Exploring the mysteries of domestication


May 2, 2014
Life & Non-humans

We all think we have a rough idea of what happened 12,000 years ago when people at several different spots around the globe brought plants under cultivation and domesticated animals for transport, food or fiber. But how much do we really know?

Recent research suggests less than we think. For example, why did people domesticate a mere dozen or so of the roughly 200,000 species of wild flowering plants? And why only about five of the 148 species of large wild mammalian herbivores or omnivores? And while we’re at it, why haven’t more species of either plants or animals been domesticated in modern times?

If nothing else, the tiny percentages of domesticates suggests there are limitations to human agency, and that it almost certainly is not true that people can step in and completely remodel through artificial selection an organism shaped for millennia by natural selection.

The small number of domesticates is just one of many questions raised in a special issue of the Proceedings of the National Academy of Sciences published online April 21.

The issue is the product of a 2011 meeting of scholars with an interest in domestication at the National Evolutionary Synthesis Center, a nonprofit science center jointly operated by Duke University, the University of North Carolina at Chapel Hill and North Carolina State University.

Of the 25 scholars at the conference, two were from Washington University in St. Louis: Arts & Sciences’ Fiona Marshall, PhD, professor of archaeology, who studies animal domestication, and Kenneth Olsen, PhD, associate professor of biology, who studies plant domestication.

Both Marshall and Olsen are currently engaged in research on the crumbling margins of domestication where questions about this evolutionary process loom the largest.

Marshall studies two species that are famously ambivalently domesticated: donkeys and cats. Olsen studies rice and cassava and is currently interested in rice mimics, weeds that look enough like rice that they fly under the radar even when rice fields are handweeded.

Both Marshall and Olsen contributed articles to the special PNAS issue (seeThe story of animal domestication retold and Genetic study tackles mystery of slow plant domestications) and helped write the introductory essay that raises the big questions confronting the field.

“This workshop was especially fun,” said Olsen, “because it brought together people working on plants and animals and archeologists and geneticists. I hadn’t really thought much about animal domestication because I work primarily with plants, so it was exciting to see the same problem from a very different perspective.”

How much of it was our doing?
Many of our ideas about domestication are derived from modern experience with animal breeding. Anyone familiar with the huge variety of dog breeds, all of which belong to the same subspecies of the gray wolf, has some appreciation of the power of selective breeding to alter appearance and behavior.

But what about self-fertilizing or wind-pollinated plants, or for that matter, domesticated animals accidentally or deliberately bred with wild relatives?

Recent evidence that cereal crops, such as wheat or barley, evolved domestication traits much more slowly than had been thought has led to renewed interest in the idea that selection during domestication may have been partly accidental.

Charles Darwin himself drew a distinction between conscious selection, in which humans directly select for desirable traits, and unconscious selection, where traits evolve as a byproduct of natural selection in crop fields or from selection on other traits.

“The big focus right now is how much unintentional change people were causing environmentally that resulted in natural selection altering both plants and animals,” said Marshall.

“We used to think cats and dogs were real outliers in the animal domestication process because they were attracted to human settlements for food and in some sense domesticated themselves. But new research is showing that other domesticated animals may be more like cats and dogs than we thought.

“Once animals such as donkeys or cattle were caught,” Marshall said, “the changes humans sought to make were pretty minimal. Really it just came down to culling a few of the males and breeding all of the females.”

Even today, she points out, African pastoralists can afford to kill only four out of every 100 cows or they run the risk that drought and disease will wipe out the entire herd. “So I think outside of industrialized societies or special situations, artificial selection was very weak,” she said.

“In the donkeys and other transport animals, it’s not affiliative [tame] behavior the herders want,” Marshall said. “What they care about more than anything else is that their animals stay alive.”

So artificial selection is acting in the same direction as natural selection, or maybe pushing even harder, because humans often place animals in harsher conditions than natural ones.

“The comparable idea for plants,” said Olsen, “is the dump heap hypothesis, originally proposed by Edgar Anderson, a botany professor here at Washington University. The idea is that when people threw out the refuse of plant foods, including seeds, some grew and again set seed, and in this way people inadvertently selected species they were eating that also did well in the disturbed and nutrient-rich environment of the dump heap.”

