On Thu, Dec 03, 2009 at 09:59:22PM -0500, Doug Franklin scripsit: > John Francis wrote: >> On Thu, Dec 03, 2009 at 05:12:53PM -0500, Doug Franklin wrote: >>> P. J. Alling wrote: >>> >>>> At 19 he was a very old dog... >>> For some reason, I have it in my head that the average lifespan for >>> pet cats is a couple of years longer than for pet dogs. >> >> That's because they are smaller. Seriously (albeit slightly tongue-in- >> cheek; different species are not directly comparable). But large dog >> breeds have, generally speaking, shorter lifespans than smaller breeds. > > Hmmm. That seems strange, to me.
The default dog is quite small; 10 to 15 kg. Moving away from that via selective breeding tends to introduce issues that there hasn't been enough time for natural selection to remove, especially since people keep up the selective breeding. > Again, going by biology classes a lot more years ago than I'd really > care to admit, I thought that larger species typically lived longer > than smaller species, when considered on the "gross scale", like > hamster versus cat/dog versus horse rather than hamster versus mouse. There's a roughly constant number of heartbeats per lifetime in mammals. Smaller critters have much higher heart rates so much shorter lives. There are exceptions to this curve; humans live about three times longer than we "ought" on the basis of that relation between heartbeats and lifespan. (Heavy selection pressure for cultural transmission, probably.) Dogs, though, are skewed by the selective breeding; the default dog lifespan is probably whatever Asian pariah dogs (which are probably pretty close to the default dog) manage. -- Graydon -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
