Early Hominid Lucy May Have Died by Falling out of a Tree

VER VIDEO

Scientists printed out 3-D models of Lucy's bones, showing a breakage pattern consistent with a fall from a tree.

This video was reproduced with permission and was first published on August 29, 2016. It is a Nature Video production.

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Like Humans, Chimps Reward Cooperation and Punish Freeloaders

Recent research challenges the notion that our closest animal relatives don’t like working as a team.

Three chimpanzees pull at the cooperation apparatus, with two others looking on. Credit: Image courtesy of Frans de Waal, Yerkes National Primate Research Center

Although humans love the playful ways and toothy grins of chimpanzees, our primate cousins have the reputation of being competitive, churlish and, at times, aggressive.

New research published today in Proceedings of the National Academy of Sciences suggests that despite being prone to occasional violent behavior, chimps actually much prefer cooperating over competing. In fact, the work shows that chimps work together at similar rates as humans—and that when violence does occur among apes, it is often directed toward an individual that is not being a team player.

Working with 11 chimps housed in a large outdoor enclosure at the Yerkes National Primate Research Center at Emory University, researchers devised an experiment to assess cooperation, defined as two or more chimps working together to access a food reward. Initially two chimps had to team up, with one lifting a barrier and the other pulling in a tray baited with small pieces of fruit. Once cooperation between two subjects was established, another barrier was added, requiring a third chimp to pitch in if all three were to obtain the spoils.

Given that the apes had nearly 100 hours to obtain their reward in the presence of bystander chimps, there were plenty of chances for competition to arise. The authors defined “competition” as episodes of physical aggression, bullying a fellow chimp to leave the scene of the reward or freeloading—stealing the prizes of others without putting in the work of retrieving them.

Although the study only looked at a small number of individuals, the results were telling. In 94 hour-long test sessions, the chimps cooperated with one another 3,565 times—five times more often than they were in competition. In addition, the animals used a variety of strategies to punish competitive behaviors, such as preferentially working with their more communal and tolerant fellow animals.
When aggression did occur, it was often used to subdue the overly competitive or prevent freeloading, perhaps an even greater affront to the chimpanzee honor code. Attempted thefts by those who did not put in the work were not well received. In fact, the researchers even observed 14 instances in which a third-party chimp—typically one of the more dominant of the bunch— intervened to punish freeloaders. “It has become a popular claim in the [scientific] literature that human cooperation is unique,” study co-author Frans de Waal, a primatologist at Yerkes, said in a statement. “Our study is the first to show that our closest relatives know very well how to discourage competition and freeloading.”

Plenty of other species exhibit cooperative behaviors—take for example the enviable coordination of ants building a subterranean metropolis. But as lead author and Canisius College psychologist Malini Suchak explains, what her team observed in chimps is even more impressive. “Although cooperation is widespread across species, cooperation in ants, for example, as well as in many other species is directed toward kin and is basically preprogrammed,” she says. “Our study shows that chimpanzees are really thinking about cooperation and actively making decisions that maximize cooperation and minimize competition.” She adds: “Cognitively, what they did in our experiment is much closer to what humans do when we cooperate than it is to what ants do when they cooperate.”

Michael Tomasello of the Max Planck Institute for Evolutionary Anthropology, a pioneer in this area of research who was not involved in the study, pointed out in an e-mail that the new work does have limitations beyond just its small size. Tomasello’s past work has shown that when given the option to work together to obtain food versus working solo, chimpanzees actually prefer to go it alone, a trait that distinguishes them from humans. The chimps in Suchak’s study were free to roam their Yerkes enclosure and had access to their usual “primate chow,” but in the wild they may have chosen to freely forage by themselves instead of cooperating to obtain food, Tomasello believes.

Still, mounting evidence supports the notion that other primates are perhaps more like us than previously thought. Earlier work by Suchak, de Waal and colleagues published in 2014 found that chimpanzees living in socially rich and complex settings spontaneously joined forces with their roommates. Beyond apes, last month Scientific American reported on research showing that monkeys, like humans, become more socially selective with age, preferring to spend time with their “friends” over other monkeys.

Unfortunately, great apes may share our more concerning qualities as well: Chimpanzees in nature will frequently form alliances with one another so they can compete more effectively against others. Field work in Uganda by University of Michigan anthropologist John Mitani found that every few weeks the males in a particular chimp community assemble single-file and carefully scope out neighboring territories. If not outnumbered, the trespassers will stage a siege in hopes of winning new territory.

Collaborative chimps, cranky old monkeys, mass conflict—in our simian relatives we increasingly see a reflection of ourselves. As Suchak points out, her new findings imply that the origins of our cooperative behaviors—those rooted in developed senses of tolerance and trust and, at times, reward through coordinated violence—may go farther back than previously thought. “In the past, chimpanzees have been characterized as overly aggressive and competitive, which resulted in people suggesting human cooperative behavior evolved relatively recently and is somehow distinct from cooperation observed in other species,” she says. “Our findings are a reminder that humans are animals, after all.”

Tomado de: http://www.scientificamerican.com/article/like-humans-chimps-reward-cooperation-and-punish-freeloaders/?WT.mc_id=SA_SP_20160829

Humanity’s forgotten family

Hominin fossils discovered near the site of the ‘hobbit’ Homo floresiensis provide yet more evidence that the human lineage is more diverse than was ever imagined.

