Is Trophy Hunting Draining the Gene Pool?

Hunters in the U.S. and Canada are the driving force behind the most amazing system of wildlife conservation ever developed. Because of its resounding success, the North American Model of Wildlife Conservation is envied by other countries because it is based on equitable access to wildlife. Unfortunately, this is a largely untold story. Most people think their government takes care of wildlife using their tax dollars.

There is a serious lack of understanding and appreciation for the true history of wildlife conservation. Even after learning about this fantastic story, some cannot reconcile the benefits of this system with their emotional qualms about wildlife being killed. Not everyone needs to be a hunter, but the superiority of this conservation model is undeniable.

With emotions come criticisms. Critics of hunting try desperately to find any information that can play in their favor. A single action of an inconsiderate or unethical hunter is portrayed as the norm. Likewise, any scientific finding showing any negative effect of hunting is paraded in the popular press with far-reaching generalizations and poetic license. Trophy hunting is one of their most frequent targets. Let's explore the charge that hunters negatively affect the gene pool of the species they strive to conserve.

The Building Blocks of a Trophy

Three factors are necessary to produce animals with qualities (such as antler size) far above average for their species. Age, nutrition, and genetics determine whether an animal is a trophy. Age is the most obvious and easily understood portion of the equation; we learned long ago that antler, tusk, and horn size increase with age. Likewise, the European gamekeepers in the 14th century were already writing about the importance of good nutrition as it relates to antler size. These are not new ideas. But the third factor, genetics, is where our knowledge has increased exponentially in recent decades.

Each animal has a different genetic potential for horn or antler growth. Some individuals have superior “antler genes," and some will always be below average—just as some humans never reach six feet in height regardless of diet or age.

Humans can alter the gene pool anytime they influence which animals are available to breed the next generation. This includes human activities such as selectively harvesting trophy males, culling undesirable animals, establishing harvest restrictions based on horn or antler size, and translocations (moving animals to a new area).

Tools of Change

In thinking about human-induced changes to the gene pool, we have to understand the concepts of heritability and selection, as each plays a role in how humans can potentially affect the genes in a population. Heritability is simply the inheritance of certain characteristics from the previous generation. Antler, horn, and tusk size or shape are heritable; thus, the potential to affect future genetic makeup exists. Selection refers to anything that disproportionately removes future breeders from the population based on some characteristic rather than randomly. Selection can be intensive enough to change the genetic makeup of future generations rapidly or so light and sporadic that it is meaningless at the population level. Taking a group of yearling bucks and breeding the five with the largest antlers to all does in captivity (as has been done with cattle and horses for centuries) is more intensive selection than removing a single trophy buck in a free-ranging population. Both actions represent selection, but the potential for changing the gene pool is dramatically different.

Deer researchers in Texas have changed antler size in herds maintained within small enclosures where they had complete control of selection. Inversely, no differences in antler size within age class were observed following eight years of intensive removal of small-antlered whitetails on a 10,000-acre portion of the King Ranch in Texas. The question is not whether hunters can be agents of selection; the intensity of the selection is the fulcrum upon which this whole issue balances.

Obstacles to Selection

Regardless of demonstrated changes in captivity, there are many obstacles to applying intensive selective pressures on a wild population. These obstacles interfere with and lessen the chance of altering the gene pool.

1. Age
   Many times, the effects of age are confused with those of genetics. Hunters deciding whether to harvest an animal rarely know if they are looking at a poor-antlered six-year-old or a “good” three-year-old. As a result, the largest-antlered bucks may be harvested, but they are mostly just the oldest deer and not the most genetically superior. Seeing fewer “big ones” is usually a lack of older animals, not a genetic deficiency. Additionally, the older bucks have learned behaviors that make their harvest far less likely.
    
2. Patterns of Breeding Success
   Mature animals usually do most of the breeding, but research on members of the deer and sheep families has shown that younger rams and bucks participate in breeding to a greater degree than previously thought. Whitetail research has shown that nearly a third of the fawns were sired by yearling and two 1/2-year-old bucks. The data further revealed that, on average, a single buck sired only one to three fawns each year that survived to enter the following year’s population. This complicates the idea that hunters are exerting a strong selection by removing large antlered/horned animals.
    
