The molecular weight of carbon is 12.01 grams per mole. Thus an average person contains approximately 1049.13 moles or 6.32 x 10²⁶ atoms of carbon. That’s 632 with 23 zeros after it.

When a person is cremated, almost all the carbon from their body is burnt (that is combined with oxygen) and is released into the atmosphere as carbon dioxide. This joins the carbon cycle and can be absorbed by plants which add the carbon into their tissue and release the oxygen. Plants are eaten and become part of the food chain up to and including humans. (Just think where the carbon in that steak and peas came from).

The bodies of people who are buried eventually break down and join the same cycles. Thus atoms from every person who ever died are being recycled.

Much of the cycling carbon on Earth is involved in the biomass. The total biomass (all living and once-living matter) weighs about 1,877.29 billion tonnes.

There are about 6.5 billion people on Earth. Many of these are children, so for the sake of approximation, lets assume the average weight of a human to be 50 kg. Thus people make up around 325 million tonnes or 0.017% of the biomass.

So if carbon atoms from a departed human are split proportionally throughout the biomass, there should be around 1.07 x 10²² atoms shared amongst humans. Assuming this spread is uniform, then that gives a staggering 1.65 x 10¹² atoms of carbon per person.

This means that you may contain around 1650 billion carbon atoms from any previously deceased person.

Of course carbon atoms will have passed through numerous people both living (from carbon dioxide exhalation) and dead.

But think of every historical figures you admire. Chances are they are now part of you!

Notes

Values and proportions except where estimations are explicitly described are all taken from Wikipedia.

All billions are given as US billions ie. 1000 million.

In the animal world reproduction between close relatives is very common. In fact it was fairly common in humans in historical times to preserve bloodlines or inheritance. Even Cain (in the Old Testament) may have married his sister.

Marriage of related individuals is still common in numerous societies including people from South-East Asia, Israel and Saudi Arabia. It is estimated that in the World, 8.5% of children have consanguineous (more closely related than 2nd cousin) parents. Some research even suggests that marriages within the family are more stable than those between non-relatives. In some cultures it is thought to be a method of providing support and protection for women.

Indeed the notion of negative effects of “inbreeding” don’t seem to have been present even in English communities until around 1888 (though marriage to a sibling is banned in Christian dogma). Thus current Western revulsion at relatives marrying may correspond more to echoes from the Eugenics programs of the early 20th century than to any long held community beliefs.

The cost of such partnerings can theoretically be high, however.

Take for example a hypothetical disease characterised by a genetic fault on gene d. Humans have two copies of each (non-X/Y sex) chromosome, and thus each gene. Most people in a population (say 99%) will have two copies of the healthy D gene (DD). One percent, however, will carry one copy of the diseased gene (Dd).

The disease is recessive. That is, people are healthy unless they have two copies of the diseased gene (dd).

If your mother carries one copy of the gene (Dd), you have a 50% chance of inheriting it. So does your sibling. If you marry a random person in the population (who has a 1% chance of carrying the disease), the probability of you both carrying the defective gene is 50/100 * 1/100 or 0.5%.

If you were to marry your sibling, the probability would jump to 50/100 * 50/100 or 25%.

Even if you both carry the gene, there is only a 25% chance that any child you had would be dd, that is will have not just the gene, but the disease. (This is an over-simplified explanation – often diseases have more than one gene, for example, but it gives an idea of the concepts).

So the likelihood of children being affected is still very small even if you do marry a relative, yet if you multiply the probabilities by the number of potential genetic diseases, they start to look a little more worrying. Research has shown that for consanguineous partnerings, the prevalence of genetic disorders may be up to twice as high as those from unrelated marriages.

The probabilities of having the same gene as a potential mate can be looked at in terms of relatedness (what proportion of your genes you would expect to share with them). For a sibling it’s 50%. For a cousin, 12.5%.

But say you marry your cousin (which is legal), and your child marries their cousin (on the same side). This gives your child and their partner a relatedness factor of 25% – the same as a half sister or brother. Continue marrying cousin to cousin for a couple more generations and, genetically, it can be equivalent to marrying a direct sibling.

This doesn’t mean that there will be genetic problems, just that the chance of them is higher. In fact if you look at the history of European royalty (with a history of consanguineous marriages) you can see some of the genetic problems surfacing – think Alexis – son of Tsar Nicholas II – who suffered from haemophilia. In a visit to Indeed if you go to the Kremlin and look at clothing from the royal lineage, you will see that many of the queens had extremely small feet – another genetic abnormality.

