Why have sex with someone else when you could do it with yourself? [Not Exactly Rocket Science]
By directing the evolution of a worm, scientists have confirmed answers to the age-old question: "What is the point of having sex with someone else?" For most people, that would hardly be a tricky query but it's no reflection on the lives of evolutionary scientists that sex has been one of biology's oldest puzzles.
The problem is this: many creatures can reproduce by fertilising themselves instead of getting someone else to do it, and at first glance they should do much better individuals that cross-fertilise. For a start, they'd ensure that all of their genes reach the next generation, while mating with another individual reproduction halves their genetic legacy. And without having to find males, self-fertilising females should be able to produce twice as many offspring. This is the "two-fold cost of males".
And yet, cross-fertilisation is the more common strategy in the animal world, so it must have advantages that compensate for its cons. Scientists typically name two. The first is that by shuffling the genes of two parents, cross-fertilisation deals the next generation with a fresh genetic hand, better equipping it to rapidly adapt to changing environments, predators and parasites. The second is that having sex with someone else prevents harmful mutations from building up (the genetic defects that plague inbred families would be even worse in lineages that only ever have sex with themselves). They're the same reasons why sex itself is usually a better long-term solution than asexual cloning.
The problem is that both of these explanations have proven very difficult to test. But that didn't stop Levi Morran and colleagues from the University of Oregon, who demonstrated that both justifications are correct, by manipulating the evolution of the nematode worm Caenorhabditis elegans.
Like humans, C.elegans has two sexes but unlike us, they are males and hermaphrodites (with males making up just one in every two thousand individuals). Equipped with both sets of genitals, hermaphrodites worms can fertilise themselves without male help - far from being rude, telling C.elegans to go &$&! itself is a feasible lifestyle suggestion. Hermaphrodites could also mate with males, but they do that on less than one in 20 occasions.
However, the genetics of this animal are so well-known that Morran managed to use two mutations to create strains of C.elegans that either always had sex with themselves, or always had sex with other worms. Morran subjected these two engineered strains, as well as a normal one, to two challenges.
Some were exposed to a chemical called ethyl methanesulphonate (EMS) that quadruples the normal mutation rate of DNA, riddling their genomes with potentially harmful genetic changes. To make matters worse, they were placed in a new environment that should weed out all but the fittest individuals.
Despite these challenges, the strain that always mated with others were still successful after 50 generations and fared much better than the strain that only had sex with itself. Even the normal worms moved towards a cross-fertilising strategy under these harsh conditions. These are all signs that having sex with others else provides a way of purging harmful mutations from a population. By contrast, Morran estimated that the genetic burden carried by the worms that only ever mated with themselves would drive them to extinction after a few hundred generations.
Morran also exposed some of his worms to a bacterium called Serratia marcescens, a bacterium so virulent that it kills 80% of the worms it infects. It was a test of their ability to rapidly adapt to new challenges, and one that the cross-fertilisers passed with flying colours. They quickly evolved to resist the bacterium, while the populations that only mated with themselves did not. As before, the normal worms shifted towards a cross-fertilisation strategy when faced with the new threat.
So both theories are correct - compared to having sex with yourself, doing it with someone else provides a way of resisting harmful mutations and adapting quickly to new challenges. Morran says that species that evolve to always self-fertilise become trapped in an "evolutionary dead-end" and are "ultimately doomed to extinction".
Reference: Nature doi:10.1038/nature08496
More on sex and reproduction:
- Bdelloid rotifers - 80 million years without sex
- Frigid echidna sex - competition drives males to mate with hibernating females
- Why do female seed beetles prefer the sperm of inferior males?
- Male chimps trade meat for sex
- Termite queen avoids inbreeding by leaving a legacy of clones
Image: C.elegans by Bob Goldstein
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CBS News on swine flu testing: Fail! [Effect Measure]
A reader (h/t MVD) sent me this link to a "CBS News Exclusive," Study Of State Results Finds H1N1 Not As Prevalent As Feared. As far as I can see the main aim was to raise CBS News's profile and gain readership. That's what news organizations do. We hope they do it by good journalism. I think this is an example where the reporters just didn't have enough knowledge of what they were reporting and put the wrong spin on it.
The central claim is that CDC stopped testing for swine flu hastily and without advance notice to the states:
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Male Chauvinist Chimps or the Meat Market of Public Opinion? [The Primate Diaries]
Female chimpanzee with her infant requests meat after a successful hunt.
