Some species of spider have such short biological clocks that it’s like they are jetlagged by more than five hours every morning. Somehow, they seem to feel no ill effects.

Small orb-weaver spiders are the most common kind of spiders that make a circular web. They become active during the night, hunting prey and rebuilding a clean web during the pre-dawn hours.

To study these spiders’ rhythms, Biologist Darrell Moore of East Tennessee State University and his team documented the activity patterns of different closely related orb-weaver species. The spiders were placed in glass tubes in darkness and their activity was monitored by infrared sensors.

Moore found that three of the species had biological clocks averaging just 17,4, 18.5, and 19 hours. He also identified two species that have exceptionally slow clocks, averaging 28.2 and 28.5 hours respectively, and one species that is completely arrhythmic — without an internal clock at all.

Out-of-sync

“We’ve never seen a circadian clock remotely like this,” said Natalia Toporikova of Washington and Lee University, who was part of the study.

Then the team conducted shift experiments, advancing or delaying daylight by 6 hours.

They found that the spiders were able to adjust within 24 hours, where other animals would be jetlagged and out of sync for about a week.

The normal selective pressures that maintain 24-hour circadian rhythms in most species have loosened in these spiders, says Moore. The shorter circadian rhythm may be an adaptation that allowed them to weave their webs before dawn, avoiding being eaten by birds or other predators. The findings were presented at the Society for Neuroscience meeting in Washington, DC, this week.

During the day, the spider sits still on its web – a strategy to remain as inconspicuous as possible to predators. When nightfall comes, the spiders burst into activity, looking for prey and building their webs. When they are kept in darkness, the spiders’ free-running clocks cue them to become active a few hours before nightfall would normally occur. That suggests that in the wild, the late afternoon daylight suppresses their activity and resets that burst of activity to coincide with sundown.

“Shorter periods are great for getting up earlier for early food sources and if food comes out right at dawn, it is likely important to get up early enough to build a fantastic web,” says of University of Pennsylvania School of Medicine, who was not involved in the study.

In humans, chronic mismatches in circadian rhythm have been linked to many conditions, from cancerĚýłŮ´ÇĚýdepression. Whether the spiders pay a cost for their dissonant clocks is unknown. To understand them better, the team is now measuring how the activity of genes involved in the circadian clock changes throughout the day.

Higher confidence

Evolution could be to blame for our autoimmune diseases, such as lupus, multiple sclerosis and rheumatoid arthritis. For the first time, we have evidence that people who are more susceptible to disorders of this kind are that way because their immune system is better equipped to combat dangerous infections, enabling them to live longer.

“There are so many autoimmune diseases affecting all sorts of tissues,” said , an evolutionary biologist at Princeton University, at the annual meeting of the International Society for Evolution, Medicine and Public Health in Durham, North Carolina, last month. So what could explain the existence of these conditions? “One potential answer is that vulnerability to immune-mediated disease is simply the price we must pay for potent and rapid defence against infection.”

Graham and her colleagues have found evidence for this idea using a long-running study of . It has tracked more than 1000 people born between 1892 and 1953 for the past 27 years.

The team analysed blood samples collected from 639 of these people in 2000 and 2006, measuring the levels of “self-reactive” antibodies – those capable of attacking the body’s own tissues. They found that individuals with higher levels of these antibodies were likely to live longer.

For any particular age, the participants with high levels of self-reactive antibodies had on average a 33 per cent lower risk of dying that year. These people also seemed less likely to have a type of chronic viral infection.

The downside is that these antibodies are precisely those implicated in autoimmune diseases. The kidney is one of the first organs to be affected by the autoimmune disorder lupus, so the team also looked at urine samples, which can indicate kidney health. They found that people who had higher levels of self-reactive antibodies may also be more likely to develop lupus.

What makes this study remarkable is that it explains in evolutionary terms why human evolution has failed to weed out autoimmune diseases, says , an evolutionary biologist at the University of Bourgogne in France.

The work was inspired by Graham’s findings from a similar study in the UK that involves not humans but sheep. For the last 30 years, researchers have been painstakingly recording the health and life details of more than 7000 Soay sheep on the Scottish island of St Kilda.

By analysing the antibodies in sheep blood samples, Graham’s team had found that there was a correlation between levels of self-reactive antibodies and those of antibodies against parasites, and that a high level of self-reactive antibodies runs in sheep families. Together, the findings suggest that genetics influences levels of self-reactive antibodies, and that this is linked to mounting a stronger defence against parasites. This seems to provide an evolutionary advantage – sheep with higher levels of self-reactive antibodies live longer.

“Autoimmunity has previously been considered to be a bad thing, and a consequence of the immune system misfiring instead of attacking what it’s supposed to,” says , an evolutionary anthropologist at the University of California, Santa Barbara. “These studies show that there may be a function for autoimmunity,” says Blackwell.

Statistical analysis of the sheep data revealed that the correlation between survival and high levels of self-reactive antibodies isn’t completely explained by being better at beating parasites. This may mean that self-reactive antibodies are not just a side effect of a strong immune system – perhaps they are doing something useful too. Other studies suggest that self-reactive antibodies can help from the body, and it is possible that they may play a role in .

The emerging picture is that physiological responses are a product of long evolutionary processes, and often serve a function that makes an animal more likely to survive under the right circumstances, says Blackwell. “I would expect these results to be applicable across many species and across different human populations,” he says.

Read more: 9/11 firefighters hit by autoimmune diseases

It’s a fresh problem. People who smoke menthol cigarettes often smoke more frequently and can be less likely to quit – and it could be because fresh-tasting menthol is changing their brains to more sensitive to nicotine.

How menthol enhances nicotine addiction has been something of a mystery. Now, Brandon Henderson at the California Institute of Technology in Pasadena and his colleagues have shown that exposing mice to menthol alone causes them to develop more nicotinic receptors, the parts of the brain that are targeted by nicotine.

Menthol can be used medically to relieve minor throat irritations, and menthol-flavoured cigarettes were . But smokers of menthol cigarettes can be less likely to quit. In one study of giving up smoking, 50 per cent of unflavoured-cigarette smokers were able to quit, while menthol smokers showed quitting rates as low as 23 per cent, depending on ethnicity.

Over time, smokers of both menthol and unflavoured cigarettes acquire more receptors for nicotine, particularly in neurons involved in the body’s neural pathways for reward and motivation. And research last year showed that .

More than a flavour

To understand how menthol may be altering the brain, Henderson’s team exposed mice to either menthol with nicotine, or menthol alone. They found that, even without nicotine, menthol increased the numbers of brain nicotinic receptors. They saw a 78 per cent increase in one particular brain region – the ventral tegmental area – which is involved in the dopamine signalling pathway that mediates in addiction.

“This data shows that menthol is not merely a flavour additive as many of us have believed in the past,” said Henderson, when he presented his findings at the 2014 Annual Meeting of the Society for Neuroscience in Washington DC, last month.

If the effect is the same in humans, this would help explain why menthol smokers have a harder time quitting than those who smoke non-menthol cigarettes.

“We had no idea whether people who chose menthol cigarettes had a higher likelihood of tobacco addiction, or whether menthol had specific effects on the brain,” says Marina Picciotto at the Yale University School of Medicine. She says these findings suggest that menthol enhances the addictive properties of the nicotine.

Menthol-flavour cigarettes are due to be banned in the EU from 2022, and the US Food and Drug Administration is considering taking .