Finches, Feathers and Apples

Finches, Feathers and Apples

Part of the Maths and Science archive

One antecedent of this article is (like A Brief Taxonomy of Numbers) some thoughts I penned on Q&A site, this time early in 2018. However, some of the themes are also ones I have touched on in my science / business cross-over blog posts for many years [1].

Some Background

“Has Evolution been proved yet, or is it still just a Theory?”

Quora – and it seems many other parts of the Internet – is plagued with a seemingly infinite number of variants of the above question. Of course it is not always Evolution that is the main topic, I have seem each of the Earth being round, Heliocentrism, Relativity and Quantum Mechanics suffer the same treatment. However, maybe because Evolution seems to have become a hot button for a certain type of fundamentalist, it is this word that I see most frequently in “Is […] true, or is it just a theory”. The layers of misconception in questions like this are piled up one upon another to a great depth. However, rather that doing what most people would do (one of ignoring it or flaming the questioner), I decided to explain where the fallacies and misunderstandings lie and to gently introduce a more accurate picture of the scientific method. This article is a revised and expanded version of my first attempt to do just this.

Words and Meanings

Evolution is not a theory, it has never been a theory. As it isn’t a theory, it can’t really be “just a theory”.

Evolution broadly means change [2] and it is the term that we have chosen to use to label well-documented changes in a very large number of organisms over time. Importantly these changes are not of individual organisms, but of overall populations over many generations. Such changes are seen in the fossil record over Geological time, but also on a human timescale in bacteria, insects and even chordates [3]. These observations are not theories, they are facts about the natural world. The have been observed for centuries, back to antiquity.

The only people who dispute the veracity of these observations about change in organisms are those who don’t like the logical destination to which these lead. Such a selective approach to evidence is to be treated with the utter disdain it merits.

Charles Darwin

So Evolution is something that happens and something that we can see happening in a variety of ways. Evolution says nothing about why things are happening or the mechanisms involved, it is simply a statement of what is seen. By way of contrast, theories are ideas about why something happens, not the actual thing that happens. Charles Darwin’s original theory to explain the fact of Evolution was called Natural Selection. Natural Selection is not true. Natural Selection is not a fact. Natural Selection is an idea which tries to explain facts, a model if you will [4].

Falling Fruit

Falling Fruit

Let’s take a parallel track. When you let go of an object you are holding (an apple is traditional); it falls down. Not only does it fall down, it accelerates. We can measure this acceleration and – making allowances for where you are in the world – it is about 9.8ms^{-2}. This is not a theory, it is observed facts. Anyone can watch the apple falling, anyone can perceive the acceleration. If you are diligent enough, you can calculate the value of the acceleration. This experiment is repeatable anywhere by anyone competent and will yield the same results.

When change occurs in populations of organisms, we call this phenomenon “Evolution”. When apples (or anything else) accelerate downwards, the chosen label is “Gravity”. Note that Gravity is not a theory, like Evolution, it is a name for observed facts. Even if observations about Gravity are extended to cover the orbit of Mercury around the Sun, these are still observed facts.

Here are three theories (ideas or models) that attempt to explain Gravity:

  1. The [flat] Earth is accelerating upwards at 9.8ms^{-2}
  2. Objects with mass (the Earth and the apple) attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance separating them. On the surface of the Earth, acceleration due to this force is about 9.8ms^{-2}
  3. Massive objects distort a 4D coordinate space consisting of three familiar spatial dimensions and a fourth time dimension (aka space-time); this space is a Minkowskian manifold. Objects follow the shortest path [5] between two points in this coordinate space. On the surface of the Earth, following such a path appears as acceleration of about 9.8ms^{-2}

The acute observer may notice something here, the intrusion of Mathematics into the arena. Indeed Mathematics is the language in which the vast majority of scientific theories are couched [6]. Which make it somewhat odd that “theory” means something different in Mathematics than in Science [7].

Hopefully the above three examples help to elucidate the difference between observed facts and theories that seek to explain them. There is one set of observed facts to do with how objects behave under this mysterious thing we have labelled Gravity, but above I have presented three theories, each attempting to account for what is seen.

We can describe each theory more succinctly. Theory 1 is balderdash [8]. Theory 2 is Newtonian Gravity. Theory 3 is Einsteinian Gravity (aka General Relativity). Let’s discard Theory 1 as it is in the same bucket at Creationism, a thing that has been invented to fit the world to people’s beliefs rather than things that are invented to explain how things actually are. Instead let’s focus on two Theories that have the benefit of actual intellect being applied to their creation.


Newtonian Gravity and General Relativity are radically different in terms of the ideas (and Mathematics) they choose to model reality. However, they are otherwise in exceptionally close accord. Pick a situation involving gravity and the chances are that the two theories will give you close to identical results. However, if you dial up the conditions, differences emerge. For the orbit of Mercury (as referenced above) Newtonian Gravity does not cut the mustard, but General Relativity matches the observed facts precisely. This does not mean that Newton was wrong, merely that his approximations fall down in some circumstances; Mercury offering one of these. Despite its more complicated Mathematics, General Relativity is best thought of as a refinement of Newtonian Gravity, not a wholesale replacement of it.

It is part of the nature of scientific theories that (unlike their Mathematical namesakes) they are not “true” and indeed do not seek to be “true”. They are models that seek to describe reality, but which often fall short of this aim in certain circumstances. General Relativity matches observed facts to a greater degree than Newtonian Gravity, but this does not mean that General Relativity is “true”, there may be some other, more refined, theory that explains everything that General Relativity does, but which goes on to explain things that it does not. This new theory may match reality in cases where General Relativity does not. This is the essence of the Scientific Method, never satisfied, always seeking to expand or improve existing thought.

