Comparing the amount of domestic animals and wild animals?

Comparing the amount of domestic animals and wild animals?

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From some material, I read about the ammonia (NH3) emission from animal waste.

I found that the emission from domestic animals are greater than wild animals.

Then, I can't help wondering the amount of wild animals and domestic animals(cow, pig, chicken, etc). Which has the greater amount on Earth? And how to estimate the amount approximately?

And how to estimate the amount approximately?

You cannot. Most of the earth is water, and fauna diversity is highest in water. We are still tagging and tracking the movement and reproduction cycles of animals, and that is a never ending task. I say we cannot reach an accurate approximation because of how these projects work. They are targeted towards the monitoring of specific species. Next, different countries have different approaches towards conservation of the same species, and above all this many countries choose not to report numbers. The example which comes to mind is the Red panda. As many animals come inside the radar of active conservation efforts, even more remain outside it.

In fact, some time ago I read a compelling article about why the WWF should change their logo to a Red panda (or known as the lesser panda) rather than the giant panda, the argument being that awareness about the giant panda is very high while red pandas are still misunderstood as pandas. Unfortunately I cannot find that article now, but you can visit the red panda network to find out more.

Which has the greater amount on Earth?

Second, what do you consider as a wild animal? are insects included? are gutter rats included? Is the infestation of wild boars near the now defunct Fukushima plant included? If yes then they outnumber domesticated animals by a long shot. I would dare to say that cities are habitats more for members belonging to Animalia but not belonging to Homo.

The pace of evolution in domestication

With such dramatic and rapid variation occurring in domestic species like dogs and pigs it could be assumed that the evolutionary rates in domestication are faster than those in the wild. But is this actually the case? Madeleine Geiger, author of a new study published in Frontiers in Zoology, explains her research investigating this.

The multitude of varieties of domestic animals is astonishing. It seems natural that for example a short-nosed bulldog, a gracile Greyhound, and an enormous St. Bernard dog all belong to the same kind of organism, or species. And yet, domestic animals represent an extraordinary case of variation.

in relation to species in the wild, which may have evolved over millions of years, the first domestic animals are “only” 40,000 years old at most

This variation is staggering if one considers that it appeared in a relatively short period of time: in relation to species in the wild, which may have evolved over millions of years, the first domestic animals are “only” 40,000 years old at most. Going one step further, many of the extreme differences in skull shape that we may observe in domesticated animals today (e.g., extremely short noses in some dog breeds), are even more recent and the results of breeding practices in the last 200 years approximately. Also other traits of domesticates, such as grain yield in crops, milk production in cattle, or size of poultry may change greatly within only a few generations.

This has led to the assumption that the pace – or rate – of evolutionary change is greater in domestic organisms compared to wild ones, although a study has found that domestication does not lead to faster changes of characteristics in plants. In short, there is still a lot in the dark concerning rates of evolution in domestication. Therefore, my colleague Marcelo Sánchez-Villagra and I set out to fill a part of this gap. Principally, our goal was to compare evolutionary rates of change of skull dimensions in domestic vs. wild mammals, using dogs and pigs as case studies.

We gathered new and previously published data on skull dimensions in different domestic dog and pig breeds as well as populations of their wild relatives (wolves and wild boar) for comparison. For this, we went to museum collections and measured skulls from individuals which have died in different years (e.g., St. Bernard dogs from Switzerland from the years 1885 – 2012).These were mostly simple, linear measurements for which we used callipers (Fig. 1).

Figure 1. This is how a typical day of taking measurements in a museum collection looks like (although this is not an example of the current study, but it is basically the same): hundreds of specimens wait in their boxes and drawers to be discovered and measured. Linear measurements of different skull dimensions are then taken with callipers and documented in data tables.

We then calculated (using statistical regressions) if these measurements got smaller or larger over time, i.e., from the oldest to the most recent skull, or if there were no directed changes at all. The magnitude of these changes are the evolutionary rates, or in other words, the amount of change over time. In a further step, we calculated if these evolutionary rates were larger, smaller, or similar in the domestic vs. the wild mammals.

We also compared our estimated evolutionary rates to previously published ones from the literature. These data included traits other than skull dimensions in species other than dogs and pigs: e.g. change of racing speed in greyhounds and horses or change of backfat thickness in pigs.

Our analyses showed that most skull dimensions do not change faster in domesticated breeds than in wild populations, i.e., the evolutionary rates are similar in wild and domestic pigs and dogs. This result was surprising, given the extensive changes of skull form in some dog breeds throughout the last decades (Fig. 2). Evolutionary rates of traits other than skull dimensions (e.g., racing speed in horses and greyhounds) vary greatly with species and breeding aim and were found to be faster as well as slower compared to evolutionary rates in wild populations.

Figure 2 illustrates the change of one of the skull measurements throughout many decades in two domestic dog breeds: the two white bars on the photographs show the plane of the snout and the braincase, respectively, and a trend towards dorsal bending of the snout in the St. Bernard and ventral bending in the bullterrier.

A comparison of animal jaws and bite mark patterns

The purpose of this study was to compare the jaw shapes and bite mark patterns of wild and domestic animals to assist investigators in their analysis of animal bite marks. The analyses were made on 12 species in the Order Carnivora housed in the Mammalian Collection at the Field Museum of Natural History in Chicago, Illinois. In addition to metric analysis, one skull from each species was photographed as a representative sample with an ABFO No. 2 scale in place. Bite patterns of the maxillary and mandibular dentition were documented using foamed polystyrene exemplars, which were also photographed. A total of 486 specimens were examined to analyze the jaw and bite mark patterns. A modified technique for measuring intercanine distances was developed to more accurately reflect the characteristics seen in animal bite marks. In it, three separate areas were measured on the canines, rather than just the cusp tip. This was to maximize the amount of information acquired from each skull, specifically to accommodate variances in the depth of bite injuries.

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Research output : Contribution to journal › Article › peer-review

T1 - A comparison of animal jaws and bite mark patterns

N1 - Copyright: Copyright 2008 Elsevier B.V., All rights reserved.

N2 - The purpose of this study was to compare the jaw shapes and bite mark patterns of wild and domestic animals to assist investigators in their analysis of animal bite marks. The analyses were made on 12 species in the Order Carnivora housed in the Mammalian Collection at the Field Museum of Natural History in Chicago, Illinois. In addition to metric analysis, one skull from each species was photographed as a representative sample with an ABFO No. 2 scale in place. Bite patterns of the maxillary and mandibular dentition were documented using foamed polystyrene exemplars, which were also photographed. A total of 486 specimens were examined to analyze the jaw and bite mark patterns. A modified technique for measuring intercanine distances was developed to more accurately reflect the characteristics seen in animal bite marks. In it, three separate areas were measured on the canines, rather than just the cusp tip. This was to maximize the amount of information acquired from each skull, specifically to accommodate variances in the depth of bite injuries.