“Cultivation practices play a huge role in selection,” said Olsen. “Traditionally in Southeast Asia, many different varieties of rice were grown simultaneously in a given field. It was a bet-hedging strategy,” he said, “that ensured some plants would survive and produce seed even in a bad season.” So it wasn’t people selecting the crop plants directly so much as people changing the landscape in ways that altered the selection pressure on plants.

How best to time travel
Questions about the original domestication events are difficult to answer because plants and animals were domesticated before humans invented writing, and so figuring out what happened has been a matter of making do with the limited evidence that has survived.

The problem is particularly difficult for animal domestication because what matters most is animal behavior, which leaves few traces. In the past, scientists tried measuring bones or examining teeth, looking for age or size differences or pathology that might plausibly be related to animals living with people.

“Sometimes there aren’t morphological shifts that are easy to find or they’re too late to tell us anything,” Marshall said. “We’ve gone away from morphological identifiers of domestication, and we’re going with behavior now, however we can get it. If we’ve got concentrations of dung, that means animals were being corralled,” she said.

Olsen, on the other hand, seeks to identify genes in modern crop species that are associated with domestication traits in the plant, such as an erect rather than a sprawling architecture. The techniques used to isolate these genes are difficult and time consuming and may not always penetrate as deeply into the past as scientists had once assumed because present-day plants are only a subset of the crop varieties that may have once existed.

So both Marshall and Olsen are excited by recent successes in sequencing ancient DNA. Ancient DNA, they say, will allow hypotheses about domestication to be tested over the entire evolutionary time period of domestication.

Another only recently appreciated clue to plant domestication is the presence of enriched soils, created through human activities. One example is the terra preta in the Amazon basin, which bears silent witness to the presence of a pre-Columbian agricultural society in what had been thought to be untouched forest.

By mapping distributions of enriched soils, scientists hope to better understand how ancient people altered landscapes and the effects that had on plant communities.

“It is really clear,” Marshall said, “that we need all the different approaches that we can possibly get in order to triangulate back. We’re using all kinds of ways, coarse-grained and fine, long-term and short, because the practical implications for us are quite great.”

After all, the first domestications may have been triggered by climate change at the end of the last ice age — in combination with social issues.

As a result, people abandoned the hunter-gatherer lifestyle they had successfully followed for 95 percent of human history and turned instead to the new strategies of farming and herding.

As we head into a new era of climate change, Marshall said it would be comforting to know that we understood what happened then and why.


23 Responses to Exploring the mysteries of domestication

  1. Abigail Dunkley 14027853 May 7, 2014 at 12:36 pm #

    I do agree that it is indeed necessary to understand past motives for plant and animal domestication, so that humans today can learn from past actions and techniques. Although domestication has proved to be beneficial, it is important to not abuse the various techniques. As mentioned in the above article, domestication became widely used, leading from a hunter-gathering era to one of farming and herding. Domestication of plants and animals, therefore, became important to human life- from cultivating plant species to breeding and training animals for specific roles. However, where must the line be drawn? Today, animals are often bred excessively for financial purposes, so much that animal rights are abused. If one was to look at the lifespan of a chicken, particularly in Southern Africa, it is estimated to be 42 days. Dogs are often bred to sell. Pigs remain in 1×2 metre enclosures until day of slaughter. When will the line be drawn? As the the article claims: humans are pushing artificial selection; so hard that they are placing plants and animals in harsher environments than natural ones. Humans need to remember that they are animals too. Treat the environment the way it was supposed to be treated, or it will soon be all gone.

