Stretching the truth

Chris Yates 10 June 2009

Chris Yates reveals the times when scientists have been really, really wrong…

Scientists are not perfect. Over the course of history scientists have come up with a wide variety of theories that have turned out to be completely wrong. Some of their theories, such as the idea of an geocentric universe, were held with confidence for many centuries before being disproved. In fact, a recent survey found that 1 in 5 Americans still believes that the Sun revolves around the Earth. While the theories presented here may now be regarded as utterly ridiculous, they were once in popular favour due to erroneous reasoning. It makes you wonder how mistaken current theories are!

Lamarckian evolution

Before Charles Darwin had even been born, a few had already tried their hand at conjuring up a theory of evolution. One widely accepted theory had been developed by Jean-Baptiste Lamarck, which stated that an organism could pass on characteristics that it had gained during its life. For example, giraffes were believed to have long neck because their ancestors had to stretch to reach the uppermost leaves, causing their necks to elongate. In other words, evolution took place by organisms actively adapting to their environment (whereas Darwin’s Theory of Evolution by Natural Selection which followed shortly, was built upon the assumption that random changes occur each generation, that may or may not be beneficial, with the beneficial ones sticking around). While Darwin’s theory has slowly displaced that of Lamarck thanks to our deeper understanding of genetics, Lamarckism is however currently undergoing something of a revival. This is no more the case than within the field of epigenetics, in which it is now believed that changes made to how DNA is packaged within the nucleus of a cell can be inherited. This means that changes in gene expression in a parent can be passed on to offspring in a similar way to the giraffe passing on its longer neck to its children. Perhaps scientific theories come back around like fashion trends.


Nowadays, heat is thought of as being an increase in the movement of the molecules that make up a substance. Before this the ‘caloric theory’ had been in favour. This theory stated that heat was caused by a fluid called ‘caloric’ which could flow from hot things (which were thought of as having lots of caloric) to cold things (containing little caloric). In fact, this concept proved rather robust and from it a wide variety of explanations can been sought for various fundamental physical properties and observations, including those for radiation, expansion of gas when heated and the changes of state from solid to liquid to gas. ‘Caloric’ lives on today through use of the word calorie as a unit for heat change in honour of the mildly amusing Caloric theory.


A burning question for scientists of the 17th century was what caused combustion. In 1667, Johann Becher proposed the existence of ‘Phlogiston’, a massless, colourless material found in all flammable substances which enables them to be burned. It was believed that when all of the phlogiston in the substance has been used up, it stops burning and is said to be dephlogisticated. Furthermore, is was thought that during burning, as phlogiston is taken up by the air around, the air can become saturated if kept within an enclosed space such that burning will eventually cease. In fact, phlogiston-saturated air is just air in which all the oxygen has been used up and it is the lack of oxygen that prevents burning. This was shown to be the case by Antoine Lavoisier, who was also an avid supporter of the caloric theory of heat. When it was first discovered, oxygen was called dephlogisticated air as it was able to keep things burning for longer than normal air, implying that it contained less phlogiston. I suppose it’s mildly plausible… if you’ve never heard of oxygen.

Emission theory of vision

When you read these words, light is coming from a light source, hitting the page and then going into your eyes. This is the Intromission theory of vision, which states that external light sources are responsible for vision, currently accepted by most people of reasonable intelligence. However, according to the Emission theory, light is produced in the eyes and reflects off an object and then back to the eyes. This idea was favoured by many Ancient Greeks, such as Empedocles, who stated that Aphrodite was responsible for putting fire in our eyes so we could see. They believed that it was because of the light emitted by their eyes that some animals, such as cats, have eyes that shine brightly in the dark (not for the more obvious reason that their eyes contain a highly reflective layer). Although the Intromission theory is widely accepted to be true, Emission theory does have its uses, particularly in computer graphics where ray tracing is used, which follows theoretical lines of sight from an observer to the image, allowing for better detail and realism to be captured.

Hollow Earth

Made famous in the 1864 Jules Verne novel A Journey to the Centre of the Earth, the idea of a hollow Earth has been around since the time of the Ancient Greeks, who had their Hades located underground. The Christian Hell has many similarities, with Jewish and Nordic equivalents. While modern geologists accept the existence of the mantle and inner and outer cores below the Earth’s crust, there are still some who believe in a hollow Earth. In fact, there are plans for an expedition to the Arctic Circle this year in search of an opening into the interior, as theorised in the 19th century by Leonhard Euler. As well as the planet being hollow, there are a plethora of theories built upon the possibility of subterranean inhabitants, although this, like the rest of the hollow Earth theory, lies mostly within the realm of science fiction.

Chris Yates