Image: David Bygott / Tree of Life Web Project
Owen Lovejoy's recent paper about Ardipithecus ramidus and human origins (see my detailed critique here) bases its argument on the male provisioning observed in chimpanzees. However, what went unacknowledged in his theory was the inherent gender bias it represented. A perfect example of this was observed in April with the release of the very study on provisioning behavior that Lovejoy used as the basis for his idea.
From the press introductions alone, you would have thought you were in a 19th-century gentleman's club enjoying cigars and brandy. "There's nothing like a prime rib dinner to boost a guy's chances of getting lucky," boasted ScienceNOW as he cleaned his monacle. The Daily Mail agreed with a harrumph, "As every Romeo knows, laying on a delicious dinner for two is one of the best seduction ploys." Chuckling along with a wink and a nudge, MSNBC added, "A savory meat dinner goes a long way, as in all the way."
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OMY did you just see that???????? Holy crap!!!!!! [Greg Laden's Blog]
For reasons you need not know, I just did something very odd ... watched about ten minutes of Oprah. And I watched as she sat and had a bite to eat with a table of atheists. Whoa.....
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Afradapis and "Ida", sittin’ in a tree… [Laelaps]
The restored lower jaw of Afradapis. From the Nature paper.
This past May a 47 million year old fossil primate named Darwinius masillae, better known as "Ida", burst onto the public scene. The lemur-like creature was proclaimed to be the "missing link" and the "ancestor of us all", but the actual science behind Ida was drowned by a tide of media sensationalism. Press releases and documentaries proclaimed that Ida would "CHANGE EVERYTHING", but despite such promises the sky remained blue, my cats continued to wake me up at 5:30 AM, and the primate evolutionary tree did not suddenly restructure itself.
So what was Darwinius? According to the descriptive paper published in PLoS One, Darwinius belonged to a group of extinct lemur-like primates known as adapids and may or may not have been related to early anthropoids, the primate group to which monkeys and apes (including us) belong. The public announcements about Ida were far less reserved. A book, a pair of documentaries, and news reports proclaimed that Ida was definitely an ancestor of anthropoids and hence one of our early primate ancestors. (Jorn Hurum, the scientist who had purchased Ida from a fossil dealer for a sum close to ,000,000 even went as far to say that Darwinius was "the closest thing we can get to a direct ancestor" of humans.) The fact that access to the scientific description of Darwinius was tightly controlled until after the media frenzy was initiated by Atlantic Productions meant that science took a backseat to hype.
Indeed, paleontologists who specialize in the study of early primates were not impressed by Darwinius. The fossil primate bore very little resemblance to the earliest known anthropoids, and critics soon found themselves fighting a battle on two fronts. The initial description of Darwinius, despite being much more reserved than the media hype, did not provide solid support that this primate was closely related to anthropoids. Much of the media coverage, by contrast, simply parroted unsubstantiated claims that Darwinius was one of our ancestors. Both the "strong" and "weak" interpretations of Darwinius had major flaws, and it was tricky responding to both versions of Ida's story.
Yet the public unveiling of Ida was hardly the last word on whether or not we could count her as a close relative. Quite the contrary; with the publication of her description real scientific debate had only just begun. The exchange of ideas which is the lifeblood of science continues today with the description of one of Ida's close relatives recovered from the 37 million year old rock of Egypt.
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David Sloan Wilson Joins ScienceBlogs [The Primate Diaries]
For those of you who don't know his work, I encourage you to check it out immediately (if not sooner). Among my favorites are Unto Others: The Evolution and Psychology of Unselfish Behavior and the book that became the title of his blog, Evolution For Everyone.
It's a testament to the power of social media to have such an influential and important working scientist joining the network here at Seed. Please join me in offering him a warm welcome.
US Chamber of Commerce Gets Punked on Climate Change [The Primate Diaries]
In a shocking reversal after denying climate science for decades, a spokesperson for the US Chamber of Commerce (the world's largest business advocacy group) announced yesterday that they have reversed their historical stance on the issue of global climate change.
According to the press release carried by The New York Times, Reuters, CNBC, the Washington Post and FOXNews:
WASHINGTON, D.C.-The U.S. Chamber of Commerce is throwing its weight behind strong climate legislation, a spokesman for Chamber President Tom J. Donahue announced today at the National Press Club.
"We believe that strong climate legislation is the best way to ensure American innovation, create jobs, and make sure the U.S. and the world are on track to reduce global carbon emissions, and to provide for the needs of the American business community for generations to come," said the spokesman, Hingo Sembra.
However, it turns out that the press conference was actually held by The Yes Men, an activist group who specializes in impersonating business organizations such as Halliburton, Dow Chemicals, the World Trade Organization and McDonald's in order to provoke questions about the role that these companies play in global issues.
