What Is 'Manhattanhenge?'

Today through Saturday marks a biannual solar event called Manhattanhenge, where the rising or setting sun aligns with the east-west grid of Manhattan streets.

Astrophysicist Neil deGrasse Tyson coined the term back in 2002, inspired by the famous Stonehenge site in the United Kingdom, where the sun sets in alignment with the stones every summer solstice.

Technically, "Manhattanhenge" occurs around the summer solstice, not on the solstice itself. That's because of the orientation of Manhattan's famous grid pattern — established by the the Commissioners’ Plan of 1811 — is not perfectly aligned with the geographic north-south line; it's rotated 29 degrees east, shifting the dates of alignment.

If that alignment had been perfect, Manhattanhenge would have occurred on the equinoxes every year: the first day of spring and autumn, respectively.

(Historical side note: The goal of the 1811 plan was "a free and abundant circulation of air" to stave off disease. The right angles were also favored because "straight-sided and right-angled houses are the most cheap to build." The rigid Manhattan grid has been much-maligned over the last 200 years, but recently has come back into favor with city planners.)

This kind of alignment is not unique to Manhattan; any city with a uniform street grid will have dates where the sun aligns with those streets, including Chicago, Toronto and Montreal.

But Manhattan also boasts a clear view of the horizon, looking across the Hudson River toward New Jersey. Plus you've got all those tall buildings lining the streets, creating the perfect vertical frame to show the setting sun to best advantage.

Tyson has been outspoken in the past about astronomical inaccuracies in film and television. For instance, you can always spot a fake sunrise onscreen, because the sun will move up and to the left as it rises. In reality, the sun always rises up and to the right. Directors tend to film a sunset for such scenes and then just run it backwards to portray a sunrise, thinking nobody will notice. (And they'd probably get away with it, too, if it weren't for those meddling astrophysicists!)

The term Manhattanhenge technically applies to the setting sun phenomenon that flanks the summer solstice, usually around May 28 and July 12, although the precise dates vary slightly year to year. A similar alignment occurs with the rising sun around the winter solstice, usually Dec. 5 and Jan. 8.

From Discovery News

This Isn’t a Spider, But It Does Have Genitals in Its Legs

This isn't slowmo. It's how a sea spider actually moves. The critter was spotted 8,675 feet deep off the coast of Vancouver by a submersible manned by Ocean Networks Canada. Clearly, it won't even give submersibles the time of day.

So, good news and bad news for those of you afraid of spiders. Good news is, this creature isn’t a spider because spiders can’t breathe underwater, so you’re safe from arachnids if you want to spend more time in the ocean. (Well, one species of spider actually can live underwater by trapping air around its abdomen—sorry, I’m really bad at good news.) The bad news is what while the sea spider may not be an actual spider, it looks like the ghost of a spider you once killed. Which might actually be worse and … totally scientific?

The 1,300 known species of sea spider are truly ancient animals that as far as scientists can tell aren’t closely related to any extant species, spiders or otherwise. At the moment, though, they’re lumped in the group that holds spiders and horseshoe crabs. They have such tiny abdomens that their guts extend into their legs. Their genitals are there in the limbs too, which makes mating … interesting. And like sea horses, it’s the males that carry the young.

Sea spiders live in both deep and shallow seas around the world, but all are carnivores, through and through. They have claw-like mouthparts known as chelicerae, which spiders also have, suggesting they may belong to the same group (appropriately enough called Chelicerata). The actual feeding happens through a proboscis, a sort of tube that can be longer than the rest of the sea spider’s abdomen in some species.

“They feed generally on things that don’t move, like sponges and corals, but also slow-moving things like worms or sea slugs,” says marine biologist Claudia Arango of the Queensland Museum in Australia. “What they do is they’ve got very sharp jaws at the tip of that tube, the proboscis, so they pierce the prey and start sucking out fluids.”

