Of Stink Bugs and Men

.. and Africa.

by Doctor Science

Like many people in the mid-Atlantic US, I've been noticing a lot of stink bugs this summer. I figured there was some kind of weather-related stink bug boom until a story about them popped up on the NY Times. It turns out that these are actually new and different stink bugs, a recent accidental arrival from China. Most species that are introduced to a new continent don't make it, but when they do they can run wild, run free! and be extremely destructive away from their home-grown predators and parasites. Researchers are looking into introducing stink-bug-specialist parasitic wasps to control them, but that will take several years -- and it looks as though the wasps are killed by agricultural insecticides to which stink bugs are naturally resistant. Oops.

But what does this have to do with Africa?

Last year, I read Africa: A Biography of the Continent by native South African John Reader. In his prologue, he states his central question of (sub-Saharan) African* history:

While the out-of-Africa population grew from just hundreds to 200 million in 100,000 years, and rose to just over 300 million by AD 1500, the African population increased from 1 million to no more than 20 million in 100,000 years, and rose to only 47 million by AD 1500. And the disparity persists to the present day, though both groups were descended from the same evolutionary stock. Both groups inherited the talents and physiological attributes that evolution had bestowed during the preceding 4 million years in Africa.

Why did the migrant population grow so much faster? Or, to approach the disparity from another direction, what prevented the African population from achieving similar levels of growth? Since the ancestral genetic stock was identical, the divergent history of the two groups implies that Africa itself was in some way responsible.

My answer to Reader's question should be obvious. Once you think of Homo sapiens as an invasive species -- like stink bugs, or kudzu, or cane toads -- the answer is blindingly obvious.

The only part of the world to which human beings are truly native is sub-Saharan Africa. Ecologically, there are no "native peoples" anywhere else in the world, because outside of Africa Homo sapiens is always an invasive alien species. You'd think that the fact that we're adapted to Africa in a way we aren't adapted to anywhere else would be an advantage, but it turns out not to work that way. The overwhelming factor, for H. sapiens as well as stink bugs, is that our native range is adapted to us -- humans or bugs become dangerously invasive when we can escape not just the limited space of our native range, but the constraints on our population that come from other co-native species: predators or parasites (including diseases).

When scientists try to find a way to control an invasive species, they generally focus on one or a very few parasites, predators, or diseases from the species' native range, hoping that will be enough. But once you think of humans as an invasive species, it looks like a less workable strategy: it's quite clear that there is no single disease, much less a predator, that historically controlled human populations in Africa. There are a whole swarm of diseases that are prevalent in Africa -- malaria, schistosomiasis, hepatitis, yellow fever -- none of which has had a population-controlling effect outside of it.

My suspicion is that the African population is more like Gulliver on the Lilliput beach: held down by many, many ropes, no one of which is very strong. Most of those ropes are probably very small parasites or microbes; many may be part of the microbiome -- the web of bacteria, viruses, and single-celled organisms that surrounds and penetrates every human body.

 

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* throughout this post, when I say "Africa" I mean "Africa south of the Sahara" as a biogeographic region.

Comments

[efgoldman]

I saw elsewhere (no cite or link, sorry) that GOBP governors and congresspersons from the effected area are begging the :::gulp::: fedrill gummint to DO something.

That's the selfsame fedrill gummint, of course, that is the root of all evil run by the commie fascist socialist imam Barak Hussein...

Whatcha' gonna do?

[geographylady]

interesting observation. i'm trying to figure out how to work it into my geography class.

[Countme?]

Yes EF, here's one cite:

http://www.bobcesca.com/blog-archives/2010/09/the_politics_of_5

My small government solution is the following: only registered Democratic farmers will receive government assistance combating the stink-bug infestation, whereas registered Republican farmers will receive none. In fact, if the latter's land is infested (with stinkbugs and Republicans), their crops will be handled like the cattle herds in England with hoof and mouth.

We can't permit elite government scientists to impose their big government solutions on Galt's Gulch at taxpayer expense.

Of course, if the Bush tax cuts are left intact, I suppose we could wait around for a private sector entity to get off its duff and come up with a solution, once they get over their uncertainty.

[bobbyp]

At long last the real reason for the introduction of Scotch Broom, Kudzu, and English Ivy is revealed.

How diabolical can you get?

[Countme?]