Watch the hilarity ensue as FOXNews learns of the hoax midway through their broadcast:
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Breaking the Link – Darwinius revealed as ancestor of nothing [Not Exactly Rocket Science]
Cast your mind back to June, when a stunning fossil animal called Darwinius (alternatively Ida or "The Link") was unveiled to the world to tremendous pomp and circumstance. Hyperbolic ads declared the day of Ida's discovery as the most important for 47 million years. A press release promised that she would "change everything", headlines proclaimed her a "missing link in evolution" and the scientists behind the discovery billed her as "the closest thing we can get to a direct ancestor".
And according to a new study, none of that is true. Mere months later, Erik Seiffert from Stony Brook University has done a comprehensive analysis of the bones of 117 primates, both living and extinct, which throws Ida's supposed direct line of ancestry to humans into serious doubt.
Central to this new work is a new fossil called Afradapis, a member of the same group of extinct primates - the adapids - that Darwinius belonged to. The two were closely related but separated by around 10 million years. Like its more famous cousin, Afradapsis's jaw and teeth contain features that are similar to those of anthropoids - monkeys, apes and humans. But far from being a sign of direct ancestry, Seiffert thinks that these features represent convergent evolution - the two groups evolved them independently.
His team compared and contrasted 360 features in the bones of over 117 living and extinct primates. Among them were 24 adapids, including Darwinius, Afradapis and eight other that had not been previously analysed. This comprehensive set of data revealed the group's family tree, charting their relationships using their overall anatomy as a guide.And it clearly shows that adapids (and Ida among them) were more closely related to modern lemurs than to anthropoids (monkeys, apes and humans). The two groups sit on a different branches of the evolutionary tree.
The analysis also reveals that even though the adapids were a successful and widespread group, they left no living descendants. For all the hype, Ida turns out to be the ancestor of bugger all.
New evidence
To those who followed the criticisms of the Darwinius hype, this volte face shouldn't come as a surprise. The the paper describing the fossil was criticised for juggling the structure of the primate family tree to shift Ida's branch closer to ours. To recap, there are three groups vying for position as the ancestors of the anthropoids: the bizarre, large-eyed tarsiers, the related and extinct omomyids, and the equally extinct adapids. The general consensus places the first two groups closest to us; Ida's discoverers think the adapids should be there instead.
To support that view, they looked at 30 traits that might help to settle the question and noted whether Ida had them or not, and concluded that placed the adapids next to the anthropoids on the basis of this single species. That approach seems positively minimalist compared to the one that Seiffert took, which included 12 times as many anatomical features and 117 times as many animals!
Seiffert's tree places the tarsiers and omomyids as the closest relatives of the anthropoids - this is the so-called haplorrhine group. The adapids, however, are part of the strepsirrhine dynasty, the group that includes lemurs, lorises and bushbabies. This is the sort of analysis that was sorely lacking in the Darwinius paper.
There is no doubt that Ida is a beautiful fossil, but Seiffert questions its worth in understanding the evolution of primates. Not only was she a growing youngster, but most of her bones have been crushed or distorted in ways that obscure important body parts. Much was made of the fact that Ida lacked a toothcomb (a set of flattened, forward-facing incisors) and a grooming claw (a special ankle bone). These are two features that modern lemurs possess and modern anthropoids don't - their absence in Darwinius was presented as evidence of a close tie to anthropoids but not lemurs. But Seiffert thinks that these body parts - the ankle and teeth - have been damaged enough that analysing them is difficult.
Afradapsis, ironically, poses no such problems. While most of its skeleton has yet to be recovered, its teeth and jaws are in excellent condition. Like those of Darwinius and some other adapids, these teeth bear a suite of features typically found in living and extinct anthropoids. The joint between the two jawbones is fused and the part of the jaw containing the teeth is deep, as is the crater in the jawbone where the chewing muscles attach. The main cusp of its upper molars - the hypocone - is very large. It's missing the second premolar, but the third has become bigger with an edge that sharpens its matching canine.
But this doesn't mean that Afradapis is an ancestor, or even a close relative, of the anthropoids. For a start, the most primitive fossil anthropoids, such as Biretia and Proteopithecus, lack these traits. If adapids were their ancestors, the early anthropoids must have jettisoned these adaptations, only to re-evolve them at a later stage. The more plausible explanation, and certainly the one Seiffert subscribes to, is that both groups evolved independently, and happened to converge on the same adaptations.
