The Limits of Humanity

Muscle Up!

The human record for high jump is 2.45m by Cuban Javier Sotomayor – 1.25 times his height – while most of us would not be able to jump half of that. The mammalian record holder is an elegant antelope called a Klipspringer, or ‘rock jumper’ in Afrikaans, which can jump about 10 times its height. Our mediocrity explodes when compared to animals that even take their body armour to the competition: arthropods. A copepod (‘oar-feet’) is a tiny crustacean that can jump 500 times its body size.
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Limits of life

Humans normally live in fairly comfortable environments, above sea level in fresh air. But thanks to a mutation of a gene that protects against hypoxia, or lack of oxygen, Tibetans can survive on the Tibetan plateau, which at 4500m is one of the highest altitudes still inhabited by humans. However, humans are outdone by bacteria in black smokers (a type of underwater volcano), which need no oxygen at all. They live on hydrogen sulphide, an acid that turns our brain into juice in minutes. The existence of life so far removed from earth’s atmosphere has led scientists to speculate that life may have started in such deep sea vaults.

Speed and Endurance

The human speed record is 35 km/h by Jamaican Usain Bolt. While most people would be happy to reach a third of that speed, the mammalian record holder is the cheetah which can reach up to 100km/h sprinting. Some hunter-gatherers can also chase down an antelope, sometimes for days, until it is exhausted. The secret: sweating. While furry mammals need to stop and pant to cool down, humans shed heat on-the-run by sweating. Among land-dwelling mammals, we’re quite tough: long distance runners such as Yiannis Kouros race from Sydney to Melbourne within five days – this might be as good as it gets in the animal kingdom!
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Reproduction

The early demographer Thomas Malthus thought that richer people would have more children, just as other animals have more offspring when resources abound, but the opposite is true: we are approaching our lower limit. Almost half of humanity produces fewer than 2.1 children per woman, which a stable population requires. Global fertility will dip below the replacement fertility by 2020, still decades before the world population will stabilise. We might be the only animal that chooses to have fewer children than required to replace itself.

Social Bubbles

We have a cognitive limit to the number of people we relate to. We form close relations with about 12 people, or the size of an extended family, and loose relations with about 150 people. The adult Facebook user has  about 200 friends (median). Can we really form close social ties with 200 people or more? Facebook tried to find out in the previous US midterm election. That day, Facebook either sent an ‘informational message’ informing about the upcoming vote and providing an ‘I voted’ button, or a ‘social message’ with the additional information of six randomly selected friends who had already ‘voted’. Only the ‘social’ message boosted the voting rate and only the inclusion of 10 or so ‘close’ friends made the difference, while the other 180 were ignored. The study was hailed as an example of real-world impact by online networks, though it may just mean the exact opposite. Judge for yourself, or ask your friends.
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The magic number seven

50 years ago, George Miller published one of the most popular psychological studies of all time, claiming to have discovered ‘the magic number 7 plus or minus 2’. The magic number refers to the number of items we can immediately recall, for example, a list of numbers such as: ‘6 7 3 2 0 6 0’. The human mind has a trick to boost this limited number: chunking. Many public phone numbers, such as that of Buckingham Palace (020 7766 7300), can comfortably be chunked into five items (020, 77, 66, 73, and 00) and we should be able to hold them in memory for at least enough time to type them into a phone. With our limited memory, chunking individual pieces of information according to patterns is key.

Outliving ourselves

In 1888, Jeanne Calment met Vincent van Gogh and was not impressed. This would not be surprising, had Jeanne not lived another 100 years to tell the tale. At 122 ½ years, Jeanne is the oldest verified human who has ever lived. How old could a human person possibly be? Our average biological lifespan is estimated to be about 85 to 95 years. The life expectancy of children born today, however, may be even higher: our time may be the point where we outlive our biological lifespan to push our artificial, technology-assisted, lifespan. Whatever it may be, we fall short of the longest lived animal of all, a quahog clam called ‘Ming’, after the Ming dynasty that ruled China when it was born in 1499. Ming died more than 500 years later.
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Illustrations by Oliver Barnstedt

Anne Petzold is a second year PhD student studying Life Sciences

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