Thoughts of an Evolutionary Botanist

Zebras in Rift Valley, Tanzania. G. Diggs

I grew up on a farm in the rolling hills of piedmont Virginia.  Among the earliest lessons I learned was that you had to give animals the appropriate food.  The black angus cattle were fed one thing, the chickens another, the pigs something else.  If animals didn’t get the right type of food, they simply weren’t healthy and didn’t grow and reproduce properly.  Although I didn’t understand it at the time, we were feeding each type of animal an evolutionarily appropriate diet.  This is also a basic concept for zookeepers—for animals to thrive in captivity they need to be fed the diet they evolved to eat, the one that matches the structure of their mouth and digestive system and that is appropriate for their particular physiology.

One of the basic tenets of the developing fields of Ancestral Health and Evolutionary Medicine is that humans are now living in a “novel” environment—a new environment very different from the one in which we evolved.  For the vast majority of the past two million years our ancestors evolved as hunter-gatherers on the African savannah.  The modern world is radically different from this ancestral home, the home that shaped our genetics.  As a result, there is an evolutionary mismatch between the conditions under which we evolved and how we now live.  The differences take many forms: we live in much more crowded conditions; we are subjected to very different types of stress; modern humans often live in much dirtier or sometimes much cleaner environments; we are exposed to a wide variety of pollutants, pesticides, preservatives, and other chemicals; and we have very different diets.  But the bottom line is that the genes our species evolved don’t match the ways in which we now are living; we are genetically “out of synch” with the modern world.

Among the most important differences is diet.  In only about 12,000 years humans have gone from living in small groups as hunter-gatherers eating wild animals and plants, to living in large, complex, agricultural societies typically eating a grain-based diet. Even more shocking, in only a little over 100 years we have gone from eating a diet based largely on unprocessed whole foods to the factory-produced, highly processed, “manufactured” diet of today.

People living only 100 years ago ate almost nothing from a box, bag, or can; their food had virtually no artificial additives, preservatives, or pesticides; it often contained large amounts of animal fat (lard, tallow, bacon fat, etc.) instead of processed vegetable oils; and it was relatively low in sugar (since sugar was expensive).

Evolution is a slow process and cultural change, including our diet, has simply outpaced the ability of natural selection to keep up.  It should thus not be surprising that many of the adaptations that were advantageous to us as hunter-gatherers might be disadvantageous under very different modern conditions.  In other words, many of our characteristics are anachronisms that evolved under different circumstances and are not appropriate under the current novel conditions.

It would be surprising if there were not consequences of being mismatched with our evolutionary past. One of the consequences is that we now face shocking rates of many health problems, the “Diseases of Civilization,” including diabetes, obesity, cancer, heart disease, and hypertension.  This is in stark contrast to the low rates of such problems in hunter-gatherers despite of the fact that some individuals lived vigorous lives into their 50s, 60s, 70s, or even beyond without access to modern medical care.  In future posts I’ll look at some of the causes of these different health outcomes and examine solutions that are being successfully applied by many people in the modern world.

Leopard on Serengeti George Diggs

If you’re a leopard on the savannahs of East Africa, what’s for dinner is clear—generally it is some type of mammal like a Thompson’s gazelle or possibly a zebra.  Likewise, lowland gorillas have a typical diet, but one that is radically different.  In this case it’s 30 to 45 pounds per day of leafy vegetation.  Wild gorillas are essentially vegetarian and have to spend a large part of their time (50% to 60% of their waking hours) feeding.  They also have very large guts (much larger than in humans) that are essentially fermentation chambers where bacteria convert much of the hard-to-digest plant material into short-chain fatty acids.  In other words, they have a digestive track that turns much of the plant material into fat (Jaminet & Jaminet 2012). Thus, the body tissues of wild gorillas are actually nourished on high-fat diets.

The bottom line is that both leopards and gorillas have evolved digestive systems and metabolisms to match their diets.

Now let’s look at what sometimes happens to animals in captivity.

An interesting example can be seen with gorillas at the Cleveland Metroparks Zoo.  First, it helps to understand that heart attacks are the leading cause of death in such captive gorillas, but virtually non-existant in the wild.

Male gorilla in SF zoo Brocken Inaglory

In 2001, Brooks, a 21-year-old male gorilla, died of heart failure and two other gorillas, Mokolo and Bebac, were overweight and unhealthy.  Instead of an appropriate 350 pounds or so, both weighed well over 400 pounds.  The gorillas were being fed a diet typical of gorilla chow at zoos.  It was high-vitamin, high-sugar, and high-starch with large amounts of processed “biscuits” (which the gorillas really liked).  Theoretically the diet was quite nutritious and contained everything the gorillas needed.  In reality, however, much of the diet was processed foods that the gorillas had not evolved to eat—they may have liked or even loved their biscuits, but these biscuits did not match the gorillas’ genetics and physiology.

In 2008, researchers decided to return Mokolo and Bebac to a diet more similar to what they would have eaten in the wild.   Instead of the processed biscuits, they were put on vegetables, including leafy greens, alfalfa hay, and even tree branches from which they strip bark and leaves. While the gorillas significantly increased their intake of calories under the new eating regime, they lost weight.  Each dropped about 65 pounds, reducing their weights to those more typical of wild gorillas (Case.edu 2011; Gabel 2011).