Similarly in other closed populations where people generally marry relatives through religious or geographical isolation, genetic problems will increase in prevalence (amongst the Amish in Pennsylvania or in Hasidic Jewish populations in New York for example).

So there are some good reasons for banning incest. But many of the laws against it were laid down long before genetics was understood. So some other forces must be at play.

In Israel, children in Kibbutz’s are raised cooperatively – that is they are raised with each other, external to any family group. In the 70′s it was noted that people brought up together in a single kibbutz rarely engaged in sexual affairs, nor married within that group – rather they looked to outsiders. This suggests that at some point in childhood the notion of kinship is developed and people become biologically programmed to avoid as potential mates those people they consider closely related. This view has been strengthened by more recent research.

There appears to be an intrinsic biological avoidance of mating with perceived siblings. While some argue that it could be a result of subconscious recognition of related individuals (perhaps by smell), the Kibbutz studies make it seem more likely due to an imprinting period early in life.

Our sense of morality has, at least recently, come from concern over potential birth abnormalities. In current European society, nearly 20% of women are choosing not to have children. Thus for numerous couples, genetic compatibility is not an issue.

With the availability of extensive genetic testing, any potential problems could be easily screened out – in techniques such as those employed in Israel – where couples can be screened for common genetic incompatibilities either prior to marriage (for those opposed to abortion) or during pregnancy.

Without the concerns for health, as a society, should we still choose to prohibit inter-family marriages?

I think I’ll leave that debate to the ethicists!

References

Bach G, Zeigler M, Zlotogora J (2007) Prevention of lysosomal storage disorders in Israel Mol Genet Metab. 90(4):353-7.

Hakim C (2004) Childlessness in Europe http://www.esrcsocietytoday.ac.uk/ESRCInfoCentre/PO/releases/2004/january/family.aspx?ComponentId=2010&SourcePageId=1405

Kaback MM. (2001) Screening and prevention in Tay-Sachs disease: origins, update, and impact. Adv Genet. 44:253-65.

Modell B, Darr A (2002) Science and society: genetic counselling and customary consanguineous marriage Nat Rev Genet. 3(3):225-9.

Patton MA (2005) Genetic studies in the Amish community Ann Hum Biol. 32(2):163-7.

Shepher J (1971) Mate selection among second generation kibbutz adolescents and adults: Incest avoidance and negative imprinting Journal Archives of Sexual Behavior 1(4)

It is also a frequent problem at schools with supervisors reluctant to let charges out of their sight, or children too embarrassed to admit their need in front of the class.

Even as adults, many people will reduce the need for frequent urination by drinking less or waiting for extended periods of time to reduce disruptions at work or to avoid unpleasant toilet facilities (if you have visited public toilets in Greece or China, you know just how long you’d wait to avoid them).

But can repeated delays lead to long term urinary problems?

The bladder is a balloon-like organ which expands to hold fluids. Once it contains a certain amount (for adults around 200 ml of liquid) the urge to urinate becomes apparent. However, unless people have incontinence problems, most people can wait up to 5 hours before urinating. So long as you continue to drink, the longer you wait, the more liquid is put into the bladder. This means that the bladder keeps expanding. Indeed this is part of toilet training for children – their bladders expand over time.

If you do this too often, or wait too long, the bladder may become oversized and weak, leading to dribbling or incontinence. For children who are forced to hold on, often employing characteristic behaviours such as holding genitalia, squatting or pressing their legs together, tension in the pelvic floor muscles may make it harder to squeeze all the urine out of the bladder and thus some may be retained – leading to more frequent urges to urinate.

Infections of the kidneys and urinary tract may also be affected, with one study showing significantly higher levels of urinary tract infections in women who voided three or less times per day compared to those who urinated 4 or more times. However, this may be due more to reduced fluid intake than urine retention.

It seems that there needs to be a balance between toilet training children by teaching them to delay urination for a while, and asking them to hold on “too long”. Also city designers should perhaps increase access to clean, public toilets.

BTW on a more cultural note, I have noticed a significant lack of public amenities in New York City and a general American tendency to avoid the word “toilet” – instead people here use euphemisms such as “restroom”, “bathroom” or the strange “comfort station”.

Anyway, I must go, I feel an urgent bathroom visit calling…

References

Nielsen AF, Walter S (1994) Epidemiology of infrequent voiding and associated symptoms. Scand J Urol Nephrol Suppl. 157:49-53.

