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Intelligent Design in Dog Spit and in Rotten Wood

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It’s not often you get a scientific paper about dog spit, but let’s see what we find in one that appeared in PLOS ONE this month: “Salivary proteomics of healthy dogs: An in-depth catalog” by Torres et al. Thank goodness scientists are willing to boldly go where few have gone before, like inside the dark cavern of a dog’s mouth. Their objective:

To provide an in-depth catalog of the salivary proteome and endogenous peptidome of healthy dogs, evaluate proteins and peptides with antimicrobial properties, and compare the most common salivary proteins and peptides between different breed phylogeny groups. [Emphasis added.]

Seven scientists decided to check the saliva from 36 dogs of 19 breeds. Using cotton swabs and collection kits, they carefully collected saliva from the gums of the dogs, including some of their own pets, after making sure the dogs were free of periodontal disease. They classified the breeds into four groups. Then they examined the saliva with state-of-the-art mass spectrometers. What they found was really quite astounding:

2,491 proteins and endogenous peptides were found in the saliva of healthy dogs with no periodontal disease. All dog phylogeny groups’ saliva was rich in proteins and peptides with antimicrobial functions. The ancient breeds group was distinct in that it contained unique proteins and was missing many proteins and peptides present in the other groups.

Thousands of proteins in dog spit! This is an order of magnitude more protein types than previous research estimated. Would you have expected so much complex specified information in a clear, sticky, unappetizing liquid? If we estimate an average of 250 amino acids per protein or peptide, three bases per amino acid codon, and four bits per DNA letter, that amounts to 7.5 megabits of CSI in dog spit! A friendly lick from your pet paints your face with intelligent design.

Each protein, you recall, is made of precise sequences of amino acids, all left-handed, representing translations of the DNA code. And as Jonathan Wells has made clear, the DNA code is only one code out of several cellular codes that guide the protein product from its initial transcription into the final translation and fold, and guide it to its place of function: in this case, the dog’s mouth. So 7.5 megabits is on the low side of the true CSI in dog saliva.

Furthermore, these proteins are there for a reason:

One of the most important functions of saliva is to protect the oral cavity and indirectly other organs against infections. In this study, 7 of the top 10 most abundant proteins have immune functions. Additionally, we identified 26 peptides and proteins (as well as some isoforms) that have been reported to have antimicrobial functions in human saliva; 4 of these were also in the top 10 most abundant in canine saliva. Six of the 26 proteins and peptides were not present in all four breed groups indicating the variability among individual dogs or dog breeds. There are likely many additional proteins and peptides with antimicrobial functions in the 2,491 identified in the study.

Needless to say, many of the proteins in saliva are also important for digestion, although dogs seem to wolf down their food without giving saliva much time to act. But as pet owners know, dogs salivate heavily. Those proteins guard the hatch with megabits of CSI. It’s a good thing they have all those antimicrobials and immune proteins handy, the way they pick up food off the floor and drink out of the toilet.

Saliva may also have behavioral functions involved in canine communication. Lest you think all that drooling shows friendship, Live Science cautions, “Your dog may be licking its mouth because it thinks you’re a jerk.” But that’s a question for another time.

CSI in Rotten Wood

Turn over a rotting log, and you are likely to see some unlovable critters scampering away from the light, and find moist mushrooms sprouting from every crevice. It’s not the kind of thing you would want to drag into the house or choose for firewood. We can be thankful that organisms love this habitat, though, because they perform a vital function, breaking down wood for the next generation of plants.

Most of us are aware of the role of fungi in decomposing wood. What surprised researchers at the Helmholtz Centre for Environmental Research was how much of it there is in a rotting log. Once again, actual counts jumped by an order of magnitude over previous estimates:

So far, little research has been conducted on fungi that live on dead trees, although they are vital to the forest ecology by breaking down dead wood and completing the element cycle between plants and soil. Soil biologists from the Helmholtz Centre for Environmental Research (UFZ) have now discovered that the number of fungus species inhabiting dead trees is 12 times higher than previously thought.

You may recall Ann Gauger’s lignin challenge to evolution based on a BIO-Complexity paper by Leisola, Pastinen, and Axe. Lignin is a tough molecule to digest, even though it is rich with energy. One would think many organisms would have evolved ways to exploit this food source, but only fungi have that ability. It’s striking that their function works for the good of the whole ecosystem. The Helmholtz Centre agrees:

Fungi that live on trees perform an important function in the forest ecosystem by breaking down dead wood. This is no easy feat, because wood is very resilient. It is held together by a biopolymer known as lignin, which together with cellulose and hemicellulose form the cell wall of woody plants and give the wood its stability. Fungi are able to break down the robust lignin and the flexible cellulose fibres by releasing enzymes that cause the polymers to degrade and become mineralised. As part of the ecosystem’s cycle, the leftover material becomes part of the humus layer, which gives the soil its stability and forms the substrate for a new generation of trees.

A photo shows how researchers measured fungi abundances. They observed 300 fallen trees from 11 species, including deciduous trees and conifers.

The trees included seven deciduous species such as beech, oak, poplar and ash and four coniferous species: spruce, Scots pine, Douglas fir and larch. Three years later they returned to see what kind of fungal communities had established themselves in the trunks. The results were astonishing: “The diversity of fungi living in the trees was an order of magnitude greater than previously thought,” says Dr Witoon Purahong, a soil ecologist based at UFZ in Halle and the first author of the study.

They couldn’t identify all the fungi, but estimated a total of 1,254 “operational taxonomic units” (unnamed species) per trunk. Surprisingly, the conifers, which in the evolutionary scheme are earlier and more primitive than deciduous trees, had the most fungal diversity. Another unexpected finding was that fungi are picky about their trees: “For example, oak and ash each harbour very specific communities [of] fungal species whose composition is very different from those found on other deciduous trees.” Even trees that have similar wood composition have distinct fungal communities.

They point to “millions of years of co-evolution between trees and wood-inhabiting fungi,” but then admit another conundrum. “What is fascinating, however, as Buscot adds, is that in some cases the specialisation of fungi on dead wood is greater than the one of symbiotic fungi on living plants.” Complexity seems to have arisen earlier.


These two research projects, unusual as they are, give valuable insights into working ecosystems (a dog’s mouth and a forest floor), that may lead to applications for human health and biodiversity conservation. Beyond that, though, you may sense the astonishment at finding more complexity than expected. Within each habitat investigated, science keeps finding vastly more complexity than simple mutation and selection could ever hope to produce. Furthermore, each protein, and each fungus, has a vital role to play in systems larger than themselves. Isn’t that what intelligent design science would have predicted?

Photo credit: Dallas Floer Photography, via Flickr.