  2. u14102669 May 6, 2014 at 5:24 am #

    An interesting and thought provoking article, unfortunately lacking in detail. One only managed to fully appreciate some of the topics briefly mentioned if the links in the text were followed.
    It seems obvious that domestication is human led, as the species seemingly has the ability to select and plan towards breeding goals, however, the understanding of selection and inheritance is a largely modern development.
    I do believe that proper study of the long term physical and behavioral changes involved in domestication needs to focus on these more “accidental” domestication, or “co-domestication” processes (as postulated between humans and dogs actively evolving together for instance; http://news.nationalgeographic.com/news/2013/03/130302-dog-domestic-evolution-science-wolf-wolves-human/, http://www4.uwsp.edu/psych/s/275/Science/Coevolution03.pdf)
    In the end, we are trying to decode multiple processes that took generations, of both domesticator and domesticatee, in cultures often more alien to our own than we can imagine, in multiple places around the world with many, many species of both plants and animals.
    I suspect we can not begin to grasp the complexity of the question from the blog article in front of us, but it serves as a good general introduction into new areas of study within the field.

  3. 14005302 May 5, 2014 at 12:33 pm #

    Pets, or as they mentioned it, domesticated animals, are on of my favorite interest from when I can remember!
    After reading this blog I finally got to understand the reasons for many domestication of animals in the past towards domestication today. In the past the humans had to rely more animals and thus did it came that more animals was domesticated, for instance how farmers uses dogs to herd the cattle and sheep, horses and donkeys was for the most of the population the only way of transportation, and farmers had to personally fed the cattle and sheep where now a days the
    are many machinery etc.
    Today most of the domesticated animals are pets to the human-being.

    Although the blog was interesting, it was still a little bit to vague (as mentions in some of the comments) and left me wanting more information.
    Like they mentioned in the blog, this topic is still to be research and there is still many aspects that is to be discovered that will hopefully answered everyone’s, in this case the bloggers, unanswered questions.

  4. Ranier U14013950 May 4, 2014 at 1:29 pm #

    My point of view is supporting some of the other blogger referring to article. Domesticating plants and animals are common around the world. This article generates contrast between the domestication of plant and animals, because the importance is no longer crucial to the existence of human beings, but the article is a little bit vague on the different subjects and because of this questions than to answer them without promoting concrete ways in which to solve these problems. This scientific blog has transformed this point of view and opened its reader’s minds to new ways of approaching the field of domestication. But, domestication carries out selective domestication done by our ancestors all those years ago has proven effective and highly beneficial to mankind to this day. Perhaps this is an indication the people have different opinions on how domestication has had an influence on human history.

  5. CM (14104335) May 4, 2014 at 11:54 am #

    It is interesting to see how the need for and purpose of the domestication of animals and plants have changed. In the past humans were very dependent on the domestication of plants and animal, but these days the focus has shifted more to the domestication of plants. This is mainly because the needs of human beings have changed. I do not believe that it is due to the fact that the remaining wild animals are “untamable”. Wolves were also wild and vicious once, but over time humans were able to domesticate them. Humans just do not have the need to spend so much time trying to domesticate animals anymore. Plants are another story though. With the growing population and growing need for food (and other human desires), humans will continuously try to domesticate plants.

    Something I find rather sad is the fact that due to the pressure humans put on the environment, animals were forced to become dependent on humans for food (accidental domestication). People take in helpless creatures because they might be cute, but they never think of the effect it might have on the animal, which will then never be able to function in the wild. Therefore domestication is not always such a good thing.

  6. u14040817 May 4, 2014 at 9:21 am #

    The article as a whole is based on a very interesting topic that does not really receive allot of attention in the modern scientific field of today. Looking at an ordinary subject like “domestication” is generally considered as quite self-explanatory, but this scientific blog has transformed this point of view and opened its reader’s minds to new ways of approaching the topic at hand.

    Although I am very intrigued by the research done, there are still to many questions that still remains unanswered; for instance: “What other animals followed the root of self-domestication and does this mean that more animals are able to become domesticated in the years to come without any human role played in the process?”

    This topic still shows allot of promise if taken further and improved with more thorough studies and research. I for one we hope that we will find all the answers in the near future.

  7. Kira u14049423 May 4, 2014 at 7:41 am #

    With reviewing all the comments this article has generated, it is interesting to see all the different aspects of how domestication has had an influence on human history. This influence has changed over time and ranges from house hold pets and garden flora, to cattle and crops for food and industrial purposes. It is clear how vital domestication has been to the evolution of mankind, thus i find this article greatly interesting and hope that more conclusive data will be collecting after further research on this topic is conducted.