It's election season, so everything is close to on-topic, right? :

http://andrewsullivan.theatlantic.com/the_daily_dish/2010/10/donald-duck-joins-the-glenn-beck-movement.html

The inchoate anger of the Tea Party movement, unleashed from its astro-turf bonds and infiltrated by the truly vicious pissed-off segment of American society, the dispossesed, the uninsured, the jobless, once Dick Armey is dead, will turn against Wall Street and the Republican Party, and kill them both.

They may murder (the NRA and Redvermin think have armed them to do so) the Democratic Party first, but it will be settled for good in justice's favor.

There will be no government left to interpose itself between justice and vengeance.

Poor Goofy.

[Countme?]

More stinkbugs try to infest Ireland after invading Ireland with their free-market stink-bug policies:

http://www.balloon-juice.com/2010/10/03/monkey-business/

[Countme?]

Stinkbugs by any other name. Turns out the private sector (not that there is anything wrong with the private sector) discovered stinkbugs and planted them to infest us forever.

http://www.balloon-juice.com/2010/10/03/monkey-business/

[Ugh]

because outside of Africa Homo sapiens is always an invasive alien species

Where have I heard something like this before? Oh yeah...

AGENT SMITH
Every mammal on this planet instinctively develops a natural equilibrium with the surrounding environment. But you humans do not. You move to an area and you multiply and multiply until every natural resource is consumed and the only way you can survive is to spread to another area.

He leans forward.
AGENT SMITH
There is another organism on this planet that follows the same pattern. Do you know what it is? A virus.

He smiles.
AGENT SMITH
Human beings are a disease, a cancer of this planet. You are a plague. And we are... the cure.

[Countme?]

Here's the problem with rants. The links become inaccurate. Here's the correct link for my 8:46 pm:

http://www.balloon-juice.com/2010/10/03/progress-5/

[Matt McIrvin]

Agent Smith doesn't know a lot about mammals.

[Gary Farber]

"Agent Smith doesn't know a lot about mammals."

He didn't have a need to know, so he came up with cockamamie reasons of his own. Turns out Agents are more like humans than they realize.

[johnw]

Well, it's fairly obvious that humans experienced environmental release after leaving Africa, but what are the evolutionary implications? When our ancestors came out of Africa, did they out-compete Neanderthal and other early humans because they brought with them both diseases and their own immunity?

[Calming Influence]

Oh yeah? Well you stink worse!

Wait; sorry, I don't care for stink bugs either.

[Collins Pt]

Great topic here.

[-spamvertisement snip-]

[Rob in CT]

Oh, look at the cute little bot.

[Ginger Yellow]

Carl Zimmer's book Parasite Rex is very informative on this topic.

[Fuzzy Face]

Huh - you've been quoted in the Atlantic by Megan McCardle...

This is tongue-in-cheek, right? I mean, McCardle is an economist, so I wouldn't expect her to see the problems with the argument, but IIRC Dr. Science majored in the life sciences.

[hairshirthedonist]

Am I really the first to bring up Guns, Germs and Steel on this thread? I was sure someone would have beat me to it. In any case, I think Jared Diamond and Doctor Science may have more than a few differences of opinion, or maybe not. I'm not sure.

[McKinneyTexas]

You move to an area and you multiply and multiply until every natural resource is consumed and the only way you can survive is to spread to another area.

That would explain the pre-columbian population explosion in the Western Hemisphere. And in Australia. Or not.

[Scott P.]

While the out-of-Africa population grew from just hundreds to 200 million in 100,000 years, and rose to just over 300 million by AD 1500, the African population increased from 1 million to no more than 20 million in 100,000 years, and rose to only 47 million by AD 1500.

"Only" 47 million? Africa has 20% of the world's land area, and in 1500 it apparently had 16% of the world's population. Considering the amount of space taken up by desert and dense jungle, that's not a huge discrepancy.

[Hogan]

Skinner: Well, I was wrong; the lizards are a godsend.

Lisa: But isn't that a bit short-sighted? What happens when we're overrun by lizards?

Skinner: No problem. We simply release wave after wave of Chinese needle snakes. They'll wipe out the lizards.

Lisa: But aren't the snakes even worse?

Skinner: Yes, but we're prepared for that. We've lined up a fabulous type of gorilla that thrives on snake meat.

Lisa: But then we're stuck with gorillas!

Skinner: No, that's the beautiful part. When wintertime rolls around, the gorillas simply freeze to death.