The deep and shallows are of course worlds apart as far as habitats go, so sea spider species have adapted accordingly. To find food in the blackness, the blind deep-sea varieties likely sniff out their prey’s chemical cues, while their shallow-water peers have four simple eyes. In the shallows, they also tend to be more colorful than in the deep sea, since in the darkness, flashy colors won’t do you no good nohow.

The sea spider Nymphon grossipes, which really got short-changed on the whole name thing.

Their body plans, too, are wonderfully adapted for their environments. The long-legged species are built like the tripods from The War of the Worlds—but with fewer legs and death rays—because sediment down in the deep can be soft and unstable, so lankier limbs keep it from sinking up to its abdomen. In the shallows, sea spiders tend to be stouter, with thicker, shorter legs that help them better hold on in rough waters, not to mention avoid shattering into a shower of limbs.

Leg Genitals and Other Adventures in Sea Spider Sex

What the many species of sea spider can agree on, though, is how to have sex: namely, very acrobatically. Both males and females have genital pores in their legs, males on just their last two pairs and females on every single limb. When a couple comes together the spindly male crawls on top of the spindly female. “So basically he climbs up and walks all over the female and then starts trying to go under the female so that both the pores come in contact,” says Arango. “The female would be standing totally normal while the male would be upside down, clinging on the female.”

Pseudopallene harrisi, from Australia. Note the claw-like chelicerae. It’s fashionably colorful not because it’s from Australia, but because that’s par for the course for shallow-water sea spiders.

When the female releases her eggs, the male combines them with his sperm and bundles them together in balls. These he holds with special appendages, known as baby björns ovigers, and “he carries the eggs all the way until they hatch, and sometimes even later you can see fathers carrying the babies,” says Arango. “It’s quite a heavy load sometimes.”

Inevitably, though, the larvae must set out on their own, and some species won’t just float at the mercy of the currents. They’ll invade the bodies of other creatures on the seafloor, including bivalves, burrowing into their flesh and feeding on them and eventually killing them. Others invade the bodies of coral, stealing the nutrients that algae produce for them.

A sea spider male carries eggs with specialized limbs called ovigers.

Still other species go after creatures called hydroids. One particular sea spider (.pdf) parasitizes the hydroid Tubularia larynx, a sort of small tube with frilly pink polyps, which grows en masse on rocks. The male sea spider will carry his young to fields of these hydroids and release them. Amid plenty of food, the young invade the hydroids’ tissues, feeding and feeding and growing and growing before erupting out of their dead hosts.

File Sea Spiders Under: It’s Complicated

It should be clear by now that sea spiders aren’t like any other creature on Earth—not by a long shot. I mean, the body plan alone is out of control. The daddy long legs is a lanky little thing, but the sea spider has so simplified its body plan that really its abdomen is little more than a joint for its legs, forcing its organs to flow into its limbs. Its heart is exceedingly simple, and because it lacks gills, it seems to absorb oxygen through its cuticle. And it has that bizarre proboscis, plus the males have those unique specialized arms used to hold eggs.

It all adds up to large-scale befuddlement for the folks studying them, and accordingly it’s a matter of controversy where exactly sea spiders fall in the tree of life. But Arango has an idea. “When you look at the morphology of the sea spiders, apart from a superficial resemblance to spiders, there’s lots of things that are unique,” says Arango. “In terms of giving them a place in the classification the best thing we can do, based on DNA mostly, is keep them at the base of the chelicerates.”

Anoplodactylus evansi may be Australian, but it looks a lot like a St. Louis Blues fan.

The problem is that sea spiders are a very, very old group of animals that likely diverged early on in the evolution of arthropods. I’m talking more than 500 million years ago, not all that long after the appearance of the first creatures we’d even recognize as animals. But for all that time on Earth, their fossils are scant, so tracing their lineage is a nightmare. And it doesn’t help that anatomically, they’re like nothing else living on this planet.