AB - The purpose of this study was to compare the jaw shapes and bite mark patterns of wild and domestic animals to assist investigators in their analysis of animal bite marks. The analyses were made on 12 species in the Order Carnivora housed in the Mammalian Collection at the Field Museum of Natural History in Chicago, Illinois. In addition to metric analysis, one skull from each species was photographed as a representative sample with an ABFO No. 2 scale in place. Bite patterns of the maxillary and mandibular dentition were documented using foamed polystyrene exemplars, which were also photographed. A total of 486 specimens were examined to analyze the jaw and bite mark patterns. A modified technique for measuring intercanine distances was developed to more accurately reflect the characteristics seen in animal bite marks. In it, three separate areas were measured on the canines, rather than just the cusp tip. This was to maximize the amount of information acquired from each skull, specifically to accommodate variances in the depth of bite injuries.

Welfare biology

Welfare biology is a proposed research field devoted to studying the wellbeing of animals in general, and focused especially on animals in their natural ecosystems. The field of welfare biology would inform measures aimed at helping animals and environmental management policies, and provide this cause with the attention and recognition it needs.

What is welfare biology?

Welfare biology can be defined as the study of sentient animals and their environment with respect to wellbeing. 1 It represents a distinct approach to the study of the lives of animals in their ecosystems. By incorporating knowledge from animal welfare science, ecology, zoology, and other well established academic fields, this new research area has the potential to improve our understanding of the wellbeing of animals living in the wild and to increase our chances of developing effective strategies to help them.

It is important to bear in mind that welfare biology would not focus on questions for which animals are considered as units or exemplars of other objects of research, as happens with the study of ecosystemic relations and biodiversity. Rather, welfare biology would be focused on animals as sentient individuals, and on what could be good or bad for them. This is what makes this field of research novel, and also what explains its applied potential in terms of animals’ wellbeing.

Some people might not consider the creation of this new field of research important, if they share an idyllic view of the lives of animals in nature. This view is not correct. Wild animals suffer in many ways, including hunger and thirst, injuries, disease, stress, extreme weather conditions, natural disasters, and antagonistic relationships with other organisms. In addition, many animals die very young, and it’s probable that in many cases the pain of their deaths outweighs the positive experiences accumulated during their short lives (see Population dynamics and animal suffering). 2 Animals living in the wild can be harmed just as domesticated animals can be, so there is no good reason to disregard animals in the wild. 3

We must bear in mind that even if animal advocates concerned with the situation of animals in the wild carry out research about it, such research will never be able to be as deep or comprehensive as what scientists in research institutions and academic departments can do. Moreover, it will not be as influential or likely to trigger further research by other academics. In addition, when it comes to social recognition and to informing policymaking, independent research seldom has the impact that established academic research can.

A different approach towards animals and their environment

This issue has not been assessed in depth in academia. The reasons for this are diverse. In some cases, this lack of concern is based on the belief that animals have mostly pleasant lives in their natural environments and do not need our help. For life scientists, it may bey because the focus of their work has been on furthering human interests. Still, as we will see next, the work they have done thus far may provide valid starting points for welfare biology.

Several decades ago, the science of animal welfare was created out of a concern by the general public regarding the terrible ways in which many animals are harmed when they are used for human purposes. While many findings in this field have been employed only to learn how to best exploit the animals studied, much of the research has allowed us to learn about animals’ sentience and how animals can be positively and negatively affected. But little work has been carried out concerning animals in the wild. Researchers on wild animal welfare science have focused on studying the wellbeing of captive animals (such as animals in zoos, wildlife parks and rehabilitation centers), 4 animals living in urban and agricultural areas, 5 animals affected by hunting and the animal trade, 6 and other animals who are directly affected by human activities. 7 They have put their emphasis on animals living in close relationships with humans and animal welfare issues caused by human action, overlooking the great majority of wild animals and all the natural harms they suffer. Nevertheless, the methods and the knowledge animal welfare scientists have gathered to date may be applied to assessing how animals in the wild can cope, or fail to cope, with the different situations they find themselves in.

As for researchers in ecology and related disciplines, while they have developed various research fields relevant to gaining a better understanding of wild animal suffering (such as population ecology, community ecology, behavioral ecology, evolutionary ecology, landscape ecology, conservation biology, ethology, wildlife management), there’s still very little information about it. Ecologists have shown interest in animal behavior, life histories, population dynamics, and evolutionary patterns (among other ecological aspects) but have failed to establish the connection that their findings have to the wellbeing of individual animals. However, some of the knowledge already gained in those fields can tell us a great deal about the likely state of wellbeing of animals in their natural environments.

Prospects for welfare biology

Despite the lack of attention to this issue, different courses of action benefiting animals living in the wild have been carried out, including the rescue of trapped animals, helping orphans, and giving medical assistance to injured or sick animals (see Helping animals in the wild). Some efforts have affected large numbers of individuals. These include, for instance, programs aimed at feeding populations of mammals and birds with the purpose of favoring endangered, hunted or charismatic species, reducing human-wildlife conflicts, answering ecological questions, or helping animals. 8

Also, many wild animals have been saved by vaccination programs from suffering from painful and often lethal diseases such as rabies, 9 tuberculosis, 10 myxomatosis, 11 and swine fever. 12 While these measures are typically carried out to stop wild animals from transmitting diseases to domesticated animals and humans, this shows that aiding wild animals is something feasible, and can also provide benefits for humans and other animals. These efforts have been based on studies in different disciplines, which don’t explicitly address animals’ wellbeing. This might explain why their impacts on the lives of individual animals’ wellbeing are not highlighted when these programs are researched and their results are presented.

It may be thought that this issue is not easy to deal with, as current knowledge and technology to improve the welfare of animals in the wild is still insufficient. But this is because there have been no serious attempts to make progress on this issue. As mentioned above, thus far, ecologists and other life scientists have shown little concern for the wellbeing of animals and, instead, have focused their efforts on other issues such as the conservation of biodiversity and other natural resources for human benefit. Establishing research on welfare biology and promoting it may thus increase our ability to successfully tackle it.

The creation of new scientific disciplines that earn respect in academia typically takes some time and the involvement of committed people, but we can find a number of recent examples. Several new fields of research appeared in the 20 th century that were not considered as relevant areas of study before and have become respected disciplines in academia. In the case of welfare biology, there are some promising perspectives for the future as more people become concerned about the suffering of animals in the wild. This is happening both among the general public and among people working in academia, especially students and young researchers.

