The questions that kids ask about science aren’t always easy to answer. Sometimes, their little brains can lead to big places that adults forget to explore. That is what inspired our series Science Question From A Toddler, which uses kids’ curiosity as a jumping-off point to investigate the scientific wonders that adults don’t even think to ask about. The answers are for adults, but they wouldn’t be possible without the wonder that only a child can bring. I want the toddlers in your life to be a part of it! Send me their science questions, and they may serve as the inspiration for a column. And now, our toddler …
“Who would win in a fight — an anaconda or a Komodo dragon?” — Glen, age 4
I’ll be honest. I was ready to throw down for the Komodo dragon here. Granted, a South American water snake and an Indonesian land lizard are unlikely to ever meet up in real life. But if they did, the Komodo dragon is longer and heavier than a football player1 and capable of running at speeds of 11 mph. It has claws and serrated, shark-like teeth that can rip through any flesh. Also, it’s venomous. Seems like a no-brainer.
But I was wrong. In a deeply unscientific poll of 125 herpetologists2 — folks who study reptiles and amphibians for a living — that I conducted for this article, nearly 66 percent favored the anaconda. And who wins a fight between two different species matters. It affects how much money my editor now owes me, for one thing. More importantly, though, it matters because real-world battles between different species can shape how those species evolve and where they live. There’s even the possibility that, someday in the future, interspecies warfare could save your life.
But let’s go back to Glen’s awesome reptile cage match for a moment. First, why were the herpetologists so confident in the anaconda? It seemed to come down to two factors. Anacondas can get a LOT bigger than Komodo dragons — like 29 feet long and 500 pounds compared with 10 feet and 330 pounds — and anacondas have been known to eat the species of toothy, clawed lizards that do live in their native environment.
The herpetologists’ votes also seemed to come under a bit of duress — I got multiple messages suggesting that the outcome was highly dependent on whether the fight took place in water (advantage: anaconda) or on land (advantage: dragon). Some scientists pointed out that the fight was likely to end along the lines of mutually assured destruction, with the anaconda maybe surviving a little longer because the dragon’s venom is slow acting. Nine of the herpetologists even refused to vote one way or the other — leaving the poll blank in protest. In the words of Harvey Lillywhite, who is a professor of biology at the University of Florida and was part of that group, “This is not a good ‘yes-no’ question. … Also, the word ‘fight’ is of questionable meaning.”
You, as a non-expert, adult reader, may have some questions about the meaning of interspecies conflict, too. After all, we’re all used to the idea that different species attack each other. How else would you describe a lion eating a gazelle? But when scientists talk about interspecies aggression, they aren’t talking about the relationship between predators and prey. Instead, they’re talking about what happens when species pick fights with each other that could have been avoided without anybody starving to death.
In these fights, there’s no clear winner or loser — just like with the anaconda and Komodo dragon. If two species of dolphins start slap-fighting each other, for example, they’re likely to end up in a place where nobody comes out ahead. “One might be dominating and winning,” said Gregory Grether, professor of biology at the University of California, Los Angeles. But in terms of lost time, energy, injuries and lost access to resources, “they’d both be better off not having to engage to begin with.”
And yet they do. What makes interspecies warfare interesting to the scientists who study it is precisely that it doesn’t appear to make a lot of sense. A shallow understanding of evolution would suggest that a species ought to evolve away from having to fight with another — that’s the entire idea behind a species developing an ecological niche that only it can fill, after all. But interspecies aggression appears to be pretty common. In a 2010 meta-analysis of 126 published papers on aggression between species, researchers found that 78 percent of the 459 experiments in those studies found interspecies conflict happening.
This is particularly true among species that are more closely related — western bluebirds (Sialia mexicana) vs. mountain bluebirds (Sialia currucoides), for instance. These two species compete for nesting spaces and food in newly burned forests. In 2015, researchers from the University of Arizona published a paper showing that competition between the two could actually contribute to evolutionary change. During times of intense competition, female western bluebirds laid eggs with higher levels of the hormone androgen, producing male offspring that were more aggressive and more likely to fight for territory. Over time, that hormone change can end up making one species of bluebirds dominant in a place that could, technically, support both species.
In this way, Grether said, interspecies competition can explain why a species that could live in a certain environment doesn’t. “We’re stumbling on lots of cases where the habitat seems suitable, but this interaction between species prevents further range extension,” he said. And it could be that the reason we see so much interspecies conflict is that we just happen to spot two species in the process of figuring out what their niches are.
But Grether’s research suggests that interspecies conflicts can sometimes represent an evolutionary stalemate — where two species are doomed to keep beating on each other forever, like a cartoon coyote and roadrunner, because they can’t seem to evolve a way out of the problem. Grether studies damselflies — winged insects similar to dragonflies — and he’s found that different species of damselfly males compete for the same females even though they can’t successfully mate cross-species. The females of both species look very much alike, Grether said, and males have only a few seconds to decide whether to grab a female while she’s flying by — so they usually just go for it. But because the males aren’t picky and the females are able to procreate no matter what they look like, there’s no pressure on the females of the two species to become more distinguishable from each other. The males keep grabbing (and fighting over) whoever comes by. The females keep on looking the same. “It’s an evolutionary catch-22,” Grether said.
Interspecies competition could be great for humans, however. Specifically, I’m talking about the microscopic battles happening inside our own bodies — conflicts that could be harnessed to protect us from deadly disease.
Joseph Mougous, professor of microbiology at the University of Washington, studies the interactions between different species of bacteria in the human gut that can kill each other on contact by secreting toxic proteins. But those weapons can also produce friendly fire — a bacterium could split in two to reproduce and then accidentally kill its own daughter cell.
Because of this, Mougous said, bacterial species have developed immunity genes that protect themselves from their own toxins. Mougous’s research suggests that these genes can be shared between species. In an environment like the gut, with lots of different species living together and sharing immunity factors, that sharing can produce a stalemate in interspecies aggression where nobody can kill anybody else, no matter how much they might want to. You could almost call it a community — a community that protects its own and kills any invading bacteria that don’t have all the immunity genes needed to survive.
And that’s where interspecies aggression turns into a good thing for us. For example, we know probiotics — “good” bacteria introduced to the body via pill or powder with the intention of improving our physical health — don’t last long in the human body. “They come in one end and out the other in a hurry … because they don’t have the defensive pathways to survive,” Mougous said. Studying bacterial interspecies aggression could help us develop probiotics that work better and last longer. It’s also not unreasonable to imagine a future in which we could harness the power of interspecies aggression to protect skin injuries against dangerous infections, Mougous said. Doctors could brush a topical coating of community-oriented bacteria on an open wound, choosing bacteria that won’t harm humans but will keep the harmful bacteria out.
So while giant reptile fights bring to mind the poster for the cinema classic “Alien vs. Predator” — “whoever wins, we lose” — interspecies battles on the microscopic scale could be exactly the opposite.