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Ancient Egyptians wouldn鈥檛 be caught dead without hair gel. Style in the afterlife was just as important as it was during life on Earth 鈥� and coiffure was key.

To this end, men and women alike would have their tresses styled with a fat-based 鈥済el鈥� when they were embalmed. The evidence of their vanity has been found in a community cemetery dating back 3000 years.

Tomb paintings depict people with cone-shaped objects sitting on their heads, thought to be lumps of scented animal fat. 鈥淥nce we started looking [for these], we found interesting hairstyles,鈥� says Natalie McCreesh of the University of Manchester, UK. 鈥淭he hair was styled and perfectly curled.鈥�

She and her colleagues examined hair samples from 15 mummies from the Kellis聽1 cemetery in Dakhla oasis, Egypt, and a further three samples from mummies housed in museum collections in the US, the UK and Ireland. The mummies were of both sexes, between 4 and 58 years old when they died, and dated from 3500 years to 2300 years ago.

When examined with light and electron microscopes, it became clear that the hairs of most mummies were coated with a fatty substance, though a few had been coiffed with something resinous.

Because they鈥檙e worth it

The team used a solvent to separate the coatings from the hairs and determined the coatings鈥� chemical composition. They found that the substances were different to those commonly used to embalm bodies. By contrast, two mummies whose heads had been shaved carried the same embalming materials on their heads as on the bandages around the body.

It seems, says McCreesh, that when a body was being coated in resinous materials, the hair would be covered and protected, or washed and restyled, in order to preserve the dead person鈥檚 identity.

of the University of Pisa, Italy, points out that Egyptians were not the only ancient society to worry about mummified hair care. In South America, bodies were preserved with resin and pitch, and the hair coloured with powder, she says.

鈥淧eople presume the ancient Egyptians shaved their heads. The priests and priestesses did, but not everyone. They did take pride in their appearance,鈥� says McCreesh.

鈥淭he whole point of mummification was to preserve the body as in life. I guess they wanted to look their best. You鈥檇 be dressed in your fancy party outfit. You鈥檇 want to look beautiful in preparation for the next life鈥�.

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VAMPIRE bats use heat detection to seek out their next meal, and the way they do it provides the latest evidence that they are more closely related to the cattle whose blood they drink than the rodents they resemble.

vampire bats sense infrared radiation using heat-sensitive pits on their faces, just as boas, pythons and pit vipers do. at the University of California, San Francisco, and colleagues had previously shown that for the task. Now her team has discovered that vampire bats do it differently.

All bats make a protein called TRPV1 to help them detect and avoid painfully hot surfaces. Unusually, vampire bats have two versions of the protein, says team member of the Carnegie Institution for Science in Baltimore, Maryland. 鈥淥ne is sensitive to painful heat, but the bats produce a version in their facial pits that is sensitive to lower temperatures.鈥�

The newly discovered protein, TRPV1-S, is shorter than TRPV1 and is activated by temperatures 10 掳C lower 鈥� corresponding to the temperature of certain spots on the bodies of animals that the bats feed on, where veins or arteries lie just below the skin. 鈥淲ithout this adaptation the bats probably would not survive as a species,鈥� says Gracheva.

Gracheva鈥檚 team found that the vampire bats have an extra length of DNA in their Trpv1 gene, which normally codes for the TRPV1 protein. In certain circumstances, this extra piece of DNA causes TRPV1-S to be made instead. Cows, pigs and dogs also have the extra DNA and so produce two forms of the protein, though both have the same sensitivity to heat. Mice and humans lack the insertion (Nature, ).

The team鈥檚 finding fits with previous studies that place bats evolutionarily closer to carnivores and ruminants than rodents, says Gareth Jones of the University of Bristol, UK, who was not involved in the study.

Species:

Habitat: Tropical forests in Panama and Columbia, hanging with the family

They鈥檙e cute, they鈥檙e helpful, they鈥檒l carry your babies. What鈥檚 more, several males are happy to club together in order to serve a single female. Female Geoffroy鈥檚 tamarins sure do have it easy.

The monkeys live in groups of three to nine, in which multiple adult males mate with a single breeding female and then cooperate to raise her young. This mating system, called polyandry, occurs in less than 1聽per cent of bird species, and is even rarer in mammals.

Here鈥檚 why: if you鈥檙e a male, you can make lots of sperm cheaply and quickly, so to maximise your chances of reproducing, it makes sense to mate with as many females as possible.

Females, on the other hand, invest energy in making few eggs and have to bear the energetic costs of pregnancy. They evolve to be picky, choosing only the best males to fertilise their eggs. So you might expect mating systems where males mate with many females, rather than the other way around. Not in tamarins.

