Hello Tusko,
tusko writes:
I can see the distinction you are drawing between my pig-breeding and my rattlesnakes...
...don't you think that if we weren't around, that rattlesnake populations might be at an advantage if they did have rattles again?
Not to state the obvious, but we
are around and we
are part of the environment - my point being that humans shouldn't be seen as 'separate' of ecology somehow...
I think the distinction between natural and artificial selection should be in part whether the environment the organism lives in is artificial (a petri dish with antibiotic; or pigs in a pen) or natural (a human taking antibiotics; or snakes on a ranch).
Even this definition tends to get a bit fuzzy, since one could argue that the addition of antibiotics to a host flips it to an artificial environment - perhaps Moose's designation of human-induced selection is indeed better terminology.
Or perhaps environment should not be the sole determinate, and human behavior should be considered:
The examples I'm turning over in my mind are hunting/fishing related. Humans tend to preferentially hunt the largest, strongest animals, often for reason of obtaining a trophy, rather than feeding oneself. [When hunting game, isn't it more 'natural' to take down weak or available game for efficiency's sake?] As a result, overall size and rack size has decreased over time in hunted populations of game animals; similarly body size at reproductive maturity has been reduced in some heavily fished populations.
Hunting:
Nature. 2003 Dec 11;426(6967):655-8.
Undesirable evolutionary consequences of trophy hunting.
Coltman DW, O'Donoghue P, Jorgenson JT, Hogg JT, Strobeck C, Festa-Bianchet M.
Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK. d.coltman@sheffield.ac.uk
Phenotype-based selective harvests, including trophy hunting, can have important implications for sustainable wildlife management if they target heritable traits. Here we show that in an evolutionary response to sport hunting of bighorn trophy rams (Ovis canadensis) body weight and horn size have declined significantly over time. We used quantitative genetic analyses, based on a partly genetically reconstructed pedigree from a 30-year study of a wild population in which trophy hunting targeted rams with rapidly growing horns, to explore the evolutionary response to hunter selection on ram weight and horn size. Both traits were highly heritable, and trophy-harvested rams were of significantly higher genetic 'breeding value' for weight and horn size than rams that were not harvested. Rams of high breeding value were also shot at an early age, and thus did not achieve high reproductive success. Declines in mean breeding values for weight and horn size therefore occurred in response to unrestricted trophy hunting, resulting in the production of smaller-horned, lighter rams, and fewer trophies.
PMID: 14668862 [PubMed - indexed for MEDLINE]
Fishing:
Nature. 2004 Apr 29;428(6986):932-5.
Comment in: Nature. 2004 Apr 29;428(6986):899-900.
Maturation trends indicative of rapid evolution preceded the collapse of northern cod.
Olsen EM, Heino M, Lilly GR, Morgan MJ, Brattey J, Ernande B, Dieckmann U.
Adaptive Dynamics Network, International Institute for Applied Systems Analysis, A-2361 Laxenburg, Austria. espeom@bio.uio.no
Northern cod, comprising populations of Atlantic cod (Gadus morhua) off southern Labrador and eastern Newfoundland, supported major fisheries for hundreds of years. But in the late 1980s and early 1990s, northern cod underwent one of the worst collapses in the history of fisheries. The Canadian government closed the directed fishing for northern cod in July 1992, but even after a decade-long offshore moratorium, population sizes remain historically low. Here we show that, up until the moratorium, the life history of northern cod continually shifted towards maturation at earlier ages and smaller sizes. Because confounding effects of mortality changes and growth-mediated phenotypic plasticity are accounted for in our analyses, this finding strongly suggests fisheries-induced evolution of maturation patterns in the direction predicted by theory. We propose that fisheries managers could use the method described here as a tool to provide warning signals about changes in life history before more overt evidence of population decline becomes manifest.
PMID: 15118724 [PubMed - indexed for MEDLINE]
I believe it arguable whether these examples are cases of natural or artificial selection.
My personal leaning is that the hunting-induced evolution of rams is artificial, since it was caused mostly by prey selection based on human aesthetic values, rather than for efficiency of gaining food.
The fishing might be more of a natural selection scenario, since the net method used to get fish is designed for efficiency of getting food.
Hopefully this doesn't seem like too much of a contradiction; one could argue that all human behavior is natural, but that would mean that no such thing as artificial selection exists, since the artifice is introduced by human behavior.
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