May 26 2017

Pyramid Homology vs Analogy

Pyramid nonsenseI saw this post on the Credible Hulk Facebook page today. It refers to an old claim by proponents of ancient astronaut theories that the fact that there are similar looking pyramids from different locations on Earth proves cultural contamination from an extraterrestrial source.

While this is a silly argument, it is interesting to explore exactly why it is silly. The underlying principles have to do with homology and analogy, and are exactly the same as they are applied in evolutionary theory. The displayed meme implies that because there are step pyramids in Mexico, Egypt, and Indonesia – countries too far removed to have had direct contact with each other – the idea of a step pyramid therefore had a common source.

This is similar to the evolutionary argument that because two structures look similar or serve a similar function, they must have had a common source, which means the feature was derived from a common ancestor. But we know that this is not always true. The wings of bats, birds, and pterydactyls have similar features, but not a common evolutionary origin. The eyes of vertebrates and cephalopods also have features in common, but evolved independently. But giraffes and humans both have seven cervical vertebrae.

So how do evolutionary biologists tell the difference? They try to determine if the features are homologous (derive from a common ancestor) or analogous (independent origins but similar structure). They can do this in a number of ways, either based on direct evidence or inference. Direct evidence would be finding a fossil of a common ancestor with the feature.

How to infer homology vs analogy is the more interesting question, and is more applicable to the pyramids. The underlying concept is this – are the similarities in structures necessary for function, or are they incidental? Animals are all subject to the same physical properties. The principles of lift and aerodynamics are not different for bats or birds, and therefore some aspects of wing design may have converged to an optimal form. In other words, the laws of physics are a common outside force driving morphology to a similar shape.

Another example are the streamlined shapes of dolphin and shark bodies. They evolved complete independently, but water dynamics provide the same sculpting force for both.

In each of these examples of analogy, however, details that are not under functional selective pressure will probably be different. Dolphins have horizontal tails while sharks have vertical tails. Bats, birds, and pterydactyls each have different finger arrangements. The cell layers of vertebrate and cephalopod eyes are reversed.

When arbitrary (not functionally necessary) details are the same, that suggests homology – common origin.

Archaeologists use the exact same principles when trying to decide if a technology or architectural design are homologous or analogous. This is a bit trickier for archaeology. We know, for example, that bat and bird evolutionary lines diverged long before either evolved wings. But cultural contamination can occur at any time. In fact homologous cultural features is one way to infer contamination. That is what the ancient astronaut proponents are trying to do here.

So the question is – are the three step pyramids displayed here homologous or analogous? The consensus of archaeological opinion is that they are analogous. The idea of designing a building like a pyramid is basic. As the meme says – it is an obvious way to pile rocks on top of each other so they don’t fall down. There may also be a survivorship bias, in that these are the stable structures that survived for thousands of years. These cultures may have built other structures that did not stand the test of time.

Are these step pyramids similar in random details, however? The answer is no. They differ in construction technique, number of steps, the structure at the top, and the presence and form of stairs. They differ in pretty much every detail. Only the fact of being a stepped pyramid is the same.

Step_Pyramid_of_DjoserWhat about the three doors? That part is fake. The pyramids area all shown from an analogous angle to enhance the similarity, and the three doors are photoshopped into place. If, for example, you look at the stepped pyramid of Djoser in Egypt, there are no such doors. The same for the step pyramid in Mexico at Chichen Itza. Those two seem to have been changed to make them look more like the third. Analogy was made to look like homology by faking it.

Many cultures also came up with quadrangular structures, with walls at 90 degree angles. That’s because it’s incredibly obvious. It is not a detail that suggests homology.

Further, there is also direct evidence for independent evolution. In Egypt, for example, there are many pyramids showing the evolution of the pyramid design and construction techniques over time. It’s all well documented – not much of a mystery there (unless all you know about Egyptian history is the Great Pyramids of Giza).

The other commonality between biological evolution and architectural evolution is this – the experts actually do know what they are talking about. It takes incredible hubris to imagine that you, as a non-expert, have cracked a massive mystery about human history that has evaded expert archaeologists around the world. Do you really think that no one has looked at the pyramids around the world and noticed their similarities and asked the obvious questions? There have been centuries of experts debating, discussing, and researching these questions.

Usually when amateurs disagree with the experts it is based on the ignorance and naivete of the amateurs. When confronted with expert opinion, the real crank will then claim a conspiracy. They disagree with me because there is a vast conspiracy to trick the public about this issue. Or they will simply assume that the experts collectively are closed-minded, and lack their brilliant insight.

The explanation is usually far simpler. If you disagree with the experts the chances are overwhelming you just don’t know what you are talking about.

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