Ned Potter is the science correspondent for ABC's "World News with Charles Gibson." He has reported on such topics as space exploration, the human genome and climate change.
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The Mystery of the Soay Sheep
July 02, 2009 5:46 PM
The island of Hirta, in the St. Kilda archipelago off the northwest coast of Scotland, is an uninhabited, windswept place, perfect for studying the wild sheep who live there. British researchers have been watching them for 25 years, and report a collision between two of the most contentious issues in science -- evolution and climate warming.
The theory of natural selection, they report online in the journal Science, would say that bigger sheep are healthier sheep. But the Soay sheep, in recent years, have grown to be a bit smaller over time.
"Sheep are getting smaller. Well, at least the wild Soay sheep living on a remote Scottish island are. But according to classic evolutionary theory, they should have been getting bigger, because larger sheep tend to be more likely to survive and reproduce than smaller ones, and offspring tend to resemble their parents," said Tim Coulson of Imperial College London, one of the study authors.
The change was small -- by the first August after birth, young females weighed 150 grams on average, or just a third of a pound, less than their mothers did at the same age. Their hind legs were smaller as well. The researchers controlled for other factors than climate, though their reason for studying Hirta was that there weren't a lot of other factors. Factor in the North Atlantic Oscillation, a periodic shift in nearby ocean temperatures, and the slight shrinkage of the sheep tracks with the gradual warming of the local climate. The abstract of the paper is HERE. (Update: Science has a writeup HERE.)
"As winters have become shorter and milder, lambs now do not need to put on as much as weight in the first months of life in order to survive to their first birthday. Even the slower-growing ones now have a chance of surviving," write the editors of Science.
July 2, 2009 | Permalink | Share | User Comments (17)
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I knew it! Global warming is true.
Posted by: Jim Bob | Jul 2, 2009 7:19:40 PM
Oh brother, all species down size when isoloted on islands. It happened to elephants and people.
Posted by: PotatoeGater22 | Jul 2, 2009 7:51:58 PM
This scientist is either an idiot or desperate and should have known about the common downsizing of isolated island species.
Posted by: PotatoeGater22 | Jul 2, 2009 7:53:20 PM
What are they gonna say next "aliens will be less likely to visit earth because of climate change"
Posted by: be natural | Jul 2, 2009 7:58:57 PM
What about those giant mice on Gough Island? Does downsizing only happen to animals larger than dogs?
Posted by: Daphni | Jul 2, 2009 8:36:57 PM
Jim Bob wrote: "Oh brother, all species down size when isolated on islands."
Yeah. Tell that to the tortoises on the Galapagos Islands and the lizards on Komodo Island!
Posted by: The_Mick | Jul 3, 2009 8:42:13 AM
There's no doubt we're experiencing Global Warming but there are so many other factors that it's not clear that it's what is affecting the weight of the sheep, or it alone. The actual article notes ""Changing [environmental] conditions on the island ... [may] have led to changes in the chemical composition and nutritional value of the plant foods the sheep eat,"
Posted by: The_Mick | Jul 3, 2009 8:47:51 AM
Everybody seems to have missed the fact that the warming has produced more rain, thus shrinking the wool. Hence, smaller sheep. :-)
Posted by: andyr | Jul 4, 2009 9:13:41 AM
Yeah but where can I find the taco shells... ive got some dog meat and its gonna go bad soon!
Posted by: Anonymous | Jul 4, 2009 11:41:25 AM
This is just another example of poor education. The value of a Ph.D. today is not much more than what was a B.S. in the 1940s-50s. What a shame.
p.s.
This new format is not inducing to arguments, let alone posting a comment.
Posted by: Quietman | Jul 6, 2009 4:11:11 PM
Island dwarfing is an incredibly common finding where there are no larger predators which would select against smaller adult size. Without this pressure, the smaller animals, which require less food and thus are able to survive shortages, reproduce more. Animals which "mature" earlier at a smaller size are able to breed sooner. It is incredibly annoying that these self-aggrandizing "scientists" couch their findings in terms of global warming (today's hot topic) rather than citing the much more probably and well known phenomenon of island dwarfing.
Posted by: Doc Savage | Jul 7, 2009 2:23:34 PM
According to the "island rule," large animals tend to get smaller and small animals tend to get larger on an island environment.
Posted by: hominatrix | Jul 10, 2009 12:09:06 PM
Being on an island in and of itself doesn't magically result in smaller or larger species. The environment impacts evolution, and the current anthropogenic climate change is affecting the environment.
Posted by: hominatrix | Jul 10, 2009 12:11:00 PM
hominatrix
Nice to hear an intelligent post again.
Posted by: Quietman | Jul 13, 2009 2:47:09 PM
The "island theory" in evolution argues that, over time, plants and animals in an isolated island tend to become smaller. This is due to the very limited resources available, necessitating that the life must be smaller in order to ensure adequate food for a population to survive and even thrive.
Posted by: me | Jul 16, 2009 6:18:26 AM
What does "island theory" say about the Galapagos tortoises? They seem to have got larger because of lack of competition. Or, will they peak, then become smaller?
Posted by: andyr | Jul 16, 2009 8:37:27 AM
hi
Posted by: randomudontknowme | Nov 16, 2009 7:44:09 PM
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