Male Geoffroy鈥檚 tamarins provide everything an infant wants except milk. They carry the young more than the females do, which is a considerable burden as infants weigh 25 per cent of adult body mass at birth and bulk up to 50 per cent before they can move independently at 10 weeks of age. Carrying the youngsters slows males down as they forage for fruit and insects, and makes them vulnerable to predators. Which raises the question: why care for offspring that are not your own?

Paternity test

, then at the University of California, Berkeley, observed six groups of wild tamarins in two rainforest sites in Panama and Columbia to find out.

He tested two possibilities. If males were closely related, they would gain an indirect benefit by helping related offspring 鈥� they would ensure that genes they shared with the father of the infants were passed on to the next generation. Or males might cooperate simply because if they stick around they could have a reasonable chance of siring offspring themselves.

D铆az-Mu帽oz needed to collect DNA samples to establish the groups鈥� family trees. But a quirk of tamarin biology complicated the process.

Extreme bromance

80 per cent of tamarin births are fraternal (non-identical) twins, formed from two sperm fertilising two separate eggs. As fraternal twins come from different eggs and sperm, they have different DNA profiles.

But even though tamarin twins develop as separate embryos, they grow within the same chorion 鈥� the outermost membrane surrounding the embryo, which contributes to the placenta.

Blood vessels connect the embryos within the chorion and exchange cells between them early in development, so even though most parts of the two embryos have their own unique DNA profile, their blood profile is identical.

鈥淧eople starting doing genotyping and found that with blood you get an identical profile,鈥� says D铆az-Mu帽oz.

The solution? 鈥淚f you go to tissue types that are blood-cell-free 鈥� such as hair 鈥� then you get different DNA fingerprints,鈥� says D铆az-Mu帽oz.

Keep it in the family

DNA showed that males were related at the levels expected for brothers or half-brothers, or fathers and sons. But males in some groups also shared paternity, even within the same litter 鈥� there were fraternal twins with different fathers.

Males walk a balance between the indirect genetic benefits they enjoy from caring for young animals they are related to, and the direct benefits of siring their own offspring, says D铆az-Mu帽oz.

Ejaculates at dawn

It鈥檚 not all happy families, though. Tamarins undergo seasonal change in testes size, with . Usually one group member has much larger testes than the other males. So though males cooperate, their sperm still competes within the female to fertilise her eggs 鈥� the male with the .

鈥淚f you have to share matings, you might as well do it with someone you鈥檙e related to,鈥� says D铆az-Mu帽oz. 鈥淎nd then you duke it out in the sperm competition.鈥�

Outside of tamarins and their close cousins the marmosets, only one other primate practises polyandry: humans. In the ethnically Tibetan Nyimba population of north-western Nepal, brothers share wives, though .

Perhaps tamarins have something to teach us about brotherly love. Captive tamarins spend most of their time in monogamous pairs, says D铆az-Mu帽oz. 鈥淵ou can keep them in trios 鈥� but only if they鈥檙e related.鈥�

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Read previous Zoologger columns: Bullied boobies develop brain of a bully, How deaf-mute frogs talk to each other, No brain, but at least it鈥檚 got personality, Pink magnet slug doesn鈥檛 need ruby slippers, The first non-human meat farmers, Biofuel powers biggest flying marsupial, Tough guys wear turquoise, Patriarchal fish punish powerful females, Clone army steals genes from other species, The snail that鈥檚 bust a gut to become toxic, The only fish that cries like a baby, Flashmob gathering of world鈥檚 largest fish.

Gotham City famously relies on a bat signal to call for help. In the rainforests of Cuba grows a flower with its own version 鈥� a device that is vital for the flower鈥檚 survival.

The rainforest vine has an unusual anatomy. It has a disc-shaped leaf suspended above a ring of flowers, below which hang cup-shaped nectaries. In cross section, the disc leaf looks like the reflector of a satellite dish: the plant鈥檚 other leaves are much flatter in comparison.

鈥淲hen I saw a picture of this plant I suspected this might be an adaptation,鈥� says of the University of Ulm in Germany. 鈥淲e saw the bats were crazy about the flowers, licking the nectar.鈥�

Using a loudspeaker-microphone combination, Simon and colleagues played sounds at the plant and analysed the resulting echoes. They found striking differences between the acoustic properties of disc-shaped leaves and the flatter ordinary leaves.

Ordinary leaves produced a strong echo when face-on to the loudspeaker-microphone, but the signal strength dropped 鈥� and its acoustic signature changed 鈥� as the loudspeaker-microphone swung round to a position edge-on to the leaf. The signal from a disc-shaped leaf remained strong and characteristic no matter where the loudspeaker-microphone was placed within an 80-degree arc in front of the leaf.

