The ID Update

The authors of a new research paper introduce their findings with the statement: "Early hominin diet is central to the study of human origins". Analysis of carbon isotopes is revealing for the kind of plant material consumed. Two important fingerprints are identifiable: from C3 resources and from C4 resources. In the C3 category are the leaves and fruits of trees, shrubs, plus some herbs, and animals eating these plants. The C4 category signifies (most) tropical grasses, sedges, and animals eating these plants. Modern chimpanzees consume C3 foods, even when grasses are plentiful. The fossil hominids are associated with savannah environments and C4 foods were dominant in their diet. The new work concerns two specimens of Australopithecus sediba from the site of Malapa, South Africa. For a previous blog on this species, go here.

"The A. sediba diet was analyzed using a technique that involved zapping fossilized teeth with a laser, said [co-author] Sandberg. The laser frees telltale carbon from the enamel of teeth, allowing scientists to pinpoint the types of plants that were consumed and the environments in which the hominids lived. The carbon signals from the teeth are split into two groups: C3 plants like trees, shrubs and bushes preferred by A. sediba, and C4 plants like grasses and sedges consumed by many other early hominids." (Source here)

A high-tech dental analysis of a 2-million-year-old hominid from South Africa indicates it had a unique diet that included trees, bushes and fruits. (Credit: Photo courtesy Paul Sandberg, University of Colorado, source here)

The findings were unexpected. We should remember that numerous papers have been published on the available fossil material for Australopithecus sediba that have made a case for considering this species a key transitional form. Those anthropologists advancing this view expected to find a diet dominated by C4 food resources.

"What fascinates me is that these individuals are oddballs," said [co-author] Sponheimer. "I had pretty much convinced myself that after four million years ago most of our hominid kin had diets that were different from living apes, but now I am not so sure." (source here)
and ""It seems like a hallmark of human evolution to be able to use savanna resources," [co-author] Passey told me. "Today, most of our energy comes from grass in one way or another, either from grain or from animals that eat grain and grass." (source here)

The authors and others favouring Australopithecus sediba as a human ancestor have not changed their views on this particular matter. They write: "Previous analyses have shown that Au. sediba has an unusual suite of morphological features, and our results present new oddities and questions." However, those of us who were not persuaded by the original research analyses, and who consider the australopithecines are an extinct family of apes (for the reasons, go here), draw a different conclusion from the data. Their diet reveals that they did not feed in savannah environments and that they were at home in trees where they could eat leaves and fruit. We should bear in mind that convergence is pervasive in the record of life and that "shared skeletal morphology does not always mean shared recent evolutionary history". Consequently, the evidence from diet gives strong reinforcement to the previous conclusion that Australopithecus sediba is an extinct ape, and we have no reason to consider them (in the words of Science Daily) "ancient human ancestors".

The diet of Australopithecus sediba
Amanda G. Henry, Peter S. Ungar, Benjamin H. Passey, Matt Sponheimer, Lloyd Rossouw, Marion Bamford, Paul Sandberg, Darryl J. de Ruiter & Lee Berger
Nature, Published online 27 June 2012 | doi:10.1038/nature11185

Specimens of Australopithecus sediba from the site of Malapa, South Africa (dating from approximately 2 million years (Myr) ago) present a mix of primitive and derived traits that align the taxon with other Australopithecus species and with early Homo. Although much of the available cranial and postcranial material of Au. sediba has been described, its feeding ecology has not been investigated. Here we present results from the first extraction of plant phytoliths from dental calculus of an early hominin. We also consider stable carbon isotope and dental microwear texture data for Au. sediba in light of new palaeoenvironmental evidence. The two individuals examined consumed an almost exclusive C3 diet that probably included harder foods, and both dicotyledons (for example, tree leaves, fruits, wood and bark) and monocotyledons (for example, grasses and sedges). Like Ardipithecus ramidus (approximately 4.4 Myr ago) and modern savanna chimpanzees, Au. sediba consumed C3 foods in preference to widely available C4 resources. The inferred consumption of C3 monocotyledons, and wood or bark, increases the known variety of early hominin foods. The overall dietary pattern of these two individuals contrasts with available data for other hominins in the region and elsewhere.