Nygaard I, Linder M (1997) Thirst at work–an occupational hazard? Int Urogynecol J Pelvic Floor Dysfunct. 8(6):340-3

Smith, D.B (2004) Female Pelvic Floor Health: A Developmental Review, Journal of wound, ostomy, and continence nursing 31(3):130–137

But why do humans have different eye colours?

It mostly comes down to the amount and location of melanin (yes, the same substance which controls skin colour) in the human eye. Pale eyes such as blue, grey or green eyes contain little melanin, dark brown eyes more. Which eye colour you get is primarily determined from genetic variation based on the eye colour of your parents.

But does your eye colour influence how you see?

It turns out that it does. The darker the eyes, the more light is absorbed as light waves pass through the eye, and the less light is available to reflect within the eye. Light reflection (scatter) within the eye can cause susceptibility to glare (eg. sun or headlights) and to poor contrast discernment. Thus it seems that people with darker eyes may have better vision in high-glare situations – perhaps this makes them better night drivers, for example.

Eye colour may also affect your colour vision. Here it seems that lighter eyes may provide some advantages.

So it seems to me that blue-eyed people should really go for dark-eyed partners – this way one can pick the paint colours, and the other can drive home at night.

References

Coppens JE, Franssen L, van den Berg TJ (2006) Wavelength dependence of intraocular straylight Exp. Eye Res. 82(4):688-92

Coren S, Porac C (1978) Iris pigmentation and visual-geometric illusions Perception 7(4):473-7.

Dain SJ, Cassimaty VT, Psarakis DT (2004) Differences in FM100-Hue test performance related to iris colour may be due to pupil size as well as presumed amounts of macular pigmentation Clin. Exp. Optom. 87(4-5):322-5.

IJspeert JK, de Waard PW, van den Berg TJ, de Jong PT (1990) The intraocular straylight function in 129 healthy volunteers; dependence on angle, age and pigmentation Vision Res. 30(5):699-707.

But could this quintessential Down Under delicacy help to protect Aussie skins from the harmful effects of UV radiation?

Sunlight can cause the formation of free radicals in the skin cells. Free radicals are atoms which exist with an unstable number of electrons in an electron shell. Ultraviolet (UV) radiation can “force” electrons from atoms such as oxygen and create free radicals. Since the electron state of a free radical is so unstable, they are likely to react with anything they touch in the cell – be it a protein or DNA strand. This can lead to temporary damage (such as sunburn) or permanent damage including cataracts – and even to cancers such as melanomas.

Tomatoes contain caretenoids such as lycopene. These are the chemicals which give tomatoes their rich colour. Lycopene is perhaps the most powerful of the anti-oxidants found in any fruit or vegetable.

Anti-oxidants react with oxygen (and other) free radicals to neutralise them before they can harm biological processes. To some extent, the more anti-oxidant molecules in a cell, the more likely a free radical is to hit one of those before hitting a vital part.

Putting caretenoids – especially lycopene – onto the skin has been shown to help prevent and even partially reverse the damage done by exposure to UV light. But it’s not just an external form of sun block – leaving the sauce your pie provides benefits too.

A diet rich in tomatoes has been shown to reduce sunburn and the effects of UV exposure. In fact concentrated cooked tomato (such as tomato paste or sauce) is an even better source of such anti-oxidants than are fresh tomatoes. Forty grams (4 tablespoons) of tomato paste eaten daily has been shown to significantly reduce visible sunburn after only a few weeks.

While not a substitute for sunblock or sun-safe practices, eating a diet rich in tomatoes could thus provide some level of continuous protection. Indeed, it is likely that increasing tomato consumption in your diet may help protect not only against sunburn, but the visible signs of aging, cataracts and skin cancer.

Perhaps in the “sunburnt country” of Australia, it is no coincidence that tomato sauce became the condiment of choice.

References

Aust O, Stahl W, Sies H, Tronnier H, Heinrich U (2005) Supplementation with tomato-based products increases lycopene, phytofluene, and phytoene levels in human serum and protects against UV-light-induced erythema.
Int. J. Vitam. Nutr. Res. 75(1):54-60.

Fazekas Z, Gao D, Saladi RN, Lu Y, Lebwohl M, Wei H (2003) Protective effects of lycopene against ultraviolet B-induced photodamage Nutr. Cancer 47(2):181-7.

Stahl W, Heinrich U, Aust O, Tronnier H, Sies H (2006) Lycopene-rich products and dietary photoprotection. Photochem Photobiol Sci. 5(2):238-42.

Stahl W, Heinrich U, Wiseman S, Eichler O, Sies H, Tronnier H (2001) Dietary tomato paste protects against ultraviolet light-induced erythema in humans. J. Nutr. 131(5):1449-51.

