Monogamy may have evolved to keep baby-killers away


Social monogamy – when a male and female of the species stick together for the long term, although may mate with others – is rare in mammals generally. However, it occurs in over a quarter of primate species, including humans, gibbons and many New World monkeys, such as titis.

To investigate what originally drove us to establish such pair bonds, a team led by Kit Opie of University College London and Susanne Shultz from the University of Manchester, UK, gathered data on the mating behaviour of 230 primate species. They selected behavioural traits associated with several possible evolutionary drivers of monogamy, including the risk of infanticide, the need for paternal care and the potential for guarding female mates.

Using data on the genetic relationships between the species, the team ran millions of computer simulations of the evolution of these traits to work out which came first.

All three were linked to the evolution of monogamy but only behaviours associated with infanticide actually preceded it, suggesting that this was the driver. Suckling infants are most likely to be killed by unrelated males, in order to bring the mother back into ovulation.

With pair-bonding in place, not only would a mother have a male to help protect the infant from marauding males, but there would then be the opportunity for the male to help care for it by providing extra resources. This means the infant can be weaned earlier, again reducing the chance of it being killed.

“Until recently, reconstructing how behaviour evolves has been very tricky as there are few behavioural traces in the fossil record. The statistical approach we have used allows us to bring the fossils to life and to understand the factors that have led to the evolution of monogamy in humans and other primates,” says Shultz.

Carel van Schaik, a primatologist at the University of Zurich in Switzerland says the results are solid but questions whether they can be extrapolated to humans. He says evidence suggests that humans were never really monogamous and that the monogamy we see today in many cultures is socially imposed.

Shultz counters that there is fossil evidence pointing to monogamy in australopithecines, the hominin genus from which modern humans descended.

“Although we suggest that infanticide may help explain the evolution of monogamy in humans, we do not argue that it is the only factor nor that monogamy is universal,” Shultz says. “I would suggest that where infanticide risk is high, as it would be with our ancestors, having a father provide protection and care would facilitate the evolution of the modern human extended childhood.”

Journal reference: PNAS, DOI: 10.1073/pnas.1307903110

Stone Age skull-smashing culture discovered


An unusual cluster of Stone Age skulls with smashed-in faces has been found carefully separated from the rest of their skeletons. They appear to have been dug up several years after being buried with their bodies, separated, then reburied. Although collections of detached skulls have been dug up at many Stone Age sites in Europe and the Near East – but the face-smashing is a new twist that adds further mystery to how these societies related to their dead.

Juan José Ibañez at the Spanish National Research Council in Barcelona says the find may suggest that Stone Age cultures believed dead young men were a threat to the world of the living.

No one knows why Neolithic societies buried clusters of skulls – often near or underneath settlements. Some think it was a sign of ancestral veneration. “When people started living together [during the Neolithic period], they needed a social cement,” says Ibañez. Venerating ancestors might have been a way of doing this. But the violence demonstrated towards the skulls in the latest cluster suggests a different story.

The 10,000-year-old skulls were found in Syria. Like those found in other caches, they have been cleanly separated from their spines, suggesting they were collected from dead bodies that had already begun to decompose. Patterns on the bone indicate that some had been decomposing for longer than others, making it likely that they were all gathered together for a specific purpose.

Most of the skulls belonged to adult males between 18 and 30 years old. One – belonging to a child – was left intact; one was smashed to pieces; the remaining nine lacked facial bones. “There was a pattern,” says Ibañez. “The top of the skull and the jaw were there, but they were missing all of the bones in between.” His team believes the facial bones were smashed out with a stone and brute force. “There were no traces of cutting,” he says (American Journal of Physical Anthropology, DOI: 10.1002/ajpa.22111).

Ibañez reckons Stone Age people believed they would receive some benefit – perhaps the strength of the young men the skulls once belonged to – by burying them near or beneath their settlements. Why the faces were smashed in invites speculation.

It may have been an act of spite or revenge, says Ibañez. Or the skulls may have been brought together to create a “community of the dead”, perhaps in order to spiritually interact with the living.

“The post-mortem violence suggests young men were seen as carrying a particular threat,” says Stuart Campbell at the University of Manchester, UK. Destroying their facial structures may have been a way of destroying the individuals’ identities, he says.

Liv Nilsson Stutz at Emory University in Atlanta, Georgia, says the act could have helped deal with grief. “Taking away facial identity could be a way of separating the dead from the living,” she says.

‘Smart Carpet’ detects falls and unfamiliar footsteps

A team at the University of Manchester in the UK has developed a carpet that can detect when someone has fallen over or when unfamiliar feet walk across it.

Optical fibres in the carpet’s underlay create a 2D pressure map that distorts when stepped on. Sensors around the carpet’s edges then relay signals to a computer which is used to analyse the footstep patterns. When a change is detected – such as a sudden stumble and fall – an alarm can be set to sound.

By monitoring footsteps over time, the system can also learn people’s walking patterns and watch out for subtle changes, such as a gradual favouring of one leg over the other. It could then be used to predict the onset of mobility problems in the elderly, for example.

The carpet could also be used as an intruder alert, says team member Patricia Scully. “In theory, we could identify footsteps of individuals and the shoes they are wearing,” she says.

But it needn’t all be about feet. The system is designed to be versatile, meaning that different sensors could instead be used to provide early warning of chemical spillages or fire.—a.html?DCMP=OTC-rss&nsref=online-news