The story of the domestication of both plants and animals is notoriously difficult to untangle. For the most part the transition from wild population to farmed species occurred such a long time ago that the process has frequently become the stuff of myths and legends. Most domestication events occurred long before people bothered or were able to formally record such things. Around the world various oral traditions tell of crops falling from heaven as gifts from the gods. Our ancestors had no need to record their actions because at the time they would have been totally oblivious of the significance of their activities for subsequent generations.
Remarkably few people other than Jared Diamond and myself have bothered to question why so few species were ever domesticated. As a botanist until now I have restricted my thinking to crops. But Jared Diamond has argued that exactly the same principles apply to the domestication of both crop and animals. He argues that even fewer animals were capable of being domesticated than was the case in plants. Think about it for a minute, we really do routinely eat only cows, sheep, pigs and chickens as domesticated animals. That’s amazing given the diversity of life on earth.
Jared Diamond claims that domestication was a rapid process that occurred a long time ago, because all the species that could potentially be domesticated were identified in the distant past and quickly made that transition to farmed crop or livestock long ago. However, it turns out that not only are we still domesticating new crop plants the same is also occurring in the animal kingdom. So we don’t have to use flimsy fossil records or myths for prehistory to understand domestication; we can actually observe the process first hand.
So what does the animal world have to tell us about the process of domestication? In the last 50 years salmon has been transformed from being an expensive luxury item caught from the wild by aristocrats, small traditional scale netting operations, with some sea trawled fish being tinned. Today salmon is a cheap everyday farmed commodity. But has the Atlantic salmon really been domesticated? Surely a farmed salmon and a wild salmon are identical. OK farmed individuals don’t get to roam the vast oceans and fight their way up river to their natal spawning grounds but surely they could, they look just the same don’t they? Because of the considerable economic importance of both wild and farmed populations of salmon, we probably know more about the unintentional genetic changes associated with its early domestication than any other species. Although they may appear superficially similar research has shown that wild and farmed salmon are quite different. Marc Gross from the University of Toronto argues that farmed salmon should actually be considered as a new biological entity – Salmo domesticus. (http://www.nrcresearchpress.com/doi/abs/10.1139/d98-024#.VswcXObkrOA)
There are very real concerns that during storm events millions of farmed salmon (which now vastly out number wild populations) are able to escape into the wild. The fear is that these escapologists will interbreed with wild fish populations that are already threatened by over fishing and chemical pollution. This could be important because it is possible that hybrid fish that are half wild and half farmed salmon may not be able to find their way home to their traditional spawning grounds. Other important behavioural and ecological characteristics could also be altered as wild populations are invaded by the new domesticated types.
It appears that these concerns about the potential genetic pollution of wild salmon stocks by farmed fish may not be fully justified. Evidence suggests that just a generation or two of domestication seem to render farmed salmon ill prepared for the rigours of life in the wild. In captivity the individuals that thrive are the fish that come to the surface and actively compete for the food pellets which are liberally scattered for them. This very same trait is probably a death sentence for wild fish. In natural conditions any fish that actively swims on the surface looking for food rapidly becomes food and is eaten by a host of predators. In the wild environment it is much better to lurk in deep water out of sight off the menu. Conversely hiding away at the bottom is a stupid thing to do for a farmed fish, because they will very quickly go hungry. As a consequence of these strong and opposing selection pressures, fishermen’s attempts to restock rivers with farmed fish have proved consistently and controversially futile. Even so, it is thought that because of the almost constant flow of massive numbers of maladapted escaped farmed fish in Norway it mean that entire fjords have ‘lost’ their wild salmon populations.
Unfortunately this is probably not the most significant problem facing wild salmon stocks. Marine survival rates are insanely low at the moment (0.5-2% versus 10-20% a century ago), implicating climate change. It is going to be a tough few decades for salmon as severe natural selection favours those fish able to find their way in a changing ocean. They will manage, but abundance is likely to remain low for some time.
This fishy tale rather suggests that Jared Diamond is correct and that domestication is a rapid and dramatic process. With both plants and animals we have frequently selected for traits that make them easy to handle and more pleasant to eat. These genetic changes often mean that domesticated species are unable to survive in the wild. This is why there are few populations of farmed animals and plants that successful escape cultivation. Wild animals that are easy to handle and good to eat are not going to survive for long.
Of course life is rarely this simple. There are examples of species that have lived in association with humans for thousands of years and have not changed that dramatically from their wild ancestors. The reindeer is one of these semi-domesticated species. Since the last ice age the Sami people have depended for their survival on herding reindeers and driving them vast distances across the tundra. After all this time and many generations the deer remain mostly unaltered and are certainly able to thrive without humans in these harsh artic conditions.
So it appears that animal domestication is similar to crop domestication. For many species their association with humans began many years ago. But this does not mean that it is impossible to domesticate new species. In fact with our modern understanding of genetics this is easier than ever before. The salmon story tells us that such genetic changes can be rapid, while reindeers are an example where genetic change is slow.
A big thankyou to Kyle Young for his comments on this post