Science and the Sacred

Science and the Sacred

Shiny Scales, Silvery Skins, and Evolution



Iridescence — a key component of certain makeup, paints, coatings of mirrors and lenses — is also an important feature in the natural world. Both fish and spiders make use of periodic photonic systems, which scatter or reflect the light that passes against their scales or skin to produce an iridescent camouflage. Previously, scientists knew that animals like the Koi fish and the silvery spider used guanine crystals of a specific size and orientation to achieve this reflectivity. However, a recent study by researcher Avital Levy-Lior and her colleagues at the Weizmann Institute of Science and York University have discovered how these structures came together through evolution.


Thanks to advanced techniques, the researchers were able to study the skin and scales intact without damaging their structure. Their findings show that while both fish and spiders used different crystal arrangements, they were both able to evolve effective structures for achieving reflectivity using the same base material (guanine crystals).

The fact that both fish and spiders were able to evolve a unique but equally effective structure for photonic camouflage is particularly intriguing. Says Prof. Peter Fratzl of the Department of Biomaterials at the Max
Planck Institute of Colloids and Interfaces, “It is very surprising that fish and spiders, pertaining to completely
different taxonomic groups, independently acquired through evolution
the ability to generate mirror-like reflections on their skin by
depositing guanine crystals. This suggests that the solution must be
quite efficient and it is, therefore, extremely promising for the
material scientists to try and understand the structural principles of
these photonic crystals working as (colored) mirrors.”



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posted December 10, 2009 at 8:18 am

A crucial point is that “both fish and spiders used different crystal arrangements” to produce iridescence. I’m counting down the moments until an evolution critic ignores that and gloats, “See? They’re saying they’re ‘very surprised’ by this! Such a specific detail leading to commonality in two unrelated species – so much for the predicted cohesion of taxonomic grouping based on shared traits. ‘Independently acquired’ similarity, my eye! Bye bye common descent.”

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posted December 10, 2009 at 8:33 am

How fortunate of the not-so-evolved unsilvered individuals to survive the millions of years process to becoming a better shinier model.
It must have been the not-so-developed-eyes-waiting-to-evolve of the predators they luckily squeaked by without being detected, while awaiting their new evolution suits, that helped them on their way to evolve a better covering.
This is the cool thing about the evolution story, seeing all of the not-exactly-a-fish-but-not-exactly-a-lizard-(or-bird-or-whatever), lying on a beach for several millions of years waiting to get a better body, and being lucky enough not to be eaten by something else (or get killed from some other means). You know, while becoming the new improved model.
Luckily there are enough years and individuals to keep the thing rolling along. Safety in numbers literally.
Maybe God is just a patient lottery player?
Because looking at animals in nature – like Wildebeests crossing a river loaded with Crocadiles – it sure looks like nature isn’t.

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Ray Ingles

posted December 10, 2009 at 10:28 am

Mere_Christian: At the level of dust motes in air, gravity’s a very minor force. Watch them for a while in a sunbeam; they head up nearly as often as they head down or sideways. Gravity’s a very tiny bias to a dust mote. But if you don’t dust your furniture regularly… (Heck, that’s why casinos make money. The odds of most games are usually only slightly in favor of the house, but over enough games, it means millions. It’s also why casinos expel card-counters; the advantage it gives players is small, but over time…)
Even a slightly better bit of camouflage can, over the long term, lead to better survival. There are a lot of opportunities for camouflage to work over the course of an organism’s life; even a little shifting of the odds can make a big difference. Eyes don’t have to be perfect to be useful (trust me; my vision’s fairly poor without glasses, but I don’t just shut my eyes when I’m swimming at the beach) and – as I’m sure you’ve heard before – the steps in eye evolution are well known.

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posted December 10, 2009 at 10:41 am

The Design Spectrum
However, a recent study by researcher Avital Levy-Lior and her colleagues at the Weizmann Institute of Science and York University have discovered how these structures came together through evolution.(sic)
The article does not explain how they evolved or why we know they evolved. It looks like they just assumed it.

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Glen Davidson

posted December 10, 2009 at 11:35 am

You mean, pds, they “assumed evolution” in the same way that physicists “assume gravity” and epidemiologists “assume germ theory.”
Yes, oddly enough, well-established facts are not treated like mere guesses forever.
Glen Davidson

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posted December 10, 2009 at 12:53 pm

If your epistemology of the historical sciences makes you comfortable making such assumptions, go ahead. Just say so in the post.
But don’t say that they “have discovered how these structures came together through evolution.”
Does the study have anything to do with evolution?

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posted December 10, 2009 at 1:12 pm

The article does not explain how they evolved or why we know they evolved. It looks like they just assumed it.

So pds, what is YOUR more thorough explanation? Hmm, let me guess…

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posted December 10, 2009 at 1:50 pm

I don’t have a more thorough explanation. And I am ok with that.

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unapologetic catholic

posted December 10, 2009 at 7:47 pm

“I don’t have a more thorough explanation. And I am ok with that.”
Scientists are not OK with that. They actually are curious about the natural world and how it works.n They investigate, and question.
From their investigations and questions they can make hypotheses and propose and test scientific theories. One of those theories proposed and tested is evolution. These results are consistent with an evolutionary theory.
No alternative to evolution exists in the same way that no alternative to gravity exists, despite the fact we don’t understand the mechanism for gravity. The explanatory power of both theories is very powerful.
All scientists to some extent work on the building blocks of the scientists before them. The work of biologists today is based on prior work of Cuvier, Lydell, Lamark, Darwin, Wallace, Haekel, Mendel, Mayr, Crick, Gould and thousands of others. There is no need to reinvent the wheel of evolution. It’s been established and reinforced through a convergence of physics, chemistry, history, geology, paleontology and genetics.
So, it’s a misrepresentation to say scientists are making mere “asssumptions” that evolution is valid. They are doign real work.

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