Chris -  It’s a very good question.  Why is it that your hair grows on your head can, in some people’s cases, can reach their waists whereas eyelashes conveniently remain only a few millimetres long.  If you had eyelashes that reached your waist that would make seeing quite difficult, I would imagine.  Similarly pubic hair under you arms, for example.  Why does that stay short and curly and the drop out before it gets really long whereas the hair on your head can become very long?

The answer is it’s all down to genes and when you’re developing as an embryo your body develops as a series of segments.  Written into those segments is a genetic pattern that tells that bit of the body where it is in the body and anything that develops on that segment inherits that genetic pattern which dictates to it how it should grow and develop. 

If you look at how hairs work - hairs have three phases to their life cycle.  They have what’s called an anagen phase and this is where they grow.  The hair follicle has a number of stem cells that are very, very active and they pump out keratin which is the hair chemical.  Keratin forms a big polymer which is a filament for hair which you see. 

After the anagen phase, which can last anything from days – in the case of an eyelash that’s about 2-3 weeks, to a head hair which can be three or four years.  That determines how long the hair grows for its ultimate length.  Then the hair goes into what’s called a catagen phase.  That’s where the follicle switches off and the hair falls out.

Then there’s a third phase which is called a telogen phase when the follicle rests.  It then resets the system and the whole thing starts again.

So the hair length is down to how long the hair grows for, the anagen phase, and that is determined by your genes.  Basically the genes that are programmed into the bit of the body that’s got the hair in it.

Kat -  I was thinking if you had some weird genetic mutation you could have pubic hair that grew down to your ankles!

Chris -  Yeah, I suppose if you similarly transplanted head hair to your pubic region or vice versa you would get hair that had that behaviour because it had pre-programmed into it that way of growing.

Kat -  Freaky!

Chris -  There’s a company in America called Allergan.  They’re the company that brought you Botox.  They’ve also got a drug for glaucoma which is this eye pressure problem where you have too much pressure inside your eye.  This can damage your optic nerve.  There’s a drug called Lumigan which can be used to treat that.  The generic name is bimatoprost for this.  What they found is one of the side effects is it makes your eyelashes grow long in some people.  They’re actually applying to the FDA (that’s the drug administration group in America) for permission to market this as an eyelash lengthener.  The slight downside is that it also makes your eyes get darker and it also makes your eyelids get darker.  The effect can be permanent.  Not only will you have luscious lashes, you will also potentially have darker eyes and darker eyelids.  If you don’t use the same amount on both eyes the effect can end up being non-symmetrical.

Kat -  So you’d look like a panda.

Chris -  You’d end up looking like a sort of David Bowie effect. It could be a bit dodgy.

Kat -  I think the evidence suggests that you probably can.  Obviously it’s not hearing as in the sense that born people hear because that’s all to do with air pressure.  I think there’s a lot of evidence that babies can really sense the vibrations in the fluid that’s around their ears.

Chris -  The US Navy did a study about five years ago where they took lambs that were developing inside the mother and they put a miniature microphone inside the ear of the developing lamb and another one in the fluid surrounding the lamb and then a microphone outside the sheep.  They played sounds using a speaker and recorded from those three sites.  They played back the sounds they recorded to a group of volunteers and asked them how much they could interpret from what they’d just heard from these recordings.  They understood 100% of what was said using the microphone outside the sheep’s body, they understood about 75% of what they recorded using the microphone sitting in the fluid around the baby inside the sheep and they understood a good 30-40% of what was being said from the recordings in the ear of the baby sheep.  What this suggests to you is you should be very careful when you’re talking around a pregnant woman because the baby may well be eavesdropping.

Kat - No swearing!

Judith from Northampton got in touch to say:

"My friends used to play the violin while I was pregnant, most notably Vivaldi or Bach.  Once the baby was born whenever it heard a piece of music by Vivaldi or Bach it used to instantly fall asleep whilst other music would have no effect or might even make it cry.  The baby must have recognised the music from when it was in the womb."

Chris -  I was thinking about this because we talked on the Naked Scientists a little while back about how researchers in Scandinavia have worked out how long a fat cell survives inside a human body by using carbon dating.  He’s saying carbon dating can be used for rocks and things like tree rings to work out how old trees are, what about humans?  The thing is when you take into your body some plant matter it’s go carbon-14 from the environment.  That gets incorporated into your body and therefore it gets written into your DNA if you have new cells being born.

What these researchers, Kirsty Spalding and her colleagues, did (they published this in Nature a couple of months ago) what they did was to take fat cells and look at how much carbon-14 they had in them.  As your fat cells age they’ll lose their carbon-14.  The amount of carbon-14 gives you an idea as to how recently that cell was born.  It will have had new DNA put into it which would have had a fresh level of carbon-14 in it when it was born.  They did actually show that fat cells have a lifespan of about ten years.

Kat -  There’s another way of doing it which is to look at your telomeres.  Inside all our cells we have chromosomes.  These are long lengths of DNA.  At the end of them, in the same way that you have a little plastic cap on the end of shoelaces you have these structures called telomeres.  These get shorter and shorter as we go through life.  Every time a cell divides it loses a bit off the end of its telomeres.  There may be some way of measuring human lifespan in terms of how long or how short your telomeres are.  The trouble is that there’s no standard length and people have different length telomeres depending on their genetic makeup.  I know that Cancer Research UK is funding a project looking at how our genes determine our telomere lengths.  It’s actually linked to cancer risk.  People who have very short telomeres are going to get shorter very quickly and that can actually increase the likelihood of getting cancer.