Obese Hastings, with smaller companion, Cassie

When you think about this example even briefly, it’s not surprising.  How well do you suppose leopards would do eating a grain-based, processed biscuit diet?  How well do many of our cats and dogs, who are simply domesticated carnivores, do when they are fed cat and dog foods that have relatively little meat and lots of processed ingredients including grains?  How well do many humans do when they eat high-sugar, high-grain, high-processed food diets?

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At first glance plants might seem defenseless. They can’t run from their predators like many animals do. They don’t have teeth or claws. However, they are far from defenseless. Some plants have thorns or spines which help against large plant-eaters, but such physical defense mechanisms provide little protection against insects and many other creatures that damage plants.

Where plants really excel is with chemical defense. They make a huge number of toxic or poisonous compounds to prevent animals from eating them. These defense chemicals often simply repel the plant-eaters, but in many cases they actually damage the bodies of the creatures eating the plants. Some Texas plants make such poisonous molecules that a few bites can be fatal. Others produce hormone-mimicking substances that can alter how an animal’s body develops or functions.  Still others severely damage the herbivore’s digestive system.  Unfortunately these same things sometimes happen when people eat certain plants.

I’ve spent a number of years researching Texas plants and have studied many that contain very effective chemical defenses.  One such master of chemical defense is the bracken fern, Pteridium aquilinum. This is a common species in the Pineywoods of East Texas where it occurs in the native forests.  It, or its very close relatives, also occur widely in many other parts of the world—where it often causes problems for humans. Bracken fern is a good example to examine because it has evolved multiple defenses. This occurrence of more than one type of protection is actually expected. Keep in mind that plants and animals are in a never-ending “arms race”—when a plant evolves a new defense, there is selection pressure for animals to evolve ways to get around the defense.

Eating bracken, whether you’re an insect, cow, human, or whatever, can have serious consequences. For example, in the British Isles it is the cause of “bracken staggers” or “bracken poisoning,” a potentially fatal condition in livestock. Symptoms include a hemorrhagic syndrome (bleeding), chronic hematuria (“red water” or blood in the urine), bone marrow depression, fever, neurological symptoms and staggering, retinal degeneration (“bright blindness”), and cancer. Among the various plant defense chemicals/toxins reported in the plant are an enzyme called thiaminase, which can cause fatal thiamine (Vitamin B1) deficiency in livestock, the toxin ptaquiloside—which is both mutagenic and carcinogenic, and a dangerous cyanide-producing glycoside—when damaged, tissues containing this defense compound release cyanide, which is quite toxic. Ptaquiloside and possibly other carcinogens can be passed to humans via cow’s milk. In Asia, particularly Japan and Korea, people consume the fiddleheads (immature leaves) as a cooked vegetable and in bars as a salty snack food. However, even the fiddleheads unfortunately have high concentrations of ptaquiloside and have been suggested as a cause of stomach and esophagus cancer. Because it is both carcinogenic and mutagenic, bracken fern should not be eaten. Another chemical defense employed by bracken fern is the production of phytoecdysones, a class of hormone-like compounds that disrupt ecdysis (= molting) in insects—insects eating the plant thus have their developmental sequence altered; they cannot properly go through metamorphisis.

Bracken fern doesn’t just practice chemical warfare against animals—it also uses chemicals against possible plant competitors.  It is known to be allelopathic (= the chemical inhibition of one species by another), with toxins leaching from the tissues adversely affecting surrounding plants—e.g., in the western U.S. the toxins can interfere with tree and shrub regeneration after fires or logging and are also known to inhibit the growth and development of potentially competing herbs. The growth of seedlings may be inhibited even after bracken fern is removed, apparently due to toxins remaining in the soil. In some places bracken fern is such an effective competitor that it can become dominant and disrupt the procession of ecological succession.

The bottom line is that bracken fern and many other plants are not such innocent sources of calories as they might seem.  They have evolved sophisticated ways of defending themselves against attack by animals.  While most of us don’t eat bracken fern, some of the plants we commonly use for food contain powerful chemical defense compounds.  It therefore seems like a good idea for us to understand as much as possible about which plants are good for us to eat and which might compromise our health…..

This material is modified from The Illustrated Flora of East Texas (Diggs et al. 2006) which is available free of charge on-line in pdf format.

with tulip tree in Virginia

I’m an evolutionary botanist in the biology department of a small liberal arts college, Austin College, located in Sherman, Texas.  I do research on the plants of Texas and on the connection between evolution and human health.  I’m particularly interested in how plant chemical defense compounds in food impact our health.  I’m part of a growing community that can be described as “paleo,” “ancestral health,” “primal,” “real food,” etc.  My partner and colleague Dr. Kerry Brock and I have been teaching about evolution, health, and nutrition for many years both individually and in team-taught courses.  We’ve recently published a book on the topic titled, The Hunter-Gatherer Within: Health and the Natural Human Diet.

I’ll be using this blog to post some thoughts on a variety of subjects of interest, particularly those related to evolution, health, and plants.  Most of my posts will focus in some way on the evolution-health connection.  However, I’ll occassionally write about other topics as well—for example, travel.

Some of the entries will be written with students in my classes in mind, while others will simply be my thoughts about new research I’ve read about or other things that seem worth commenting on.

I’ll look forward to your comments.