Read more at Wired Science

Dinosaurs May Have Been Warm-Blooded

Dinosaurs were warm-blooded animals that had many traits in common with mammals, finds controversial new research.

The study, published in the journal Science, counters other popular theories, which say that dinosaurs were either cold-blooded and reptile-like, or occupied a unique intermediate category of animals that were neither fully cold nor warm-blooded.

“Upon re-analysis, it was apparent that dinosaurs weren’t just somewhat like living mammals in their physiology — they fit right within our understanding of what it means to be a ‘warm-blooded’ mammal,” author Michael D’Emic, a Stony Brook University paleontologist, said in a press release.

The “re-analysis” refers to D’Emic’s work revisiting yet another Science paper, published last year, which compiled a huge dataset on growth and metabolism of hundreds of living animals. D’Emic admits that this dataset was “remarkable” and “unprecedented.”

Yet, that earlier study found that dinosaurs would have fit into the intermediate category between ectothermic (cold-blooded, with body temperature controlled largely by the surrounding environment) and endothermic (warm-blooded, like us).

D'Emic looked at that study again, focusing on two primary aspects.

First, the original study had scaled yearly growth rates to daily ones in order to standardize comparisons.

"This is problematic," D'Emic said, "because many animals do not grow continuously throughout the year, generally slowing or pausing growth during colder, drier, or otherwise more stressful seasons. Therefore, the previous study underestimated dinosaur growth rates by failing to account for their uneven growth. Like most animals, dinosaurs slowed or paused their growth annually, as shown by rings in their bones analogous to tree rings."

He added that very stressful or seasonal environments can also impact growth, and would have really affected dinosaurs. He believes that these factors were underestimated in the earlier study.

The second aspect of his re-analysis took into account the widely held view that all dinosaurs did not become extinct: some evolved to become birds. Today’s birds are warm-blooded, so he argues that dinosaurs must have been this way too.

"Separating what we commonly think of as 'dinosaurs' from birds in a statistical analysis is generally inappropriate, because birds are dinosaurs–they’re just the dinosaurs that haven't gone extinct," he explained.

If D'Emic's theory about warm-blooded dinosaurs holds, then this would lead to still more re-evaluation of other data on things like the big sails and head ornaments on some dinosaurs. Certain past studies have linked these to body temperature regulation. If they didn’t serve that function, then perhaps they were used more for flashy mating displays or other types of visual communication.

Holly Woodward, an assistant professor in the Center for Health Sciences at Oklahoma State University, supports re-examining prior studies, even those that appear seamless.

As she said, "D'Emic's study reveals how important access to the data behind published results is for hypothesis testing and advancing our understanding of dinosaur growth dynamics."

Read more at Discovery News

Mystery Deepens Over Rare Roman Tombstone

Mystery has deepened over a Roman tombstone unearthed earlier this year in western England, as new research revealed it had no link with the skeleton laying beneath it.

The inscribed stone was discovered during the construction work of a parking lot in Cirencester.

Made from Cotswold limestone, it was found laying on its front in a grave — directly above an adult skeleton.

When it was turned over, the honey colored stone revealed fine decorations and five lines of Latin inscription which read: “D.M. BODICACIA CONIUNX VIXIT ANNO S XXVII,” possibly meaning: “To the shades of the underworld, Bodicacia, spouse, lived 27 years.”

The discovery was hailed as unique since the stone was believed to be the only tombstone from Roman Britain to record the person found beneath.

In fact, while the dedication on the tombstone is to a woman, the skeleton beneath it was that of a male.

It turns out the gravestone and skeleton were also laid at different times — the inscribed stone was early Roman, dating to the 2nd century A.D., while the burial was most certainly late Roman, from the 4th century A.D..

“We believe the tombstone to have been re-used as a grave cover perhaps as long as two centuries after it was first erected,” Ed McSloy, Cotswold Archaeology’s finds expert, told Discovery News.

