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Women’s faces get redder at ovulation, but human eyes can’t pick up on it

fpjl2 — Tue, 30 Jun 2015 18:01:38 +0000

Previous studies have shown that men find female faces more attractive when the women are ovulating, but the visual clues that allow this are unclear. Now, new research investigating whether it might be to do with subtle changes in skin colour has shown that women’s faces do increase in redness during ovulation, but the levels of change are just under the detectable range of the human eye.

Researchers say this may mean that facial redness in females was once an involuntary signal for optimal fertility, but has since been “dampened” by evolution as it is more beneficial for females to hide or control outward signs of peak fertility.

Involuntarily signalling ovulation can prevent longer-term investment from males. In primate species that advertise ovulation, males only express sexual interest in females when they appear to be fertile. In humans, ovulation is less conspicuous and sexual behaviour is not restricted to the period of peak fertility.

̽��ֱ��research, published today in the open-access journal PLOS ONE, is the most complete objective study of female faces during the ovulatory cycle, say researchers. Twenty-two women were photographed without make-up at the same time every working day for at least one month in the same environment and using a scientific camera modified to more accurately capture colour (usually used for studying camouflage in wildlife).

A computer programme was designed to select an identical patch of cheek from each photograph. ̽��ֱ��participants also self-tested for hormone changes at key times dictated by the research team’s “period maths”.

A surge in luteinising hormone told researchers that ovulation would occur in roughly the next 24 hours, so they knew which photographs were taken when the women were most fertile. ̽��ֱ��team converted the imagery into red/green/blue (RGB) values to measure colour levels and changes.

They found that redness varied significantly across the ovulatory cycle, peaking at ovulation and remaining high during the latter stages of the cycle after oestrogen levels have fallen. Skin redness then dips considerably once menstruation begins. ̽��ֱ��research suggests facial redness closely maps fluctuations in body temperature during the cycle.

However, when running the results through models of human visual perception, the average difference in redness was 0.6 units. A change of 2.2 units are needed to be detectable to the naked human eye.

“Women don’t advertise ovulation, but they do seem to leak information about it, as studies have shown they are seen as more attractive by men when ovulating,” said Dr Hannah Rowland, from the ̽��ֱ�� of Cambridge’s Zoology Department, who led the study with Dr Robert Burriss, a psychologist from Northumbria ̽��ֱ��.

“We had thought facial skin colour might be an outward signal for ovulation, as it is in other primates, but this study shows facial redness is not what men are picking up on - although it could be a small piece of a much larger puzzle,” she said.

Primates, including humans, are attracted to red, say the study’s authors. Women may subconsciously augment the naturally-occurring facial redness during ovulation through make-up such as blusher or red clothing, they say.

“As far back as the 1970s, scientists were speculating that involuntary signals of fertility such as skin colour changes might be replaced with voluntary signals, such as clothing and behaviour,” said Burriss. “Some species of primate advertise their fertility through changes in the colour of their faces. Even if humans once advertised ovulation in this way, it appears that we don’t anymore.”

It may be that, during ovulation, women have a greater propensity for blushing when around men they find attractive, say the researchers. “Other research has shown that when women are in the fertile phase of their cycle they are more flirtatious and their pupils dilate more readily, but only when they are thinking about or interacting with attractive men,” said Burriss. “We will need to do more research to find out if skin redness changes in the same way”.

Rowland and Burriss first conceived of the experiment seven years ago, but it wasn’t until Rowland arrived at Cambridge that they were able to do the research, thanks to the ̽��ֱ��’s collegiate system. “We were able to recruit undergraduates in a number of colleges and photograph the women just before they had dinner in the college hall every evening. ̽��ֱ��collegiate routines and networks were vital to collecting data with such regularity,” said Rowland.

Past research shows men find female faces more attractive at peak fertility. A new study shows an increased redness of women’s face skin at the most fertile point of ovulatory cycle, but just under the threshold for detectability, ruling out skin colouration as a driver of the attractiveness effect.

