Don’t mess with horned females

IT WAS one of the many mysteries pondered by Darwin: why do some female animals have horns? Horns on cloven-hooved mammals are thought to have evolved for fighting each other, but most female cattle and deer don’t do this.

Now Theodore Stankowich of the University of Massachusetts and Tim Caro from the University of California, Davis, have a solution. They noted the presence or absence of horns in 117 species of bovid and set up competing mathematical models to examine whether evolution of horns was likely to have been driven by body size, openness of habitat, territorial behaviour, group size or conspicuousness.

This showed that horns were most likely in conspicuous species – those living in open habitats and large enough to be clearly visible to predators – suggesting that they evolved as defensive weapons (Proceedings

of the Royal Society B, DOI: 10.1098/rspb.2009.1256).

Behavioural ecologist Craig Roberts of the University of Liverpool, UK, is not convinced. “They haven’t shown that female competition for food could not be the reason why horns evolved.”

Eye movements reveal processing of hidden memories

YOU can tell a lot about a person from their eyes – including information about memories hidden from their conscious awareness, it seems.

By relating subtle eye movements to brain activity, Deborah Hannula and Charan Ranganath at the University of California, Davis, have shown that a brain structure called the hippocampus can be working with memories of previous experiences even when people have no conscious recollection of them.

The researchers showed volunteers images of faces paired with a variety of background scenes. They were later shown one of the scenes as a memory cue followed by three faces superimposed over that scene and asked to choose which face had originally been presented with it.

During the memory cue and choice test, Hannula and Ranganath tracked what the volunteers were looking at while scanning their brains. Even when volunteers announced an incorrect choice, those whose

THEY might be bald and ugly, but

naked mole rats never get cancer. If

their trick can be copied it could help

humans resist cancer too.

It’s almost impossible to culture

naked mole rat cells in the lab, which

made Andrei Seluanov and Vera

Gorbunova from Rochester University,

New York, wonder if this might be

linked to their ability to resist cancer.

They found that a dilute solution

of naked mole rat skin cells did start

to proliferate, but stopped once the

cells reached a certain, relatively low

density. Such “contact inhibition” is

also used by human cells to inhibit

growth, but cancer bypasses this

mechanism so cells keep growing.

The researchers also found that

contact inhibition in naked mole rats

is controlled by two genes, p16 and

p27, while in humans it is primarily

controlled by p27. “Naked mole rats

have an additional barrier in the

way of tumour progression,” says

Seluanov, who presented the results

at the Strategies for Engineered

Negligible Senescence meeting

in Cambridge, UK, last week.

If this check could be stimulated

in humans, it could halt the growth

of cancerous tumours.

Naked mole rats may help cure cancer

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hippocampus was more active when they were looking at the scene cue subsequently spent the most time looking at the correct face while trying – and failing – to consciously identify it (Neuron, DOI: 10.1016/j.neuron.2009.08.025).

“This study has provided the clearest evidence to date that the hippocampus is very much engaged, even when one is incorrect,” says Howard Eichenbaum of Boston University , who studies the structure’s importance for memory in rats.

Charged water and its odd antics

OPPOSITES always attract, right?

Not quite. A new experiment has

shown that a drop of water with

positive electrical charge can be

made to “bounce off” a negatively

charged object.

William Ristenpart of the

University of California at Davis

accidentally applied a strong

electric field to a beaker filled with

oil and water. At first the mixture

erupted into a turbulent mess, but

as he turned down the voltage

Ristenpart saw droplets of water

suspended in the oil bouncing

between the electrode at the top

of the beaker and the oil-water

boundary below. The droplets were

positively charged, so why didn’t

they merge with the negatively

charged body of water?

Ristenpart set out to reproduce

the happy accident, now filming

with an ultra-high-speed camera.

The video shows that when a

droplet nears the water-oil

boundary it elongates slightly,

forming a tiny bridge. Ristenpart

thinks that positive ions drain out of

the droplet and negative electrons

come in through the bridge, so the

droplet, now negatively charged, is

drawn up to the positive electrode,

where it regains its original positive

charge, and so on. The discovery

could lead to new microfluidic

devices and better methods for

separating salt water from crude oil.

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19 September 2009 | NewScientist | 17