Five scientific mysteries - D.G.

https://medium.com/starts-with-a-bang/ask-ethan-which-fundamental-science-question-is-the-most-important-a537c63d74b1

Ask Ethan: Which Fundamental Science Question Is The Most Important?

Out of five vital questions, which one should we most desire the answer to?

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Despite all we’ve learned about physics, science, and the Universe before us, there are still some incredibly fundamental questions whose answers are still elusive. Each one is a challenge to humanity, and the answers are thoroughly uncertain, with tremendous implications depending on what the answer actually is. From our cosmic birth to the fundamental laws governing everything, and from the origin of life to what actually makes up the Universe, there is so much left to discover. If we could only know the answer to one, which one should we choose? That’s what our Patreon supporter Chris Shaw wants to know, as he asks:

If you could have a complete answer to one of these 5 questions what would it be?

* Did cosmic inflation happen or was there another process?
* Is earth the only place in the cosmos with life?
* How [can we] merge general relativity and quantum mechanics?
* What is dark energy and dark matter?
* How did life begin on Earth?

These are all incredible questions, and they’re all open questions that probe our deepest mysteries about the Universe. Here’s why each one matters.

1.) Cosmic inflation: We know that the Big Bang happened, and that the hot Big Bang wasn’t the very beginning of the Universe. There are a number of finely-tuned, unexplained phenomena that need to be set up as initial conditions to give us the Universe we have today, or the Universe wouldn’t exist as-is. Cosmic inflation is the theory that provided the first accurate explanation for these conditions, reproduced the Big Bang, plus made a slew of other predictions, many of which have been confirmed to great precision. It would be great to know exactly what occurred before the hot Big Bang, and whether it was a particular variant of cosmic inflation, or something inflation-like that turns out to be quite different.

2.) Life beyond Earth: Surely, we can all agree that life exists on Earth. But is there any place beyond Earth that also has life? And what would be a good definition of life, anyway? Do other worlds in our Solar System, which certainly have the building blocks of life, have either past or present life on them? What about worlds around other stars? How likely are they or aren’t they to have life, and how advanced, by comparison to us, have they gotten? These are questions that we truly don’t know the answers to, even though we have extremely strong suspicions that all the same conditions that occurred here on Earth have occurred many trillions of times elsewhere in our Universe.

describing the Universe, with General Relativity accounting for gravitation and Quantum Field Theory accounting for the properties of the Universe’s particles and their interactions. But if you passed an electron through a double slit, what would happen to its gravitational field? What happens at the singularity inside a black hole? And is spacetime fundamental, or is itself composed of discrete quanta? Without a quantum theory of gravity, and a theoretical merging of General Relativity and Quantum Field Theory, we may never know. Is it possible? We think so. Does our Universe actually have a theory of everything? Is gravity truly quantum in nature? That we don’t know.

4.) Dark energy and dark matter: Do they exist? The evidence certainly strongly suggests it. What, exactly, are they? Those are big, open questions that we don’t know the answer to. Dark energy appears to be a constant form of energy uniformly distributed throughout space; dark matter appears to behave like a particle, clumping and clustering under the influence of gravitation. But is dark matter actually particle-based? Does dark matter interact with either itself or normal matter through any force other than gravitation? How did it come to be? And what about dark energy? Is it a property inherent to space itself? Is it a separate field? And why does it have the numerical value that it has? The answers to all of these have so far proved elusive.

5.) The origin of life: How did life on Earth begin? We know that the building blocks of life can be found throughout the galaxy, in interstellar space, and even in the Solar System. Complex, carbon-based molecules are found all over, from cyanide to sugars to ethyl formate, the last of which is the molecule that gives raspberries their characteristic smell. We’ve found meteorites originating from the asteroid belt with amino acids inside, including more than 60 that aren’t involved in life processes here on Earth. And finally, we’ve found circumstantial evidence supporting the idea that Earth-based life originated prior to our planet’s formation. Yet, we haven’t managed to create life from non-life to this point. And thus, we still don’t know how life on Earth began.