Martin Henig and Roger Tomlin, leading experts in Roman sculpture and inscriptions at the University of Oxford, noted that the back of the stone is very roughly worked, almost unfinished, in strong contrast to the finely sculpted front.

Unlikely to have been a free-standing tombstone, the five-foot-long inscribed stone may have rather been set into walls, possibly those of a mausoleum.

Who the grave belonged to remains a mystery.

“Reading the letters, the most plausible interpretation of the name is Bodicacia, a previously unknown Celtic name,” McSloy said.

Indeed the name appears to be a variant of a Celtic name with same root as Boudicca. This was the rebel queen of the Iceni, a British tribe, who unsuccessfully attempted to defeat the Romans.

Bodicacia’s tombstone was also unique. The pediment, which is the decorated, triangular portion at top of the stone, shows the Roman god Oceanus.

A divine personification of the sea in the classical world, the god was portrayed with a long mustache, stylized long hair, and crab-like pincers above the head.

Read more at Discovery News

Sacrificed Humans Discovered Among Prehistoric Tombs

A prehistoric cemetery containing hundreds of tombs, some of which held sacrificed humans, has been discovered near Mogou village in northwestern China.

The burials date back around 4,000 years, before writing was developed in the area. In just one archaeological field season — between August and November 2009 — almost 300 tombs were excavated, and hundreds more were found in other seasons conducted between 2008 and 2011.

The tombs were dug beneath the surface of the ground and were oriented toward the Northwest. Some of the tombs had small chambers where finely crafted pottery was placed near the deceased. Archaeologists also found that mounds of sediment covered some of the tombs, which could have marked the location of these tombs.

Within the tombs, archaeologists found entire families buried together, their heads also facing the Northwest. They were buried with a variety of goods, including, necklaces, weapons and decorated pottery.

Human sacrifices were also evident in the burials. In one tomb, “the human sacrifice was placed on its side with limbs bent and its face toward the tomb chamber. The bones are relatively well preserved, and the individual’s age at death is estimated at around 13 years,” archaeologists wrote in a paper published recently in the journal Chinese Cultural Relics.

Predicting the future

The goods found in the tombs included pottery decorated with incised designs. In some cases, the potter made numerous incisions shaped like the letter “O,” with the O’s forming patterns on the vessel. Sometimes, instead of making O’s, the potter would incise wavy lines near the top of the pot.

The researchers also discovered artifacts that could have been used as weapons. Bronze sabers were found that researchers say could have been used for cutting. They also found stone mace heads. (A mace is a blunt weapon that can smash a person’s skull in.) Axes, daggers and knives were also found in the tombs.

Archaeologists also found what they call “bone divination lots,” or artifacts that could have been used in rituals aimed at predicting the future. Bone divination was practiced widely throughout the ancient world. In fact, when writing was developed in China centuries later, some of the earliest texts were written on bones used for divination.

Qijia culture

Most of the tombs belong to the Qijia culture, whose people used artifacts with similar designs and lived in the upper Yellow River valley.

“Qijia culture sites are found in a broad area along all of the upper Yellow River as well as its tributaries, the Huangshui, Daxia, Wei, Tao and western Hanshui rivers,” Chen Honghai, a professor at Northwestern University in China, wrote in a chapter of the book “A Companion to Chinese Archaeology” (Wiley, 2013).

Honghai wrote that people from the Qijia culture lived in a somewhat arid area. To adjust to these conditions, the Qijia people grew millet, a cereal suited to a dry environment; and raised a variety of animals, including pigs, sheep and goats.

People from the Qijia culture lived in modest settlements (smaller than 20 acres), in houses that were often partially buried beneath the ground. “Remains of buildings are mainly square or rectangular, and they are usually semi-subterranean. The doors usually point south, identical to the current local custom of building houses, as rooms on the sunny side receive more light and warmth,” Honghai wrote.