Echo guide

Simon reckons the predictable echo signal of the disc-shaped leaf might help bats find Marcgravia flowers against the random and variable echo background of the rainforest.

鈥淭he disc leaf has a signature which is constant from many different directions 鈥� from every direction you get the same echo,鈥� says Simon. 鈥淭hat鈥檚 very conspicuous to a bat.鈥�

To test this, he trained three male nectar-feeding bats () to search for a feeder 2.5 centimetres wide 鈥� roughly the same size as a single nectary 鈥� in a chamber filled with artificial foliage.

The time it took the bats to find the feeder halved when a replica of the disc-shaped leaf was fastened above it. Attaching a replica of an ordinary leaf instead made no difference to the search time.

Though the disc shape makes the leaf less efficient at photosynthesis, Simon says that the benefits of attracting bats outweigh this energetic cost: bats are good pollinators, and their large home range means they can take pollen to plants far apart from each other, and so help their reproduction, he says.

Cleared to pollinate

鈥淎n ultrasonic beacon is an astonishingly effective thing 鈥� it鈥檚 the same principle that airports use to guide aircraft in to land,鈥� says of the University of Western Ontario in London, Canada, who was not involved in the study.

Given there are several hundred species of bat-pollinated flower in Central and South America, and 40 bat species highly adapted as nectar feeders, Simon鈥檚 team expects to find more strangely shaped bat signals on plants.

鈥淭he plants are obviously exploiting the bat,鈥� says Fenton. 鈥淭here are all these little jewels waiting out there for someone to pursue.鈥�

Journal reference: , DOI: 10.1126/science.1204210

The most common form of bariatric 鈥� anti-obesity 鈥� surgery is the 鈥淩oux-en-Y鈥� gastric bypass, which involves stapling the stomach so a small pouch is made at the top, which is then connected directly to the small intestine. This bypasses most of the stomach and the duodenum so the patient feels full quicker.

The vertical-banded gastroplasty is an alternative technique which reduces the volume of the stomach without bypassing any part of the intestine, restricting how much the patient can eat at any one time.

After people undergo gastric bypass operations, it is not uncommon for them to report that their eating habits have changed. To investigate these claims, and colleagues from Imperial College London asked 16 people who had undergone either type of bariatric surgery six years before to fill in a survey about their dietary preferences after the operation.

People who had had a gastric bypass reported eating a lower proportion of fat after surgery than those with a vertical-banded gastroplasty.

Low-fat rats

To find out why this was so, the team carried out either a gastric bypass or a sham operation on 26 rats.

They found the rats with the gastric bypass ate less and regained less weight after recovering from the surgery than the others. In just 10 days after the operation, the gastric bypass rats had, on average, increased the proportion of low-fat food in their diets by a factor of four.

In a separate experiment, researchers gave other post-operative rats sugar water while infusing corn oil directly into their stomachs. This meant that their digestive system encountered fat but the animals had not tasted it. The bypass rats learned to avoid the water nevertheless, but the sham-operated rats did not. This suggests that the preference for low-fat food may have been a result of the bypass rats finding it harder to digest high-fat food after the operation, rather than it somehow affecting their sense of taste.

It鈥檚 their hormones

Le Roux鈥檚 team also found that levels of hormones which promote satiety 鈥� such as glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) 鈥� were higher in rats with a gastric bypass after eating than in the sham-operated rats.

鈥淎fter gastric bypass operations in both humans and rats these hormones are greatly elevated,鈥� says le Roux. 鈥淕LP-1 may be important when it comes to food preferences.鈥� The hormone, which promotes insulin production, is already used to treat diabetes. 鈥淲e are currently doing studies to see if it can be used to tackle obesity鈥� says le Roux.

鈥淎 gastric bypass is a free injection of GLP-1,鈥� says bariatric surgeon , a member of the Royal College of Surgeons in the UK, who was not involved in the study.

鈥淲hen patients say 鈥業 don鈥檛 like fatty foods any more,鈥� we can now say this effect has a real physiological basis,鈥� says Welbourn. 鈥淕astric bypass is a profoundly effective operation. We鈥檙e operating on the gut, but we鈥檙e changing the brain.鈥�

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Species:

Habitat: The Galapagos islands and eastern Pacific Ocean, wearing silly masks and killing their siblings

It ain鈥檛 easy being the youngest in the family. If you鈥檙e a Nazca booby, it can get you killed.

