral evolution, which later becomes essential due to mutations. The speaker also touches on the concept of 'constructive neutral evolution,' where complexity builds through neutral processes before being shaped by natural selection. They conclude by emphasizing the importance of considering both neutral evolution and natural selection when studying biological complexity.