See also:

Ancient Human Ancestors Had Unique Diet, ScienceDaily (June 27, 2012)

Nearly a decade ago, Darwin's thinking on sexual selection was considered by numerous scientists to be overdue for revision. At the 169th annual meeting of the American Association for the Advancement of Science, researchers took "dead aim at one of Charles Darwin's pet evolutionary theories - the theory of sexual selection, which says that males should compete among themselves for access to mates, or compete for the favours of choosy females." Two leading voices were those of Joan Roughgarden ("There are too many exceptions for the theory to hold") and Patricia Adair Gowaty, who said that the theory may still hold, but researchers have been accepting it without good evidence ("What's wrong is our failure to test the theory adequately"). It has taken a long time for these critiques to mature, but we are now in a position to revisit this issue because some crucial experiments have been repeated. To start, let's remind ourselves of Darwin's much-cited words:

"The female, on the other hand, with the rarest exceptions, is less eager than the male. [. . .] she is coy, and may often be seen endeavouring for a long time to escape from the male. Every observer of the habits of animals will be able to call to mind instances of this kind."
Charles Darwin, The Descent of Man (1871) Part Two - Sexual Selection, Chapter VIII - Principles of Sexual Selection, page 273.

A new sexual selection study replicates an iconic 1948 study and finds it flawed. The graphic shows that children of fruit fly parents with different mutations have an equal chance of inheriting just the mother's mutation, just the father's mutation, both mutations or neither mutation. (Credit: Kim DeRose, source here)

The concept of sexual selection became accepted by Darwinists, although the evidential base was circumstantial. A big impact was made by Angus John Bateman in 1948 drawing on his experimental work with fruit flies. He concluded that for many species, there is a combination of "undiscriminating eagerness in the males" and a "discriminating passivity in the females". He considered that in derived monogamous species (such as man) "this sex difference might be expected to persist as a relic". This analysis of sexual selection became the new orthodoxy, dignified by the term Bateman's principle, as indicated by Knight (2002):

"The explanation, Bateman argued, is that sperm are small and cost next to nothing to produce - so the wider a male can spread them, the better off he will be. A female, on the other hand, produces many fewer eggs, and invests a relatively large amount of energy in each one. All she really needs is one good male to fertilize them to reach her maximum reproductive output. It all seemed to make sense, and Bateman's principle soon became one of the grounding truisms of behavioural biology."

Moving to the year 2007, Brian Snyder and Patricia Gowaty published their concerns about this classic study, documenting numerous flaws in his methodology. They concluded that Bateman's results were unreliable and his conclusions were questionable. However, it still remained to put some rigour into developing an evidential base. They wrote: "We call for repetitions of Bateman's study using modern statistical and molecular methods".

It has nevertheless taken several more years to do the work and publish the findings. This has now been done. The results are of far-reaching significance because Bateman's conclusions have dominated discussions of sexual selection - in academia as well as in education.

"Bateman's 1948 study is the most-cited experimental paper in sexual selection today because of its conclusions about how the number of mates influences fitness in males and females," said Patricia Adair Gowaty, a distinguished professor of ecology and evolutionary biology at UCLA. "Yet despite its important status, the experiment has never been repeated with the methods that Bateman himself originally used, until now. Our team repeated Bateman's experiment and found that what some accepted as bedrock may actually be quicksand. It is possible that Bateman's paper should never have been published." (Source here)

For those wanting the details of the experiments and the flawed methodology of Bateman, the best option is to use the links provided. Of greatest interest here is what can be learned about science from the new findings. Undoubtedly we can note the self-correcting nature of science - although 64 years is a long time to wait. Of even more relevance to us today is the power that some concepts have to grip the minds of students and scholars alike and gain a dominant place in their thinking. The evidence for dominance is found in the many biology textbooks that passed down Bateman's work to successive cohorts of students, and in the fact that Bateman's paper has been cited in nearly 2000 other scientific studies. Here is Gowaty again:

"Here was a classic paper that has been read by legions of graduate students, any one of whom is competent enough to see this error," Gowaty said. "Bateman's results were believed so wholeheartedly that the paper characterized what is and isn't worth investigating in the biology of female behavior." Repeating key studies is a tenet of science, which is why Bateman's methodology should have been retried as soon as it became important in the 1970s, she said. Those who blindly accept that females are choosy while males are promiscuous might be missing a big piece of the puzzle. "Our worldviews constrain our imaginations," Gowaty said. "For some people, Bateman's result was so comforting that it wasn't worth challenging. I think people just accepted it." (Source here)