New research projects focused on appraising the wellbeing of animals in the wild and considering the best ways to improve their situation can be designed and accomplished by addressing several different topics. Examples include further research into vaccination programs, as we saw above, work on urban welfare biology for the sake of animals living in urban, suburban, or industrial areas, research on the impact of hostile weather conditions and shelter building for animals’ wellbeing, assessment of parasites, population dynamics and the feasibility of deparasiting efforts, and many others. The importance of these projects being successfully developed is not only that they will be useful to implementing measures and policies to help animals, but also that successful projects can help to raise more interest in carrying out further research on the topic. This can potentially increase the amount of work and publications in this area of research until it becomes established as a new discipline.

Further readings

Bovenkerk, B. Stafleu, F. Tramper, R. Vorstenbosch, J. & Brom, F. W. A. (2003) “To act or not to act? Sheltering animals from the wild: A pluralistic account of a conflict between animal and environmental ethics”, Ethics, Place and Environment, 6, pp. 13-26.

Broom, D. M. (2014) Sentience and animal welfare, Wallingford: CABI.

Clarke, M. & Ng, Y.-K. (2006) “Population dynamics and animal welfare: Issues raised by the culling of kangaroos in Puckapunyal”, Social Choice and Welfare, 27, pp. 407-422.

Cohn, P. (ed.) (1999) Ethics and wildlife, Lewiston: Edwin Mellen.

Dawkins, R. (1995) River out of Eden: A Darwinian view of life, New York: Basic Books, ch. 5.

Dorado, D. (2015) “Ethical interventions in the wild: An annotated bibliography”, Relations: Beyond Anthropocentrism, 3, pp. 219-238 [accessed on 29 September 2018]

Faria, C. (2013) Animal ethics goes wild: The problem of wild animal suffering and intervention in nature, Barcelona: Universitat Pompeu Fabra.

Gregory, N. G. (2004) Physiology and behaviour of animal suffering, Ames: Blackwell.

Horta, O. (2017) “Animal suffering in nature: The case for intervention”, Environmental Ethics, 39, pp. 261-279.

Jones, M, & MacMillan, A. (2016) “Wild animal welfare”, Veterinary Record, 178, 195.

Kirkwood, J. K. (2013) “Wild animal welfare”, Animal Welfare, 22, pp. 147-148.

Kirkwood, J. K. & Sainsbury, A. W. (1996) “Ethics of interventions for the welfare of free-living wild animals”, Animal Welfare, 5, pp. 235-243.

Lauber, T. B. Knuth, B. A. Tantillo, J. A. & Curtis, P. D. (2007) “The role of ethical judgments related to wildlife fertility control”, Society & Natural Resources, 20, pp. 119-133.

McLaren, G. Bonacic, C. & Rowan, A. (2007) “Animal welfare and conservation: Measuring stress in the wild”, in Macdonald, D. & Service, K. (eds.) Key topics in conservation biology, Malden: Blackwell, pp. 120-133.

McMahon, C. R. Harcourt, R. Bateson, P. & Hindell, M. A. (2012) “Animal welfare and decision making in wildlife research”, Biological Conservation, 153, pp. 254-256.

Sainsbury, A. W. Bennett, P. M. & Kirkwood, J. K. (1995) “The welfare of free-living wild animals in Europe: Harm caused by human activities”, Animal Welfare, 4, pp. 183-206.

Scientific Committee on Animal Health and Animal Welfare (2015) “Update on oral vaccination of foxes andraccoon dogs against rabies”, EFSA Journal, 13 (7) [accessed on 15 August 2020].

Wobeser, G. A. (2005) Essentials of disease in wild animals, New York: John Wiley and Sons.


1 Ng, Y.-K. (1995) “Towards welfare biology: Evolutionary economics of animal consciousness and suffering”, Biology and Philosophy, 10, pp. 255-285.

2 We must bear in mind also that the number of animals living in the wild is very high. Rough estimates suggest that the global population of wild vertebrates may be up to 10 14 , and that of arthropods maybe up to 10 18 , and other invertebrates that might be sentient are even more numerous. See Tomasik, B. (2015 [2009]) “How many wild animals are there?”, Essays on Reducing Suffering [accessed on 3 July 2018].

3 All this is explained in more detail in the different texts included in these two sections of our website: The situation of animals in the wild, Why wild animal suffering matters.

4 Brando, S. & Buchanan-Smith, H. M. (2017)“The 24/7 approach to promoting optimal welfare for captive wild animals”, Behavioural Processes, 4 November. Kagan, R. Carter, S. & Allard, S. (2015) “A universal animal welfare framework for zoos”, Journal of Applied Animal Welfare Science, 18, sup. 1, pp. S1-S10 [accessed on 17 June 2018]. Hill, S. P. & Broom, D. M. (2009) “Measuring zoo animal welfare: Theory and practice”, Zoo Biology, 28, pp. 531-544.

5 Ferronato, B. O. Roe, J. H. & Georges, A. (2016) “Urban hazards: Spatial ecology and survivorship of a turtle in an expanding suburban environment”, Urban Ecosystems, 19, pp. 415-428. Souza, C. S. A. Teixeira, C. & Young, R. J. (2012) “The welfare of an unwanted guest in an urban environment: The case of the white-eared opossum (Didelphis albiventris)”, Animal Welfare, 21, pp. 177-183. Ditchkoff, S. S. Saalfeld, S. T. & Gibson, C. J. (2006) “Animal behavior in urban ecosystems: Modifications due to human-induced stress”, Urban Ecosystems, 9, pp. 5-12.

6 Baker, S. E. Cain, R. van Kesteren, F. Zommers, Z. A. d’Cruze, N. C. & Macdonald, D. W. (2013) “Rough trade animal welfare in the global wildlife trade”, BioScience, 63, pp. 928-938 [accessed on 18 February 2020].

7 Kirkwood, J. K. Sainsbury, A. W. & Bennett, P. M. (1994) “The welfare of free-living wild animals: Methods of assessment”, Animal Welfare, 3, pp. 257-273.

8 Dubois, S. D. (2014) Understanding humane expectations: Public and expert attitudes towards human-wildlife interactions, PhD thesis, Vancouver: University of British Columbia [accessed on 2 September 2018].

9 Slate, D. Algeo, T. P. Nelson, K. M. Chipman, R. B. Donovan, D. Blanton, J. D. Niezgoda, M. & Rupprecht, C. E. (2009) “Oral rabies vaccination in North America: Opportunities, complexities, and challenges”, Neglected Tropical Diseases, 3 (12) [accessed on 9 July 2018].

10 Díez-Delgado, I. Sevilla, I. A. Romero, B. Tanner, E. Barasona, J. A. White, A. R. Lurz, P. W. W. Boots, M. de la Fuente, J. Domínguez, L. Vicente, J. Garrido, J. M. Juste, R. A. Aranaz, A. & Gortázar, C. (2018) “Impact of piglet oral vaccination against tuberculosis in endemic free-ranging wild boar populations”, Preventive Veterinary Medicine, 155, pp. 11-20.

