Corante

Corante: technology, business, media, law, and culture news from the blogosphere
<$MTBlogName$> OUR PUBLICATIONS:
Corante Blogs

Corante Blogs examine, through the eyes of leading observers, analysts, thinkers, and doers, critical themes and memes in technology, business, law, science, and culture.

The Press Will Be Outsourced Before Stopped

Vin Crosbie, on the challenges, financial and otherwise, that newspaper publishers are facing: "The real problem, Mr. Newspaperman, isn't that your content isn't online or isn't online with multimedia. It's your content. Specifically, it's what you report, which stories you publish, and how you publish them to people, who, by the way, have very different individual interests. The problem is the content you're giving them, stupid; not the platform its on."
by Vin Crosbie in Rebuilding Media

Travels In Numerica Deserta

There's a problem in the drug industry that people have recognized for some years, but we're not that much closer to dealing with it than we were then. We keep coming up with these technologies and techniques which seem as if they might be able to help us with some of our nastiest problems - I'm talking about genomics in all its guises, and metabolic profiling, and naturally the various high-throughput screening platforms, and others. But whether these are helping or not (and opinions sure do vary), one thing that they all have in common is that they generate enormous heaps of data.
by Derek Lowe in In the Pipeline

Disrobing the Emperor: The online “user experience” isn't much of one

Now that the Web labor market is saturated and Web design a static profession, it's not surprising that 'user experience' designers and researchers who've spent their careers online are looking for new worlds to conquer. Some are returning to the “old media” as directors and producers. More are now doing offline consulting (service experience design, social policy design, exhibition design, and so on) under the 'user experience' aegis. They argue that the lessons they've learned on the Web can be applied to phenomena in the physical and social worlds. But there are enormous differences...
by Bob Jacobson in Total Experience

Second Life: What are the real numbers?

Clay Shirky, in deconstructing Second Life hype: "Second Life is heading towards two million users. Except it isn’t, really... I suspect Second Life is largely a 'Try Me' virus, where reports of a strange and wonderful new thing draw the masses to log in and try it, but whose ability to retain anything but a fraction of those users is limited. The pattern of a Try Me virus is a rapid spread of first time users, most of whom drop out quickly, with most of the dropouts becoming immune to later use."
by Clay Shirky in Many-to-Many

The democratisation of everything

Over the last few years we've seen old barriers to creativity coming down, one after the other. New technologies and services makes it trivial to publish text, whether by blog or by print-on-demand. Digital photography has democratised a previously expensive hobby. And we're seeing the barriers to movie-making crumble, with affordable high-quality cameras and video hosting provided by YouTube or Google Video and their ilk... Music making has long been easy for anyone to engage in, but technology has made high-quality recording possible without specialised equipment, and the internet has revolutionised distribution, drastically disintermediating the music industry... What's left? Software maybe? Or maybe not."
by Suw Charman in Strange Attractor

RNA Interference: Film at Eleven

Derek Lowe on the news that the Nobel Prize for medicine has gone to Craig Mello and Andrew Fire for their breakthrough work: "RNA interference is probably going to have a long climb before it starts curing many diseases, because many of those problems are even tougher than usual in its case. That doesn't take away from the discovery, though, any more than the complications of off-target effects take away from it when you talk about RNAi's research uses in cell culture. The fact that RNA interference is trickier than it first looked, in vivo or in vitro, is only to be expected. What breakthrough isn't?"
by Derek Lowe in In the Pipeline

PVP and the Honorable Enemy

Andrew Phelps: "Recently my WoW guild has been having a bit of a debate on the merits of Player-vs.-Player (PvP) within Azeroth. My personal opinion on this is that PvP has its merits, and can be incredible fun, but the system within WoW is horridly, horribly broken. It takes into account the concept of the battle, but battle without consequence, without emotive context, and most importantly, without honor..."

From later in the piece: "When I talk about this with people (thus far anyway) I typically get one of two responses, either 'yeah, right on!' or 'hey, it’s war, and war isn’t honorable – grow the hell up'. There is a lot to be said for that argument – but the problem is that war in the real historical world has very different constraints that are utterly absent from fantasized worlds..."
by Andrew Phelps in Got Game

Rats Rule, Right?

