Mammal’s lifespans linked to brain size and immune system function, says new study

(Press-News.org) Why do cats generally live longer than dogs? New research suggests that longer livespans of mammals like cats could be linked to their bigger brains and more complex immune systems.

An international team of scientists led by the University of Bath studied evolutionary differences between mammal species and found that those with bigger brains and longer lifespans tend to invest more heavily in immune-related genes. Their findings show how broad genomic changes, rather than individual genes, shape longevity.

The researchers looked at the maximum lifespan potential of 46 species of mammals and mapped the genes shared across these species. The maximum lifespan potential (MLSP) is the longest ever recorded lifespan of a species, rather than the average lifespan, which is affected by factors such as predation and availability of food and other resources.

The researchers, publishing in the journal Scientific Reports, found that longer-lived species had a greater number of genes belonging to the gene families connected to the immune system, suggesting this as a major mechanism driving the evolution of longer lifespans across mammals.

For example, dolphins and whales, with relatively large brains have maximum lifespans of 39 and up to 100 years respectively, those with smaller brains like mice, may only live one or two years.

However, there were some species, such as mole rats, that bucked this trend, living up to 20 years despite their smaller brains. Bats also lived longer than would be expected given their small brains, but when their genomes were analysed, both these species had more genes associated with the immune system.

The results suggest that the immune system is central to sustaining longer life, probably by removing aging and damaged cells, controlling infections and preventing tumour formation.

The study shows that it’s not just small mutations (like in single genes or pathways) but larger genomic changes (duplication and expansion of whole gene families) can be crucial in shaping lifespan.

Dr Benjamin Padilla-Morales, from the Milner Centre for Evolution and the University of Bath’s Department of Life Sciences, was first author of the study.

He said: “It’s been known for a while that relative brain size is correlated to longevity – the two characteristics have a shared evolutionary path, and having a larger brain potentially offers behavioural advantages.

“However, our study also highlights the surprising role of the immune system not just in fighting disease, but in supporting longer life across mammalian evolution.

“Bigger-brained species don’t just live longer because of ecological reasons; their genomes also show parallel expansions in genes linked to survival and maintenance.

"This shows that brain size and immune resilience seem to have walked hand-in-hand in the evolutionary journey toward longer lives.

The researchers next plan to investigate the cancer-related genes highlighted in the study, to further unpick the relationship between these genes and lifespan to understand why there is such a difference in lifespans in mammals.

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