If we can magically snap our fingers and know the answer to one of these, which one should we pick? There are two important considerations:

1.      Which one is the “hardest problem” in terms of knowing how to find the answer, and

2.      Which one would be the most revolutionary and beneficial to our society?

We can throw out cosmic inflation, since we already have many strong lines of evidence that not only support inflation, but also tightly constrain which models of inflation are still valid. We’re too close, and if the next 20–30 years are kind to us, we may even learn how inflation occurred. For the same reason, we should throw out the questions of life beyond Earth, or how it arose. These are active questions we’re making huge progress on, and as much as I want to know that we’re not alone, the amount that we’re learning, both in terrestrial biology and astrobiology, is too important. When you learn the answer, you miss out on all the lessons of finding things out, and over the rest of our lifetimes, we’re likely to see the answers to these questions slowly revealed.

Which leaves the merger of General Relativity with the quantum Universe, and the origin/nature of dark matter and dark energy. These are both incredibly hard problems that have many ideas behind them, but realistically, have seen very little progress. It’s not even a certainty that our Universe has a quantum theory of gravity, or that dark matter and dark energy truly exist, although there are many good reasons to believe all of these are so. All would be revolutionary, and as with all fundamental physical discoveries, the societal benefits are hard to envision.

The cosmic web is driven by dark matter, with the largest-scale structure set by the expansion rate and dark energy. The small structures along the filaments form by the collapse of normal, electromagnetically-interacting matter.

But if we had to choose one, I’d pick the knowledge of dark energy/dark matter. If dark matter turns out to be a particle, it’s possible that we’ll be able to manipulate it in a new way that could be tremendously beneficial to society. It could lead to free, abundant energy, not just here on Earth but anywhere we travel to in the galaxy. It may be as efficient as matter-antimatter annihilation, and if we can harness it, it’ll be there no matter where we go. It’s the majority of the Universe, and our attempts to detect it have all come up empty thus far. It may turn out that we’re looking in all the wrong ways, but until we look in the right way, we have no way of knowing.

Even though the majority of dark matter in the galaxy exists in a vast halo engulfing us, each individual dark matter particle makes an elliptical orbit under the influence of gravity. If dark matter is its own antiparticle, and we learn how to harness it, it may be the ultimate source of free energy. Image credit: ESO / L. Calçada.

There aren’t right and wrong answers here, just choices. The important thing is to realize what we know, what we’re wondering about, what the possibilities are, and what we’re doing to try to learn the definitive answers. If we could simply know something that’s far out of reach today, it could guide us down the correct path. But don’t underestimate the value of the investigative process, or the power of the lessons learned as we make these discoveries. The pleasure lies not just in knowing, but in the act of finding things out!

Scientific "measurements"....

From Torah Explorer by Yoram Bogacz

Chromium Opprobrium

December 18, 2017

https://torahexplorer.com/

Perhaps the most serious error that contemporary society makes about science is that all its results are equally credible. One of the main themes of Genesis and Genes is that science operates on different levels; results in some realms of science are credible, while results in other areas should be treated with considerable scepticism. In particular, one should be wary of claims about events that allegedly occurred millions or billions of years ago and are not amenable to direct observation.
This is a point that is misunderstood not only by the vast majority of laymen, but also by professional scientists. Here is an excerpt from Genesis and Genes.
[Beginning of excerpt]
With this in mind, let us consider this statement by a contemporary scientist and author:

Radioactive carbon-14 had a 5600-year half-life in the early universe just as it has now.^[1]

