A pair of ancient Egyptian mummies, known for more than a century as the Two Brothers, were actually half brothers, a new study of their DNA finds.

These two, high-ranking men shared a mother, but had different fathers, say archaeogeneticist Konstantina Drosou of the University of Manchester in England and her colleagues. That muted family tie came to light thanks to the successful retrieval of two types of DNA from the mummies’ teeth, the scientists report in the February Journal of Archaeological Science: Reports. The finding highlights the importance ancient Egyptians placed on maternal lines of descent, Drosou’s group contends.
Questions have swirled about the biological backgrounds of the mummified men ever since they were found together in a tomb near the village of Rifeh in 1907. The tomb dates to ancient Egypt’s 12th Dynasty, between 1985 B.C. and 1773 B.C. Coffin inscriptions mention a female, Khnum-Aa, as the mother of both men. And both mummies are described as sons of an unnamed local governor. It has always been unclear if those inscriptions refer to the same man, but discoverers decided the mummies were full brothers, because the two were buried next to each other and had the same mother.

Over time, differences discovered in the men’s skull shapes and other skeletal features raised suspicions that the Two Brothers were not biologically related at all. And some researchers argued that the inscriptions indicating the men had the same mother were misleading.

Adding to those doubts, a 2014 paper reported differences between the two mummies’ mitochondrial DNA, suggesting one or both had no biological link to Khnum-Aa. Mitochondrial DNA typically gets inherited from the mother.

But that study extracted ancient DNA from liver and intestinal samples using a method susceptible to contamination with modern human and bacterial DNA, Drosou’s team argues. In the new work, researchers isolated and assembled short pieces of mitochondrial and Y-chromosome DNA from both mummies’ teeth using the latest methods. The Y chromosome determines male sex and gets passed from father to son. This approach minimizes potential contamination from modern sources (SN Online: 5/31/17).
That new DNA evidence “proves the hieroglyphic text [on the mummies’ coffins] to be accurate,” at least in saying the mummified men had the same mother, says Egyptologist and study coauthor Campbell Price, curator of the Egypt and Sudan collections at the Manchester Museum in England.

Unlike the deference given to Khnum-Aa as a named parent of both interred individuals, he says, the coffin inscriptions must refer to different fathers who were considered peripheral family members and thus left unnamed. “Power may have been transferred down the female line rather than simply by a son inheriting [high rank] from his father,” Price suggests. Khnum-Aa’s background, social standing and genetic makeup, however, remain a mystery.

Genetic evidence that two half brothers were buried in the same tomb and placed in coffins that name only their mother makes sense, says Egyptologist Joann Fletcher at the University of York in England. Many written sources from ancient Egypt show precedence to the maternal line, “from the official lists of Egypt’s early kings whose names are accompanied by those of their mothers to nonroyal individuals, who likewise cite only their mother’s name,” Fletcher explains.

Dates of death on the mummies’ linen wrappings suggest that Khnum-Nakht died first, at around age 40, Price says. A few months later, Nakht-Ankh died at about age 60. The causes of their deaths are unknown.

Unless you are a recent arrival from another universe, you’ve no doubt heard that this one is expanding. It’s getting bigger all the time. What’s more, its growth rate is accelerating. Every day, the universe expands a little bit faster than it did the day before.

Those day-to-day differences are negligible, though, for astronomers trying to measure the universe’s expansion rate. They want to know how fast it is expanding “today,” meaning the current epoch of cosmic history. That rate is important for understanding how the universe works, knowing what its ultimate fate will be and even what it is made of. After all, the prime mission of the Hubble Space Telescope when it was launched in 1990 was to help determine that expansion rate (known, not coincidentally, as the Hubble constant, named for the astronomer Edwin Hubble).
Since then evidence from Hubble (the telescope) and other research projects has established a reasonably precise answer for the Hubble constant: 73, in the units commonly used for this purpose. (It means that two independent astronomical bodies separated by 3.26 million light-years will appear to be moving away from each other at 73 kilometers per second.) Sure, there’s a margin of error, but not much. The latest analysis from one team, led by Nobel laureate Adam Riess, puts the Hubble constant in the range of 72–75, as reported in a paper posted online January 3. Considering that as late as the 1980s astronomers argued about whether the Hubble constant was closer to 40 or 90, that’s quite an improvement in precision.

But there’s a snag in this success. Current knowledge of the universe suggests a way to predict what the Hubble constant ought to be. And that prediction gives a probable range of only 66–68. The two methods don’t match.