  8. Bruce Crossey (u14137951) May 4, 2014 at 3:36 am #

    The article seems to lack a definitive focus and direction “jumping” from one field of study to the next drawing on the general connection of domestication; This leads to the article being somewhat vague on a variety of subjects and raising more questions than answering them without promoting concrete ways in which to tackle these problems (aside from largely inaccurate archaeological findings which serve as little more than “suggestions” as to possible explanations for breeding phenomena and the use of “Ancient DNA”, scientifically this leaves the reader questioning the origin of the DNA being used, is this mitochondrial DNA?). The authors should perhaps focus on fewer questions such as why only certain mammalian species have been domesticated by humans via the means of both natural and artificial selection rather than leaving this to be postulated by the reader post reading the article. It is however pertinent to highlight the main point of the article which is that artificial selection and human means of domestication are by no means “foolproof” and as a result the field if domestication remains shrouded in mystery; whether by natural selection or other avenues and means nature itself will find a way to develop past what humanity dictate and towards what is biologically efficient for the organism involved.

  9. u14105854 May 3, 2014 at 4:34 pm #

    The article is of great importance as it explains how we research and determine the domestication of animals and plants while also touching on previous methods of historical determination of the domestication process. Additionally it briefly explains the when and why humans began domesticating plants and animals.

    What is an interesting question that this article proposes is why we humans have not succeeded in domesticating more species of animal in modern times. in my personal opinion it may be because humans have reduced the need to use animals for industrial purposes.

    However, the need for domesticated animals is still massive. Animals are still largely used in less industrialised countries for industrial purposes (in contrast to what previous posts suggest).

  10. u14008883 May 3, 2014 at 1:54 pm #

    The article creates a slight contrast between the domestication of animals and plants. Domesticated animals in no longer of crucial importance to the existence of human beings. They are merely companions of animal lovers, because industrialization has taken control of work previously done by animals. In contrast to animals, plant domestication is vital. Human beings must eat and food cannot be manufactured by machines.Through domestication new species can be developed to the benefit of mankind and the environment. So I conclude that the origin and reason behind the domestication is fundamental in moving the human population foreword and keeping diversity.

  11. u14103959 May 3, 2014 at 9:32 am #

    This article tells us about how domestication of both plants and animals were useful in the olden days and how further people benefit from them. As seen in the article, domestication of both plants and animals largely occurred by different human communities altering natural environmental landscapes, therefore changing natural section and leading to the domestication of various plants. Question about the original domestication events are difficult to answer because plant and animals were domesticated before humans invented writing and so figuring out what happened has been a matter of making do with the limited evidence that has survived. If there was no domestic animals in the olden days it would have difficult to transport certain things and the case of food also.

  12. u14022339: Alexandra Law May 3, 2014 at 8:39 am #

    This topic has always been of great interest to me and when reading this article I wanted to do some research of my own. The act of domesticating animals and plants first took place in the Middle East for the purpose of food production. Later, domesticating animals and plants became common around the world. Although domesticating animals and plants around the world is common, the types of animals and plants being domesticated is not. As seen in the article, the species of animals and plants being domesticated is limited and I believe this is so because mankind can simply not control every wild animal and plant or mankind does not find any use in domesting these species. In many of the above comments, animals being domesticated for family pets has been mentioned and I’d like to add to this. I myself have dogs and cats and believe if these animals were introduced back to the wild, they would simply not survive because we have taken that ability away from them and altered the way they behave and even look. In South Africa most families believe in keeping dogs and cats as pets but in other countries such as China dogs and cats are used for human consumption. As an animal lover I disagree with this practice but who really has a say as people in South Africa eat pigs, cows, etc. The world sees animals and even plants in a different light so when is it acceptable to use animals and plants for human consumption and when is it not?

