For mammals, one secret to a long life may be spending it living with friends and family.

An analysis of the life spans and social lives of nearly 1,000 mammal species shows that species that live in groups, such as horses and chimpanzees, tend to live longer than solitary beasts, like weasels and hedgehogs. The finding suggests that life span and social traits are evolutionarily entwined in mammals, researchers report January 31 in Nature Communications.
The maximum life span of mammals ranges widely. The shortest-lived shrews, for example, survive about two years, while bowhead whales (Balaena mysticetus) can reach roughly 200 years of age (SN: 1/6/15).

When evolutionary biologist Xuming Zhou of the Chinese Academy of Sciences in Beijing was studying the longest-lived mammals to understand the evolution of longevity, he took particular note of naked mole-rats (Heterocephalus glaber). The rodents are exceptionally long-lived, sometimes reaching over 30 years of age. They also live in huge, complex, subterranean societies. In contrast, other rodents like golden hamsters (Mesocricetus auratus), which are solitary, live to only about four years.

Some previous research on specific mammal species showed an effect of social behavior on longevity, Zhou says. For instance, female chacma baboons (Papio ursinus) with strong, stable social bonds live longer than females without them.

Zhou and his colleagues decided to see if there were any links between longevity and social habits shared across a wide range of mammal species.

The researchers compiled information from the scientific literature on the social organization of 974 mammal species. They then split these species into three categories: solitary, pair-living and group-living. When the researchers compared these three groups with data on the mammals’ known longevity, they found that group-living mammals tended to live longer than the solitary species — roughly 22 years compared with nearly 12 years in solitary mammals.

Zhou and his colleagues then accounted for body mass — bigger mammals tend to live longer than smaller ones — and the effect of social bonds held. A stark example comes from shrews and bats. Both are similarly tiny mammals, but the loner shrews live only a few years, while some far more social bat species can live for 30 or 40 years.

“We were so surprised, because individuals who live in groups also face a lot of costs, such as competition for potential mating partners and food,” Zhou says. Frequent social contact in group settings can also encourage the spread of infectious disease.
But there are benefits to living in a group too, he says, such as banding together for protection against predators. Living together may also reduce the risk of starvation if, for instance, group members increase foraging efficiency by finding and gathering food together. These factors may allow social mammals to live longer.

The evolution of a long life may also be more likely in group-living species: Living in a group allows animals to potentially aid the survival of their family members, which carry their genes.

Evolutionary biologist Laurent Keller of the University of Lausanne in Switzerland lauds the study for the sheer size of the sampling effort. “But it would have been useful to be a bit more precise about different levels of sociality.” There are more variations of social organization within the three categories used in the study, he says, and the relative degree of sociality could influence any patterns you see.

Still, fine tuning the social categories “is not an easy task,” Keller notes.

To get an idea of how genes might produce the link between longevity and group living, Zhou and his team took brain tissue samples from 94 mammal species and analyzed the transcriptome — the full complement of RNA — giving insights into different genes’ activity levels. This can reveal whether genes are turned on or off, or how much protein the genes may be instructing cells to produce.

The researchers found 31 genes whose relative activity levels were correlated with both longevity and one of the three prescribed social categories. Many of these genes appear to have roles in the immune system, which may have importance when countering pathogens spreading through the social group. Other genes were associated with hormone regulation, including some thought to influence social behaviors.

In studying these genes in more detail, Zhou envisions uncovering more about how mammals’ social habits and life spans have evolved together.

Early versions of the Bible describe Goliath — an ancient Philistine warrior best known as the loser of a fight with the future King David — as a giant whose height in ancient terms reached four cubits and a span. But don’t take that measurement literally, new research suggests.

Archaeological findings at biblical-era sites including Goliath’s home city, a prominent Philistine settlement called Gath, indicate that those ancient measurements work out to 2.38 meters, or 7 feet, 10 inches. That’s equal to the width of walls forming a gateway into Gath that were unearthed in 2019, according to archaeologist Jeffrey Chadwick of Brigham Young University in Provo, Utah.

Rather than standing taller than any NBA player ever, Goliath was probably described metaphorically by an Old Testament writer as a warrior who matched the size and strength of Gath’s defensive barrier, Chadwick said November 19 at the virtual annual meeting of the American Schools of Oriental Research.

People known as Canaanites first occupied Gath in the early Bronze Age, roughly 4,700 to 4,500 years ago. The city was rebuilt more than a millennium later by the Philistines, known from the Old Testament as enemies of the Israelites (SN: 11/22/16). Gath reached its peak during the Iron Age around 3,000 years ago, the time of biblical references to Goliath. Scholars continue to debate whether David and Goliath were real people who met in battle around that time.

The remains of Gath are found at a site called Tell es-Safi in Israel. A team led by archaeologist Aren Maeir of Bar-Ilan University in Ramat-Gan, Israel — who Chadwick collaborated with to excavate the Gath gateway — has investigated Tell es-Safi since 1996. Other discoveries at Gath include a pottery fragment inscribed with two names possibly related to the name Goliath. Evidence of Gath’s destruction about 2,850 years ago by an invading army has also been recovered.
Archaeologists have long known that in ancient Egypt a cubit corresponded to 52.5 centimeters and assumed that the same measure was used at Gath and elsewhere in and around ancient Israel. But careful evaluations of many excavated structures over the last several years have revealed that standard measures differed slightly between the two regions, Chadwick said.

Buildings at Gath and several dozen other cities from ancient Israel and nearby kingdoms of Judah and Philistia, excavated by other teams, were constructed based on three primary measurements, Chadwick has found. Those include a 54-centimeter cubit (versus the 52.5-centimeter Egyptian cubit), a 38-centimeter short cubit and a 22-centimeter span that corresponds to the distance across an adult’s outstretched hand.
Dimensions of masonry at these sites display various combinations of the three measurements, Chadwick said. At a settlement called et-Tell in northern Israel, for instance, two pillars at the front of the city gate are each 2.7 meters wide, or five 54-centimeter cubits. Each of four inner pillars at the city gate measure 2.38 meters wide, or four 54-centimeter cubits and a 22-centimeter span. Excavators of et-Tell regard it as the site of a biblical city called Bethsaida.

Chadwick’s 2019 excavations found one of presumably several gateways that allowed access to Gath through the city’s defensive walls. Like the inner pillars of et-Tell’s city gate, Gath’s gate walls measured 2.38 meters wide, or four cubits and a span, the same as Goliath’s biblical stature.

“The ancient writer used a real architectural metric from that time to describe Goliath’s height, likely to indicate that he was as big and strong as his city’s walls,” Chadwick said.

Although the research raises the possibility that Goliath’s recorded size referred to the width of a city wall, Chadwick “will need to do more research to move this beyond an intriguing idea,” says archaeologist and Old Testament scholar Gary Arbino of Gateway Seminary in Mill Valley, Calif. For one thing, Arbino suggests, it needs to be established that the measure applied to Goliath, four cubits and a span, was commonly used at the time as a phrase that figuratively meant “big and strong.”