Here is the important point: while some worldviews allow people to open their minds to evidence, other worldviews act to close up the imagination and discussion. This case reinforces the importance of bringing an awareness of philosophy into education at an early stage and embedding it in the curriculum (as is discussed here). This new work will have the effect of clearing the decks, sweeping away the old paradigm and allowing a new conceptual framework to emerge. But what is needed is a willingness to follow the evidence wherever it leads. Many of us fear that the old Darwinian paradigm will rise up again and try to reassert its dominance. Let us not forget that on the issue of sexual selection, the old paradigm has been discredited.

Yet shaking the bedrock of the Bateman paradigm may help the field examine new perspectives.
"Paradigms are like glue, they constrain what you can see," she said. "It's like being stuck in sludge - it's hard to lift your foot out and take a step in a new direction." (Source here)

No evidence of sexual selection in a repetition of Bateman's classic study of Drosophila melanogaster
Patricia Adair Gowaty, Yong-Kyu Kim, and Wyatt W. Anderson
Proceedings of the National Academy of Sciences, Online June 11, 2012 | doi:10.1073/pnas.1207851109 [open access]

Abstract: We are unique in reporting a repetition of Bateman [Bateman AJ (1948) Heredity(Edinb) 2:349-368] using his methods of parentage assignment, which linked sex differences in variance of reproductive success and variance in number of mates in small populations of Drosophila melanogaster. Using offspring phenotypes, we inferred who mated with whom and assigned offspring to parents. Like Bateman, we cultured adults expressing dramatic phenotypes, so that each adult was heterozygous-dominant at its unique marker locus but had only wild-type alleles at all other subjects' marker loci. Assuming no viability effects of parental markers on offspring, the frequencies of parental phenotypes in offspring follow Mendelian expectations: one-quarter will be double-mutants who inherit the dominant gene from each parent, the offspring from which Bateman counted the number of mates per breeder; half of the offspring must be single mutants inheriting the dominant gene of one parent and the wild-type allele of the other parent; and one-quarter would inherit neither of their parent's marker mutations. Here we show that inviability of double-mutant offspring biased inferences of mate number and number of offspring on which rest inferences of sex differences in fitness variances. Bateman's method overestimated subjects with zero mates, underestimated subjects with one or more mates, and produced systematically biased estimates of offspring number by sex. Bateman's methodology mismeasured fitness variances that are the key variables of sexual selection.

See also:

Snyder, B.F and Gowaty, P.A. A Reappraisal Of Bateman's Classic Study Of Intrasexual Selection, Evolution, Volume 61, Issue 11, pages 2457-2468, November 2007 | DOI: 10.1111/j.1558-5646.2007.00212.x

Bateman, A. J. Intra-sexual selection in Drosophila. Heredity, 1948, 2: 349-368.

Knight, J. Sexual stereotypes, Nature, Vol 415, 17 January 2002, 254-256.

How should schools and universities teach their students? Pedagogy occupies the minds of all educators, although there are many different applications of this aspect of educational theory. For example, some answer the question above by advocating learning-by-doing. Students are given projects which involve a structured activity such as experimentation. This is enquiry-based learning. Others favour a process of information gathering to reach answers. This is resource-based learning. Although not recommended by educationalists, some students learn by rote or memorise the way to solve problems but this typically means the student has little understanding of what they are doing. Earlier this year, in an editorial in the journal Science, Bruce Alberts wrote about the trivialisation of science education. He commented:

"Tragically, we have managed to simultaneously trivialize and complicate science education. As a result, for far too many, science seems a game of recalling boring, incomprehensible facts - so much so that it may make little difference whether the factoids about science come from the periodic table or from a movie script."