Nazca boobies are monogamous, ground-nesting seabirds. Yes, monogamy is sweet and 鈥渂ooby鈥� is an amusing name, but they are far from kind to their nest mates.

During each breeding season, a female Nazca booby will lay two eggs several days apart. If both hatch, the elder sibling pushes the younger out of the nest area, where it is either picked off by predators or dies of thirst and cold.

The younger chick doesn鈥檛 stand a chance: firstborn chicks can be up to 30 per cent larger, and once the young chick is outside the nest area, its parents ignore it and leave it to die 鈥� sometimes just centimetres away.

Sorry, you鈥檙e just the spare

This is an evolutionary insurance policy taken to the limit 鈥� the second egg is simply a back-up in case the first doesn鈥檛 hatch.

A linked the murderous behaviour to high levels of testosterone and androgens in hatchlings. Given that they may be fighting to the death the moment they鈥檙e out of the egg, it鈥檚 not surprising that Nazca boobies hatch with higher circulating levels of hormones such as testosterone than the closely related blue-footed boobies (Sula nebouxii), which kill their siblings only when food is scarce.

The bullying doesn鈥檛 stop in the nest. When the siblicidal Nazca booby grows up, it sometimes seeks out unrelated chicks in the colony and 鈥渃ourts鈥� them with aggressive sexual intent. There is no apparent benefit to the behaviour as the unlucky chicks are sexually immature, and they can incur fatal cuts from these attacks.

Bad upbringing

It turns out that, like the human cycle of violence that leads some people who were abused by their parents to later abuse their own children, Nazca boobies that are bullied as nestlings are more likely to become bullies themselves. of Wake Forest University in Winston-Salem, North Carolina, and colleagues wanted to find out how this cycle was passed on.

In a given breeding season, a large fraction of the adult population either doesn鈥檛 breed, or tries and fails. About 80 per cent of non-breeding Nazcas, both male and female, display non-parental adult visitor behaviour 鈥� bullying unguarded nestlings 鈥� at least once.

The nestlings are vulnerable from about 30 days of age, when their foraging parents leave them unguarded, till about 80 days, when they鈥檙e large enough to repel attacks by themselves.

Grace鈥檚 team protected some nestlings from this aggression with portable wire mesh enclosures when the parents were absent. They compared levels of testosterone and the stress hormone corticosterone in these protected nestlings with those in chicks that had been bullied.

They found that corticosterone concentration increased five-fold in nestlings during bullying episodes, and stayed 2.8 times higher until at least the morning after the event.

Birdbrains gone bad

The researchers argue that these increased levels of hormone could have a long-term effect on the birds鈥� brains and behaviour 鈥� affecting particularly the hypothalamic-pituitary-adrenal axis by repeated activation 鈥� leading bullied birds to later become bullies themselves.

The name 鈥渂ooby鈥�, by the way, comes from British seamen鈥檚 slang for 鈥渟tupid鈥�. On nesting islands sailors could walk right up to the birds and hit them over the head 鈥� a distasteful practice, but perhaps in some cases booby bullies were getting their comeuppance.

Journal reference:

Read previous Zoologger columns: How deaf-mute frogs talk to each other, No brain, but at least it鈥檚 got personality, Pink magnet slug doesn鈥檛 need ruby slippers, The first non-human meat farmers, Biofuel powers biggest flying marsupial, Tough guys wear turquoise, Patriarchal fish punish powerful females, Clone army steals genes from other species, The snail that鈥檚 bust a gut to become toxic, The only fish that cries like a baby, Flashmob gathering of world鈥檚 largest fish, Genetic superpowers of the common shrew.

and at the University of Oxford analysed 73 adult skulls belonging to people who lived at different latitudes. They found that both the overall skull volume and the volume of the eye socket increased with latitude, but the increase in eye socket volume 鈥� which is thought to relate to eyeball size 鈥� was larger than expected from the change in skull size alone.

Visual acuity 鈥� the ability to resolve fine detail 鈥� should be subtly worse at higher latitudes because of the dimmer light found there. But when the pair reviewed available data they found acuity was the same in populations at all latitudes. Pearce and Dunbar suggest their measured increase in eye socket volume, and inferred increase in eyeball size, could explain this.

鈥淲e were surprised to see how strong the effect was. Humans have only been in northern Europe for 40,000 years,鈥� says Dunbar.

Physical anthropologist at the University of Texas at Austin thinks the idea is interesting, but is not convinced as the link between socket volume and eyeball size is relatively loose. To confirm the hypothesis 鈥測ou would have to go back and measure the eyes鈥�, he says.

Journal reference: , DOI: 10.1098/rsbl.2011.0570