16 | NewScientist | 25 May 2013

EARTH is shoving the moon away faster now than it has done for most of the past 50 million years, says a new model for the way tides influence the lunar orbit. The result helps solve a mystery concerning the moon’s age that has long vexed astronomers.

The moon’s gravity creates a daily cycle of low and high tides. This dissipates energy between the two bodies, slowing Earth’s

spin on its axis and causing the moon’s orbit to expand at a rate of about 3.8 centimetres per year. If that rate has always been the same, the moon should be 1.5 billion years old, yet some lunar rocks are 4.5 billion years old.

Enter Matthew Huber of Purdue University in West Lafayette, Indiana. His team gathered data on ocean depths and continental contours that existed 50 million

These wings were made for diving

A CANADIAN seabird may help explain why penguins cannot fly.

The thick-billed murre (Uria lomvia) is a diving bird that flies – just not very well. In fact, when Robert Ricklefs at the University of Missouri at St Louis and his colleagues studied murres in flight, they found the bird used almost three times as much energy as the bar-headed goose, previously considered the least efficient flying bird. Underwater, though, the murre can swim with an efficiency only 30 per cent below the level expected of a penguin of similar size (PNAS, DOI: 10.1073/pnas.1304838110).

“You can’t have a wing that’s both good for propulsion in water and in air,” says Ricklef.

The murre may ultimately reach a point where using wings as flippers would trump using them for flying, though Ricklef says it would take millennia for this to happen.

Arctic thaw makes polar bears vulnerable to disease

MORE grim news for polar bears: they may be particularly vulnerable to pathogens spreading northwards as the climate warms.

Diana Weber at the New College of Florida, Sarasota, and her colleagues sequenced DNA from 98 polar bears in Canada. They looked specifically for genes encoding the major histocompatibility complex (MHC) – a crucial component of the immune systems of most vertebrates.

In many species, the genes that code for the MHC’s molecules are variable, allowing them to detect and bind to many pathogens. The polar bears had low diversity in

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Tides are pushing the moon away faster years ago, and fed that into a model to simulate ancient tides. Energy dissipation back then was only half what it is today, so the moon was pushed away at a slower rate (Geophysical Research Letters, doi.org/mjz).

The key is the North Atlantic Ocean, which is now wide enough for water to slosh across once per 12-hour cycle, says Huber. Like a child sliding in a bathtub, that creates larger waves and very high tides, shoving the moon faster.

their MHC genes, so their immune system may lack this versatility (Animal Conservation, doi.org/mht).

This could be an adaptation to life in the Arctic, which is relatively free of diseases and parasites compared with lower latitudes. But it could leave the polar bear at risk from an influx of infections as global temperatures rise. “There are a number of diseases now observed in Arctic animals [that were] not previously seen,” Weber says.

Polar bears are likely to have survived periods of warming before, but Axel Janke at the Biodiversity and Climate Research Centre in Frankfurt, Germany, points out that this time the warming is more rapid and is happening in tandem with human-driven habitat destruction, illegal hunting and pollution. “All this adds up to a very real threat to polar bear survival,” he says.

NEANDERTHALS may have begun weaning their babies at 7 months, and ceased breastfeeding altogether 7 months later.

Manish Arora from the University of Sydney in Australia and colleagues discovered that levels of barium in tooth enamel rise while a child is breastfed but drop off when they are weaned. So they tested barium levels in a 100,000-year-old molar from a Neanderthal child and concluded it was weaned at 14 months (Nature, DOI:10.1038/nature12169).

This is “intriguingly early”, says Louise Humphrey at the Natural History Museum in London. It suggests they matured faster than modern humans, who tend to be weaned at 30 months in hunter-gatherer and agrarian societies.

Neanderthals quick to leave the breast?

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