11 Ferrera, C. Ramírez, E. Castro, F. Ferreras, P. Alves, P. C. Redpath, S. & Villafuerte, R. (2009) “Field experimental vaccination campaigns against myxomatosis and their effectiveness in the wild”, Vaccine, 27, pp. 6998-7002.

12 Rossi, S. Poi, F. Forot, B. Masse-Provin, N. Rigaux, S. Bronner, A. & Le Potier, M.-F. (2010) “Preventive vaccination contributes to control classical swine fever in wild boar (Sus scrofa sp.)”, Veterinary Microbiology, 142, pp. 99-107.

Comparing the amount of domestic animals and wild animals? - Biology

Wild Rats in Captivity and Domestic Rats in the Wild

What happens if you bring a wild animal into captivity? Because of its "hardy" constitution, is it actually more fit than its "degenerate" domestic cousins? What happens to wild animals that are kept for generations in captivity?

What about the reverse -- releasing a domestic animal in the wild? Is it helpless, a soft urbanite released into the harsh natural world? Does it revert to its wild roots?

These two situations are actually very similar. In both cases, an animal adapted to a particular environment is placed in a drastically different environment. The criteria for success are dramatically changed. In the wild environment, a successful rat is one who is reactive to changes, flees humans, finds rats of the opposite sex to breed with, finds food and shelter in a complex environment and avoids predators. In the domestic environment, the successful rat is one who is passive to changes, tolerates humans, breeds willingly with whatever members of the opposite sex are provided, tolerates confinement, bright lights, poor hiding places, a simple environment, and handling by human "predators."

Change their places, and many rats will have a lot of trouble making the switch.

Natural selection is severe in the early generations after the switch from the wild to captivity or from captivity to the wild. Natural selection acts on populations: individuals that are poorly adapted to their new environment die or fail to breed. Hence, mortality and reproductive failure are high in wild rats moved to captivity, and on domestic rats released in the wild. The survivors are those that happen to have the traits that are compatible with these new circumstances.

Here's an analogy. Consider a national sports team of your choice. The players are extremely good at what they do: playing the sport. Some are better than others, but all the members are very good. If they weren't, they'd be eliminated from the team. Now transport them to a new environment: put them all in a room and tell them that the only way out is for them to demonstrate fluency in four languages. All of a sudden, these sports stars find themselves poorly adapted to their new environment. A small number of them may happen to speak four languages, and they'll survive. The rest will fail.

The reverse situation is true too: place a group of linguists who speak four languages in a room and tell them the only way out is to demonstrate world-class mastery of a sport. A few of these linguists may happen to have superb sporting ability, but most will fail.

It is the same with wild animals in the domestic environment or domestic animals in the wild. The criteria for success have changed, and most of the animals, well-adapted to their former environment, find themselves poorly adapted to their new one. Many fail, some survive.

The survivors form the basis of the next generation of animals in the new environment. The second generation, and all subsequent generations, will pass through the same seive, and only those who survive and breed will pass on their traits to the next generations. After generations, the new population may look and act quite differently from the original population.

Natural selection isn't the only force acting on animals in new environments. Relaxed selection (removal of natural selection on certain traits) also plays a role in both environments, and artificial selection (preferential breeding of animals with certain traits by their human managers) plays a role in captivity.

Lastly, animals are not passive subjects of natural selection. They can act on and respond to their environment, and many of them may learn and adjust individually to their changed circumstances.

Wild animals, including rats, are more active and reactive than animals that have been domesticated for many generations.

Wild animals can be extremely stressed by the captive environment. Compared to the wild, the captive environment is extremely confined, provides few hiding places, is full of bright lights, and is surrounded by human "predators" who approach and handle the animal. These stressful conditions frequently lead to death or reproductive failure in captive wild animals.

Mortality of wild animals in captivity

Mortality of wild animals in captivity can be severe during those first few generations. For example, Blus (1971) established a breeding colony of short-tailed shrews in captivity and found that only 11% of his wild-caught shrews, and 9% of his captive-born shrews, survived for 12 months. The mean age at death was only 5 months (reviewed in Price 2002).

Reproductive failure in captivity

Reproductive failure includes the failure to mate, failure to produce normal-sized litters, and failure to rear young successfully.

Reproductive failure is common in wild and early generation animals in captivity. Only 49% of first-generation wild Norway rats copulate successfully in captivity (Price 1980). Of rats who do give birth, only 43% successfully raised some offspring to weaning age -- the rest were cannibalized or abandoned (Clark and Price 1981). Trut (1999) found that only 14% of field-trapped Norway rats produced offspring that survived to adulthood (see Price 2002).

Litters are generally smaller (averaging 6 offspring) in these first-generation wild rats (Clark and Price 1981). In contrast, wild rats in the wild, and domestic rats in captivity, produced similarly-sized large litters, averaging about 10 offspring (Davis 1951, Boice 1972). It takes about 20 generations in captivity for rat litter sizes to come back to normal (King 1929, 1939). Of course, other changes are happening (e.g. reduction in brain size, Rohrs 1999, Kruska 1975a and b) that are not found in the wild stock, but I won't go into those here.

Domestication: adapting to captivity

As a general rule, when a wild species is brought into captivity it has an enormous adjustment to make to become successful in the captive environment. This adjustment means the death or reproductive failure of many, many individuals who just can't make the switch to captivity.

Sometimes, the animals who die or fail to breed are the very individuals who would be most successful in the wild: the flighty, active individuals with low tolerance for humans. It is the passive, less reactive, less fearful, calm individuals who survive and breed best in captivity. These individuals form the foundation of the domestic stock and their offspring carry on those traits (see Price 2002 for more on this).

This process is called natural selection in captivity , and it is a huge watershed during those first few generations, with large numbers of animals dying or failing to breed, regardless of the actions and wishes of the human breeder. The resulting population of animals, descended from the survivors, may be quite different from the original wild stock, as these animals become adapted to their new, captive environment. (Natural selection in captivity is a problem for programs that breed endangered animals for release in the wild, but that's another topic).

Natural selection in captivity is combined with artificial selection , in which the human preferentially breeds some animals over others in order to produce more animals with a desired trait in the next generation.

Tamability is an important factor in domestication. Animals that can tolerate the presence of and handling by humans are more likely to survive and breed, due to both natural and artificial selection. Natural selection plays a role because animals who cannot tolerate human presence and handling may die or fail to breed. Artificial selection also plays a role because humans prefer to work with animals that are easy to capture and handle, and preferentially breed animals with these traits.

