Why did the human brain size evolve? A way forward.

Area of Science:

• Evolutionary biology
• Paleoanthropology
• Computational neuroscience

Background:

• The evolution of human brain size is a long-standing question in evolutionary biology.
• Experimental approaches are impossible for this unique evolutionary event, necessitating novel inferential methods.
• Simulation-based inference (SBI) provides a framework for addressing complex, unique historical events.

Purpose of the Study:

• To outline a strategy using simulation-based inference to investigate the drivers of human brain size evolution.
• To test mechanistic models predicting evolutionary and developmental trajectories of brain and body size.
• To determine if human brain size evolved as a direct adaptation or a byproduct.

Main Methods:

• Formulating hypotheses as mechanistic models to generate quantitative predictions.
• Comparing model predictions with empirical data on brain and body size evolution in hominins.
• Utilizing simulation-based inference to select models that best explain observed data.

Main Results:

• A recently published model successfully predicted evolutionary and developmental trajectories for six hominin species.
• The model demonstrated that human brain size evolution can be explained as a spandrel or byproduct.
• Selection for fertility-determinant traits emerged as a potential driver for brain size evolution.

Conclusions:

• Simulation-based inference is a viable and powerful approach for inferring the causes of unique evolutionary events like human brain expansion.
• The findings challenge direct selectionist explanations for human brain size, proposing a byproduct model.
• This methodology opens new avenues for understanding the complex evolutionary history of the human brain.