This is the voice of faith. The truth is that we do not know and cannotknow the half-life of carbon-14 in the early universe. We were not there, and any conclusions made on the basis of current measurements, no matter how plausible, will be based on assumptions about how nature’s laws operated in the past. Often, these assumptions are left unstated, so that the public is convinced that measurement of the cosmic background radiation, for example, is a direct measurement of some parameter that characterised the early universe. It isn’t. The theory from which the measurements derive their importance assumes, at the very least, that certain laws of nature operated at specific rates throughout the past, all the way back to the beginning. We shall never know whether this assumption is justified. Nonetheless, many contemporary scientists are committed to the principle of the immutability of natural laws. Whatever laws are operative today, they maintain, have always operated, and always at the same rate.
[End of excerpt]
One of the most important parameters in Origin-of-Life research is the atmospheric concentration of oxygen. All models that deal with the emergence of life on Earth rely on conclusions about how much oxygen our atmosphere contained at various points of Earth’s history. One reason for this, of course, is that large mammals like human beings need a high concentration of atmospheric oxygen to “operate”. A second reason is that too much oxygen in the atmosphere would lead to spontaneous fires erupting everywhere, not a scenario guaranteed to provide comfort to any emerging life. But perhaps the most important point is that oxygen, being a reactive (that is, destructive) molecule, makes it immensely unlikely that delicate organic reactions could have happened in the remote past. Abundant atmospheric oxygen would simply have wrecked these fragile processes before they had a chance to even begin.
So, how do you measure the atmospheric concentration of oxygen in Earth’s atmosphere billions of years ago? Not surprisingly, the answer is, “With great difficulty.” One of the standard techniques involves measuring the ratio of two isotopes of the metal Chromium in ancient rocks. [Isotopes are versions of the same element; every atom of the element has the same number of protons in its nucleus, but different isotopes contain different numbers of neutrons.]
New research sheds interesting light on the possible pitfalls in this kind of research.^[2] A report about research done at the Georgia Institute of Technology begins with the following paragraph:

For researchers pursuing the primordial history of oxygen in Earth’s atmosphere, a new study might sour some “Eureka!” moments. A contemporary tool used to trace oxygen by examining ancient rock strata can produce false positives, according to the study, and the wayward results can mask as exhilarating discoveries.

What is going on? The article continues:

Common molecules called ligands can bias the results of a popular chemical tracer called the chromium (Cr) isotope system, which is used to test sedimentary rock layers for clues about atmospheric oxygen levels during the epoch when the rock formed. Researchers at the Georgia Institute of Technology have demonstrated in the lab that many ligands could have created a signal very similar to that of molecular oxygen.

In other words, you think you’re measuring A, but in reality B is interfering and giving you results that mislead you. The result is

“There are some geographical locations and ancient situations where measurable signals could have been generated that had nothing to do with how much oxygen was around,” said Chris Reinhard, one of the study’s lead authors.

This is not just theory. The article states,

But some researchers confronted with odd Cr signals have thought they had perhaps stumbled upon a radical find, and they developed explanations for how O2 [oxygen] may have been surprisingly bountiful on the lonesome spot where a particular rock layer formed, while molecular oxygen was scant on the rest of the globe. Others puzzled that atmospheric O2 levels may have risen much earlier than overwhelmingly broad evidence has indicated.

“A lot of that could be chalked up to other chemical processes and not to interactions with oxygen,” Reinhard said.

&&&

There are at least two important conclusions to draw from this research. Firstly, when you read popular accounts of scientific research, words like measure pop up frequently, and provide a misleading impression of the process used to obtain the results. Very often, research does not directly measure whatever quantity the scientists are after. Rather, there is a proxy that is believed to serve as a reliable marker for the desired quantity. What the public fails to appreciate, however, is that the line between the proxy and the desired quantity is not straight; it is not even a line. It is a convoluted and intricate curve, and it is vulnerable to many obstacles.
Dr. Gerald Schroeder often confuses the proxy and the desired quantity in Genesis and the Big Bang. Here are typical statements from his book:

Cosmologists measured the age of the universe…; The age of the universe has been measured using a variety of independent… systems; …Phenomena that are readily measurable by modern archaeological, paleontological and cosmological instrumentation;