Genetic and experiential factors influence tameness: individuals inherit a greater or lesser capacity to be tamed (tamability), and the experiences each animal has with humans determines the extent to which that potential tameness is reached (Price 2002).

Tamability has a heritable component that responds well to artificial selection. In rats, some coat colors are associated with tameness: non-agouti (black) rats and hooded rats of wild stock are more docile than their solid-colored agouti counterparts (more on coat color and how it affects behavior) (Keeler 1942, Cottle and Price 1987). Today, about 80% of domestic laboratory rat strains are homozygous for the non-agouti allele (Price 2002). This association between tameness and coat color has been found in other species as well (e.g. deermice, Hayssen 1997 foxes, Trut 1999).

Early handling by humans has a big effect on tameness as well. Galef (1970) reared second and third generation wild rats (the direct descendants of wild rats captured on Philadelphia wharfes) under several conditions: with their wild mothers or with domestic mothers, with wild or domestic litter mates, with minimal or maximal exposure to humans, and with or without regular handling by humans (2 minutes per day from age 10 days to 23 days). Only direct handling experience was associated with ease of capture and handling. However, handling did not affect the wild rats' timidity toward novel objects or aggression toward other rats or mice. Handled wild rats were just as timid as unhandled wild rats. Therefore, handling is quite context specific: handling reduces aggression toward humans, but has little effect on other behaviors typical of wild rats.

In a similar experiment, Hughes (1975) raised wild rats under three conditions: (1) he let domestic mother rats rear one group of wild babies, (2) he provided an enriched environment for a group of post-weaning babies, and (3) he regularly handled a third group of wild babies before they were weaned. He found that early handling had a far greater effect on tameness than the other two conditions. Handled rats showed less emotionality and were more like domestic rats in their behavior. In contrast, being reared by a domestic mother or playing in an enriched environment had only minimal effects on tameness.

Evidence suggests that such early handling leads to major changes in the neuroendorcine system (Denenberg et al. 1967). One possible mechanism involves the responsivity of the adrenal glands. Levine et al. (1967) handled 1-20 day old rats each day by picking them up, placing them individually in a can partly filled with shavings for three minutes, then replacing them in their home cage. At age 80 days, the adrenal glands of the handled rats were less responsive to stress when placed in an open arena for 3 minutes (see also Levine 1968).

The biochemistry of taming: The brain biochemistry underlying tameness involves the serotonergic system. Rats selected for tameness had more of the neurotransmitter serotonin and serotonin receptors (Naumenko et al. 1989, Popova et al. 1991, Hammer et al. 1992). Serotonin is involved in inhibiting fear-induced aggression. Serotonin is also implicated with gonadal hormone regulation and stress responses. Interestingly, tameness can be induced pharmacologically with the injection of serotonergic agonists (Blanchard et al. 1988).

Domestic rats in the wild

Not surprisingly, there is less information on domestic animals adapting to the wild ( feralization ) than on wild animals adapting to captivity ( domestication ). We humans aren't often around to observe feralization, but we are definitely around for domestication.

Domestic animals released in the wild may have a number of handicaps compared to their wild counterparts. They may lack some of the structural, physiological and behavioral responses to environmental stimuli that are normally acquired by their free-living counterparts, usually early in life. These deficits may lead to increased mortality of domestic rats released in the wild (see Price 2002 for more).

Physical condition: Living in the wild may require greater physical condition than in captivity. The large size of some captive animals may be due to better nutrition and lack of exercise. Such large size may be a handicap in the wild if it impairs mobility and agility (Price 2002).

Structural attributes: Many domestic rats are white or have white patches on their fur. These patches may be conspicuous to predators, leading to higher predation on animals with white fur. In addition, albino animals have poor vision, which may impair their chances of survival even more.

Behavioral responses: Released animals must find food and shelter, develop anti-predator skills, interact appropriately with conspecifics if they encounter them, and orient (disperse, navigate etc.) in a complex environment (Price 2002). Deficits in behavior may result in slower growth and higher mortality.

Success of domestic rats in the wild

Domestic rats are therefore at a disadvantage as compared to their free-living counterparts. Reports of domestic rats establishing feral populations in the wild are rare. Donaldson (1916) made four attempts to feralize albino rats but was unsuccessful. King and Donaldson (1929) tried five times to establish populations of feral albino rats, at sites ranging from Massachusetts to an island group in the Gulf of Mexico. All attempts failed.

However, in some cases, domestic rats may survive and establish populations under natural or semi-natural conditions.

Domestic rats in semi-natural conditions

Albino rats in an outdoor pen in Missouri, USA: Boice (1977) released ten domestic rats (5 males, 5 females) in a large, fully-enclosed outdoor pen and studied them for two years. He found that the rats constructed and lived in burrows that were indistinguishable from wild rat burrows. They followed regular pathways above ground like those seen in wild rats. The rats were hardy throughout climactic extremes, surviving cold temperatures as low as -30º C. The rats reproduced successfully, producing litters mainly in the spring and fall. They established a stable population that stayed around 50 rats, for a total of five generations.

  • Behavior: Only females hoarded more than a few food pellets. Pairs of males were aggressive toward each other (leaping, kicking, sidling, and squealing) but serious fighting was not observed. One rat was an outcast who never went into a burrow. He huddled outside even during storms and survived under these conditions for three months. Rats formed a deep rat-pile of as many as 20 rats during cold weather, probably for heat conservation. The rats followed pathways above ground and marked them with urine. Feces were twice as likely to be above ground as below it.
  • Burrows: All group members, male and female (except for old males) burrowed. Rats of 90-110 days dug with the greatest intensity. The burrows resembled those of wild rats: They started with an entrance hold with dirt scattered around half of it, they constructed a nest chamber at the end of the first tunnel, they always constructed a bolt hole, dug from within, from the second tunnel. The diameter, depth, and length of the tunnels and the number of nest chambers were very similar to those of wild rats.

Boice's experiment demonstrates that domestic rats can survive harsh temperatures, construct shelter for themselves and breed successfully under such conditions. They have not lost these abilities even after hundreds of generations in captivity. Note, however, that Boice's experiment was not a true release into the wild: these rats were given food and water daily and were protected from predators.

Albino and hooded rats in a farmyard in Oxfordshire, UK: In another report, Manuel Berdoy released 75 albino and hooded laboratory rats into an enclosure in a farmyard in Oxfordshire. The rats found water, food, and shelter. They established paths through their environment and dug burrows. They built social hierarchies and bred successfully. Due to the enclosure, they were not confronted with natural predators or with wild rats (documentary film Berdoy 2003, reported in Peplow 2004).