Read more at Discovery News

New Spacecraft Photos Hint at a Rich and Complex Pluto

As NASA’s New Horizons spacecraft blasts closer to Pluto at a pace of 750,000 miles per day, increasingly detailed images are beginning to come our way.

In the latest series of images beamed back to Earth from the mission’s Long-Range Reconnaissance Imager (LORRI) instrument, a complex small world is beginning to reveal itself — vast, dark regions are coming into focus. Now we are in a new regime of Plutonian discovery; these pixelated views are the highest resolution photos we have ever seen of the dwarf planet.

“As New Horizons closes in on Pluto, it’s transforming from a point of light to a planetary object of intense interest,” said NASA’s Director of Planetary Science Jim Green in a news release today (Wednesday). “We’re in for an exciting ride for the next seven weeks.”

“These new images show us that Pluto’s differing faces are each distinct; likely hinting at what may be very complex surface geology or variations in surface composition from place to place,” said New Horizons Principal Investigator Alan Stern of the Southwest Research Institute in Boulder, Colo. “These images also continue to support the hypothesis that Pluto has a polar cap whose extent varies with longitude; we’ll be able to make a definitive determination of the polar bright region’s iciness when we get compositional spectroscopy of that region in July.”

In less than 2 months New Horizons will make its Pluto close encounter and as these gradually-sharpening images are showing us, it seems likely that Pluto will be a rich and complex place.

“By late June the image resolution will be four times better than the images made May 8-12, and by the time of closest approach, we expect to obtain images with more than 5,000 times the current resolution,” added Hal Weaver, New Horizons project scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

These latest photos are derived through a method known as “image deconvolution”, which allows us to see the broad differences in surface morphology. These changes in surface albedo likely real features, revealing the (possible) bright polar ice caps and vast regions that appear to absorb more light. However, some of the image processing can generate spurious details that will disappear in later observations.

Read more at Discovery News

CIA Stops Sharing Climate Change Info With Scientists

In a recent speech, President Obama proclaimed that climate change “constitutes a serious threat to global security (and), an immediate risk to our national security,” and warned that it actually could exacerbate other menaces, such as terrorism and political instability.

“Severe drought helped to create the instability in Nigeria that was exploited by the terrorist group Boko Haram,” Obama said. “It’s now believed that drought and crop failures and high food prices helped fuel the early unrest in Syria, which descended into civil war in the heart of the Middle East.”

But even as the White House is affirming its focus, the CIA reportedly is ending a key program that shared the agency’s climate change data — some of it gathered by surveillance satellites and other clandestine sources.

Investigative magazine Mother Jones broke the story last week that the intelligence agency is shutting down the Measurements of Earth Data for Environmental Analysis program. MEDEA allowed a select group of scientists access to classified information about climate change. Mother Jones said that the data included not only satellite observations, but also ocean temperature and tidal readings gathered by U.S. Navy submarines.

The CIA began gathering climate data for global security purposes during the Cold War, when it tracked the effect of climate change on Soviet grain harvests. According to one document mentioning MEDEA on the CIA website, the program was created in the early 1990s, in part through the efforts of then-U.S. Sen. Al Gore (D-Tenn.), as part of an effort to share intelligence related to environmental problems. It included about 60 scientists with security clearances. The researchers found, among other things, that “found that historical imagery from our early satellite systems could provide a more accurate picture of climate change over time.”

In a 1996 speech, then-CIA director John Deutch said that MEDEA  ”will give scientists an ongoing record of changes in the earth that will improve their understanding of environmental processes. More importantly, it will greatly enhance their ability to provide strategic warning of potentially catastrophic threats to the health and welfare of our citizens.”

In the early 2000s, MEDEA was shut down by President George W. Bush, who initially took the position, contrary to the great majority of climate scientists, that it was unclear whether human activity was driving global warming. (He eventually changed his view.)  The program was revived in 2010 by Obama.