3. Genetic Contribution of Does
   Female ungulates contribute at least as much to their male offspring's antler and horn quality as do the sires. Experiments have shown that whitetail fawns born from the same doe but sired by very different bucks often have antler conformations similar to each other and share characteristics with their mother’s father. A male-to-female ratio of 1:2 or 1:3 means that 66-75 percent of the total gene pool comprises females that cannot be subjected to selective pressures related to horn or antler quality. It would be tough to manipulate the quality of horns or antlers by incomplete selection on only 25-34 percent of the gene pool
   
4. Movements
   Although exceptions exist, most big game populations are not isolated from genetic exchange. Even seemingly separate bighorn populations exchange genes with one another. This clustering of interrelated populations into one metapopulation dilutes any selection applied to a population and helps to maintain genetic diversity. In whitetails, approximately 70 percent of 1 1/2-year-old bucks disperse from their birth area, traveling one to five miles on average, with many going 10 miles or more. Likewise, areas inaccessible to hunters serve as genetic reservoirs that contain animals not exposed to this source of selection.
    
5. Nutrition
   It is no secret that poor nutrition affects the growth of antlers and horns. Substandard nutrition results in animals not expressing their real genetic potential, and thus, any selection based on the size of their headgear may be confounded by the lack of nutrition.
    
6. Linked Genes
   All genes reside on a set of chromosomes. We don’t know where most genes are located, but we do know that genes located close to one another on the same chromosome are usually inherited together. When this happens, these are referred to as "linked genes." For example, if a gene related to small horn size resides close to one that increases survival, these two genes may be inherited together most of the time. In this example, if you remove males with inferior horns, you will be removing animals that survive better through some other mechanism, thereby confusing the idea of simple selection.
    
7. Other Environmental Pressures
   Hunters are not the major selective force in most big game populations. Even if managers exert an intensive selective removal on adult animals, it is not the only selection. Many other factors (predation, malnutrition, disease, weather, etc.) remove individuals from the population irrespective of genetic potential for horn or antler size, and these other removals are not always random but due to many other selective pressures. Each year, a population produces a new batch of DNA in the form of lambs, calves, or fawns. At least half of this new genetic material never makes it into the breeding gene pool due to these environmental factors, with absolutely no relation to any selection that may occur in the adult population by hunting.
    
8. The Intensity of Selection
   There is a misconception among some that hunters select mature animals most of the time. The reality is that a very small percentage of hunters are truly passing over young animals and waiting to harvest the largest trophies. A trophy, though, is open to interpretation. We find that a trophy is in the eye of the beholder. One hunter may be very satisfied with a buck that another hunter has already passed up in their search for a bigger one. If one hunter's trophy is another's rejection, it becomes very difficult to discuss the genetic effect of removing "trophies." Most trophy hunters take the oldest male, not the most genetically superior. Except in a few very limited cases, trophy hunters do not take the largest males in each age class, but rather the largest they encounter within range during the season, during daylight hours, while in the field. Remember, hunting is not merely an open selection process like grocery shopping. The animals are quite adept at avoiding the hunter while afield, particularly as they mature.

We could only measurably affect the age-specific horn or antler size in the most intensive selection scenarios. The many obstacles to selection discussed above cushion against any hunter-induced selection on the population. In theory, wide buck-to-doe ratios (rather than trophy harvest) have the most potential to selectively change the gene pool because there are fewer males in the population passing on a lower diversity of genes.

Change You Can Believe In?

Research has also illustrated that deer with more genetic diversity have higher Boone and Crockett scores, higher body weights, and better reproductive rates. Gene pools have measurable differences that relate to real population performance. Because of this, we need to be aware of factors that have the potential to negatively affect genetic diversity. Luckily, genetic work has shown that most hoofed animals have remarkably high levels of genetic diversity, and whitetail deer, in particular, are among the most diverse mammals.

Over the past decade, newspaper and magazine articles have charged that trophy hunters are degrading the gene pool. "Evolution in reverse," they call it. These arguments make good headlines because the case is presented to the public without messy details or professional accountability. A 2009 article in Newsweek casts wide, sweeping aspersions on trophy hunters. Many disingenuous and/or uneducated writers have generalized this even further to say “hunters” are degrading the gene pool. As evidence of this assertion, writers trot out the same list of species (fish, elephants, deer, sheep) said to be changed due to human selection.

One species of fish in the Atlantic Ocean became smaller and started maturing later, apparently due to human exploitation. Extensive use of certain-sized mesh nets had intensively gleaned only larger fish from the population. This change is well-documented, but there is some debate about how much of this change is due to genetic factors and how much is due to changes in the physical environment (water temperature or disturbance of the ocean bottom by heavy beam trawlers). It is conceivable that nets of a certain size used extensively may apply an intense selection on any fish not small enough to slip through, but this is obviously unrelated to individual harvest that occurs in typical big game hunting situations.

