From: Oz@upthorpe.demon.co.uk (Oz) Subject: Re: "Fire in the Mind" (long) Date: Fri, 01 Dec 1995 23:44:27 GMT Lines: 60 firstname.lastname@example.org (Andrew Cooke) wrote: > in the case of skin colour the pigment provides protection > against the sun but has a higher risk of something or other > (i don't know what, but it must be something or we'd all be > dark). For info. Production of vitamin D from sunlight & ergosterol. For example Indian Subcontinent immigrants to northern England suffered a significant increase of rickets since they were vegetarian and wrapped up well when going outside and didn't get enough sunlight through their skins. So in primitive times a pale skin in winter was a very significant advantage far from the equator. > in the case of dog breeds the selection is artificial and in > only some cases has it been taken far enough to be irreversible > (like i couldn't imagine a rottweiler mating with a minature poodle, > or vice versa). after all, the kennel club has only been around > for a few hundred years. presumably if we kept breeding dogs > as we do today for a longer time they would become more > distinct (although that might depend on how we select them - if > we keep them like they are now, then they won't, of course, > become more distinct. unlike nature we don't keep pressing to > an extreme, but only to satisfy an aesthetic sense - or because > of snob value). Just a couple of observations here. Firstly do you think there is any real difference between natural selection where humans select for a characteristic than where any other bit of nature does? If in our ecology a red and purple dog is selected as successful is it any different than being selected successful in the (well known) red and purple grasslands of suwari-segondo or being selected as unsuccessful on the bright yellow plains of zakaytak-ulla? If you ever have a dog of your own be very careful. It is quite amazing how they manage to cross-breed (or actually just breed) at all and any opportunity despite apparent impossibilities. I remember one astonishing cross between a standard english sheepdog (large, definitely) and a miniature (male) dachshund (sausage dog). NB neither were mine. I regret to say that this cross produced very unsuccessful puppies, sad. I will leave it to your imagination what the poor little things looked like. On a very topical note an accidental crossing between a tiger and a lion occurred in S.Africa producing 'Ligers'. The last survivor died this week (I think in Belgium) aged about 33 years. Nobody thought they could produce offspring. See London Times in the last 7 days. One would imagine that these genetic lines would have been separate for at least many hundreds of years. ------------------------------- 'Oz "When I knew little, all was certain. The more I learnt, the less sure I was. Is this the uncertainty principle?"
From: email@example.com (Steven B. Harris ) Subject: Re: EVOLUTION: I can't believe it; can you? Date: 30 Jul 1995 Newsgroups: sci.skeptic In <ts_zemanian-2907951659520001@ts_zemanian.pnl.gov> firstname.lastname@example.org (Thomas S. Zemanian) writes: >I was under the impression (from my high school biology class) that the >definition of a "species" was that if two animals, one male and one >female, could breed to produce _fertile_ offspring, then they were of the >same species. > >Of course, this doesn't speak to critters which reproduce asexually, and >I still puzzle over that wolf/dog thing, but I think the _fertile_ >argument comes into play with the lion/tiger mixes, as with the common >everyday mule. > >Am I mistaken? Are ligers sterile, as I had assumed? I don't think ligers are sterile, but would welcome input from those who know. Even mules aren't always sterile. The males are, but the females can be fertile. However, their ova carry only horse chromosomes, so they produce either full mules or horses. No fractional animals possible. The concept of species is a bit more elastic than the one you give. Species are reproductively isolated normally, but that doesn't necessarily mean they cannot be inter-fertile in artificial conditions. For instance, brown bears (grizzlies, Kodiacs, Alaskan browns, etc) are interfertile with polar bears in zoos, but this probably never happens in the wild. And the offspring are fertile also, without any of the mule problems (so you can get any mix, as with wolves and coyotes and dogs). Are brown bears and polar bears different species? Most would say yes. Steve Harris, M.D.