The price of hype
The arrival of a paper like this was almost inevitable given the interest that Ida stirred up. Obviously, Seiffert's analysis isn't the final word on the subject (although his study looks more convincing to me) and I'm sure that there will be a healthy debate for days to come. But what of the public impact?
Jorn Hurum, one of the key ringleaders in the Ida circus, famously said, "Any pop band is doing the same. We have to start thinking the same way in science." The key differences, of course, are that pop music is impossible to analyse objectively and its quality depends on personal taste. The same cannot be said of scientific truth, and that changes the extent to which you can use marketing tactics to promote a discovery.
Hurum and his colleagues have played a dangerous game - they may claim to have been marketing science but they were, in fact, marketing their opinions and ones that may not stand the test of time. It's debate by media, and it's fantastically dangerous.
Consider the fact that for all the interest that the new paper will undoubtedly instigate, there will still be a book, website and documentary out there firmly enshrining the increasingly dubious view that Ida is our direct ancestor. Consider also that contradicting that view now makes the scientific establishment look like buffoons, given all the publicity and to-do a few months back. When John Hurum makes grandiose statements, he gains in the eyes of the public. When those statements are later shown to be dodgy, it's science as a whole that takes a beating.
It's also worth noting how the different publishers handled the two papers. This time, Nature made the paper available to reporters several days ahead of its publication, giving us time to analyse the paper, prepare our stories and, if necessary, contact experts for their views. The situation with the original Darwinius paper couldn't have been more different.
As Mark Henderson notes, select journalists were allowed to see the paper at a specific location and under non-disclosure contracts that prevented them from seeking further opinions. PLoS ONE admitted to rushing the publication of the paper in time for John Hurum's press conference, and indeed, it became publicly available mere minutes before said conference kick-started a blitzkrieg of media attention. In rushing the publication of the paper, the journal allowed itself to be held hostage to hype and actively hindered science writers who were trying to do their job responsibly.
Update: Already up on the Times blog is an excellent interview with Seiffert. Brian Switek has his typically thorough take on the new paper too.
Reference: Nature doi:10.1038/nature08429
More on Ida: Darwinius changes everything
Nate Silver’s top ten reasons the public option is surging [Neuron Culture]
1. The tireless, and occasionally tiresome, advocacy on behalf of liberal bloggers and interest groups for the public option. Whatever you think of their tactics -- I haven't always agreed with them -- the sheer amount of focus and energy expended on their behalf has been very important, keeping the issue alive in the public debate. 2. The fact that the CBO thinks it will save money. 3. The seeming inevitability of health care reform, which neuters the voices of those who aren't opposed to the public option per se so much as the entire project of health care reform. 4. The fact that the locus of power has shifted from the Gang of Six -- Bingaman/Conrad/Baucus/Snowe/Grassley/Enzi to the Group of Six -- Pelosi/Dodd/Obama/Reid/Baucus/Snowe. 5. The "innovation" of the opt-in/opt-out family of compromises, which have more liberal "street cred" than co-ops or triggers and are potentially also much more politically advantageous. 6. The fading from memory of the tea party protests and the "government takeover" meme.
There are four more -- I didn't want to steal the thing outright, so you should follow the link below. Also of interest is Aaron E. Carroll's HuffPo piece on why, even as a single-payer advocate, he feels the public option is less than vital. His valid point is that the option doesn't necessarily provide coverage to more people than other measures do. But I think he downplays one important aspect and misses another. First, he says that it'll save only about 0 billion over 10 years. We need to save more -- but that's plenty of reason to include a public option. And he misses altogether the other reason people want a public option: It will, symbolically at least, declare that coverage of everyone is a direct public good and even obligation, just as Medicare establishes that we agree we'll look after the elderly. This has not just symbolic significance but long-term political and policy significance. And it gives people (and potentialy companies, down the line) at least the chance to vote with their feet and their wallets for whether they want private insurance or a government payer to look after their insurance money. These are less than feel-good issues. . That said, a public option runs a risk of collecting just the highest-risk, most heavily subsidized part of the risk pool. You can call that a zero-sum game, I suppose, if you figure those people will be insured anyway (as they should be) in a heavily subsidized, take-everybody private market. But on the books, it'll weigh heavily on public monies and look like more a loser than it really is: the public option market would bleed while the private market would gather the healthier, wealthier customers and look healthier than ever. Which could in turn be used as an argument against public solutions.
Ethiopia appeals for food aid for 6.2 million (Reuters)
ADDIS ABABA, Oct. 22, 2009 (Reuters) -- Ethiopia appealed on Thursday for 159,410 tons of emergency aid to feed 6.2 million people, 25 years after more than a million perished in the country's notorious famine. ... > read full story