These remarks are phenomenally misleading. The supposed measurement that is spoken of here consists of numerous intricate steps, each of which depends on its own assumptions and is subject to unstated pitfalls.
This is precisely what you see in the Georgia Tech study. Popular accounts of this type of research omit the necessary caveats, and describe scientists as measuring the concentration of atmospheric oxygen. They do no such thing. There is a complicated process which is believed to reflect the desired quantity. If one understands this, and is aware of how often proxies turn out to be unreliable indicators of various quantities, the credibility of such reports is considerably diminished.
The second major lesson to take home is that – surprise! – science is not infallible. Until the research at Georgia Tech, nobody was aware that ligands could mimic the effects of various isotopes of chromium and thereby throw off the researchers. As the article makes clear, “some researchers confronted with odd Cr [chromium] signals have thought they had perhaps stumbled upon a radical find, and they developed explanations for how O2 may have been surprisingly bountiful on the lonesome spot where a particular rock layer formed…”
All sorts of theories and conclusions flowed from various findings which, in hindsight, turn out to be mistaken. Informed consumers of science would do well to adopt a more sceptical stance towards origin-of-life research.
SOURCES:
[1] Genesis and the Big Bang, Gerald L. Schroeder, Bantam Books, paperback edition 1992, page 29.
[2] http://www.rh.gatech.edu/news/598840/popular-tool-trace-earths-oxygen-history-can-give-false-positives. Last retrieved 18^th December 2017.

Textbook Wisdom on Human Origins Is Wrong!

Günter Bechly

December 12, 2017, 1:03 AM

https://evolutionnews.org/2017/12/its-official-textbook-wisdom-on-human-origins-is-wrong/

In three earlier articles at Evolution News (Bechly 2017a-c), I’ve written about the numerous paleoanthropological discoveries this year that generated media headlines announcing one “rewrite” of human evolution after another. I hardly dared to dream that, as an early Christmas present, 2017 would close with a final blow to the Out of Africa story. Yet guess how Discover Magazine announced this latest development? That’s right: “It’s Official: Timeline for Human Migration Gets a Rewrite” (Tarlach 2017).

As the article demonstrates, even mainstream paleoanthropologists now acknowledge that there is a problem with the ruling paradigm on human origins and with the way scientists have handled the accumulating evidence against it. We read:

The wealth of new paleoanthropological, archaeological and genetic evidence has passed the tipping point: In a review published today in the prestigious journal Science, researchers acknowledge that the conventional timeline of human migration out of Africa “can no longer be considered valid”….

Unfortunately, many researchers clung to the idea of a single migration out of Africa, no earlier than 60,000 years ago, for too long. Finds such as a human presence in the Levant 100,000 years ago, for example, were dismissed…

Today, however, writing in Science, researchers say that no one can ignore the preponderance of evidence. It’s time, at long last, to revise that tired old timeline of human migration.

The article in Science, Bae et al. (2017), states in unambiguous terms:

A rigid definition of the OoA model positing that modern humans dispersed from Africa only after 60 ka and simply replaced all indigenous populations…with no interbreeding can no longer be considered valid.

The rewrite, though, is not the necessary rethink we may have hoped for (Bechly 2017c). Instead we find the usual fudging on the conventional story, with the minimal changes required to accommodate the conflicting evidence. Darwinian just-so stories are reconsidered, but Darwinism itself may not be questioned.

Nevertheless, Gemma Tarlach, writing for Discover, comments critically:

Okay, so, science solved that, thanks, we know everything now, right? Nope. The new timeline for human migration still has some big holes to fill. Let’s start with where our species evolved.…

Our birthplace remains a mystery. Also big questions: how the first modern H. sapiens left Africa and where they went….

Acknowledging that our Out of Africa saga has many chapters stretching farther back in time is an important advance for the field. But some paleoanthropologists are unlikely to sign on: that small but vocal group of researchers who advocate a regional model for our species’ evolution….