“This is very surprising, I think, and very interesting,” Riess, of the Space Telescope Science Institute in Baltimore, said in a talk January 9 at a meeting of the American Astronomical Society.

It’s surprising because astrophysicists and cosmologists thought they had pretty much figured the universe out. It’s made up of a little bit of ordinary matter, a lot of some exotic “dark matter” of unknown identity, and even more of a mysterious energy permeating the vacuum of space, exerting gravitational repulsion. Remember that acceleration of the expansion rate? It implies the existence of such energy. Because nobody knows what it is, people call it “dark energy,” while suspecting that its real name is lambda, the Greek letter that stands for “cosmological constant.” (It’s called a constant because any part of space should possess the same amount of vacuum energy.) Dark energy contributes something like 70 percent of the total mass-energy content of the universe, various lines of evidence indicate.
If all that’s right, then it’s not all that hard to infer how fast the universe should be expanding today. You just take the recipe of matter, dark matter and dark energy and add some ghostly subatomic particles known as neutrinos. Then you carefully measure the temperature of deep space, where the only heat is the faint glow remaining from the Big Bang. That glow, the cosmic microwave background radiation, varies slightly in temperature from point to point. From the size of those variations, you can calculate how far the radiation from the Big Bang has been traveling to reach our telescopes. Combine that with the universe’s mass-energy recipe, and you can calculate how fast the universe is expanding. (You can, in fact, do this calculation at home with the proper mathematical utensils.)

An international team’s project using cosmic microwave background data inferred a Hubble constant of 67, substantially less than the 73 or 74 based on actually measuring the expansion (by analyzing how the light from distant supernova explosions has dimmed over time).

When this discrepancy first showed up a few years ago, many experts believed it was just a mirage that would fade with more precise measurement. But it hasn’t.

“This starts to get pretty serious,” Riess said at the astronomy meeting. “In both cases these are very mature measurements. This is not the first time around for either of these projects.”

One commonly proposed explanation contends that the supernova studies are measuring the local value of the Hubble constant. Perhaps we live in a bubble, with much less matter than average, skewing expansion measurements. In that case, the cosmic microwave background data might provide a better picture of the “global” expansion rate for the whole universe. But supernovas observed by the Hubble telescope extend far enough out to refute that possibility, Riess said.

“Even if you thought we lived in a void…, you still are basically stuck with the same problem.”

Consequently it seems most likely that something is wrong with the matter-energy recipe for the universe (technically, the cosmological standard model) used in making the expansion rate prediction. Maybe the vacuum energy driving cosmic acceleration is not a cosmological constant after all, but some other sort of field filling space. Such a field could vary in strength over time and throw off the calculations based on a constant vacuum energy. But Riess pointed out that the evidence is growing stronger and stronger that the vacuum energy is just the cosmological constant. “I would say there we have less and less wiggle room.”

Another possibility, appealing to many theorists, is the existence of a new particle, perhaps a fourth neutrino or some other relativistic (moving very rapidly) particle zipping around in the early universe.

“Relativistic particles — theorists have no trouble inventing new ones, ones that don’t violate anything else,” Riess said. “Many of them are quite giddy about the prospect of some evidence for that. So that would not be a long reach.”

Other assumptions built into the current cosmological standard model might also need to be revised. Dark matter, for example, is presumed to be very aloof from other forms of matter and energy. But if it interacted with radiation in the early universe, it could have an effect similar to that of relativistic particles, changing how the energy in the early universe is divided up among its components. Such a change in energy balance would alter how much the universe expands at early times, corrupting the calibrations needed to infer the current expansion rate.

It’s not the first time that determining the Hubble constant has provoked controversy. Edwin Hubble himself initially (in the 1930s) vastly overestimated the expansion rate. Using his rate, calculations indicated that the universe was much younger than the Earth, an obvious contradiction. Even by the 1990s, some Hubble constant estimates suggested an age for the universe of under 10 billion years, whereas many stars appeared to be several billion years older than that.

Hubble’s original error could be traced to lack of astronomical knowledge. His early overestimates turned out to be signals of a previously unknown distinction between different generations of stars, some younger and some older, Riess pointed out. That threw off distance estimates to some stars that Hubble used to estimate the expansion rate. Similarly, in the 1990s the expansion rate implied too young a universe because dark energy was not then known to exist and therefore was not taken into account when calculating the universe’s age.

So the current discrepancy, Riess suggested, might also be a signal of some astronomical unknown, whether a new particle, new interactions of matter and radiation, or a phenomenon even more surprising — something that would really astound a visitor from another universe.