The Science of Sniffer Dogs

Plants eat humans and belch cadaver odor? (part 2)

This is part 2 of exploring a current belief being circulated that plants are able to sequester human remains in their leaves, give off the decomposition odor, and that dogs thus alert on vegetation to indicate a grave. Here’s what would have to happen for this to hold true: The human remains would have to pass through the plant from roots to leaves intact and without compromise such that the odor given off was the same as that given off by the body in situ. Problem number one: we do not know what it is that dogs recognize as human remains target odor, but it seems to be more than one single compound. Keep the idea of complexity in odor signature in mind as you read further.

There isn’t an evolutionary purpose for altruism in plants. There also isn’t a biological mechanism that allows this to happen. In fact, I haven’t been able to find any colleague who can think of a mechanism to support this (taking up human tissues) biologically or physiologically. But wait, what about how plants take up heavy metals? Wetlands are used for bioremediation, because the plants take up the heavy metals. Isn’t that proof?

Nope. Heavy metals are simple molecules or elements (eg. Hg – mercury, Pb – lead). Here’s a USDA link to read more about phytoremediation, which is the use of plants to remove pollutants from soil (the environment): http://www.ars.usda.gov/is/AR/archive/jun00/soil0600.htm These elements can mimic the behavior of nutrients sort of tricking the plant into uptaking them. The plant can take them up but they don’t get the benefit of the nutrient. If you look at the periodic table you will see Hg (mercury) is in the same column as Zn (Zinc). Zn is a key nutrient. Here is a link to the periodic table of the elements http://www.chemicool.com/

Remember, human remains are not elements. They are tissues and organs. Tissues are a collection of cells and organs are a collection of tissues. Skin is the largest organ in the human body. With heavy metals we’re talking simple, basic things. Atoms and ions. Not tissues. Not organs. Not blood or bone or fat or hair or brains or liver or… you get the picture.

Let me offer another way to think about it. Fish emulsion fertilizer. It smells like fish. You put it on/in the soil at the base of your roses. The rose plants take up the nutrients and use those nutrients to grow. The flowers are lovely. You clip a few and put them in a vase on your table. You lean over and inhale the acrid smell of rotting fish… uhhh, no… you lean over and inhale the lovely smell of roses!

Nutrients come from living things that die. Elemental carbon, nitrogen, and phosphorous is the same element regardless of origin. There is no evidence to suggest an odor difference between nitrogen from plants versus nitrogen from a human. Or deer. Or dog. Or other plants. Or fish.

But wait, didn’t we all do the little experiment in elementary school where we chopped a celery stick in half lengthwise, put it in a dixie cup with red or blue dye and water and watched the progress of the dye/water moving up the plant? Yes in the old days we did that. It is a lesson in what is called “capillary action”. Here’s a link explaining this exercise http://ga.water.usgs.gov/edu/capillaryaction.html There’s no roots involved. Most terrestrial plants have roots. Even epiphytic bromeliads like spanish moss.

There are many other things to write about regarding plants eating humans and burping cadaver odor. I haven’t addressed the logical consistency aspect yet either and it would be helpful to hear from handlers specific observations on when they’ve observed this behavior with their dogs, for those instances where they have “the answer” (meaning, they witnessed where the body was located relative to the dog’s indication). I guess there will have to be a part 3. In the meantime let me offer you this -

One thing about science is that it is always changing. Over time the instrumentation we use for analyses becomes more sophisticated, our understanding of physical and biological processes advances, the analytical methods and statistics advance, etc. That is the beauty of science, it is always progressing. The knowledge base is continually updating and we are able to explain and understand the natural world a little more with each new development. It’s dynamic and that’s a big part of what I love about research. What you read here is a stepping stone, which is what each scientific study is. Down with magic, smoke and mirrors… in with fact and truth.

In that light for now let’s be glad that we understand what isn’t likely happening so we can focus our attention to establish what actually is happening… Fortunately there is some compelling evidence of odor displacement by water (H20) from pesticide research. There are other physical processes involved to examine. Stay tuned for a summary of what we can learn about olfaction and odor availability from toxic chemicals and our food!