LUCA to Brain Turning Points: Sperm Origins, Mind Maturity, and Climate Emergency | New Scientist Weekly

Overview

This New Scientist Weekly episode blends three major science themes: the evolutionary origin of sperm via the Last Universal Common Sperm Ancestor (Lucas), a study identifying four turning points in brain connectivity, and a National Emergency Briefing in London addressing the escalating climate crisis and its health, security, and economic implications.

Sperm Origins

Experts discuss how sperm proteins and genes trace back to a single-celled ancestor that predates animals, suggesting we are all sperm that later acquired a multicellular stage. The dialogue also touches on sperm diversity, head versus tail evolution, and intriguing examples across species.

Brain Turning Points

The episode reports four key brain-wiring turning points at ages 9, 32, 66, and 83, with adolescence potentially extending into the early 30s, a finding that reshapes how we think about cognitive development and aging.

Climate Emergency Briefing

Clinicians, ecologists, and economists discuss how climate breakdown affects health, security, biodiversity, and the economy, emphasizing interconnected risks and the case for rapid policy action.

Introduction and Themes

New Scientist Weekly presents a multi-segment discussion that connects biology, neuroscience, and climate science. The conversation is anchored by Dr Penny Sasha and Dr Rowan Hooper as they unpack a recent study on the evolutionary origin of sperm, reveal discoveries about the brain's changing wiring across the lifespan, and report from a National Emergency Briefing in London focused on climate risks and societal resilience.

Segment 1: The Last Universal Sperm Ancestor and Sperm Origins

The hosts examine the concept of LUCA, the Last Universal Common Ancestor, and apply it to sperm biology. Arthur Maat and colleagues at Cambridge reconstruct a hypothetical ancestral sperm by comparing the proteins and genes of modern sperm across animals. They identify a toolkit of around 300 gene families shared by sperm in diverse lineages and find that related single-celled organisms like coanoflagellates possess analogous machinery such as flagella, implying a pre-animal, unicellular origin for the sperm toolkit. The discussion emphasizes a provocative view: we are all sperm that acquired a multicellular body later in evolution. The conversation also covers the diversity of sperm forms, including very long sperm in certain beetles and the practice of sperm fusion in some mammals, illustrating how tail and head structures have different evolutionary trajectories.

Segment 2: Sperm Evolution, Anatomy, and the Testes Conundrum

Attention shifts to how sperm have adapted to different reproductive ecologies, with head structures driving much innovation but tails remaining relatively conserved due to the universal requirement of swimming. The hosts discuss why male mammals often have external testes, exploring hypotheses such as cooler temperatures for sperm development and the display hypothesis, where external genitals might signal fitness. They weigh historical experiments and modern observations on scrotal evolution, including variations among species such as marsupials and aquatic mammals, and consider how these ideas fit into broader evolutionary logic about reproduction and performance under different environmental pressures.

Segment 3: Brain Wiring and Four Turning Points

The episode then shifts to neuroscience, where a study of MRI data from thousands of individuals identifies four major turning points in brain wiring: at birth to age 9, age 9 to 32, age 66 to 83, and 83 to 90. The 9 to 32 window is highlighted as a period of increasing efficiency in inter-regional connections, possibly extending adolescence into the early 30s, while later phases show a gradual decline in long-range connectivity and a shift toward hub-centric processing with aging. The discussion also differentiates white matter wiring from grey matter pruning and notes the variability among individuals and populations, stressing that these patterns are population averages and not destiny for any one person. The potential links between these brain changes and cognitive reserve, mental health, and dementia risk are explored, along with caveats about demographic representation in the data.

Segment 4: Climate Emergency Briefing and Interconnected Risks

The final main segment reports on a London National Emergency Briefing, featuring experts across climate science, health, and economics. Speakers warn of escalating climate risks and possible societal disruption, including potential food security shocks, price volatility, and mental health impacts. The briefing underscores the connections among biodiversity loss, climate breakdown, health, security, and the economy, arguing that proactive policy measures and rapid deployment of “non-sexy” yet effective technologies could reduce risk. Public support for climate action is reported as stronger than political rhetoric suggests, and experts call for scaled action now rather than later. The episode closes with encouragement to engage in science-based action and to explore the briefing’s resources for more information and practical steps.

Conclusion

Across these segments, the episode links deep questions of origin and development in biology with practical concerns about aging brains and global climate risk, illustrating how diverse scientific threads converge on managing the future of life on Earth.