We like to promote evidence based science, but we need our peer review safeguards (source here)

Despite extensive research into these issues, there is still a widespread perception that additional approaches are needed to engage students in every curriculum area. The contribution of two educationalists brings some fresh issues for consideration:

"In this article we will argue for wide-ranging change in the school curriculum, more particularly for the inclusion of philosophical inquiry within every learning area. We will begin with this claim: If students are to develop an understanding of the world and what there is in it, then as teachers we must engage them in philosophical inquiry. This is our first premise. The second is that both social and individual good depend upon the development of such understandings." (p.305)

Although addressing issues arising in primary school education, the research paper communicates principles that are just as relevant to secondary and tertiary education. The issue is not the content of the curriculum, but understanding the underlying assumptions of a discipline. The challenge is to help students develop a coherent worldview that allows them to make sense of the subject matter and enables them to see it in context. Some have approached this by having "philosophical inquiry" as a discipline in itself, but Knight and Collins advocate another approach:

"We want to argue that it is worth considering another model: philosophy embedded in the existing curriculum areas. We do not wish to deny the value, the remarkable depth, complexity and comprehensiveness of the narrative-based curriculum material. [. . .] But we think there are reasons for trying a different approach, for developing materials which fit into the current curriculum areas. Elsewhere, we have examined the arguments in support of separateness and the use of narrative. We have claimed that these arguments fail to establish any marked advantage for the standard approach. Here, we will simply go on to put the case for the alternate model which embeds philosophy in the existing curriculum areas." (p.310)

Examples are given for primary school students studying "Society and Environment", mathematics, science and the arts. Taking mathematics as an example, questions of a philosophical nature include: Why do we count? Where do numbers come from? Are numbers part of the world around us (like shapes)? Are numbers human inventions or are they discovered?

"To sum up: Mathematics houses a rich store of genuine inquiry questions, appropriate for students of any age level. By raising such questions in the classroom, we are likely to foster one of the intellectual dispositions necessary for engagement in the pursuit of mathematical understanding." (p.315)

Why is this topic relevant to science and origins? In my experience, making reference to the philosophical presuppositions of science is often derided as an irrelevance. Many people who participate actively in forums that deal with these issues appear often to be woefully ignorant of worldviews affecting the subjects they are debating. Many senior figures in the world of science contribute to the problem. For example, the case of Stephen Hawking is considered here, and Richard Dawkins also appears to have thrown philosophy into the same trash can as theology, as is pointed out here. There are many leaders who have endorsed definitions of science that are underpinned by philosophical materialism. Yet they rarely acknowledge publicly the worldview they are espousing. Furthermore, they rarely admit that their way of doing science is not the only way - as is evidenced by the fact that all the pioneers of science in the 17th Century developed their thoughts on the philosophical foundations of theism.

We often hear people saying things like: 'science is based on evidence, whereas Christianity is based on tradition/feelings/values' (select whatever word is appropriate). This is effectively a mantra that stifles meaningful debate. When Christians use evidence-based arguments, these are dismissed as rhetoric, because only 'science is based on evidence'. This is why Hawking and Dawkins are actually advancing scientism, and it explains why they have such a low view of philosophy.

Not only should teachers help students understand the philosophical underpinnings of the curriculum under consideration, but also educationalists and policy-makers should expect schools and universities to provide worldview statements regarding their mission in society. For example, a prominent atheist and his atheist team are setting up a college but worldview issues have not been probed as they should (but see here).

Parents and students have a right to know whether their school or university has adopted the mindset of secularism and materialism, or whether it seeks to operate within a theistic framework. Recognising the importance of philosophy in understanding how disciplines of knowledge develop would also help greatly change the polarised nature of the origins and design debates. The modest proposals of Knight and Collins deserve to be seriously considered, as the far-reaching change they envisage is much needed.

Enlivening the curriculum: The power of philosophical inquiry
Sue Knight and Carol Collins
Theory and Research in Education, November 2010, 8: 305-318 | doi:10.1177/1477878510381630

Abstract: In this article we argue for the necessity of far-reaching change in school curricula and pedagogy. More particularly, we argue that developing students' understanding and engagement in the disciplines which make up the school curriculum requires an unearthing of the philosophical issues underlying science, mathematics, the arts, geography, history, and so on. This means that philosophical inquiry must be embedded in every curriculum area. While at first sight this task might appear unattainable, we go on to illustrate by means of detailed examples how the goal might be realized and point to theoretical and empirical evidence to support this contention.