No article on the perils of trophy hunting is complete without reporting about the African elephant populations purported to be evolving into tuskless freaks. In 1969 and 1972, surveys revealed 10-12 percent of the females were without tusks, but then when surveyed again in 1988-93, the estimate was 28-38 percent. They surmised (without data) that the change was due to heavy ivory poaching. The problem with this is that there was no monitoring between the two early years and the later period and no evidence at all for cause and effect. Even the original paper concedes that the proportion of the population without tusks changed with movements of elephant groups on and off the study area.

Some deer harvest restrictions based on antler characteristics could apply more intensive selective pressures by age category. This has concerned biologists in some areas, but these are unfounded fears in all but a few very limited circumstances where regulations are not adjusted to local antler development data.

Most articles on this topic have cited a short letter that appeared in the journal, Nature, in 2003 that highlighted research conducted on a small, isolated sheep population on Ram Mountain in Alberta. This long-term research was well-designed, thorough, and found strong evidence that hunters removing trophy rams in that population had reduced average horn size within age classes. This selection was possible because a ram had to be 4/5 curl to be legally harvested. This resulted in most rams with fast-growing horns (genetically superior) being removed before they could breed and some old rams with slow-growing horns that never reached 4/5 curl and were never removed. This intensive selection, coupled with genetic drift from the small gene pool (as few as 26 sheep at one point) and complete isolation from other sheep populations allowed for these genetic changes in horn size. Those responsible for the management of this herd changed the harvest restrictions to full curl before the study was even complete and effectively eliminated the intensive selection.

Researchers of Ram Mountain acknowledged that nutrition and age played a larger role than genetics in determining horn size, and subsequent work in this population and elsewhere showed that when nutrition increased, so did horn size. In fact, the largest horns in that population were produced by increasing nutrition.

Historical Heritabilities or Heretical Hysteria?

The New York Times (1/13/09) followed up the Newsweek article with a related piece subtitled "…hunting, fishing and even conservation efforts may have ill effects on some species." The ridiculous game continues. It's hard to understand the near-hysteria in these popular articles when even the most prominent researcher from the Ram Mountain study has stated: "While the potential evolutionary impacts of trophy hunting are worthy of consideration, there is currently not enough evidence to determine when they should be seen as a significant concern for conservation." Some of the articles on this topic contain so many silly quotes from "researchers" that one has to wonder if there is really that much ignorance in the sciences these days. Perhaps some researchers have trouble seeing the forest of facts through the trees of their own biases.

To continually warn about the dangers of trophy hunting based on this one exceptional case and a few poorly supported anecdotes takes significant ignorance or bias--neither of which is flattering for a scientist or writer. This is not to say human selection and maintenance of genetic diversity should be ignored. The demonstrably high genetic diversity in wild sheep and deer, gene flow among populations, and all the other selective pressures work to "reshuffle" the genetic card deck to inhibit detrimental change in horn and antler size.

The public needs to be told the truth that hunters have always been, and will continue to be, the vanguards of an incredibly effective system of wildlife conservation. Researchers, wildlife managers, and their conservation partners in the hunting community will continue to do what they have done so well for nearly a century: execute the most successful conservation paradigm ever devised.

Boone and Crockett Club's Records of North American Big Game has kept consistent records since 1950, containing data back to 1830. Since 2000, eight new World’s Records have been set including pronghorn, bighorn, Rocky Mountain goat, and elk.

ABOUT THE AUTHOR Jim Heffelfinger is a regional game specialist with the Arizona Game & Fish Department, a Professional Member of the Boone and Crockett Club, and author of Deer of the Southwest (www.deernut.com).

Trophy Hunting Facts

• Three factors contribute to producing trophy animals: age, nutrition, and genetics.
• Several obstacles make it difficult for hunters to apply intensive selective pressure on wild populations, such as age confusion, breeding patterns, genetic contribution of females, animal movements, nutrition, linked genes, and other environmental pressures.
• High genetic diversity is beneficial for population performance, and most hoofed animals have remarkably high levels of genetic diversity.
• Claims that trophy hunting is degrading gene pools are often exaggerated or based on limited evidence.
• The well-studied case of Ram Mountain sheep is an exceptional situation and not representative of most hunting scenarios.
• Record book entries for many species have increased dramatically in recent decades, contradicting claims of genetic degradation.
• Hunters are the vanguards of effective wildlife conservation and work to maintain healthy, genetically diverse populations.

 

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