Beige dumbo rats under a chicken coop in New Orleans, US: In the spring of 2004, a litter of six 5-6 week old beige dumbo rex and standard-haired rats escaped from their cage, which was kept outside on a porch in an urban neighborhood. The rats discovered a chicken coop in the backyard and began living in the space underneath the coop's floor, with a few deep tunnels. Food was provided to the chickens every day so the rats had an easy food source. Attempts to catch them were unsuccessful. As they did not harm the chickens they were allowed to stay. When the floorboards to the coop were removed, the rats moved to tunnels deeper underground. At least one litter was produced under the coop, which was discovered when the coop floor was taken up. The new litter born under the coop was brought back into captivity, but the original escapees were not captured. No other litters were known.

The rats had been extensively handled before their escape, and were quite tame. After their escape, however, they became shy, though not as shy as a wild rat. Most of the rats rarely emerged from the coop, though a single bolder one made forays back onto the porch. The original boldest rat, a female, probably died from an infected tail injury that occurred during a failed capture attempt. She was succeeded by a male. This male was quite unafraid and allowed a hand to get almost, but not quite, within grabbing distance before fleeing. The entire human family, including the dog, could stand on the porch and watch him and he remained unperturbed, as long as nobody moved quickly. If an attempt was made to catch him, he fled, but was usually back the next night [L. J. pers. comm. 2005].

Note: Two additional adult rats that found their way out of the cage eventually returned to captivity. One of these was the escapees' mother, who had never been particularly tame. After a month outdoors, she started coming to the porch again, and one day walked up to one of the humans and sat on his shoe to receive a treat. She also came through the open back door and into the house several times. She was taken back into captivity and has since become quite tame. The other adult escapee was an adult agouti female who was not very tame. She escaped but refused to leave the vicinity of the porch and after a day and a half managed to find her own way back into her cage during cage cleaning [L. J. pers. comm. 2005].

Domestic rats in the wild

Albino rat colony in Montana, USA: Minckler and Pease (1938) mention a colony of albino rats living in a landfill in Montana, which numbered about 2,000 rats in 1937. The exact source of these rats was unknown, but they were presumed to have been released by students from the local university. Abundant food, water, refuge and few predators created a sheltered environment in which an albino colony could survive, even in harsh winters with temperatures as low as -25 F.

Interestingly, these albino rats traveled on paths through the refuse heap, and they never left these paths, even to try a fragrant food source just a few inches to one side of the path. Apparently, these rats had to come directly on the food, almost touching it, before they responded to it.

Albino and hooded rats on Lanai, Hawaii, USA: Svihla (1936) reported albino and "spotted" (white belly and sides -- probably hooded) Norway rats living in fields under natural conditions on the island of Lanai, which is an island southeast of Hawaii. This island environment is sheltered: food is abundant, there is no competition for habitat, and there are few predators (no mongooses, few feral cats and native owls). The rats were presumed to be the descendants of escaped pet rats belonging to Filipino plantation hands. The escaped rats interbred and became common in the pineapple fields, houses, and buildings of Lanai City.

Interactions between wild and domestic rats

Very few studies place domestic and wild rats together, so there is little information on how wild and domestic rats might get along.

Note, however, that resident rats usually attack intruders in their colony -- domestic rats attack domestic intruders, and wild rats attack wild intruders. Studies of rat aggression against intruders are very common. To read more about them, visit the aggression page. Therefore, a reasonable prediction about wild and domestic rat interactions is that resident wild rats would attack a domestic rat intruder, and domestic rats would attack a wild rat intruder.

How are domestic rats received in wild colonies?

To my knowledge, no studies have examined how wild rat colonies receive a domestic intruder in the wild.

However, one study has examined how colonies of wild rats in captivity received a domestic intruder. The wild rats attacked the domestic intruder intensely. Most attacks were performed by the dominant male, who lunged and leaped at, sidled, chased, and bit the intruder. The intruder fled, froze, and spent time on his back. The wild dominant rat inflicted about 10 bites on the intruder in 10 minutes, and most of the bites were to the intruder's back. For comparison, wild intruders introducted to wild colonies in captivity receive about 6.9 bites in 10 minutes (Takahashi and Blanchard 1982).

How do domestic rats receive wild rats?

When a wild Norway rat was placed in a colony of domestic rats in captivity, the level of dominant male rat attack on the intruder was low. This may have been because the wild intruder displayed intense defensive behavior, and the wild intruder was also much faster than the domestic rats. Therefore, the dominant male chased him but rarely managed to catch him. In addition to chasing, the domestic rat sidled, and when possible, bit the wild intruder. The intruder displayed defensive behavior: he fled, froze, boxed, and spent time on his back. The dominant rats inflicted about 1 bite on the wild intruders in 10 minutes, and most of the bites were to the intruder's back. For comparison, domestic intruders introduced to domestic colonies receive about 5.6 bites in 10 minutes (Takahashi and Blanchard 1982).

Wild-domestic rat interactions are similar to wild-wild and domestic-domestic interactions. Regardless of whether the rats are wild or domestic, resident rats, especially the dominant males, tend to attack intruders. The two asymmetries uncovered between wild and domestic rat are that wild rats display a lunging or leaping attack rarely seen in domestic males, and wild rats are faster than domestic rats. This speed difference means that wild rats may have an advantage in wild-domestic interactions: when the wild rat is the resident, he can press a more effective attack, and when the wild rat is the intruder, he can elude attack more easily.


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Our research plans


Theoretical projects investigate fundamental principles that govern welfare outcomes in nature. These projects often use modeling techniques to explore underlying dynamics, particularly when data is scarce.

Estimating welfare distribution and capacity across taxa

Both the capacity for subjective experience and the average quality of life are likely to vary greatly across taxa. In order for welfare biology research to have the greatest impact possible, we will need to know which animals are in greatest need of help. We’re interested in developing conceptual frameworks and identifying species traits that can inform prioritization efforts.

Our work so far: We developed the concept of welfare expectancy to roughly estimate the distribution of welfare across species using only basic demographic data.

What we’re doing in 2020: We’re combining the welfare expectancy model with empirical estimates of neuron count for different species. While neuron count is a highly imperfect proxy for sentience, testing how the model combines with empirical data will help us understand how to use the model for cross-species comparisons once better proxies are identified.

Frequency of different causes of death

When and how an animal dies are major factors in the overall quality of that animal’s life. Reducing the most painful causes of death seems like a highly promising approach to improving wild animal welfare. However, an animal spared from one cause of death will still die eventually. For example, a raccoon successfully vaccinated against rabies might die of starvation instead. The net effect of programs that target a particular cause of death depends on how different causes of death substitute for each other.

Our work so far: We developed population models that can report on the relative frequency of different causes of death under given conditions.

What we’re doing in 2020: We’re exploring insights from those models and attempting to parameterize them using real-world data on the ecology of predator-prey pairs. We will also review prior empirical research on mortality factors, which will help us to identify promising methodologies for academic research into causes of death among wild animals, as well as informing our judgement of how important this set of questions may be.