So, while the conventional timeline that has dominated for half a century finally takes a tumble, don’t think that this is the end of the great debate regarding the early days of our species.

Who said it all along, yet was ridiculed by incompetent Darwinist bulldogs (e.g., Needle 2017) on the Web? Yes, indeed, you read it here first.

Literature:

• Bae CJ, Douka K, Petraglia MD 2017. “On the origin of modern humans: Asian perspectives.” Science358(6368): eaai9067.
• Bechly G 2017a. “Fossil Footprints from Crete Deepen Controversy on Human Origins.” Evolution News, September 6, 2017.
• Bechly G 2017b. “Human Origins: Out of Africa, or Out of Germany?” Evolution News, October 23, 2017.
• Bechly G 2017c. “What, Another ‘Rewrite’ of the Human Origins Story? How About a Rethink, Instead?” Evolution News, November 20, 2017.
• Needle B 2017. “Bechly belches!” Marmotism, October 28, 2017.
• Tarlach G 2017. It’s Official: Timeline for Human Migration Gets a Rewrite. Discover Magazine, December 7, 2017.

Why Is Giving Birth So Hard?

New theories are challenging a long-standing notion that the difficulty of childbirth is simply an evolutionary trade-off.

A newborn is examined at a maternity ward in England.Suzanne Plunkett / Reuters

·      JOSIE GLAUSIUSZ

·       DEC 4, 2017

·       HEALTH

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Harvey Karp, the best-selling author of The Happiest Baby on the Block, has some advice on his website for frazzled new parents: “Remember—your baby’s brain was so big that you had to ‘evict’ her after nine months, even though she was still smushy, mushy, and very immature.”

It’s not an idea unique to Karp. Scientists have long struggled to explain the myriad challenges attending human childbirth compared to other primates, from the relative helplessness of human infants, to the very “tight fit,” as some researchers have put it, between the female human pelvis and the typical size of a child that must pass through it.

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The mystery was the catalyst for what became known as “the obstetrical dilemma,” a long-debated though widely accepted hypothesis suggesting that the upright gait of Homo sapienswas accompanied by a narrowing of the pelvis—an evolutionary trade-off that resulted in increased risks to pregnant mothers as they struggled to push large-brained babies through ever-slimmer birth canals. Among other things, the dilemma has been used to suggest that the wider, birth-giving hips of women have hindered them locomotively and athletically—and perhaps even evolutionarily—compared to men.

That has always struck some scientists as too pat an explanation, though it is only in the last decade or so that the theory, which still has many subscribers, has received substantive pushback. Today, challenges abound for the idiosyncrasies of human gestation and birth—including new notions that look beyond evolution to more proximate and modern factors like poor diet and obesity.

Of course, rigorous debate over the relative strengths and weaknesses of theories in this cul-de-sac of physiological science will surely continue. But for all the back-and-forth, one thing seems quite clear: The days of simply describing the human birth process—and women themselves—as evolutionarily compromised seem to be coming to an end.

For some researchers, that change in thinking is long overdue.

* * *

Sherwood Washburn, the physical anthropologist who coined the phrase“obstetrical dilemma,” first published his theory in the September 1960 issue of Scientific American. He argued that, “in man, adaptation to bipedal locomotion decreased the size of the bony birth canal at the same time that the exigencies of tool use selected for larger brains. This obstetrical dilemma was solved by the delivery of the fetus at a much earlier stage of development.”

Early delivery, he concluded, foisted far greater responsibility on the “slow-moving mother,” who was now forced to hold her “helpless, immature infant,” while the men went out hunting.

The assumption that “women are compromised bipedally in order to give birth,” is widely accepted, says anthropologist Holly Dunsworth of the University of Rhode Island. But Dunsworth sees flaws in this premise. Women already have a range of dimensions in their birth canal, she thought, and they are all walking just fine. Indeed, research on human skeletons by anthropologist Helen Kurki of the University of Victoria in Canada has shown that the size and shape of the human birth canal varies very widely, even more so than the size and shape of their arms.