    (Fixed errors)

  13. u14022339: Alexandra Law May 3, 2014 at 8:34 am #

    This topic has always been of great interest to me and when reading this article I wanted to do some research of my own. The act of domesticating animals and plants first took place in the Middle East for the purpose of food production. Later, domesticating animals and plants became common around the world. Although domesticating animals and plants around the world is common, the types of animals and plants being domesticated is not. As seen in the article, the species of animals and plants being domesticated is limited and I believe this is so because mankind can simply not control every wild animal and plant or mankind does not find any use in domesting these species. In many of the above comments, animals being domesticated for family pets has been mentioned and I’d like to add to this. I myself have dogs and cats and believe if these animals were introduced back to the wild, they would simply not survive because we have taken that ability away from them and altered the way they behave and even look. In South Africa most families believe in keeping dogs and cats as pets but in other countries such as China dogs and cats are used for human consumption. As an animal lover I disagree with this practice but who really has a say as people in South Africa eat pigs, cows, etc. The world sees animals and even plants in a different light so when is it acceptable to use animals and when is it not?

  14. Sello (14326044) May 3, 2014 at 7:57 am #

    I have to second ^14044782 Chanel^ point of view because in the olden days humans were domesticating animals for their personal needs such as for transport and food,but in the modern times it shows how vastly human beings have evolved because they have developed a great deal of love and compassionate for just feeling the need to keep certain animals as pets. And to add to ^u14008794^ point of view,I think the mystery to finding the origin of domestication lies in the type of animal or plant that is thought of because there are certain types of animals that are very difficult to tame and might have dangerous poisons which could lead to death.Also there are certain plants that contain toxic poisons.

  15. u14025354 May 3, 2014 at 5:51 am #

    The article mentioned that very small sample of all species on Earth were domesticated. Could it be that there was a shift in the mindsets of the typical hunter-gatherers and those animals that made up the major part of their diets were captured and ‘tamed’ whereas other large species may have proven to be too inherently wild to ‘tame’? Could it be that cats and dogs (or wolves as they would have been then) somehow managed to win the affections of the people and gradually made the transition from scavenger to pet, whereas other scavengers proved to be too vicious to ‘tame’?

  16. Kira u14049423 May 3, 2014 at 5:23 am #

    In conjunction with the topics referred to by 14047099, another effect of domestication comes to mind. To further elaborate on the topic of loss of biodiversity in natural habitats, haven’t humans in a small sense domesticated a larger percent of organism than originally thought and therefor caused a decrease in biodiversity.

    As earlier stated, domestication was brought about by humans unintentionally altering natural habitats and therefore changing natural selection, and predominantly domesticating a specif organism. But if one refers to the idea of natural habits consisting of multiple food webs, by altering the natural environment humans do not just domesticate one organism, but cause a chain reaction and in a sense domesticate a broad array of organisms. By altering the natural environment to suit human needs, we are in turn forcing all the organism with in that habitat to adapt to the new environment and therefor in turn have in a small way domesticated these organisms. By changing natural selection and the survival requirements of these organisms due to a change in their natural habitats, a decrease in biodiversity has occurred, as extinction of the organism which could not adapt has occurred.

    This is the natural order of things and is essentially evolution. But with today’s advanced technology, humans are able to alter the rate of evolution to an extent. This is a breakthrough for Human science, but scientist should still study the history of domestication so as to not further decrease the world biodiversity, but instead increase it so as to benefit human use.

  17. 14044782 Chanel May 3, 2014 at 3:44 am #

    This is very interesting because in the old days most of these plants and animals were domesticated to help the people make a living, but nowadays many animals are being domesticated for the purpose of simply being someones’ pet, flowers are being domesticated for people to use in their gardens. It just shows how people evolve as time passes.

  18. 14006473 May 3, 2014 at 2:18 am #

    The domestication of plants and animals have lead the a huge shift in the way that human beings live, I think it is vital to understand how this happened and why. Because it happened so long ago I can understand why we have so many questions. the discovery of the cause of domestication might also shed some light on our future and our way of life on earth. This is a really interesting topic!