Trophic dynamics

Predation is a stereotypical example of suffering in nature. However, wild communities are complex. Changing animal populations can have consequences throughout the food web, both in terms of animal interactions and in terms of the total number of individuals the ecosystem can support.

What we’re doing in 2020: We’re using population modeling to review the complex relationships between consumer populations, trophic structure, and total welfare.

Density-dependence of welfare

The concentration of animals relative to a resource (such as space or food) will influence a range of welfare-relevant dynamics. How total welfare varies with population size is, in particular, a complex relationship. As long as animals are living good lives, it seems better for more individuals to exist. But increasing population density can lead to lower welfare by increasing competition, disease transmission, or social stress.

Our work so far: We demonstrated how the tradeoff between population size and density suggests that, for a given set of resources, there could be an optimal population size that maximizes welfare. Whether that optimum exists and how hard it is to achieve depends on the actual relationship between population density and individual welfare.

What we’re doing in 2020: We’re exploring that relationship with an observational study comparing the population densities and welfare indicators of rock pigeons (Columba livia) across different US cities.


Methods projects develop techniques and best practices for wild animal welfare projects. At this early stage, this work primarily involves developing tools to measure welfare or identify welfare threats.

Welfare metrics

Welfare is hard to measure because it is subjective by definition and most animals can’t directly report their experiences. While a variety of tools have been developed for the captive context, very few have been applied to wild animals, and most cannot be used to compare between species. Developing such metrics is critical to being able to assess the welfare status of a wild population and determine whether projects aimed at improving their welfare are successful.

What we’ve done so far: Biomarkers of aging seem like they could be a promising step towards developing welfare metrics that are objective and broadly applicable across different taxa. We’ve written a report summarizing the promise of telomere length and hippocampal volume as welfare metrics.

What we’re doing in 2020: We’re looking for collaborators to develop an experimental test of telomere length as a welfare metric.

Remote monitoring

Technological advances in camera traps, tracking devices, and logging instruments have led to an unprecedented ability to study animals remotely. One promising technology for welfare monitoring is biologgers (specifically, tri-axial accelerometers paired with satellite-GPS locators), which can give detailed information about the movement, behavior, morbidity, and mortality of wild animals. Biologgers are already used to study animal welfare, and are increasingly used in wildlife ecology.

What we’re doing in 2020: We’re reviewing how biologger data can be used to evaluate welfare along the Five Domains model. We’re also exploring how to link biologger data with environmental data to determine the relationships between environmental context and wild animals’ wellbeing.


Improving wild animal welfare at scale will require the resources and coordination of large institutions. This includes governments and the research and advocacy communities that influence them. Our policy projects seek to incorporate wild animal welfare into institutional decision-making processes, benefiting wild animals either by changing policy in the short term or by normalizing wild animal welfare as a policy priority in the long term.

Regulation of novel technologies

Technological advances could make wildlife management much more humane, cost-effective, scalable, targeted, or sustainable. However, new technologies can carry new ecological, social, and ethical risks. Government regulation plays a pivotal role in determining how quickly novel technologies are developed, what safety standards they are held to, how the public perceives their safety, and how they can be used in the wild.

What we’ve done so far: One of the roles of regulation is to enforce an appropriate balance of risk and reward in technology development. We sought to inform these decisions with our investigation of the tradeoffs between persistence and reversibility in the design of potentially long-lasting interventions to improve wild animal welfare.

What we’re doing in 2020: We are interested in exploring which novel technologies are most promising for wild animal welfare, how they might be regulated in the United States, and what, if anything, wild animal welfare advocates can do to promote safe and effective regulation.

The OneHealth paradigm

Reducing the burden of disease seems like one of the most technically feasible and publicly popular approaches to improving wild animal welfare. OneHealth is a global public health paradigm linking the health of humans to that of animals and their shared environment. As a rare policy framework that explicitly addresses wild animals’ quality of life, it presents a unique opportunity to advance institutional concern for wild animals, secure funding for welfare biology research, and convene relevant expertise.

What we’re doing in 2020: We’re reviewing the contributions of OneHealth to wild animal welfare to date and identifying opportunities for further research and collaboration.

Coordinating with allied communities

Many other advocacy communities want humans to have a stronger relationship with the natural world. Some, such as the Compassionate Conservation movement, explicitly value the welfare of individual wild animals. By engaging more with adjacent research and advocacy communities, we may be able to more effectively promote welfare policies.

What we’ve done so far: We published a paper suggesting how restoration ecology can incorporate wild animal welfare in order to promote both restoration and welfare goals.

What we’re doing in 2020: We’re exploring areas of shared goals between wild animal welfare and conservation, particularly focusing on the conservation community’s goal of fostering environmental attitudes among the public that favor environmental stewardship and highlighting the importance of common animals.

Climate change mitigation

Mitigating climate change will require massive land-use changes, including planting forests or grasslands for carbon sequestration, building solar and wind farms, and changing agricultural practices. As we work to make the earth more habitable for humans, we should make sure our efforts benefit nonhuman species as much as possible. Comparative studies of different approaches to carbon sequestration or renewable energy production could inform policy decisions on which implementation strategies to prioritize.

What we’re doing in 2020: We’re looking for partners to explore this research area and develop advocacy strategies.


Our applied research focuses on projects that can be implemented in the near term to improve wild animal welfare.

Fertility control programs

Managing fertility is a highly promising approach to improving wild animal welfare. For species where intraspecific competition has a strong influence on juvenile mortality, fertility reduction can increase survivorship (see: compensatory survivorship in mosquitoes paper). For wild animal populations that humans already control, fertility management offers a humane alternative to lethal management. Fertility management can also be paired with efforts to decrease the frequency of painful deaths to keep target populations stable, limiting any unanticipated ecosystem effects of such projects.

What we’re doing in 2020: We’re using urban rock pigeon (Columba livia) populations as a case study in fertility management for wild animal welfare. Pigeons are highly numerous, and many cities already manage their populations with lethal poison. Pigeon management drugs are commercially available and have the potential to be highly cost-effective. Using population modeling, literature reviews, and observational studies, we will explore the welfare consequences of replacing lethal management with fertility management.

Agricultural insect management

Agricultural pest management kills vast numbers of insects every year. Even though we are uncertain about insect sentience, there is at least some risk that current pest management practices are causing harm to trillions of individuals. Shifting to more humane pest management practices could be a highly cost-effective way to improve insect welfare with minimal risk of unanticipated side effects.

What we’ve done so far: We released a report on agricultural pest management practices and their potential effects on insect welfare. As a supplement to this report, we developed a database of insecticidal compounds and their modes of action, as well as a method for estimating the number of insects affected by pest management programs.