So in 2007, Dunsworth went looking for evidence to support the obstetrical dilemma as it has traditionally been understood.

“When I couldn’t, I thought I was crazy,” she says. Intrigued, she enlisted Anna Warrener, a professor of biology and biomechanics, then at Harvard University, to test the notion that wider pelvises in women decrease the efficiency of locomotion. After measuring the chain reaction of forces moving through the body—from the foot to the leg to the hip—Warrener and her colleagues found that wider hips do not increase the cost of locomotion. Indeed, both women and men are equally efficient at walking and running, and in hunter-gatherer societies, women walk, on average, 5.5 miles per day, often while carrying and feeding infants as well.

“The obstetric dilemma, in its definition, has housed this idea that women aren’t as good as men in some things because they have to give birth,” adds Cara Wall-Scheffler, an evolutionary anthropologist who studies human locomotion at Seattle Pacific University. “I have a number of papers that show that women are great walkers, and in some particular tasks women are better—they don’t use as much energy, they don’t build as much heat, they can carry heavier loads with less of an energetic burden.”

Dunsworth has an alternative theory as to why human pregnancy ends when it does: It’s called EGG, for “energetics of gestation and fetal growth,” and it applies not just to humans but to other mammals too. While a mother’s metabolic rate doubles during pregnancy, the fetus’s energy needs to increase exponentially toward the end of pregnancy. “As the fetus gets bigger and bigger and costlier and costlier to grow inside of the uterus,” Dunsworth explains, the mother’s metabolic rate reaches a limit. But the baby has to continue growing, “so the only way to do that is to get born.”

She is currently testing EGG on pregnant marmosets, measuring their energy use and metabolic rate during pregnancy over time, “to see if they give birth when they reach their maximum sustainable metabolic rate, as we do.”

Still others seek to explain why human brain volume has tripled over the past 2.5 million years, from the time of the Australopithecines. In a 2016 paper, brain and cognitive-science researchers Steven Piantadosi and Celeste Kidd of the University of Rochester argue that helpless, larger-brained but early-born babies select for parents with advanced intelligence who must interpret their wordless signals; these larger-brained parents produce babies with ever-increasing brain size, a self-reinforcing process leading to “runaway selection for premature infants and big brains.”

Dunsworth readily acknowledges that childbirth can be difficult, and that the human birth canal is indeed a tight fit for the fetus, even though humans are born with the smallest relative brain of all primates (only 30 percent of our adult brain size, compared to chimps, whose brains at birth are 40 percent of adult size). Globally, an average of 216 women die for every 100,000 live births, according to data from UNICEF. But the disparity between high- and low-income countries is gigantic: The lifetime risk of maternal death in rich countries is one in 3,300, compared to one in 41 in poor countries.

As such, blaming reproductive complications on evolution, writes Pamela K. Stone of the Culture, Brain, and Development Program at Hampshire College in Amherst, Massachusetts, “conceals the larger health disparities and risks that women face globally.”

Childbirth is difficult for many reasons, she writes—among them the 19th-century switch from birthing in the upright position, which allows the pelvic girdle to expand in response to contractions, to the supine position (still common among women in the West) which often requires the use of forceps.

* * *

Enter Jonathan Wells, a professor of anthropology and pediatric nutrition at the Great Ormond Street Institute of Child Health at University College London, who argues for a competing hypothesis on the obstetrical dilemma. For starters, Wells argues, long-term ecological trends have likely played a role in changes in both pelvic dimensions and offspring brain size. One such trend was the rise of agriculture about 11,500 years ago in the Levant, which led to a shift from a high-protein diet common among foragers to one replete with cereals. A high-carb diet is associated with both increased birth weight and shorter stature in the mother, and short stature is linked to smaller and flatter pelvises.