See also:

Alberts, B., Trivializing Science Education, Science, 20 January 2012: Vol. 335 no. 6066 p. 263 | DOI: 10.1126/science.1218912

Tyler, D. Creationism and Intelligent Design in science lessons, ARN Literature Blog (9 September 2011)

Bipedalism, walking and running are characteristics that we tend to take for granted because they are so much a part of human experience. Yet, each of these traits requires a set of inter-related components and information processing machinery. To appreciate this, all we need to do is to reflect on the challenges faced by robot engineers attempting to mimic human behaviour (see also Walking with arthropods). New insights into the physiology of walking are provided in a recent analysis of the heel-sole-toe stance of the human foot. The authors recognise that the morphology and action they are studying is unusual among cursors, and this leads them to make a design inference. The hypothesis is that there are physiological reasons for the design of the human foot (rather than the structure being a spandrel and a witness to evolutionary tinkering).

"While humans have been considered by some as specialized endurance runners, the role - even the presence - of the heelstrike in natural running is controversial. We therefore consider the potential benefits of the peculiar human foot and heel-sole-toe walking strategy from the perspective of the mechanics and physiology of walking."

"Humans appear more specialised for walking" (source here)

The key tool for gathering gait data is the forceplate. As a result of numerous studies in the past, the "inverted pendulum" model of walking has been adopted. There are three phases: I. Heel impact, with energy-dissipating compression in the foot/ankle/leg; II. Stiff-limbed, passive vaulting, as the other leg moves forward; III. Impulsive push-off by the front of the foot and toes. However, the forceplate measurements show that there are only minor differences between the forces obtained during normal walking and those obtained when walking on tiptoes, or walking on high heels, and even when an ostrich walks (despite having no functional heel). This means the heel is contributing something to human walking which has not been previously recognised.

Dr Tatjana Hubel from the Royal Veterinary College explains: "Despite vastly differing arrangements of joints and hip wiggles, humans walking normally, women in extremely high heels and ostriches all produce strikingly similar forces when walking. This is the most mechanically economical way of walking. We do everything we can to make the forces follow the same pattern, which is why for example women wiggle their bottoms when they're in high heels. The question for us is, why is the human foot shaped the way that it is and not, say, like an ostrich's?"
From the research paper: "Our simplification provides an alternative reduction of walking to a previous attempt to account for human foot structure and the translation of the centre of pressure during stance, which supposes that 'the plantigrade human foot rolls over the ground during each walking step, roughly analogous to a wheel'."

Stance I is when the moving foot/leg contacts the ground and becomes stationary. This requires a loss of mechanical energy of the centre of mass. It is concluded that this mechanical energy is lost rather than stored, as there are no elastic structures feeding energy back into Stance III. After considering options for energy dissipation, the researchers concluded that the tibialis anterior muscle "primarily acts as an energy-losing specialist". This is a culture shock for physiologists, opening up new avenues for research:

"The full implications of a muscle that might, unusually, be specialized for energy loss is exciting, but beyond the scope of this study."

New insights apply also to the vault (Stance II). The ground reaction force is essentially vertical, so there is very low loading on the energy-dissipating muscles active during Stance I, and very low loading to the powering muscles active during Stance III. Whilst these muscles are performing no work, they are not loaded and they can rest.

"We argue here that, to account for the stiff plantigrade human foot (as distinct from other, more compliant, ape feet), with heel behind ankle and toe in front, and the heel-sole-toe walking strategy, requires an appreciation of both the energetically optimal powering/ support strategy of vaulting, impulsive inverted pendular walking and the cost of muscle force - which may be reduced by simple mechanisms that alter the mechanical advantage between the muscle and the ground reaction force. [. . .] In general, human walking is achieved with relatively high muscle mechanical advantages (compared with running), allowing ground reaction forces to be supported with relatively small muscle forces."

These two findings point to the uniqueness of the human foot. The researchers suggest that simplistic evolutionary storytelling should not be confused with scholarship. This is particularly relevant to those who have constructed a story about humans being "specialized endurance runners". Justice needs to be done to the uniqueness of human foot design in its capacity for bipedalism and for walking.

"Any inference of function from a single evolutionary origin must be treated with caution. However, the mechanical form of the human foot, based on the interpretation of function presented here, suggests adaptation for economical walking from both the whole body mechanics and muscle physiology perspectives."

