See my post #7 in this thread. The short answer is that current Hox gene arrangements dictate how, for example, fingers are formed, as well as how many. To add to what I mentioned in the linked thread, it is currently thought that in addition to Hox4 genes controlling finger/toe phalangeal development (among other things), parts of Hox1 may have been involved as well (thus allowing for more than 5 digits). The coupling between Hox1 and Hox4 for digit development has since been lost, and those gene suites are now likely constrained to the point where they cannot be re-coupled.
Note, though, that I said it may not be possible to acquire new digits. As Colibri mentions, there are a select few lineages who have managed it. I don’t know anything about the developmental aspects of either ichthyosaurs or cetaceans, so I couldn’t tell ya how they develop(ed) the extra digits. And it may be worth noting that the other secondarily-aquatic critters of the Mesozoic – plesiosaurs and mosasaurs – had more traditional (from a terrestrial standpoint) numbers of digits in their assorted flippers.
So, yeah, it’s not completely outside the realm of possibility for new digits to arise, but it seems pretty clear that in terms of overall evolutionary likelihoods, loss and fusion are “easier” than gaining and/or splitting digits to form new ones.
Again, the main point being not so much about digit formation, but the fact that there are tendencies for directional trends in evolution (and trends do not translate to evidence for intelligent design) that are not easily reversable. It is not the case that all possibilities are equally likely, especially given a finite amount of time.
And the reason it’s different with antibiotics is that there, you want something that’s deadly to bacteria (or whatever other pathogen you’re dealing with), but harmless to humans (or whatever you’re giving the meds to). So you have to find some subtle difference between human metabolism and bacteria metabolism, and the bacteria can evolve resistance to the antibiotic by stumbling across the same trick humans use to be immune to it (or by some other trick, but the point is that there’s known to be at least one biologically-plausible method to resist it).
The statement is imprecise to an extent that renders it false.
Evolution is a phenomenon which includes random elements. Everything in the universe also includes random elements. Random elements are a part of the existence of the universe itself. Yet somehow the statement “the universe is random” is false.
Evolution is the results of a great number of processes that are so non-random that a name was given to this process, survival of the fittest. (It would more precisely be named promulgation of the survivors, but that ship has sailed.) Where random survival exists, you do not have speciation, you have diversification of genome within a species. Death is the bringer of new species, and even then, it is only when death is prejudiced that it occurs.
I suppose if you posit a state in which random fatalities are the predominant cause of death for all species then evolution would be random. Or, perhaps survival would depend on luck, and only the lucky would breed. A lucky gene? That is a philosophical consideration that is perhaps beyond the realm of science.
BTW, it was certainly not my intention to imply that they were. My question was whether or not the specific example you gave was a good one or not.
Shodan: I read your post exactly the way Colibri did, and I suspect most others did as well. You started talking about speciation and then jumped to eels and lions. There is no eel --> lion speciation event, and I’m sure you already know that.
Oh, I know. I was merely re-iterating the point of this hijacking, which was to counter Shodan’s statement that “all evolutionary adaptation is equally likely”; it’s not, by a long shot, and the whole number of digits thing is just one example wherein there are constraints in place which limit how an organism can evolve. And another one being, per the main topic, a cockroach’s inability to evolve immunity to boric acid.