Derek Lowe: "So, you're developing a drug candidate. You've settled on what looks like a good compound - it has the activity you want in your mouse model of the disease, it's not too hard to make, and it's not toxic. Everything looks fine. Except. . .one slight problem. Although the compound has good blood levels in the mouse and in the dog, in rats it's terrible. For some reason, it just doesn't get up there. Probably some foul metabolic pathway peculiar to rats (whose innards are adapted, after all, for dealing with every kind of garbage that comes along). So, is this a problem?.."
by Derek Lowe in In the Pipeline

Really BAD customer experience at Albertsons Market

Bob Jacobson, on shopping at his local Albertsons supermarket where he had "one of the worst customer experiences" of his life: "Say what you will about the Safeway chain or the Birkenstock billionaires who charge through the roof for Whole Foods' organic fare, they know how to create shopping environments that create a more pleasurable experience, at its best (as at Whole Foods) quite enjoyable. Even the warehouses like Costco and its smaller counterpart, Smart & Final, do just fine: they have no pretentions, but neither do they dump virtual garbage on the consumer merely to create another trivial revenue stream, all for the sake of promotions in the marketing department..."
by Strange Attractor in Total Experience

The Guardian's "Comment is Free"

Kevin Anderson: "First off, I want to say that I really admire the ambition of the Guardian Unlimited’s Comment is Free. It is one of the boldest statements made by any media company that participation needs to be central to a radical revamp of traditional content strategies... It is, therfore, not hugely surprising to find that Comment is Free is having a few teething troubles..."
by Kevin Anderson in strange
In the Pipeline: Don't miss Derek Lowe's excellent commentary on drug discovery and the pharma industry in general at In the Pipeline

The Loom

« The Tubercular Hominid | Main | A View From the Left (Sigh) »

August 23, 2005

Malaria For Brains

Email This Entry

Posted by Carl Zimmer

malaria cross-section.jpg

The red blob in this picture is a human red blood cell, and the green blob in the middle of it is a pack of the malaria-causing parasites Plasmodium falciparum. Other species of the single-celled Plasmodium can give you malaria, but if you're looking for a real knock-down punch, P. falciparum is the parasite for you. It alone is responsible for almost all of the million-plus deaths due to malaria.

How did this scourge come to plague us? In a paper to be published this week in the Proceedings of the National Academy of Sciences, scientists have reconstructed a series of molecular events three million years ago that allowed Plasmodium falciparum to make us its host. They argue that a change in the receptors on the cells of hominids was the key. Ironically, this same change of receptors may have also allowed our ancestors to evolve big brains. Malaria may simply be the price we pay for our gray matter.

To uncover this ancient history, the researchers compared the malaria humans get to the malaria of our closeest relatives, chimpanzees. In 1917, scientists discovered Plasmodium parasites in chimpanzees that looked identical to human Plasmodium falciparum. But when some ethically challenged doctors tried to infect people with the chimpanzee parasites, the subjects didn't get sick. Likewise, chimpanzees have never been known to get sick with Plasmodium falciparum from humans. In the end, scientists recognized that chimpanzees carry a separate species of Plasmodium, known today as Plasmodium reichenowi. Studies on DNA show that Plasmodium rechnowi is the closest living relative to Plasmodium falciparum--just as chimpanzees are the closest living relatives of humans.

The authors of the new study set out to find the difference between these parasitic cousins. They focused on how each species of Plasmodium gets into red blood cells. Every Plasmodium species uses special molecular hooks on its surface to latch onto receptors on the cell, and then noses its way through the membrane to get inside. The parasite has a number of hooks, each of which is adapted to latch onto particular kinds of receptors. One of the most important groups of receptors that Plasmodium needs to latch onto are sugars known as sialic acids, which are found on all mammal cells.

These sugars play a crucial but mysterious role in human evolution. As I've written here (and here), almost all mammals carry a form of the sugar called Neu5Ac on their cells, as well as a modified version of it, known as Neu5Gc. In most mammals, this modified form, Neu5Gc is very common. In humans, it's nowhere to be found. That's because the enzyme that converts the precursor Neu5Ac into Neu5Gc doesn't work. We still carry the gene for the enzyme, but it became mutated about three million years ago and stopped working.

Since chimpanzees make Neu5Gc and we don't, the researchers hypothesized that the two Plasmodium species must use different strategies to latch onto red blood cells. To test their hypothesis, they genetically engineered cells to produce the molecular hooks used by human Plasmodium falciparum, and other cells to produce the chimp parasite hooks. The researchers then mixed the engineered cells with red blood cells from humans and chimpanzees to see how well they attached. In another set of experiments, they made human blood cells more chimpanzee-like by adding Neu5Gc sugars to them, to see if the change helped the chimpanzee parasites attack them, or if it impaired the attacks of human parasites.