By that reasoning, the emergence of agricultural diets could have impacted “maternal mass and brain size, and may therefore have exacerbated the obstetric dilemma,” he says.

More recently, Wells has pointed to trends in both malnutrition and obesity as culprits in what he describes as a “new” obstetrical dilemma. According to Wells, this “dual burden” is contributing to a rising toll of obstructed labor, gestational diabetes, and larger-than-average newborns. Wells describes his theory in the April 2017 issue of The Anatomical Record.

Between 1980 and 2013, the percentage of overweight and obese women globally rose from 29.8 percent to 38 percent. At the same time, one in three people are malnourished in one form or another. “There is rapidly accumulating evidence,” Wells says, “that the dual burden of malnutrition can occur within the same individuals: those who experienced poor nutrition and became stunted in early life, but who have also been exposed to obesogenic pressures from childhood onward and who have therefore gained excess weight subsequently.”

As Wells notes, obstructed labor, where delivery of the baby causes harm to the mother, child, or both, accounts for 12 percent of maternal mortality worldwide. It also increases substantially the risk of serious long-term maternal injuries, such as obstetric fistula. Dunsworth’s EGG theory can’t explain this frequency, he says.

But the combination of obesity and malnutrition can: Malnutrition and infectious disease in childhood is linked to short stature, which is associated with smaller pelvises in adulthood. Obesity, which is rising fastest in populations most prone to childbirth complications, increases the risk of delivering a “macrosomic” baby, whose birth weight exceeds the 90th percentile in any given population. “Overweight women in most populations are more likely to develop gestational diabetes if they are also short,” Wells adds. The combination of gestational diabetes and maternal obesity doubles the risk of macrosomic babies. So in theory, Wells says, a short overweight woman has two different risk factors for obstructed labor: smaller pelvic dimensions, and a higher probability of producing a large newborn.

This scenario is further aggravated by the persistence of child marriage, in which teens give birth before pelvic growth is completed, and gender inequality. A recent study of 31 countries in sub-Saharan Africa conducted by Alissa Koski, a postdoctoral scholar at the University of California, Los Angeles, Fielding School of Public Health, found that more than one-third of girls in more than half of the countries studied married before the age of 18. In another study of 96 countries, Wells and his colleagues found “strong associations” between societal gender inequality and the prevalence of low birth weight, stunting, wasting, and child mortality. “On this basis,” he says, “societies with high levels of gender inequality are more likely to produce adult women of smaller body size,” which will impact the dimensions of the pelvis.

At the other extreme, he notes, obesity is increasing in prevalence faster in women than in men. Given these rapid increases in obesity, overweight women are more likely to experience difficulties in delivering babies if they were also stunted in childhood, Wells predicts—although so far, he doesn’t have the data to prove it. It is clear, however, that cesarean delivery has become one of the most common surgical procedures worldwide, increasing to “unprecedented levels” between 1990 and 2014 and ranging from 6 to 27 percent of all births in the least- to most-developed regions, respectively.

Dunsworth sees this as something of a self-fulfilling prophecy. “I worry that this idea [of the obstetrical dilemma] is justifying status-quo high rates of C-sections and other childbirth interventions,” Dunsworth says. “People say, ‘It’s just evolution—there’s nothing we can do, and here’s how technology helps, and that’s fabulous.’ But I know we’re overdoing it. Everybody knows that.”

While Dunsworth says she admires Wells’s research, she adds that she wishes he would come out a little more strongly against the evolutionary obstetrical dilemma.

For his part, Wells describes the work of Dunsworth and her colleagues as being of “major importance.” But “that doesn’t mean that Washburn had no important message,” he adds. “We have to acknowledge that the process of birth is surprisingly complex in humans, compared to other apes.”

“It is very clear from maternal mortality statistics that the contemporary burden of the obstetric dilemma is highly unequally distributed amongst women,” Wells says. “This suggests that if we had a better understanding of its biological basis, we could improve our efforts to reduce the burden of maternal and child mortality.”