By "kind" I mean kind as in back on the farm. If you can show me that one animal actually did, unquestionably, (which means during my lifetime, in this case) descend from another, then I will consider myself to know that those two animals and all that's between them will be the same kind. If they look like the same kind to me (but they are non interbreedable and I didn't see them descend from the same granddaddy) then I will consider myself to believe them to be the same kind. If they can breed and produce viable offspring, they are almost certainly the same kind. Lack of inter-fertility does not however (by my definition of kind) disprove kindness: It is clear that if one species gets separated into two different geographically isolated regions for long enough, they will no longer be able to interbreed -- but they were still the same kind to begin with and are (by my definition) the same kind to end with.(and always will be the same kind.)
The fact that my car's lug nut fell of and got run over by a hundred and 50 loaded trucks and no longer fits onto my car's lug doesn't prove that it's now a different kind of nut -- it's just lost some of it's geometrical information.)
I realize that my definition of kind doesn't mesh perfectly with yours. I also realize that it's not perfect. For example, by genetic engineering if by no other means, a cat could be turned into any other kind (by my definition) or any creature that has never before existed, just like a computer program can be rewritten to become something entirely different. But my definition of kind has served me well for all practical purposes. Hopefully that answers your question.
You said the horse skeletons appeared to you to be variations within a species or genus--or whatever you meant by "kind"--and compared the variation to different kinds of dogs. My question, which I guess I didn't express very well, is how then do you account for the fact that these variations succeed each other in the fossil record?
I thought you would have known this (or maybe I don't understand your question) but intentional dog breeding has produced sort of a ring species, if I may speak loosely, where each of the different varieties have been preserved. But if, instead of wanting different varieties, dog breeders had only wanted the tiniest dog, we would have only the teacup poodle and all the other intermediate species would exist only as fossils. Same thing with the horses -- had selective pressure preserved some of each the many different intermediate species along the way, we would still have living specimens of many of the intermediate stages. Think of two trees growing: In the case of dogs, lots and lots of branches were allowed to grow. But in the case of horses, only one branch was left on, (or only a few) and so even though it could have had more branches, they got cut off and it doesn't have more branches -- but there's no reason to think that it couldn't have, just like the dogs. (I imagine it would have taken somewhat more generations since selective pressures may not have been as strong as those exercised by dog breeders. Maybe 10 times as long, but I highly doubt a hundred or thousand times as long.)
If they're just variations like dogs, how come there aren't any fox-sized horses running around now?
There are! Or very nearly! There are whole clubs relating to the raising of miniature horses!
Beech Island, SC Check this one out! Notice that these people riding and leading these horses are small children. Also notice that many of these small horses have well grown out mains, tails, and forelocks. (They aren't born with hair like that. And besides you wouldn't want to by riding a baby horse anyway. They don't obey very well. Not sure if you know much about horsemanship, but horses are trained for several years before being ridden by casual riders -- especially by children (I'm certainly no horse trainer, but I've watched horse trainers training and I've ridden horses and that one milk cow we had. I'm telling you, that cow was level headed -- nothing spooked her. And the looks from the people in passing cars was totally worth it.))
Anyway, just search google for miniature horse and you'll find plenty of info about them.
This is my favorite, because it's pretty extensive and has nice pictures. You'll find fish showing up about halfway down the orange-red group at the top left, near the label "450 m yrs." Mammal-y things show up a few branchings above that, in the same group.
Thanks very much! Exactly what I was looking for!
I did venture to go to the website that hosted it, and, well, it looks like the fellow's sort of a funny religious thing or something, I couldn't quite tell. Unless that's a website for a strange movie. Anyway, I guess if we have to go to a religious website to get good scientific documents so be it :-)(To be honest, I sort of expected a university or something. I hope this chart is accurate.)
Thanks again,
-Jesse
But it didn't, so the intermediate stages went extinct. Isn't that pretty much the definition of evolution?
Think of two trees growing: In the case of dogs, lots and lots of branches were allowed to grow. But in the case of horses, only one branch was left on, (or only a few) and so even though it could have had more branches, they got cut off and it doesn't have more branches -- but there's no reason to think that it couldn't have, just like the dogs.
Right. In the case of horses, environmental changes did the branch trimming--again, pretty much the definition of evolution. I don't think you're suggesting that humans made the decisions about which branches of the horse to keep, are you?
I did venture to go to the website that hosted it, and, well, it looks like the fellow's sort of a funny religious thing or something, I couldn't quite tell.
That's funny. I just found it by doing a Google image search for "evolution tree"--I had no idea what the rest of the site was about. I'm glad you like it. There are a bunch of other versions on the same results page, so you can see if there's one you like better, and see how well they all agree. If you really want to get into it, check out the Tree of Life Web Project, where you can click branches to move up and down the tree. I find it a little confusing, but it's certainly extensive.
And I think I get what you mean about "kind." But that's the funny thing about common ancestry. Here's the context around that quote I posted earlier about why Eohippus is grouped with the horses:
"Matthew (1926) pointed out, but latter students mostly ignored, the fact that eohippus was not a horse, that it is about as good an ancestor for Rhinoceros as for Equus. In effect, there was no family Equidae when eohippus lived. The family and all its distinctive characters developed gradually as time went on. Eohippus is referred to the Equidae because we happen to have more complete lines back to it from later members of this family than from other families."
In other words, Eohippus is called an early horse because we have a better chain of fossils leading from it to horses. If we had more fossils leading from it to rhinoceroses, it'd be called an early rhinoceros; and if I'd posted photos of that chain of fossils, you might say that they all looked like the same kind. Or maybe you wouldn't--maybe you'd still think that first one looked more like a horse. But to Simpson, anyway, it wasn't at all clear what "kind" of animal, in your sense, Eohippus was.