Their results show that humans are uniquely vulnerable to Plasmodium falciparum because our ancestors lost the Neu5Gc sugar. Plasmodium falciparum prefers to bind to Neu5Ac, the sugar we still carry. At the same time, the sugar we lost somehow blocks Plasmodium falciparum's hooks from latching onto Neu5Ac. That's why chimpanzees don't get sick with Plasmodium falciparum, despite carrying both kinds of sugars. On the other hand, we don't get sick with chimpanzee malaria, because Plasmodium reichenowi prefers attaching to Neu5Gc, the sugar we lost.

The scientists argue that some seven million years ago the common ancestor of chimpanzees and humans carried both kinds of sugars on their cells. This ancient ape would sometimes get sick with malaria, caused by the common ancestor of today's P. rechnowi and P. falciparum. This ancient parasite preferred to latch onto Neu5Gc to get into its host's blood cells.

Hominids then branched off from other apes, walking upright and moving out of the jungle into open woodlands. They still got sick with the old malaria, because they still produced both kinds of sugars. But then, about three million years ago, our ancestors lost the ability to make Neu5Gc. Initially this was a great relief, because the malaria parasites had a much harder time gaining entry into our cells.

But this relief did not last, the scientists argue. Sometimes mutant parasites emerged that did a better job of latching onto the one sugar hominids still made, Neu5Ac. They now could get into hominid red blood cells, while other Plasmodium parasites were still making do with the other apes. Over time these parasites evolved a better ability to infect hominids. But at the same time, they surrendered the ability to infect other apes, such as chimpanzees. Thus Plasmodium falciparum was born.

This new research is yet another example of how studying evolution yields new insights into medicine. (I've blogged before about similar examples with tuberculosis and HIV.) And it may also reveal something about the downside of our unique intelligence. Our ancestors lost Neu5Gc around the time that the hominid brain began to get significantly bigger than a chimp's.

In other animals, Neu5Gc is abundant on the cells of most organs, but exceedingly rare in the brain. It is very peculiar for a gene to be silenced in the brain, which suggests that it might have some sort of harmful effect. Once a mutation knocked out the gene altogether, hominids didn't have to suffer with any Neu5Gc in the brain at all.

Perhaps Neu5Gc limited brain expansion in other mammals, but once it was gone from our ancestors, our brains exploded. Along with a big brain, however, came our very own form of malaria.

Comments (14) + TrackBacks (0) | Category: Evolution


COMMENTS

1. Dave on August 23, 2005 04:39 PM writes...

Dolphins have relatively large brains in comparison to body mass. Is it known if their cells express as much Neu5Gc as other mammals?

Permalink to Comment

2. Doug on August 23, 2005 04:48 PM writes...

In this scenario, Carl has pointed out the following two genetic changes as the cause of Malaria's success against humans. First human ancestors lose the Neu5Gc sugar.

...because the enzyme that converts the precursor Neu5Ac into Neu5Gc doesn't work. We still carry the gene for the enzyme, but it became mutated...

This change is a result of a loss of function. This is an example of a mutation that provides a benefit, at least initially, but does nothing to suggest that new function is evolving, only "disolving".

Carl goes on to say:

But this relief did not last, the scientists argue. Sometimes mutant parasites emerged that did a better job of latching onto the one sugar hominids still made, Neu5Ac...But at the same time, they surrendered the ability to infect other apes, such as chimpanzees.

This event is not quite as specific as the previous one but it may share a similar problem. The change resulted in some of the parasites having a greater affinity for the Neu5Ac sugar but it came at a cost. The net result is that it is better at doing something that it already did which doesn't suggest the emergence of a new ability only the honing of a skill which came at the cost of losing function.

Carl writes, "This new research is yet another example of how studying evolution yields new insights into medicine."

This is an excellent example of the vague use of the term evolution. In saying "evolution" the audience generaly assumes a molecules-to-man or common descent definition. The truth is, in the first event, this is merely an instance of a loss of genetic information through mutation. While less is described about the second event it appears to be the result of natural selection selecting genes with greater affinity for Neu5Ac. Similar to the "unnatural" selection of farmers when attempting to increase the sugar content of the sugar beet. The genetic information already existed. It is therefore not evidence for common descent. If the research were conducted under a creationist methodology the result would be the same.