DocSci: You've probably already read Alfred W. Crosby's _Ecological Imperialism_, but if not, I recommend it.

[Hogan]

Huh. On review, that last paragraph looks like another piece of the previous dialogue. Which it isn't.

[Doug]

Was it in Guns, Germs and Steel that I read the speculation that in our ancestral home we had hunted to death all the easily domesticable draft animals before we were at the stage where we could use them to multiply food production?

[Jacob Davies]

DocSci: While the out-of-Africa population grew from just hundreds to 200 million in 100,000 years, and rose to just over 300 million by AD 1500, the African population increased from 1 million to no more than 20 million in 100,000 years, and rose to only 47 million by AD 1500.

Scott P: "Only" 47 million? Africa has 20% of the world's land area, and in 1500 it apparently had 16% of the world's population. Considering the amount of space taken up by desert and dense jungle, that's not a huge discrepancy.

Right, the low initial population numbers for "rest of world" make for a good percentage-increase story, but the real question is, did the rest-of-world population increase to a higher level in terms of density (or density-related-to-land-productivity)?

I do think the story of human evolution and movement is fascinating, and the distinct genetic differences between sub-Saharan Africans and other humans are really, really interesting - that bit about the majority of the (limited) genetic variation in the human species being in African genes, for instance. But I'm not sure the story even in broad terms is "Why did humans do so much better outside of Africa?"

Humans did exceptionally well in Africa too.

Not that the idea of a limiting personal microbiome isn't also really interesting. I always wonder to what extent our fellow-travelers (with non-human DNA) are involved in, say, cognition. Do my intestinal microflora send delegations to my brain to have their interests represented? If not, how do they communicate their needs and wants as part of a symbiotic system in which they supply valuable services?

[hairshirthedonist]

Was it in Guns, Germs and Steel that I read the speculation that in our ancestral home we had hunted to death all the easily domesticable draft animals before we were at the stage where we could use them to multiply food production?

My (possibly flawed) recollection is that there were very few domesticable animals, perhaps none of which were draft animals, in sub-Saharan Africa. I don't remember if that was a result of earlier human hunting.

I specifically remember Diamond mentioning how onery zebras were as compared to horses, and posing a "what if" regarding fictional domesticated rhinos being riden into war, possibly changing many outcomes in African history, particularly as regards European colonization.

[Hogan]

fictional domesticated rhinos being riden into war,

No no, that definitely happened. I saw it in _300_. Or maybe it was a Frank Frazetta comic.

[liberal japonicus]

Here's Diamond's point. I also found that if you Google for Jared Diamond zebras, you call up a fragrant mix of sites. One post says

Diamond’s argument isn’t so much wrong as incomplete. He’s a super smart Jew ...

I leave it to the reader to imagine the rest of the rant.

Also, upthread, johnw used the term 'environmental release'. Is that the technical term? Googling it finds a lot about the release of various kinds of crap in the environment, so if its not the term of art, it should be.

[McKinneyTexas]

I saw it in _300_. Or maybe it was a Frank Frazetta comic.

It was Meet the Spartans.

[RogueDem]

Ecological release is the technical term.

[liberal japonicus]

Thanks RogueDem.

[russell]

domesticated rhinos

Dude, that is only going to end in tears.

[Jim Parish]

Dude, that is only going to end in tears.

With both pronunciations, even.

[Philip Schienbein]

"The only part of the world to which human beings are truly native is sub-Saharan Africa. Ecologically, there are no "native peoples" anywhere else in the world, because outside of Africa Homo sapiens is always an invasive alien species."

The above cannot be construed as an accurate statement in any sense.

Our immediate (and direct)ancestor Homo erectus was found from Western Europe to Oceania. Later Homo heidelbergensis who is also the immediate ancestor of H. sapiens idaltu and H. neanderthalensis has been found outside of Africa.
And now that we know that all humans living outside of sub-Saharan Africa have a significant amount of Neanderthal ancestry (an exclusively Eurasian species), we can confidently say we have been native in one form or another, whether as H.erectus, H.neaderthalis, or H.sapiens, to the entirety of the "Old World" for at least 1.8 million years.

It is only in the Americas were this could possibly be true, but then we would have to say the same about the gray wolf, bison, mammoth, armadillo, american lion, etc...

As for the term "invasive alien species", that could apply to 99.99% of every species that has ever existed. Every species has expanded it range at one point or another.