Lengthening of the imprinting period is of vital importance in understanding domestication
You know, I do not really think that humans, despite displaying some of the characteristics of “domestication” – such as reduced snout and body size, reflect the same pattern of selection.
The fact that humans have generated a niche, – an anthro-ecology – to which other mammals have become adapted through natural and “artificial” selection, is clear. […] [I]t is quite true that humans, being part of nature, constitute agents of natural selection along with other species like wolves and ants which also alter the selection pressures on their prey and/or symbiotes. So […] the term “artificial” for human-associated selection pressures is special pleading… and, of course, even Darwin recognized this.
Can we really make the case for humans being an examples of domesticated animals, however? I am not persuaded. Can we really think that there has been analogous -or homologous – domestication in humans during any recent period of our species history? Are contemporary hunter-gatherers more aggressive than the residents of London or New York? Is the “egalitarian syndrome” the opposite of the “domestication syndrome”?
I think this is a fair question.
In almost every case, alterations to polymorphisms effecting neural crest have occurred due to specific changes in levels of adrenal response. The triggering of the fear and fight/flight in response to human presence happens at much higher levels of stimulation in domestic dogs vs tamed wolves. The aggressive dominance behaviour normal for wild wolves is also constrained, — although Chihuahuas may be an exception, haha– and there is also evidence, discussed in the paper by Wilkins et al […] at least in dogs, of a prolonged and more generalized imprinting period, permitting puppies to imprint on humans if handled even for short periods of time before the age of three to seven months, which is three to five times longer than in wolf puppies.
There is a lot of past research already being put to practical use here, especially in horses and other large mammals that need to be handled at some point during their adult lives. So the lengthening of the imprinting period is of vital importance in understanding domestication. It also, of course, has long been employed in the training of sheep guard dogs, and other flock guardians, and appears to redirect aggression in breeds that guard humans, such as wolfhounds and other sighthounds, as part of a dual utility (as the sighthounds were also expected to be hunters). I was fascinated that the prolongation of this imprinting period is actually related to the other aspects of domestication via the neural crest-related down-regulaiton of adrenaline. For further examples of imprinting see the material here: http://animalbehaviour.net/Imprinting.htm
Recent research into the genetics of behaviour, especially aggressive behaviour, in dogs indicates that there are many different genes involved, with polymorphisms affecting several different neurotransmitters either through altering their production (repeater variance affecting dopamine do exist in dogs as well as in humans and most other mammals: and I quote:
“…dopamine D4 receptor, the long form of which is associated with risk seeking behavior in humans (Noble et al. 1998) and monoamoine oxidase A, an enzyme which breaks down dopamine and a mutation of which is associated with incarceration of humans, if they had a bad childhood environment (Caspi et al. 2002)…”
However, a paragraph further on in the paper cited above on dog behaviour, the authors say:
“…The results of the candidate gene approach to canine aggression have been uniformly disappointing so far. Although Nimi and colleagues (1999) showed that a usually gentle breed of dog, the golden retriever, had the short form of the dopamine D4 receptor and the territorially aggressive Shiba has the long form, this is not associated with behavior but rather with the genetic differences between an Asian and an Anglo-American breed (Parker et al. 2006).”
Cattle show genetic signatures of domestication similar to that in dogs:
“…Domestication of cattle provides an excellent model of animal evolution. During the domestication process, cattle have adapted in morphology, physiology and behavior to captive life… The phenotypes associated with domestication include milk and meat production, fertility, appearance including coat coloration, decreased fearfulness, social motivation, and mild temper …..”
More recent research on domesticated cattle has revealed that there was likely to have been a third centre of Taurine domestication in Africa. As with dogs, it impossible that different genes for aggressive behaviour were targeting by humans during domestication, accounting for the complex differences in this kind of behaviour , especially in bulls http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1004254
Down-regulartion of the adrenal response, due to its complex links with neural crest deficiencies, is not altogether benign. Selection for tameness in white tailed deer has become associated with both albinism and pie-bald colouring, and these are furthermore linked to defects of metabolism, hearing, and joint problems. As long ago as 1980, there were cautions that use of hypo pigmented (albino) animals in research was not to be recommended due to the other abnormalities associated with it – this could be related to abnormal neural crest development as well ( http://www.sciencedirect.com/science/article/pii/009130578090461X).