What we’re doing in 2020: We’re expanding these supplemental materials, developing promising directions for research collaboration, and exploring next steps for insect welfare interventions.

Influence of domestic cats on small wild animals

Domestic cats (Felis catus) can harass, injure, and kill small wild animals. Owned outdoor cats are also at higher risk of injury and disease, and have shorter lifespans on average than indoor cats . Keeping cats indoors represents an interesting opportunity to potentially reduce the suffering incurred by predation while improving the lives of the predator species.

What we’ve done so far: We partnered with a Pennsylvania animal shelter to conduct a messaging study about outdoor cats. Adopters were randomly provided with a leaflet about the positive impacts of indoor living on cat health, a leaflet about the negative impacts outdoor cats have on wildlife, or no leaflet. Shelter staff followed up with adopters over three months to determine if wildlife or cat welfare information affected the adopters’ choice to allow their cats outdoors.

What we’re doing in 2020: We’re analyzing the data from this study. Our goal is to establish if the messaging methods tested in this case were effective, and to see if it would be worthwhile to pursue further outdoor cat interventions. We expect to deprioritize this work, both because initial results suggest the leaflets had little or no effect and because we are uncertain about the net effect of keeping cats indoors (see research by Rethink Priorities on this topic).

Hereditary Foundations: Genetic vs. Epigenetic Changes

We now briefly reexamine the genetic foundations of the DS, in light of our hypothesis. To date, as we have stressed, no single gene mutants have been found that mimic the entire DS phenotype. Given the relative ease of selecting the condition, this is not surprising, since the spontaneous mutation rate of single genes, approximately 10 𢄦 /gene/generation, should be too low for efficient response to selection. Presumably, therefore, the DS is a polygenic condition. Furthermore, it probably does not require homozygosity of recessive alleles: the Novosibirsk group produced the DS in their selected animals by outbreeding, thus reducing homozygosity, using animals from different fox farm populations (Trut et al. 2004, 2009). The simplest inference, therefore, is that the DS arises from preexisting genetic variation consisting of mutations of small semidominant effects in several to many genes. Given that the DS has been produced in so many mammalian species, that preexisting variation might be common. A possible explanation for such ubiquity is that the alleles confer some sort of heterozygous advantage, as found in cystic fibrosis and sickle-cell anemia (Quintana-Murci and Barreiro 2010). Alternatively, the mutations may individually be of nearly neutral effect but when brought together, in various combinations, produce the dramatic phenotype of the DS. A possible relevant example of such polygenic synergism is the recent report that the “splashed white” phenotype in horses, identified by large white blazes, has such a multiple-gene basis (Hauswirth et al. 2012). As shown in that study also, not all the heritable variation required to produce the phenotype need be preexisting in one of the horse lines, a new mutation contributed.

These general genetic characteristics of the DS accord with our hypothesis that it is neural crest genes specifically that are the ultimate source of the DS and, in particular, that it involves multiple mild loss-of-function mutations in several of these genes. Such genes should be individually dosage sensitive, a feature signaled by haploinsufficiency, and their mutations should exhibit interactions, additively or synergistically, to generate the effect. The available evidence on these genes fits these predictions and this material is summarized in Table 2 . Correspondingly, mild loss-of-function mutations (hypmorphs) in such dosage-sensitive genes, which all affect the same cell type/developmental process, would be expected to give mutual enhancement of their effects. Finally, the large numbers of genes known to be required for NCC development or migration are consistent with the proposal of polygenic origins and, in principle, would constitute a large target size for the condition, facilitating its selection. (For information on NCC genetics, see reviews by Nikitina et al. 2009 Kulesa et al. 2010 Minoux and Rijli 2010).

Conventional point mutations, however, are not necessarily the sole genetic source of the condition. Recombination-generated alterations of particular repeat elements are correlated with morphological changes in carnivores (Fondon and Garner 2004) and might also be involved here (Trut et al. 2004). It is potentially relevant that some conserved noncoding elements (CNEs) are repeated elements (Kamal et al. 2006) and CNEs are associated with various neural crest genes associated with known neurocristopathies (Amiel et al. 2010). Recombination-generated changes among repeated elements can take place at much higher rates than point mutations.

It is also worth considering that some of the initial changes may not be DNA-sequence alterations but epigenetic changes. In particular, the Novosibirsk group has long argued that hormonal states in the mother, associated with the less stressful conditions of domesticity, are involved in generating the DS (Belyaev 1979 Trut et al. 2004, 2009). Findings consistent with this idea, though opposite in effect, involve maternal stresses in mice that create epigenetic chromatin state changes and behavioral phenotypes in offspring (Meany and Szyf 2005 Bagot and Meaney 2010). Whether epimutations have the requisite stability in trans-generational transmission to generate true heritable states is always a key question about their evolutionary potential (Slatkin 2009) but strong trans-generational transmissibility of epigenetic states has been shown for two genes affecting coat color patterns in the mouse, Agouti and Axin Fu genes (Morgan et al. 1999 Rakyan et al. 2003). With respect to the DS, the most convincing evidence for an involvement of epigenetic effects concerns the “Star gene” in foxes, proposed by Belyaev to explain the initial appearance of a white forehead patch early in development of the DS. Star has a high rate of heritable change, in both directions, approximately 10 𢄢 per generation, a rate far too high for conventional mutation (Belyaev et al. 1981 Trut et al. 2009). It is also possible that quasistable epimutations become converted to true genetic mutations (Karpinets and Foy 2005). We suggest that Belyaev’s hypothesis, positing inducible epimutations as initiating events in the DS, though unconventional, deserves reconsideration.

A final point: in different domesticated species, all three mechanisms—point mutations, recombination of repeat elements, and epimutations—might be involved but in different combinations and in different genes. Once the loci involved in the DS have been identified (see below), it should be possible to tell which explanations pertain to particular genes in specific breeds.

Why Domestic Animals Have Developed Much Smaller Brains Than Their Counterparts In the Wild

MinuteEarth explains through amusing animation, exactly why the brains of domestic animals (pets, farm animals) are far smaller than the brains of their wild counterparts. Much of it has to do with the fact that the domestic animals feel safe in their surroundings, which allow them to let down their guard far more easily and reduces the fight or flight response. Additionally, domestic animals no longer have to hunt for food, again reducing the area of the brain necessary to hunt.

When you compare wolves and dogs between individuals of the same size, the wolves have bigger brains no matter what that body size is. What’s more, across different domesticated animals, a disproportionate amount of the shrinkage happened in parts of the brain that monitor information from the outside world and tell animals when and how to freak out sort of like the brain’s panic button.

Watch the video: The man and his beloved animals. domestic animals. wild animals. nothing good comes easy. pets (May 2022).


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