What is a tickle?

It’s a sensation between an itch and a brush, yet it can often provoke laughter and a pleasant response. It can play a social role. Your niece may merely giggle because of the sensation, but it could also be due to conditioning – tickling might be a learned way for adults and children to bond, for example. Tickling can also be a form of couples-bonding or sexual foreplay – perhaps the laughter and retreat may be a way of showing some level of submission to your partner.

So why can’t you tickle yourself?

Part of this may be psychological. If social conventions play a role, you may not react because tickling yourself involves no interaction with another person. This is not the whole story, however as studies have shown that tickling by a perceived machine is as effective as tickling by another person.

So it probably comes down to prior knowledge. When you move your hand, your brain accurately predicts the movement and then attenuates or dampens responses at the expected tickle location.

Experiments using a progressively less controllable robotic arm showed that as the ability to predict the touching sensation is reduced, the tickliness increases. When another person (or machine) tickles you, you cannot predict the motion exactly and thus it feels more tickley.

References

Blakemore SJ, Wolpert D, Frith C (2000) Why can’t you tickle yourself? Neuroreport 11(11):R11-6.

Blakemore SJ, Wolpert DM, Frith CD (1998) Central cancellation of self-produced tickle sensation. Nat Neurosci. 1(7):635-40.

Harris CR, Christenfeld N (1999) Can a machine tickle? Psychon Bull Rev. 6(3):504-10

Selden ST (2004) Tickle J Am Acad Dermatol. 50(1) 93-7

This is a difficult theory to test. Since it is impossible to predict exactly when someone will die, it is not possible to see if a will to survive will keep them alive longer.

A number of studies have looked at personality variables such as positivity and calmness on longevity. These have shown that contentedness, both early and late in life is linked to slightly longer life spans. Indeed mortality rates for the neurotic, unhappy and angry elderly people were often more than twice that of their contented peers.

It is possible that happier people have a stronger will to live. Or, conversely, that healthier people (who are more likely to live longer) are happier.

But happiness should not necessarily translate into a stronger will to live. Hasn’t everyone heard of the grumpy old grandfather hanging on just to spite the relatives? It could be that reduced mortality in the chirpy set is due to the health benefits of stress reduction.

So how could you test the will to live? Scientists have looked for occasions people may wish to live for. Religious, cultural or family-oriented days may provide a focal point – perhaps grandpa can will himself to live until his birthday so that he can see his family once again.

Thus a number of studies have looked at death rates before and after major events. These have included birthdays, Christmas, Passover and Chinese lunar celebrations. By testing specific events which are only important for a selection of the population at any one time, mortality rates can be compared between those for whom it may be important, and those for whom the date is irrelevant.

Many studies have demonstrated reduced death rates prior to such occasions, with a significant surge directly after the event. The importance of these events has apparently delayed deaths from diseases including cancer and heart disease.

No clear mechanism is obvious. Possible explanations have included reduced stress levels, better adherence to medication schedules, benefits of companionship or some psycho-biological process as a results of religious or emotional feelings.

There are confounding factors. Many of these events involve over-indulgence and high fat meals are known to cause heart attacks. Also, the holidays can be very stressful. This could lead to slightly higher death levels after the holiday. Only a few studies take into account the cause of death. Road deaths from drink driving or celebratory shootings (this is an American term relating to people accidentally killed when people shoot guns to celebrate holidays) and other such seasonally affected events may skew calculations.

Indeed reanalysis of the data presented in many of these accounts often alters the conclusions. Secondary research re-examining the spread of diseases covered, the specific time periods before and after an event and the calculation of the mortality percentages seems to deny any effects of willpower.

So, while tantalising, the evidence is not conclusive. Though, if I were a betting person, I would put money on willpower overcoming death in the short term. From personal experience I have seen the terminally ill hang on months beyond the best estimates of doctors, only to fade fast when they suddenly lose the will to survive.

References

Skala JA, Freedland KE (2004) Death takes a raincheck Psychosom Med. 66(3):382-6.

Danner DD, Snowdon DA, Friesen WV (2001) Positive emotions in early life and longevity findings from the nun study. J Pers Soc Psychol 80: 804–13

Lee P, Smith G. (2000) Are Jewish deathdates affected by the timing of important religious events? Soc Biol. 47(1-2):127-34.

Phillips DP, King EW (1988) Death takes a holiday: mortality surrounding major social occasions Lancet 2(8613):728-32.