For a short article summarizing the creationist view on genetics I encourage you to read this article by Dr Lane P. Lester. He is a graduate of the University of Florida and holds a Ph.D. in genetics from Purdue University, and M.S. in ecology.

Genetics: No Friend of Evolution


Incidently, I hope you don't mind me referring to you as Carl instead of the more formal Mr Zimmer. It should not be regarded as a lack of respect. Your style strikes me as someone laid back enough not to care. There certainly are those that would take it as being condescending in nature. They would be wrong, but I'm happy to address you however you prefer.

Permalink to Comment

3. John S Bolton on August 23, 2005 05:39 PM writes...

This information fits with the idea that escape from malaria correlates positively with evolution of greater brain capacities. The spread of falciparum malaria, in its more modern and virulent form, into subtropical regions in classical antiquity, is associated with cultural and even population decline. Sallares and Coluzzi say that Rome suffered irreparably from this. Perhaps the intelligent design believers will explain that this was a delayed punishment of the ancients for their impiety.

Permalink to Comment

4. Richard Dietzel on August 23, 2005 06:05 PM writes...

So if we engineered Neu5Gc out of Chimps they might develop bigger brains? Cool.

Permalink to Comment

5. Nick (Matzke) on August 23, 2005 06:51 PM writes...

Creationists/IDers couldn't come up with a rigorous definition of "information increase" vs. "information decrease" if their life depended on it. They employ these terms in contradictory, arbitrary ways to discount any proposed example, and their arguments rely on a vague colloquial definition of "information" rather than anything resembling real information theory, which is entirely about the transmission and storing of messages, and not at all about "meaning". See:

Information Theory and Creationism
http://www.talkorigins.org/faqs/information/infotheory.html

For examples of the evolution of new genes with new functions, which should count as "new genetic information" in anybody's book, see:

Evolution of new information
http://www.evowiki.org/index.php/Evolution_of_new_information

And don't give us any rubbish about these just being examples of mere "reshuffling". If you end up with two different genes with different functions, where you originally had one, you've got more "information", using any reasonable definition.

Note to creationists: Not every writing on evolution is an attempt to your peculiar half-baked argument and quarter-baked definitions. In this post, was Zimmer trying to show how "new information", whatever the creationists mean by that slogan, arises? Clearly not.

PS: On a completely different topic: The loss of Neu5Gc in the brains of hominids could simply be another step in malaria avoidance. Malaria gets particularly deadly when it gets into the brain.

Permalink to Comment

6. Dan S. on August 23, 2005 10:14 PM writes...

Doug, you're missing the point again, I think. The entire scenario is based on chimps and humans evolving from a common ancestor; likewise with P. rechnowi and P. falciparum.

Frankly, I can't understand what you're saying. People have used genetics to study the relationship between different varieties and species of brassicas (although it gets a little hinky what with hybridization and weird plant stuff). They're descended from a common ancestor, although in this case many of the changes result from artificial selection. Sugar and table beets are related to swiss chard, they're related to spinach, and they're related to lambquarters (Chenopodium spp.) (I may be garbling the details here, but this is the general idea). Common descent. What's the problem?

In regard to the use of the word "evolution," remember that for science, beet to sugar beet and goo* to you (I do love that phrase, although adding in 'zoo' makes it too unwieldy, methinks) is essentially the same thing.

* living goo, though. Evolution doesn't deal with how life started, just what it did once it showed up.
___________

Something Carl is very good at is conveying the excitement - both of pure discovery and practical knowledge - of such research. Creationism, for its adherents, surely offers a kind of satisfaction, but it is of a very different nature. The scientific-wonder-and-productive-usefulness content of creationism seems to me to be essentially nil.

"So if we engineered Neu5Gc out of Chimps they might develop bigger brains? Cool."
Great, just what we need, intelligent poop-flingers . . .

. . . wait. Don't we have those already . . .?

Carl, any chance you'd toss something off here about recent work using genetic material extracted from ancient bones to work out evolutionary relationships, etc? Besides the thing with the horses, there was something cool released earlier this month about cougars, cheetahs, Miracinonyx and sabretooths . . . (oh my!)

Permalink to Comment

7. Dan S. on August 23, 2005 10:19 PM writes...

To be fair, the moral and ethical values content of evolutionary theory is likewise basically nonexistant.* Of course, nobody expects science to provide such things (unless they're very, very, very silly people . . .