The New York Times reported in 2010 that the shared CIA data reportedly included a trove of images of Arctic sea ice, which enabled scientists to distinguish summer melts from longer-term climate trends.

University of Washington scientist Norbert Untersteiner, one of the scientists given access to the CIA’s climate data, told The New York Times that the intelligence data was “really useful.”

Though Republicans in Congress for long have criticized the use of intelligence resources to study climate change, the reasons for shuttling down MEDEA remain murky.

Read more at Discovery News

Modern Human Leg Mummified Using Ancient Egyptian Methods

The ancient Egyptians famously mummified the dead to preserve their loved ones in perpetuity, and now, scientists have mummified fresh tissue from a human corpse to gain insight into these ancient preservation techniques.

The team adhered to ancient Egyptian techniques to mummify part of the human body, which had been donated to science. They placed the tissue in a salt solution, and measured the progress of preservation using state-of-the-art microscopy and imaging techniques.

The findings, detailed Friday (May 22) in the journal The Anatomical Record, give researchers some fascinating new clues about the ancient Egyptian embalming process.

“We wanted to have an evidence-based methodology” for understanding what the mummification process looked like, said Christina Papageorgopoulou, one of the researchers on the new study and a physical anthropologist at the Democritus University of Thrace in Greece. “The only way you can do this is by the experiment yourself.”

Making a mummy

Most of what scientists know about ancient Egyptian mummification comes from the Greek historian Herodotus, who lived during the fifth century B.C. First, embalmers would have removed the dead individual’s organs — including the brain, which would be extracted through the nose. Then, they would sterilize the chest and abdominal cavities, before placing the body in a salty fluid containing natron — a mixture of soda ash and sodium bicarbonate — which would drain the bodily fluids and prevent the body from rotting. Finally, they would swaddle the body in strips of linen and bury it in a tomb or grave.

Some studies have attempted to use these techniques to mummify animals or human organs, and there have been one or two attempts to mummify a complete human body. But the process had never been studied using modern scientific techniques while the mummification was in progress.

In this new study, Papageorgopoulou and her colleagues used the Egyptian salt-based preservation method to mummify the leg of a female human body that had been donated to the University of Zurich in Switzerland, where the experiment was conducted. “If we used the whole body, we would have had to cut it up and take out the intestines [and other organs],” Papageorgopoulou told Live Science.

For comparison, they also attempted to mummify a limb “naturally,” using dry heat, but that attempt failed and was stopped after a week.

The researchers took samples of the tissue every two to three days, and examined it using a variety of methods: the naked eye, a microscope, DNA analysis, and X-ray imaging methods.

Ancient process revealed
For the most part, the mummification was successful, but it took nearly seven months (208 days), which is much longer than the two months the ancient Egyptian method took, according to Herodotus. (Other accounts report that it took even less time.)

“We were not so quick like the ancient Egyptians,” Papageorgopoulou said. She suspects the cooler, damper conditions in the lab in Zurich, compared with the arid environment of ancient Egypt, may explain the discrepancy.

The salt solution effectively removed the water from the leg tissue, which prevented bacteria and fungi from degrading it. The microscopic analysis revealed good preservation of the skin and muscle tissue, as well.

Read more at Discovery News

Gory Remains of First Known Murdered Human Found

The first known murder in human history took place 430,000 years ago in Spain, suggests a new study that describes the mutilated remains of the victim.

While the study, published in the latest issue of the journal PLOS ONE, does not specify the species of human, the site and the time of the likely crime indicate that the first known murder victim was a proto-Neanderthal, meaning an early member of the Neanderthal lineage.

The victim’s skull appears to have been bashed twice, leading to his or her demise.

“The type of injuries, their location, the strong similarity of the fractures in shape and size, and the different orientations and implied trajectories of the two fractures suggest they were produced with the same object in face-to-face interpersonal conflict,” lead author Nohemi Sala and colleagues write.

