25 July 2011

I will give you a reason to fear the night

The lion wasn’t roaring.

It was making sounds, all right, while I was sitting next to the lion enclosure in the Melbourne Zoo. Metal fences separated the lions and me when one started vocalizing.

The lion wasn’t growling, either. It’s hard to describe the sound it was making. It was a raspy, open mouthed sound, almost like someone breathing hard after exercise. But the lion was just walking slowly, not in any way winded.

But that sound had so much power.

I think I almost stopped breathing when I heard the lion, and blew out a “Whoa”-like sound when it stopped. The phrase “spine tingling” described the sound and my response to it. You could feel the size of the animal making that sound.

I never felt so vulnerable in my entire adult life.

When I heard that sound, I stopped thinking of myself as a fairly tall man in an urban setting, and suddenly imagined what would be different if that metal didn’t separate us. I understood as I never had before, in that deep in your bones kind of way, how completely helpless a human faced with a lion would be. No wonder that lions made such a deep mark on human culture.

ResearchBlogging.orgThat experience sprung back to my mind when I saw the title of a new paper on lion attacks on humans. The authors compiled over 20 years of data on lion attacks on humans and other animals to figure out when lions pose the greatest threat.

After sorting through over 1,000 attacks in Tanzania – including what must have been a slightly distressing task of following up and doing interviews about 500 of the attacks – Packer and colleagues found a pattern that is surprisingly easy to describe.

First, lions are most likely to attack humans right after sundown.

Second, the risk increases in the nights after the full moon. The authors claim this pattern claim other lion prey suffer elevated risk both before and after the full moon, not just after it as with humans. (This conclusion is based on observations of lions’ belly size rather than actual attack records.)

This part of the research is sold and interesting, albeit perhaps slightly plagued by some strange decisions in the graphics. For instance, Figure 1 has regression lines that the authors say are “only presented to provide a visual guide to the overall trends.” I’m not sure what that means, but I suspect it means those lines are meaningless and could have been left out.

The paper disappoints in the introduction (one paragraph) and discussion (two paragraphs). The paper is a super short four pages, excluding all the supplemental materials, so it’s not as though the authors didn’t have the space to elaborate a little.

The authors make the speculative claim that these results explain two human behaviours: Why humans are afraid of the dark, and why people associate the full moon with trouble.

The first one is certainly the less controversial idea of the two. Let me put it this way. This is not a mistakes our ancestors could not have made if they wanted to survive:

I will note that for centuries, human attacks on other humans were also widely reported to have occurred at night. Any unease with darkness we inherited from our ancestors could certainly have been enhanced by other dangers.

The idea that these patterns might explain why humans associate the full moon with trouble is not well supported. Packer and colleagues rightly note that lions used to have a wider range, but they say:

(T)igers, jaguars and leopards still co-exist with people in Asia, Africa and tropical America.

They are implying that all those big cats are likely to have the same preference for attacking humans in the nights following the full moon, just like lions. But there are no data supporting that. Different species are different. Humans aren’t like other prey species to lions, so it may well be that lions aren’t like other predator species to humans.

Although we are safest from lion attacks during well-lit nights, the full moon accurately indicates that the risks of lion predation will increase dramatically in the coming days.

But that’s not any “attitude” or “superstition” about the full moon that I’ve ever heard. The superstition isn’t that monsters come out after the full moon goes away, it’s that humans act differently during the full moon. It’s rather odd to offer an explanation for attitudes that people don’t believe.

That said, I freely admit I have not completed an exhaustive cross-cultural study of human superstitions regarding the moon. But the paper is rather light on cultural references in that regard, too.

I’m puzzled as to why the authors wanted to play up this strange evolutionary psychology angle to the story. Speculative “just so” stories of adaptation seem so insignificant in a project about humans getting attacked and eaten by lions.

Just like I felt looking across the zoo at that lion.

External links

Other takes on this paper:

Moon wanes, Leo rises by Ed Yong
The lion eats tonight by Scicurious


Packer C, Swanson A, Ikanda D, Kushnir H. 2011. Fear of darkness, the full moon and the nocturnal ecology of African lions. PLoS ONE 6(7): e22285. DOI: 10.1371/journal.pone.0022285

Photo by by jsohn1@pacbell.net on Flickr; used under a Creative Commons license.

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