Women don’t advertise ovulation, but they do seem to leak information about it

Hannah Rowland

Greg Peverill-Conti

Faces

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Poisons, plants and Palaeolithic hunters

amb206 — Sat, 21 Mar 2015 10:30:00 +0000

We’re surrounded by poisonous plants: they thrive in our parks and gardens, hedgerows and woodlands. Foxgloves (Digitalis) look charming but their seeds can kill. ̽��ֱ��flowers of monkshood (Aconitum napellus) are a stunning blue but its roots can be deadly. Hemlock (Conium maculatum) is both common and extremely toxic as Shakespeare reminds us in Macbeth with the incantations of the witches.

Archaeologists have long believed that our ancestors used poisons extracted from such plants to make their weapons more lethal and kill their prey more swiftly. By dipping an arrow head into a poisonous paste, the hunter could ensure that an animal would receive a dose of toxic chemicals - alkaloids or cardenolides - that would either kill it immediately or slow it down.

Until very recently it has been impossible to prove that poisons extracted from plants were used by early societies. Now Dr Valentina Borgia, a specialist in Palaeolithic hunting weapons and Marie Curie Fellow at the McDonald Institute for Archaeological Research, believes that she is on the brink of being able to prove that our ancestors used poisons as far back as 30,000 years ago.

Borgia has approached the likely use of poisons by our distant ancestors from a number of viewpoints. Her research looks at the ubiquity of poisonous plants in many local environments and their use both historically and by modern hunter-gatherers. Working with a forensic chemist she has also developed techniques capable of detecting tiny residues of poison on archaeological objects. She is now putting those techniques to the test with samples obtained from museum collections.

“We know that the Babylonians, Greeks and Romans used plant-based poisons both for hunting animals and in war. In fact, the word ‘toxic’ come from toxon, the Greek for bow. Taxus is a genus of the yew tree with a springy timber traditionally used to make bows. It also produces seeds used to poison arrows. In Britain, yews grown for their timber were planted in churchyards so that animals wouldn’t be poisoned by eating their berries,” says Borgia.

“Few hunter-gatherer societies remain today but all the groups that have survived employ poisons. ̽��ֱ��Yanomami people of the Amazonian rainforest use curare - a mix of Strychnos genus plants - to poison their arrows. In Africa, a variety of different plants are used to make poisons. Acokanthera, Strophantus and Strychnos are the most common.”

Many Northern Asian populations used monkshood (Aconitum) to kill large animals such as bear and Siberian ibex. Poisonous plants also feature in folklore. In Malaysia, darts are poisoned using Antiaris toxicaria, a poison that comes from the Upas tree. A Malaysian legend says: “Seven up, eight down and nine no life”. ̽��ֱ��victim takes seven steps uphill, eight steps downhill and a ninth final step.

In 2014, Borgia enlisted the expertise of forensic chemist Michelle Carlin (Northumbria ̽��ֱ��) to help her devise a method for identifying residues of poison. Carlin’s day-to-day work is focused on crime and the detection of illegal substances through chemical analysis. Using a highly specialist technique called liquid chromatography-mass spectrometry, she is able to detect invisible traces of drugs – such as cocaine in pocket linings.

̽��ֱ��same technique can be used to detect the presence of poisons used thousands of years ago. Together Borgia and Carlin have created a database listing toxic plants and have developed a non-destructive method of collecting samples of residues from archaeological materials, by simply touching the item with cotton imbued with pure water.

Samples of poisonous plants were supplied to the researchers by the Botanic Garden at the ̽��ֱ�� of Cambridge and Alnwick Castle in Northumberland. Alnwick has a Poison Garden where visitors can see 150 poisonous plants. Some (such as monkshood) are so toxic that Alnwick has to obtain a licence from the Home Office in order to cultivate them.

Another route to identification of plant residues is to look for the presence of starches which remain on the surface of the prehistoric weapons. Starch grains can be used to determine plant taxa: each species has distinctive size, shape and structure. Borgia has collaborated with a major expert in this methodology, Dr Huw Barton ( ̽��ֱ�� of Leicester) in order to use starching testing as one of her research tools.

