Posted in Philosophy

Ship Of Theseus

An ancient Greek philosopher named Plutarch pondered this scenario. Imagine that the Greek hero Theseus was to repair his ship after a long journey by replacing broken parts with new timber. If he was to embark on so many journeys and repair his ship so much that all of the original material that made the ship were replaced, is that ship still the same ship of Theseus?

This is an interesting philosophical question where some may argue that the ship is still, by definition, the “ship of Theseus” while some may argue that it is no longer the same ship Theseus once owned, but merely a replacement.

Although it is hard to grasp the significance of this question when using an analogy of ancient Greek heroes and ships, it comes closer to home in the field of biology. It is a known fact that the human body is under constant change; cells divide to produce a new lineage of fresh cells while shedding away old, dead cells. Different cells turnover at different rates; skin is almost completely replaced every 4~6 weeks, the lining of the gut is turned over every 4~6 days, while brain cells are almost never replaced (but contrary to popular belief, they can regenerate). If this is the case, are you the same “you” as you were a year ago when the majority of your skin and gut cells were technically “different” (but genetically identical) cells to what they are now? Or are you simply a replacement shell for your brain?

A simpler way of thinking about this would be to consider the case of clones: are clones the “same” as their originals?

The paradox of the ship of Theseus can be extended into a larger scale. Consider a large city like New York. If we were to assume that all of the inhabitants of a city are replaced over a hundred years, then is that city still “New York”? Not only would it looks different because of its new buildings and whatnot, but the people that make up the culture and substance of the city would be completely changed. However, New York is still called “New York” just as it was in the early 1900’s. So is the modern day New York still New York or New New York?


Posted in Psychology & Medicine

Skin Colour

The world is full of people of all creed and races and it is a common fact that people from certain races have different skin colours to people from other races. But other than the range of normal skin colours, there are certain skin colours that can occur with specific medical conditions.

The most common reason for a change in skin colour is a suntan, which damages the skin and causes darkening of the skin (hyperpigmentation). However, some diseases are also known to cause hyperpigmentation, such as Addison’s disease or haemochromatosis.

The converse is lightening of the skin (hypopigmentation) and can happen with diseases such as leprosy, vitiligo or albinism. Alternatively, people can look pale when they are anaemic or extremely frightened, triggering a sympathetic nervous response, shutting down blood circulation to the face and extremities.

It is common to see red skin with flushing, sunburns, skin infections or numerous dermatological conditions such as rashes. Occasionally, these rashes may be associated with serious diseases such as lupus or Crohn’s disease.

Cyanosis (literally “blueness” in Latin) causes the skin to bluish-purple and it is due to the lack of oxygen in the blood. This could be caused by any number of reasons that causes hypoxia. For example, babies can be born with a heart defect that causes mixing of oxygenated and deoxygenated blood, leading to something called “blue baby syndrome”.

Liver dysfunction can present as jaundice, which is yellowing of skin and the white of the eyes due to a build-up of bilirubin.

Some stranger skin changes can be caused by certain chemicals. Carrots contain beta-carotene (which gives carrots their orange colour) and excess consumption can cause carotenosis (or carotenodermia), a yellowing of the skin. Eating too many tomatoes causes a similar condition called lycopenodermia, which presents as reddened skin (lycopene gives tomatoes their red colour). A combination of the two produces a distinctively orange colour. Both conditions are harmless and disappear after reducing the amount of carrots and tomatoes eaten.

Even stranger still is a condition called argyria, which can be caused by exposure to silver, either through medications especially alternative medicine), mining or contamination of the water supply. Silver causes skin to turn a deep blue colour and the pigmentation is irreversible. Similarly, copper can turn skin green and gold can turn skin grey.