Why do bats spread so many diseases? They’re evolutionary marvels.
There are more bats than you think. After rodents, bats make up about a fifth of all mammals, with more than 1,500 species of winged moths. But it is this vast biodiversity that also contributes to their (somewhat undeserved) reputation as vectors of disease. Biologists say 50 million years of evolutionary adaptation make bats uniquely suited not only to contract and spread pathogens, but also to resist them.
“[Infectious disease] “People are always looking for an excuse as to why bats are magical, and the truth is that bats have just been exposed to a lot of things and selected for those genes accordingly.”
Wellehan argues that the most important factor for an animal population to thrive from an evolutionary perspective is its genetic diversity. A wide spectrum of variation greatly increases the chances that at least some individual animals will have effective immunity genes against any new pathogenic strains that might come their way. Ideally, these immune creatures survive long enough to reproduce and pass on these valuable genes to the next generation of offspring.
“When I first heard about Darwin and evolution, ‘survival of the fittest,’ I assumed it meant ‘smartest, fastest, and strongest,’ but if you look at our genomes, [it] It turns out that’s not true,” Wellehan explained. “The selected genes are mostly related to the immune system.”
In bats, these pathogens spread even more because many species live in highly social colonies. Overall, this means that bats transmit diseases to each other in tandem with the genes needed to develop immunity better than most other animals.
But what can making animals dangerous is also what mainly distinguishes them from all other mammals: their wings. Flight has greatly expanded bat habitat over millions of years, allowing them to cross humanity’s artificially constructed geopolitical boundaries without a second thought. This is how disastrous pathogens like Ebola, the Nipah virus and even the SARS-CoV-2 virus that causes COVID-19 can wreak such havoc on society.
That said, don’t start blaming bats just yet. They simply live in a world increasingly disrupted by the encroachment of society. This avoidable close contact between humans and bats is what can ultimately cause disease to spread between species.
“Transmission of pathogens to humans and conservation efforts go hand in hand. When populations are under stress, ecological balances shift and zoonotic jumps occur,” Wellehan said. “It turns out that if we think of ourselves as something separate from nature, it doesn’t work very well.”
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