Many museums with ethnographical collections have poisoned weapons in their displays and stores. Borgia has been able to collect samples from objects held by the Museum of Archaeology and Anthropology in Cambridge, the Pitts Rivers Museum in Oxford and the Museo Etnografico Pigorini of Roma (Italy) with the collaboration of her Italian colleague, Dr Jacopo Crezzini. ̽��ֱ��objects include a Chinese pot with Aconite poison inside (wrapped in a newspaper dated 13 July 1926), Malaysian darts poisoned with Upas, various African arrows and a glass tube containing curare.

“ ̽��ֱ��wonderful craftsmanship used to create objects so strongly associated with poison is also significant. As the French philosopher Simondon says, there is no pure technical device free from symbolic meaning,” says Borgia. “These artefacts fully express this concept, as they show a high degree of care. A scary-looking Borneo harpoon, wonderfully carved, in the Cambridge museum is thought to have been made from a human bone. A card, conserved with it, warns ‘Care. Has been poisoned’.”

Carlin’s analysis of these samples of materials has shown that residues of poisons are easily detectable on the objects a century later and that the residues retained their chemical characteristics. Now the real challenge for the researchers is to go much further back in time.

Testing of a sample of six stone-tipped pre-dynastic Egyptian arrows, dating from 4,000 years BC and conserved in the Phoebe A Hearst Museum of Berkeley (USA), is now taking place. At the time these arrows where first studied, 40 years ago, the researchers removed small portions of the black residue present on the tips, and injected into a cat. ̽��ֱ��reaction of the poor animal (which did survive) was evidence of the presence of a poison on the arrows.

“Nowadays we have the right instruments to get more information without cruelty to animals. Initial tests strongly suggest the presence of Acokanthera, a poisonous plant on our database, but we can’t be completely certain as there are a number of components in the compound,” said Borgia.

“It made good sense for people to use poisons. On their own, Palaeolithic weapons with stone arrowheads may not have been deadly enough to immobilise or kill a large animal such as a red deer. Poisons plants were plentiful and the Prehistoric population knew the environment where they lived, they knew the edible plants and their potential as medicines and poisons. To fabricate a poison is easy and economic, and the risk is minimal. In addition, the making of poisons is often part of the tradition and the rituality of hunting.”

When archaeologists remove items from the ground in the course of field work, they brush off the soil adhering to the finds and sometimes even wash objects. Borgia is appealing to fellow archaeologists to contact her when they find weapons and not to clean up their finds. “Now we have this technique available, and have shown that it works, we need to test it as much as possible on archaeological samples,” she says.

Borgia denies that her family name (Lucrezia Borgia is legendary as a devious poisoner) prompted her interest in poisons but she delights in the Latin quip ‘nomen omen’. It translates roughly as ‘significant name’ and certainly the name Borgia has powerful historic resonances. Luckily for Borgia’s colleagues, her objectives are honourable and entirely academic.

She says: “Investigation of the use of poisons in Prehistoric periods adds to our understanding of hunting techniques and rituals, and also how the plant world was exploited. ̽��ֱ��Renaissance physician Paracelsus wrote that dosis facit venenum (the dose makes the poison). Ethnographic studies tell us that the most common toxic plants used in poisons were also used to treat diseases. Not surprisingly, the same substances are the basis for many medications still in use today.”

Inset images: Aconitum napellus, credit Wikimedia Commons; starches of Aconite; pot of Aconitum wrapped in the 1926 newspaper, copyright of Museum of Archaeology and Anthropology, Cambridge; Egyptian arrow with poison, copyright of Phoebe A Hearst Museum of Berkeley (USA); poisoned arrows for crossbow, China, copyright of Museum of Archaeology and Anthropology, Cambridge; pot of curare, Peru, copyright of Pitt Rivers Museum, ̽��ֱ�� of Oxford.

Dozens of common plants are toxic. Archaeologists have long suspected that our Palaeolithic ancestors used plant poisons to make their hunting weapons more lethal. Now Dr Valentina Borgia has teamed up with a forensic chemist to develop a technique for detecting residues of deadly substances on archaeological objects.

Spatula to poison darts, Malaysia

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