Phillips DP, Smith DG (1990) Postponement of death until symbolically meaningful occasions JAMA 263(14):1947-51.

Smith G. (2004) Asian-American deaths near the Harvest Moon Festival.
Psychosom Med 66(3):378-81.

Wilson RS, Bienias JL, Mendes de Leon CF, Evans DA, Bennett DA (2003) Negative affect and mortality in older persons Am J Epidemiol. 158(9):827-35.

Wilson RS, Mendes de Leon CF, Bienias JL, Evans DA, Bennett DA (2004) Personality and mortality in old age J Gerontol B Psychol Sci Soc Sci 59(3):P110-6.

Young DC, Hade EM. (2004) Holidays, birthdays, and postponement of cancer death.
JAMA 292(24):3012-6.

It’s a common enough opening, and the interesting part is not the drink of choice, but how you could understand the question.

Every day, in buses, trains, crowded restaurants and open plan offices, most people easily understand other people talking. It hardly seems exciting and yet it has fascinated scientists for over half a century – ever since Cherry first described “the cocktail party problem”. The mechanisms underlying this talent are still not fully understood.

Why is it such a mystery?

The ear hears by collecting soundwaves and passing them along the ear canal, though a series of small bones, to the inner ear, where the soundwaves vibrate the basilar membrane (a tiny organ curled inside the spiral cochlear). The basilar membrane tapers along its length and different parts vibrate depending on the frequency of the sound waves. The narrow end vibrates in response to high frequencies (high pitch sounds), and the wide end to low frequencies (low pitch sounds). Hair cells pick up the vibrations and pass them along into the brain.

Since sounds are comprised of a number of frequencies (the average human voice ranges from the buzz of a mosquito to the highest note on a piccolo), all sounds sum to create the vibrations. Thus your brain knows only which frequencies are present in a room of noise, not which frequencies belong to the person you are trying to hear.

So how can we isolate just one person?

The tempo of their speech is different from that of the music, the conversation flows unlike the sporadic clink of glasses; they may have a lovely accent or a deep voice. Similarly hand gestures, facial expressions and lip movements also add to the experience. All of these speech cues can help you work out which sounds belong to the person you are listening to and which to unwanted intrusions.

Expectation is a factor. When someone is speaking about the latest football results, you can safely ignore any words and phrases relating to politics.

Having two ears also helps. Speech coming from a person on your left side will hit your left ear first and be louder in that ear than in the right ear. The brain can then use that time and volume difference to separate frequencies belonging to that person from those belonging to someone standing on your right.

But all this is done without thought. Can you consciously help?

How often have you missed a sentence because you “weren’t paying attention”? Concentrating on a person makes it easier to follow them. But when you concentrate on understanding a person, are you attending to their accent? their location? the cadence of their speech? or a mix of everything? Experiments are currently trying to work out which factors you can attend to and how this attention can make understanding easier. For example, do you increase your brain responses to speech when you are paying attention or do you just put more resources into interpreting the responses you subconsciously receive?

Who cares HOW you understand since it’s so easy?

If you don’t already, you will. As you age you will slowly lose the ability to listen to a friend in a noisy environment. This is the greatest hearing-related complaint from the aged and from hearing aid users.

Until we understand how a person with normal hearing can solve the cocktail party problem, we cannot work out what is going wrong as people age, nor can we design better hearing aids or assist those with impairments.

So next time you are offered a drink at a noisy party, spare a thought for your auditory system. Chances are its miracles are being wasted on acquiring luke-warm chardonnay.

References

This is the topic of my thesis, so to date I have well over 200 references. They would not all fit here, so I shall limit the list to the original paper that started the scientific debate:

Cherry EC (1953) Some experiments on the recognition of speech, with one and with two ears. J. Acoust. Soc. Am. 25: 975-979

Egg yolks (these contain lecithin) are used to emulsify mayonnaise. It’s easy to test how good an emulsifier these are by shaking them with a little water and oil and seeing how long the mixture takes to settle back into layers.

Milk is a mix of fats and liquids. If you leave fresh milk to sit for a while, the fat will eventually settle out, leaving a cream layer. This can be collected for sale as cream, or used to make butter. To prevent this, milk for drinking is homogenised. This involves forcing the milk at high pressure through a narrow opening. Cream globules are broken into very small droplets. These have larger surface areas, and are more spread out throughout the milk. This and the emulsifiers naturally found in milk (including casein and lecithin) allow the cream to stay evenly distributed throughout the liquid for longer.Thus the milk you buy in the supermarket does not have a cream layer even when left to stand for a few days.