For many years I’ve been pondering and puzzling about the interesting deviations in the patterns on these snake skins. It has stimulated lots of creative thoughts and speculation about ecology, embryology, and evolution, as well as insights into the will of the creator. Your comments, insights, and suggestions are welcome. This is herpetologically geeky I admit, but fun to think about.
The venomous copperhead snake (Agkistrodon contortrix) is a master at camouflage.
Below is a photocopy of the skins of six unfortunate copperheads. They are arranged in a progression — from the most orderly pattern on the left to the most “free-form” on the right.
Here are some of my attempts to articulate my thoughts and questions about what I see:
#1 is an example of the “standard edition” basic, unmodified design. Consistent “hourglass-shaped crossbands with dark margins and pale lateral centers”. (As herpetology text, Reptiles of N.C., states.) Because of these pale centers on the sides of the snake (where the crossband pattern meets the belly pattern) they appear like dark x’s when the snake’s hide is stretched out flat.
#2 shows the same basic pattern repeated down the snake except for what seems like an irregularity on the right side (after the fourth “X from the top). Doesn’t it appear that these crossbands are created as separate halves that are “supposed” to meet in the center over the vertebrae but sometimes the “design production teams” in charge of producing and spacing their half of the crossband patterns get out of sync with each other. In this one the right side has an extra crossband pattern half which “caused” a misalignment of the one above and two below.
On #3 it is the right side again with an extra pattern half in two places.
#4 The two halves on #4 don’t meet at all in the upper mid-section. Is that “caused by” the extra pattern half on the left side down further?
#5 Some of the crossbands on #5 become abstracted to where they are barely recognizable as hour glass- or X-shaped
#6 More so on #6
It looks like there’s a basic plan, theme, program, or “intelligent design” that allows a certain amount of variation. One of the purposes of these patterns is camouflage, to break up the outline of the snake. So, too big an unvariegated space = heightened visibility = death (and those genes are out of the pool).
I am told that the word that deals with these issues is “stochastic”—“denoting the process of selecting from among a group of theoretically possible alternatives those elements or factors whose combination will most closely approximate a desired result.” (Funk and Wagnall’s Dictionary)
But why the pattern sometimes seems to split along the spine might come down to embryology. As an embryo begins to develop the skin is formed during a process called neurulation where the neural plate folds to form the neural tube and the two parts with the epidermis meet at the dorsal ridge. This link shows it:
In reptiles and amphibians, there are three types of colored cells–melanophores (black/brown), xanthophores (yellowish), and iridophores (reflective). Together these are called the “dermal chromatophore unit”. As the neural tube curls, these cells migrate. There must be some kind of genetic instructions about where they should end up.
I’m thinking that as the two sides come together, the two halves of the crossbands reach across to join over the dorsal ridge and then somehow adjust to “fudge” when they don’t meet up. That’s as far as I’ve gotten with this so far. I’m open to any comments, clarifications, corrections, or suggestions.
Meanwhile check out this John Muir quote:
“When a page is written over but once it may be easily read; but if it be written over and over with characters of every size and style, it soon becomes unreadable, although not a single confused meaningless mark or thought may occur among all the written characters to mar its perfection. Our limited powers are similarly perplexed and over taxed in reading the inexhaustible pages of nature, for they are written in characters of every size and color, sentences composed of sentences, every part of a character a sentence. There is not a fragment in all nature, for every relative fragment of one thing is a full harmonious unit in itself. All together form one grand palimpsest of the world.”
– 1867 John Muir (Thousand Mile Walk to the Gulf)
(Palimpsest–A parchment, manuscript, etc. written upon two or three times, the earlier writing having been wholly or partially erased to make room for the next. [Greek, palimpsestos, lit., scraped again]) Early paper recycling!
Thanks to Emily Lutkin for coloring the photo-copy of the snake skins.
Check out the pattern on this copperhead!
Contemplating the will (and the methods) of the creator…
Bilaterally symmetrically (sorta) yours, Doug