“Given that either of the two traumatic events was likely lethal, the presence of multiple blows implies an intention to kill,” they added.

Sala, a researcher at Centro Mixto UCM-ISCIII de Evolución y Comportamiento Humanos in Madrid, and an international team came to this conclusion after studying the skull in detail. It was unearthed at a well-known Spanish site called Sima de los Huesos (SH) where at least 28 Neanderthals and proto-Neanderthals have been found.

During the time that bones began to accumulate at the site, the only possible access route to the place was “through a deep vertical chimney,” the authors said.

The origin of the accumulation has been hotly debated, with four different theories proposed: 1- non-human carnivores dragged their prey there, 2- geological activity somehow led to the accumulation, 3- accidental falls, and 4- intentional accumulation of bodies by early humans.

Could the victim described in the study have tripped and fallen down the shaft, hitting his or her head a couple of times on the way down?

The scientists reject that remote possibility.

They explained that “any scenario related to the free-fall would require the highly improbable occurrence of the same object striking the skull twice.”

The orientation of the hits, based on damage to the skull, further suggest that someone wielding an object bashed the head with near equal force, resulting in two fractures that would have penetrated the bone-brain barrier. Sala and colleagues therefore believe that the victim “did not survive these cranial traumatic events.”

Then there’s the question of how the murdered remains wound up going down the shaft. The researchers propose that the site was reserved for disposal of dead individuals.

Read more at Discovery News

Big-Toothed Prehistoric Human Lived Alongside 'Lucy'

The human family tree has a new member: a big-toothed early human ancestor that lived in Ethiopia 3.3 to 3.5 million years ago, according to a paper in the latest issue of the journal Nature.

The newly discovered human, named Australopithecus deyiremeda, overlapped in both time and region with yet another prehistoric human, "Lucy" (Austrolithecus afarensis). The find is strong evidence for the presence of more than one closely related early human ancestor species prior to 3 million years ago.

Because this particular species' teeth had super thick enamel and its jaws were built to last, "it probably engaged in heavy chewing and consumed harder, tougher, and more abrasive dietary resources," lead author Yohannes Haile-Selassie, curator of physical anthropology at The Cleveland Museum of Natural History, told Discovery News.

Haile-Selassie and his team analyzed the remains, which were collected from the central Afar region of Ethiopia. Combined results from three established different dating processes yielded the estimated age of the fossils.

The location where the fossils were found is just 21.8 miles south of where "Lucy" lived in Hadar, Ethiopia. The researchers think the species could have lived in even closer proximity. The two might have co-existed, which would be like Homo sapiens now sharing turf with another type of human.

While such a scenario today seems unfathomable for humans, it was likely common back in the day.

As for why, Haile-Selassie said, "There is some evidence that during the middle Pliocene time period (about 3.3 million years ago) when multiple hominins (early humans) were running around, there were rivers supporting gallery forests that laterally extend to woodlands and grasslands."

"It was an ecosystem that supported numerous and varied habitats," he continued. "With niche partitioning, a number of related taxa can co-exist in such an ecosystem."

Anthropologists debate about which species is the stem of Homo sapiens, meaning that it should be positioned at the very bottom of the human family tree. Candidates now include two other early humans, Ardipithecus ramidus and Australopithecus anamensis, but it could also be an as-of-yet undiscovered species.

Whichever it was, the stem species, via evolution and divergence, could have later resulted in more than 20 different types of humans, including Homo sapiens.

In terms of what happened to this crowded field of early relatives, Haile-Selassie said, "Some of them gradually gave rise to a new form and went extinct. Others went extinct with no descendants."

He added, "When the environment changes and their habitat diminished, or when they faced harsh competition with others for resources and failed to be good competitors, they had no alternative but extinction."

The fossil evidence for the earliest anatomically modern humans comes from Ethiopia, so it cannot be ruled out that A. deyiremeda and/or "Lucy" is our direct ancestor.

Read more at Discovery News