Since there is a tendency for evolutionists to latch on to any human-like trait in animals and portray this as bridging the gap between animals and humans, it is worth reminding ourselves also of fundamental differences:

"The contrast provided by chimpanzee feet and gait is striking, and the mechanical significance, to some extent, long been recognized: while they show the heel-sole-toe plantigrade stance, they completely lack the longitudinal arch that stiffens the human foot, and 'the digits do not provide an effective 'toe snap' of the sort that is significant in 'smoothing' the human stride at the end of the stance phase'"

As the evolutionary mind-set has become entrenched in the world of scholarship, it has become fashionable to present the human body as an example of poor design. The latest contributor to this is Elizabeth Pennisi in the journal Science. Her piece is entitled "The Burdens of Being a Biped" and the theme is bad design: "A brief tour of the body reveals a number of design flaws, the legacy of our past". This is what Pennisi says about feet:

"Feet. To cope with the added load on just two feet, the foot evolved a shock-absorbing arch by bringing what was a grasping big toe into line with the other toes. When that arch fails to form fully, as in people with flat feet, fatigue fractures can result. And when the big toe's tendon gets misaligned from improper shoes, bunions develop. Latimer blames heel spurs, plantar fasciitis, hammer toes, shin splints, chronically sprained ankles, and even varicose veins on our erect posture."

These quoted words reveal a strange form of logic - musculoskeletal disorders are painted as indicating imperfect evolutionary adaptations. However, it is our everyday experience that designed objects malfunction! Things wear out with use; they can fail when improperly used; circumstances may arise that were not part of the design brief and can result in inferior performance. Pennisi is aware of this when she writes about "Our relatively inactive life-styles" and wearing "improper shoes". She might have added something about our penchant for unbalanced diets. Many of our problems are of our own making! I am not writing this as an observer - I am in a hospital waiting room, waiting for the results of a blood test that will help diagnose what's wrong with my lower leg. My experience does not undermine in the least my appreciation of the wonderful design of human anatomy and physiology.

Design perspectives are sometimes maligned as a science-stopping approach. However, examples to 'prove' this are always made-up! By contrast, it appears to me that the attempts to portray the human body as a showcase of evolutionary imperfections provide a much better fit for the description 'science-stopper'. Design perspectives raise questions about functionality and lead inevitably to research programmes. For example, whilst 'junk DNA' was perceived as junk, it was ignored, but when questions were asked about functionality, research blossomed! Feet display astounding design features, and if there are aspects we do not understand, the first thing to do is to develop some hypotheses based on the presumption of design. This is exactly what the authors of this paper have done. (This is not to claim that the authors advocate intelligent design, but only that they have a meaningful concept of design that allows them to use the phrase "human foot design".) They have demonstrated that asking questions that presuppose design and functionality is a fruitful approach. What more can one ask from any paradigm in science?

The human foot and heel-sole-toe walking strategy: a mechanism enabling an inverted pendular gait with low isometric muscle force
J. R. Usherwood, A. J. Channon, J. P. Myatt, J. W. Rankin and T. Y. Hubel
Journal of the Royal Society Interface, online May 9, 2012 | doi: 10.1098/rsif.2012.0179

Abstract: Mechanically, the most economical gait for slow bipedal locomotion requires walking as an 'inverted pendulum', with: I, an impulsive, energy-dissipating leg compression at the beginning of stance; II, a stiff-limbed vault; and III, an impulsive, powering push-off at the end of stance. The characteristic 'M'-shaped vertical ground reaction forces of walking in humans reflect this impulse-vault-impulse strategy. Humans achieve this gait by dissipating energy during the heel-to-sole transition in early stance, approximately stiff-limbed, flat-footed vaulting over midstance and ankle plantarflexion (powering the toes down) in late stance. Here, we show that the 'M'-shaped walking ground reaction force profile does not require the plantigrade human foot or heel-sole-toe stance; it is maintained in tip-toe and high-heel walking as well as in ostriches. However, the unusual, stiff, human foot structure - with ground-contacting heel behind ankle and toes in front - enables both mechanically economical inverted pendular walking and physiologically economical muscle loading, by producing extreme changes in mechanical advantage between muscles and ground reaction forces. With a human foot, and heel-sole-toe strategy during stance, the shin muscles that dissipate energy, or calf muscles that power the push-off, need not be loaded at all - largely avoiding the 'cost of muscle force' - during the passive vaulting phase.

See also:

How a study of walking in high heels could help improve prosthetic limbs, BBSRC Press Release (9 May 2012)

Pennisi, E. The Burdens of Being a Biped, Science, 25 May 2012: Vol. 336, 974 | DOI: 10.1126/science.336.6084.974