* Of course, other (mainstream) religious interpretations and traditions, as well as many non-religious systems, offer these values, often without pretending to be science out of some strange sense of aggrieved inferiority.

Now back to the science . . .

Permalink to Comment

8. João Carlos on August 24, 2005 09:52 AM writes...

An interesting issue here is that is possible say that Plasmodium falciparum speciated 3 million years ago. When Plasmodium falciparum get stuck inside hominid red blobs it lost the hability to infect other primates red blobs. A reprodutive barrier was formed when that happened.

So, the data give us information about a speciation event. But creationists will lie and say that there is no proof that evolution will give speciation.

Creationists are liars, they forget that there is a Commandement to not lie inside the Bible. They will go to Hell. :p

João Carlos

Sorry the bad english, my native language is portuguese.

Permalink to Comment

9. Juan on August 24, 2005 10:31 AM writes...

Just curious:
Doug wrote:"If the research were conducted under a creationist methodology the result would be the same." Isn't this a self contradictory sentence or oxymoron.
I always thought that creationism is faith based: you belief in it or not. Period. Ergo, there can not be any methodology or research in creationism as they are mutually exclusive.

Permalink to Comment

10. ruidh on August 24, 2005 12:12 PM writes...

Doug,

Any mutation *increases* the information content of the species genome. The assertion that the mutution reduces information content of the genome is contrafactual.

Natural selection then operates to reduce that information content over long periods of time by selecting for strongly advantageous mutations and selecting against strongly disadvantageous mutations.

This ebb and flow of information over time is how evolution works. The net result is a tendancy to increase the information content of all genomes summed across all species corresponding to biological diversity.

Permalink to Comment

11. John S Bolton on August 24, 2005 09:24 PM writes...

Deletion mutants decrease information content. Mutations are randomization and thus destruction of genetic information, except for the very rare ones which actually improve the informational content functionally. If not so, then why would lethal mutagenesis be lethal, rather than an enrichment of genetic informational diversity?

Permalink to Comment

12. Dan S. on August 25, 2005 02:35 PM writes...

"Deletion mutants decrease information content. Mutations are randomization and thus destruction of genetic information"

I'm not a scientist, and don't even have much informal education about this, besides some pop science stuff. But as far as I can understand, this is missing the point that DNA isn't a book (although spoken and written language is so redundant that up to a a point even extensive garbage, duplications, etc, won't effect the the abilty to ndrstnd wht s bng sd dnt you gurble agree?). It's sort of a like a house blueprint that actually makes a house. If some of the details get changed, there might be a big problem - uh oh, no outside door! toliet draining into bedroom! loss of structural support!- it might not make a difference (unseen supporting beams are a different color), it might be an improvement - hey, a window there? I like that! There might be minute changes in insulation thickness, pipe material, wiring that might be improvements, problems, etc., depending on living conditions (thicker insulation in Alaska? Good. In Brazil? Maybe not?) But a lot more complex.

I don't get ID creationism. It insists that things are very complex, yet very simple. Doesn't seem interested in actually appreciating how cool thing are.

Permalink to Comment

13. John S Bolton on August 25, 2005 06:49 PM writes...

There is a huge disproportion between the chances for a good versus a bad mutation. If this is not so, why are we wasting so much time and money on protecting people from mutagenic radiation? Why aren't the bold seekers of new possibilities exposing their germline cells to radiation, if the chances for a good mutation are within range of what some might try? A deletion mutant which disbles part of the deliberate design, so to speak, only to frustrate a parasite, looks like natural selection, not like the intelligent way to make man.

Permalink to Comment

14. Homer on August 29, 2005 12:20 PM writes...

It would be interesting to see if there were any connection between this shift of sugar hooks and autism, which might be a mutation of human brain development processes. Might chimpanzee malaria be able to attach to the blood of autistic individuals?

Permalink to Comment


EMAIL THIS ENTRY TO A FRIEND

Email this entry to:

Your email address:

Message (optional):




RELATED ENTRIES
Talking at Woods Hole
Invisible Gladiators in the Petri Dish Coliseum
Synthetic Biology--You are There
Manimals, Sticklebacks, and Finches
Jakob the Hobbit?
Grandma Manimal
Hominids for Clinical Trials--The Paper
The Neanderthal Genome Project Begins