  19. 14047099 May 3, 2014 at 12:25 am #

    This article provides an excellent example of how many fields in science can collaborate, genetics, plant- and animal-ecology and biodiversity and archaeology. The use of DNA-sequencing techniques to investigate the history of domestication shows just how far our technology has come. Domestication as a process of natural and artificial selection raises concern about environmental issues, such as the loss of biodiversity due to genetic modification as mentioned by Kira u14049423. While domestication has provided benefits to humankind in the form of food, protection and companionship; it has also had some negative effects. The domestication of cattle may have inadvertently contributed to deforestation and erosion. if farmers breed more cattle than the environment can provide for then those cattle exhaust the natural resources of the area. The extinction of certain species due to domestication is concerning however we must keep in mind that this is also a part of the evolution of biodiversity on earth. Either way uncovering more about the domestication of plants and animals is important. With new advances in technology and science we may be able to find ways in which domestication could benefit humans without harming the environment

  20. Kira u14049423 May 2, 2014 at 12:30 pm #

    This article has ignited questions on how further domestication of both plants and animals can greatly benefit humans, specifically in the regions of possible new food sources. Which with the exponential growth of the human population, and increasing strain on the worlds resources, further research on this topic can be key to solving the challenges of in a sense, “too many mouths to feed, but not enough food to go around.”

    However if you look at this with a different view, the question of how further domestication of plants and animals can negatively impact the human population, is raised. As seen in the article, domestication of both plants and animals largely occurred by accident, but it was further influenced by different human communities altering natural environmental landscapes, therefore changing natural selection and leading to the domestication of various plants and animals.

    Today the extent of natural environments being altered due to human influence, has lead to a vast number of negative effects. For example the domestication and essentially genetic altering of various crops has lead to a decrease in biodiversity, a great concern to many scientist. Many concerns have been raised to how this one effect of domestication and have devastating consequences i.e. extinction of an entire species.

    So is further domestication of both plants and animals (which with today’s technology includes genetic modification), really going to benefit the human population and be a sustainable option, or will further domestication of plants and animals further decrease biodiversity and continue to deplete the worlds resources?

  21. hannah 14096057 May 2, 2014 at 9:43 am #

    If new species of plants and animals are to be cultivated and domesticated respectively, new and improved sources of food and fibre could become available for human use.

    However, the lengthy process of domesticating a species is energy intensive. The required energy input should rather be used to develop the current relatively substandard farming methods mentioned by Leeche Storm(14006333).

    In addition, the technology of today would ensure that successful methods of domestication used in the past are not repeated. This would mean that genetic modification would be used in conjunction with artificial selection. As a result a species would arise which is completely developed by man unlike dogs, cats and cattle whose domestication was somewhat independent.

    On the other hand, domestication carried out by our ancestors all those years ago has proved effective and highly beneficial to mankind to this day. Perhaps this is an indication that we owe it to future generations to up the percentage of domesticated species.

  22. Leeche Storm (14006333) May 2, 2014 at 7:50 am #

    Although the hunter-gatherer technique have been mastered and followed for the large part of our human life, modern times and improved technology have lead us in another, more luxurious way of life. This blog article sparks interest and question. Why do we still use domestication as a means to our food? Although the farming industry no longer use the traditional way of producing meat from livestock, some big companies still spend a number of finance to bring up these animals as their own, i.e. domestication. And as for domesticated plants, the cultivated crops creates new species and new species means more domestication. If man believes that we’ve evolved from our traditional and labour times how come agriculture industries still use old methods with a twist? Instead of modernising all the methods we need to improve the old ways and prevent human-kind from changing course with a tragic destination.

  23. u14008794 May 2, 2014 at 6:32 am #

    This research sparks thought on actually why domesticated animals were singled out to be certain animals like cats and dogs. Its quite peculiar why out of the vast range of possible transport animals only animals like horses, donkeys and oxen were picked for that task. Its a mystery and something that definitely needs to be further explored, because if we find out the answers to the origin of domestication other animals could probably be tamed. Plants that are cultivated are very useful in terms of food production and nutrition as a whole it would come as a great source of help if the genes in them could be isolated and properly observed. But the improvement in technology makes one believe that we can find an answer to the mystery.

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