As an aside, I might mention that in the domestication of fermenting yeast the domestication process was primarily metabolic: http://www.sciencedirect.com/science/article/pii/S0960982212005866
However, back to humans… I find the suggestion by Wilkins et. al. that there might be “epi-mutations” involved, due to cross generational epigenetic effects (especially lower stress levels) rather farfetched. We do not after all, know what the rate of conception vs fetal loss is, and this might be altered by levels of maternal stress, and could result in prenatal selection favouring certain pre-existing mutations over the wild type – and this might account for the higher than expected incidence of variants such as the “Star” mutation.
However, what if we explore, not human “domestication” as the opposite of egalitarianism, but as it’s cause, we set back the timing of this hypothetical process by some 3 million years. Assume that our common ancestor with Pan troglodytes and Pan paniscus was more aggressive in social interactions, and had groups typically incorporating a dominance hierarchy which affected reproductive success.
I don’t think I am suggesting we are going out on any precarious limbs here.
These animals were undoubtedly using branches and rocks and bones as tools… and possibly as weapons. Further, assume that this dominance hierarchy, and particularly the kind of aggressive behaviour towards subordinates, thus became too dangerous to be tolerated. A cuff or bite is one thing, but getting hit with a big rock or tree branch is something else entirely.
What if we assume that severely aggressive behaviour was systematically disabled by groups of subordinate individuals ganging up and either killing or marginalizing the most aggressive males (as Christopher Boehm has suggested in “Moral Origins” and elsewhere? Furthermore, assume that this process, over the course of fairly short periods of time, resulted in a positive selection for cooperative and “tame” behaviour among members of social groups. this wold reduce the need for big canines, and result in shorter snouts. Behavioural shifts would result in less stressful social inter-actions, and more access to food for young and therefore subordinate animals. Movement of individual, males and females, among groups would be less difficult if it no longer meant aggressively working one’s way up a dominance hierarchy.
This leads us to another twist in the selection process, of course. For you cannot get a bunch of wimps to take on the big bully, even if they have numbers on their side. If cooperative action against a dangerous aggressive male is to result in ouster or assassination, rather than him beating you and all your buddies up in retaliation, you can’t afford to be TOO tame. You still need that mobilizing capacity for outrage, and considerable capacity for courage and steadfastness. School children routinely practice all these moves, although at times bullies manage to form gangs of their own followers, and the mayhem, without adult supervision, can be truly awful.
What this means is possibly that the domestication syndrome had to shift gears at some point and become the egalitarian syndrome. High courage became attached to the protection of the young and the weaker (women, children and younger and well as elderly males) from the strong (big dominant males). furthermore, collective preventative action was the most likely to succeed. There may be a very good reason humans almost universally root for the under-dog and tell stories of how youngsters -especially boys – learned to become men by taking on a scary opponent with the help of friends. Today we have to wonder if we humans can afford to be domesticated, for it is this same courage in the face of injustice that brings out crowds at protests, that speaks truth to power, and fights for freedom and democracy all over the world.
If the population was small and very scattered, the role of mate preferences, based on sensed heterogeneity, especially the Major Histocompatibility Complex, could be more easily accommodated by freer movement of personnel between groups over a wide area. Tolerance, by males, of female mating preferences might have led to lengthening consort-ships, mutual provisioning, and co-parenting between couples. More involvement in care of the young appears to be linked to reduced testosterone in modern humans; might this have contributed to lessening of hormone-fueled hostility among males? Shortening of the snout, and reduced body size might have made sense in an animal adapting to a marginal habitat on the forest edges, especially if food sharing was facilitated by less aggression.
Once this degree of “domestication/egalitarianism” was achieved, the stage would be set for changed entrained by control of fire. Using it for food processing and protection permitted them to sleep wherever they made camp, and to use the safety and convenience of its heat and light, to form a sharing place, where several couples and their young could rest and play on the ground. And Richard Wrangham’s hypothesized reduction of teeth and jaws, “the cooking hypothesis” might explain just what other selection factor kicked in at this point, at the dawning of the genus Homo.
I might also add that research into the effects of alcohol on developing mammalian fetuses results in abnormalities also traceable to neural crest: http://onesci.com/journals/science_journal_20.pdf As do the effects of the toxin in Corn lilies (cyclopamine) and a number of other toxins. This means that during domestication, interference with neural crest development is often constrained by increasing levels of debilitation and lethality (see also: http://dev.biologists.org/content/125/5/813.full.pdf )
-- Helga Vierich
Quoted on Sun Jul 20th, 2014