Chris -  So we could look at the cells, see what the length of the telomeres are and that would give you some idea as to the age of that cell?

Kat -  It would give you some indication and maybe if you compared it to other cells in the body like maybe your germ cells that don’t go through this kind of process.

We put this question to Professor Russell Foster:

I think it’s such an interesting idea because we’ve published a paper last year on an individual who has no rods and cones but can still regulate their body clock using these new receptors to the light-dark cycle.  It’s only with the discovery of these cells that we can ask question like that.  The assumption then, has been – well, you’re depressed because you can’t see.  We’re starting some studies to look at depression in individuals who have those cells but don’t have the capacity to see.

We put this question to Professor Russell Foster:

Russell - If the light is bright enough it actually doesn’t matter too much which wavelength it is.  When we say these receptors are most sensitive to blue light that’s the wavelength if you were to lower the light levels it would then be blue that is effective.  If you’re using a full spectrum lamp that’s bright enough it will be perfectly good.

Chris - So this is where people would perch themselves in front of a bright lamp in the morning?

Russell - That’s right, yes.

Chris - And this works, does it?

Russell - Remarkably enough it works.  Now we’re beginning to understand the mechanisms behind it.

We put this question to Professor Russell Foster:

Let’s kill this one dead!  In ’98 a group of researchers at Cornell University suggested that red light behind the knee would train the body clock.  This got huge amounts of publicity.  A lot of us thought it was nonsense at the time.  It was published in Science, incidentally.  Five studies around the world tried to replicate the findings and all completely failed.  It looks as though there was some artefact in the experimental design of that original paper which was fundamentally flawed and they got it badly wrong.  It did cause a huge amount of commotion.  Let me assure you, it is nonsense.

We put this question to Professor Russell Foster:

We talked about those clock genes [see Russell's interview] of which we think there are 12-14 of them.  Tiny changes in those genes are now being associated with a morning preference – larks as distinct from an evening preference – those people we would describe as owls.  You’re absolutely right.  There are some people, about 10% of the population that light to get up very early, We’re talking about 5 in the morning but then they go to bed very early, sort of 7 o’clock in the evening.

Chris - And we’ve got genes that we can map onto those different behaviours?

Russell - In fact there’s one extraordinary study called familial advance sleep-phase syndrome where it’s been followed through five generations now.  It’s one tiny amino acid, a change in one of those proteins.  One of those 14 proteins that make up the clock.  It’s an extraordinary study.  We’re starting to pick up more and more subtle changes in these genes with morning and evening preference.  I should say that this morning and evening preference does shift with time.  As one grows up from the age of ten through adolescence into the early 20s there is this tendency to want to go to bed later and later and later and get up later and later.  That seems to be a real biological phenomenon.  There’s some very important consequences I think in terms of our education systems that we might want to discuss.

Kat - So maybe having classes later?

Russell - Well, the evidence suggests from the University of Toronto. They tested pupils mid morning or mid afternoon and their scores went up by ten percent in the mid-afternoon.  What was fascinating was that the older teachers’ went down over the same time period.

We put this question to Professor Russell Foster:

What he’s talking about and what I think many of us experience is that you wake up a few minutes before the alarm goes off.  The mechanisms behind this have been much discussed.  If we jump from our species and talk about honey bees.  Honey bees will use their body clock almost like a daily events calendar.  They will consult this internal clock to determine when they will visit a specific type of flower at different times of the day.  For example they will visit one species at 12 noon and then another species 12 hours later.  They’re using their body clock to time specific daily events.  It’s thought that we may be able to do the same.  It’s not absolutely clear and there may be other mechanisms but the evidence is pretty good that we can act like little bees.

We asked Professor Russell Foster:

No. It depends on the individual but most of the time it’s an eight hour block. Sometimes you can separate it in the middle with a slight waking up phase and then you go back to sleep again. On the whole, no.

We put this question to Harriet McWatters:

They’re very much the same thing. They’re periods of dormancy to avoid inclement conditions. Hibernation is usually when an animal is trying to avoid winter. Aestivation is in hot countries where it’s trying to avoid summer. It’s avoiding the worst times of year.

We asked Professor Russell Foster:

Melatonin is a hormone produce in the pineal gland. It’s highly regulated by light. It’s produced at night. There’s two bits of evidence to suggest it might be useful. 1, if you take melatonin about 70% of people will fall asleep; 2, it may help you shift your body clock. The evidence emerging is that yes, it may help you sleep.

Chris -  Is it harmful?

Russell - We don’t have any evidence that it’s harmful. I certainly wouldn’t recommend using it without discussing with your GP first.

We put this question to Dr Harriet McWatters:

Ordinary bacteria such as you would find in your gut probably not.  There is a class of blue-green algae which are often called cyanobacteria which have very strong circadian rhythms.

We put this question to Dr Harriet McWatters:

Plants can detect it when you damage them in some way.  They are usually more sensitive to things like caterpillars eating them, which will happen in their natural life.  For example, an oak tree which is being attacked by caterpillars will respond by producing tannins in its leaves, which makes its leaves bitter.  What’s even more interesting is that trees adjacent to the one that’s being attacked can somehow detect some signal and will also start to produce tannins in their leaves, even before caterpillars have been eating.  So given that, I think they can almost certainly detect if a branch has been cut off.  The problem is that they don’t really have any response to that except to grow another branch.