So let’s come back to Biology again. Darwin propounded his original theory many years ago. At that point, he suggested that there must be some mechanism by which characteristics were passed from parents to child, but he did not hazard a guess as to what form this would take, Later scientists [9] discovered just such a mechanism and today we understand it in exquisite detail; this bolsters Darwin’s insight. Today Darwin’s initial ideas have been amended and revised in many ways and the theories that we have now to explain Evolution are not 100% identical with what the great man propounded. However the general shape is the same and Darwin’s work has more than stood the test of time.


Darwin was not 100% correct (and would not have claimed to be so), the adaptation of his ideas that represents state of the art in Evolutionary Biology is not 100% correct, it just has more explicative power than unmodified Natural Selection and matches a range of observation better.

Maybe some radical new theory for explaining Evolution will be proposed by someone in coming years. It will of course have to explain everything that the descendant of Darwin’s ideas does, plus some things that Darwin does not. But, this will no more make Darwin wrong than Einstein made Newton wrong; refinement is more likely than rejection. Equally, even such a new theory would not be immune to being upstaged by yet another more powerful later theory. To reiterate, this is the nature of Science. Always challenge, always seek to generalise and to expand.

So never expect Scientific insight to stop being a theory. But equally try to understand that theories are all we have to usefully explain the world. They may not be 100% correct and should not claim to be so, but they are the single most useful element of the human enterprise to date and underpin all aspects of our modern world, including the ability of people to place questions like “why is Evolution just a theory?” on the Internet and for me to seek to answer these.

Scientific theories are not perfect, but they are the best we have and – in most circumstances – more than good enough.


Some interactions relating to this post have led me to realising that I should provide some additional clarification about the nature of Scientific Theories. The simplest type of Theory arises in the following manner:

\begin{aligned}&\text{Observation}&\longrightarrow\hspace{5mm}&\text{Hypothesis}&\longrightarrow\hspace{5mm}&\text{Mathematics}&\longrightarrow\\&\text{Experiment}&\longrightarrow\hspace{5mm}&\text{Results}&\longrightarrow\hspace{5mm}&\text{Theory}& \end{aligned}

Ideally the Experiment part is one that can be repeated by other people – this is essentially lab-based Science; things that could be repeated at the bench of another Scientist. Even findings from the Large Hadron Collider should be reproducible, you just need to build your own multi-billion euro facility.

However, some things you cannot design an experiment for and cannot repeat – the most obvious (and biggest) example is the Big Bang itself. Here the flow is different:

\begin{aligned}&\text{Observation}&\longrightarrow\hspace{5mm}&\text{Hypothesis}&\longrightarrow\hspace{5mm}&\text{Mathematics}&\longrightarrow\\&\text{More Data Gathering}&\longrightarrow\hspace{5mm}&\text{Results}&\longrightarrow\hspace{5mm}&\text{Theory}& \end{aligned}

Given the inability to create a custom experiment, validation is sought by gathering more or better data (a new telescope, a more extensive survey etc.). An experiment creates more data, in this second scenario, more data cannot be created, but more of existing data can be obtained and analysed.

Increasingly Mathematics has become a crucial part of Physics in recent years. Where some Mathematical object is used to describe a physical reality, Theoretical Physicists might explore the additional Mathematical properties of this object and then see if they have any physical implications. This could apply to either of the above scenarios, for the first one we get:

\begin{aligned}&\text{Mathematics}&\longrightarrow\hspace{5mm}&\text{Hypothesis}&\longrightarrow\hspace{5mm}&\text{More Mathematics}&\longrightarrow\\&\text{Experiment}&\longrightarrow\hspace{5mm}&\text{Results}&\longrightarrow\hspace{5mm}&\text{Theory}& \end{aligned}

Equally, some Scientific endeavours are not hypothesis driven at all, in some ways more resembling Engineering – Structural Biology is one example that comes to mind here. This looks more like:

\text{Do Lots of Technical Work}\longrightarrow\hspace{5mm}\text{Structure}

All of these approaches are perfectly valid. People sometimes criticise some Scientific endeavours because they do not lead to repeatable experiments. Such criticisms expose a significant lack of understanding about the Scientific method on the part of the questioner.


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Peter James Thomas


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Part of the Maths and Science archive.


For example in 2010’s Patterns patterns everywhere and 2009’s A single version of the truth?.
Evolution: 2. The gradual development of something. ‘the forms of written languages undergo constant evolution’

Oxford Dictionaries

Definition 1 refers to the scientific usage, I was more interested in the general definition at this point.

Try Googling “lizard gut evolution”.
See also my Quora article: The Origin of Theories.
Something called a geodesic.
See the Introduction to my book on Group Theory and Particle Physics, Glimpses of Symmetry.
For a brief discussion of this, see my Quora article The Speciousness of Origins.
It is perhaps worth noting that if the Earth was initially at rest, then (ignoring Relativity) 355 days later it will have reached an upward velocity exceeding the speed of light (it remains unclear where the energy to effect this impressive acceleration comes from). I guess this short time-frame is another reason why the Earth must be young!
For some background on this area, see Data Visualisation – A Scientific Treatment.

Text & Images: © Peter James Thomas 2018.
Published under a Creative Commons Attribution 4.0 International License.