Arthur C. Clarke wrote in 2001: A Space Odyssey that behind every person now living stand 30 ghosts, for that is by how many the dead outnumber the living. That was in 1968 — the number reckoned today would probably be greater. The human lineage diverged from that of chimpanzees some 5 million to 7 million years ago. Were we able to mark the remains of all our ancestors from that point, the world would be one enormous cemetery.

The most likely fate of any living organism is dissociation into its component molecules, if not reabsorption as food into something else. That makes the chance ineffably remote that the remains of any one individual will be fossilized in any recognizable form, and, this having been achieved, be recognized as such by a passing palaeontologist before the fossil, too, crumbles to dust.

It is possible that many human species once existed, but became extinct with such finality that even those few that were fossilized have since disappeared, leaving absolutely no trace that generations of a distinct species lived and died on this planet — a kind of double extinction, without hope of memorial or discovery. Fossils from the human lineage are scarce, and, given the numbers that must once have lived, the percentage recovered must hardly be significantly different from zero. (You can read about some of those that have been found in our Nature collection at go.nature.com/1zjssjs.)

Long-lost relations
Hence the surprise when, in 2004, a group of scientists in Indonesia and Australia announced the discovery of what became known as Homo floresiensis, a species of unusual, dwarfed hominin — that is, a creature living or extinct more closely related to us than to chimps — whose remains were found in Liang Bua cave on the island of Flores in Indonesia (P. Brown et al. Nature 431, 1055–1061; 2004).

There was some doubt at the time that H. floresiensis represented a real species rather than a variant of modern humans affected by some disease or pathological condition, but this dissent was gradually eroded, not only by a long palaeontological record at Liang Bua, but also by a rich archaeological record in the island’s Soa Basin, some distance to the east, showing that hominins of some sort had lived in the region for up to one million years (A. Brumm et al. Nature 464, 748–752; 2010). Yet direct evidence, in the form of bones and teeth, was elusive. Until now.

In this week’s issue, researchers report a fragment of mandible and six isolated teeth of hominins from Mata Menge in the Soa Basin that they describe as similar to those of H. floresiensis, but more primitive in some respects and — if anything — even smaller. In an accompanying paper, they show that the remains were deposited 700,000 years ago, many thousands of years before those from Liang Bua.

The researchers take the appropriately cautious and parsimonious view that these hominins were most closely related to early Asian Homo erectus, on the grounds that this is the only species of hominin otherwise known to have inhabited that part of the world at that time. However, it remains possible, as an accompanying News & Views explains, that these creatures might represent some very early, pre-H. erectus exodus from Africa. If so, that expands our ignorance from a barely manageable ocean into a gulf of inter­stellar magnitude, implying that a wholly unknown plethora of hominins lived in Eurasia millions of years earlier than anyone suspected, just one of whose number has been found in the region’s southeastern extremity to betray the possibility that such an array of species ever existed.

Is this unwarranted speculation? Perhaps not: the discovery of H. floresiensis prompted a sea change in palaeoanthropologists’ attitudes to the unknown. Researchers are less eager than they once were to string fossils together into confident chains of ancestry and descent. They are more likely to reappraise the various oddities of human evolution, no longer dismissing them as fossils that are hard to fit into the current paradigm of ancestry and descent, but seeing them as representatives of entirely unsuspected branches of the human family tree. One thinks of the many hominin remains recovered over the past few decades from China, some of which do not quite fit into any current species. Or of Homo heidelbergensis, an increasingly unwieldy catch-all for hominins from the Middle Pleistocene epoch (781,000–126,000 years ago); or of H. erectus itself, a grouping of such variety that some have found it hard to accept that all the fossils ascribed to it comprise a single species. And there are others less familiar, such as skulls from Iwo Eleru in Nigeria that look surprisingly archaic, despite being assigned a relatively recent date of as few as 11,700 years ago (K. Harvati et al. PLoS ONE 6, e24024; 2011).

Studies on human DNA, ancient and modern, have reinforced this trend. The recovery of an entire genome of a hitherto unknown archaic hominin from a single finger bone from Denisova Cave in Siberia was — and is — an astonishing achievement, both for the discovery itself and for its implications (D. Reich et al. Nature 468, 1053–1060; 2010). It reinforces hints that the scarcity of human fossils belies what might once have been hitherto unimaginable diversity. The finding, reported in the same paper, that Denisovan DNA lives on in people from southeast Asia and the western Pacific, just as Neanderthal DNA survives in Eurasians generally, proves that fossils tell us much less than we would like of the human career. And as with Iwo Eleru, so with DNA: there are signs that the genomes of some modern Africans contain elements derived from archaic hominins not found in the fossil record (M. F. Hammer et al. Proc. Natl Acad. Sci. USA 108, 15123–15128; 2011).

These early human relatives left signs of their passing as evanescent and enigmatic as the Cheshire Cat from Alice’s Adventures in Wonderland — slowly fading from view, with just its smile hanging on, until that, too, disappears.

Nature 534, 151 (09 June 2016) doi:10.1038/534151a