A lot of people are under the misconception that different "species" can't interbreed.  The fact is, most species "don't" interbreed.  To put it very simply, when two animals are related closely enough, they can usually produce an offspring, though infertility, dwarfism, and other maladaptations are very common.

If you think about it, cross-species breeding isn't unique to modern science.  Before we get to your questions of safety and morality, consider that people have been doing this for hundreds, maybe thousands of years.  Mules are a hybrid of a male donkey and a female horse.  Sometime in the distant past, somebody thought, "Wow... I wish I could have a work animal with the temperment of a donkey and the strength and work ethic of a horse."  Horse and donkey were encouraged to know each other biblically, and viola!  Mule.

Contrary to popular belief, mules are not all sterile.  There are rare cases of fertile mules, and in at least one case, there's been an offspring that was 75/25 instead of 50/50.  Donkeys have 62 chromosomes.  Horses have 64.  Typically, when two individuals have differing numbers of chromosomes, any offspring will be sterile.

There has never been a report of a crossbreeding that produced a three headed fire breathing hydra that destroyed the village, if that's what you're asking.  Yes, it's safe from the human perspective.

I suppose that's a matter of opinion.  Here's an article I wrote concerning morality.  You should read it before you go on:

What Does Sugar Have To Do With Murder?!

There's a section in there dealing with human empathy towards animals.  However, before you reach any conclusions, you should know that nearly every piece of fresh produce you've eaten in your entire life was the result of crossbreeding.  Not only that, but almost all the meat you've eaten was the result of very careful breeding between different "breeds."  Now, before you go making arbitrary lines in the sand, you need to know something about species.

Carl Linnaeus was a Swedish botanist who established the protocols for Linnaean taxonomy, which is where we get the idea of a species.  This was in the 18th century.  What's important about that is nobody knew what a gene was, nor did they know that all life is descended from the same ancestor.  So, the concept of a "species" is not as useful as it used to be.

The fact of the matter is, species is a mostly useless term.  Today, scientists group organisms into things called clades based on their DNA.  While it's true that humans are very different from chimps, and chimps are very different from monkeys, we share virtually all the same DNA because we are very closely related, as relation goes in the animal kingdom.  The lines are pretty clear between us, but it's not the same throughout the whole of life.  Some species are almost indistinguishable from others.

So, your question of ethics is really a question of the dividing line.  We've been interbreeding for thousands of years, and it's made our life substantially better.  If you have a problem with it, it can only be in interbreeding certain kinds of things.  

Better to think of the implications of not interbreeding.  Your diet would be far less palatable, and food would be far less plentiful if we didn't interbreed.  I think it's safe to say that without interbreeding, the earth probably couldn't sustain as many humans as there are now.  (Then again, I think there are too many humans.... hmmm.... dilemmas, dilemmas, dilemmas....)

I think it was an episode of "Married With Children" that said it all. I forgot the context. But Al was fanticising about women having 3 breasts, one being on her back "for dancing".

In all seriousness, all kidding aside. There are side affects to every discovery and throughout history every new discovery has been utilized for both benifit and harm.

Fire has been used to heat ancient huts and it has been used to burn innocent people to death. We cant throw out the future of discovery because some fear ill wishers have mal intent.

I might get hit by a bus tommorow, but the only way to avoid that is to ban busses.

Yes, busses in most unicipalities will be running, probibly on a limited schedual, with the good intent of getting people to their familys for the holiday, but at the same time emmiting the same carbon exsaust that we tend to want to avoid.

And if you want to blow up a checkpoint in a disputed area, what better ploy than mass transportation. And if you want to avoid that calamity then you put the entire nation in a big brother police state where anyone who farts wrong is arrested. Lets face it, living in fear is pop culture today. They live in fear of us and we live in fear of them and as long as we get them before they get us at least we save face, or if they get us first they save face.

Oh, BTW, Happy Holidays, Merry Christmas, Happy Hanukkah, Kwanza, Winter Solstice. May every arbitrary day where without special pleading or favoritism wasn't argued, that we would all, as a species go on a rampage because we couldn't figure out that we can do the same kind things to each other any day of the week any day of the year.

 I can't speak for the specific researchers, but I imagine they find this stuff to be fun.  As far as what we're learning, I hope you'll be ok with a basic answer.  Genes are a lot like computer code.  That is, in computers, everything eventually reduces down to a sequences of ones and zeros.  In life, everything reduces down to four letters, or more precisely, four chemical building blocks.

With computers, we invented the code, so we pretty much know everything about it.  With life, we just discovered the code in the last century, and there's still a lot we don't know about it.  Even though we've sequenced the human genome, the fruit fly genome, the chimp genome, and lots of bacteria and viruses, it doesn't mean we can say precisely what every gene does, much less what effect each letter has on the finished product.

When we get something that isn't "supposed to happen" like a lion-tiger mating, we can learn an awful lot about what particular genes do.  Science works best when it has more information.  If we have a lion gene, a tiger gene, and then we get to see what happens when we put them together, we can essentially "triangulate" to figure out what a particular gene might do.  This isn't a very scientific explanation, but I'm trying to keep it simple for you.  It's not a perfect analogy, but it gets the point across.

I don't know a lot about ligers, but I imagine most of them are first or second generation.  This kind of interbreeding is basically unstable.  Mixing in and of itself isn't necessarily good for a species.  In fact, most of the time, it's going to be bad.  Richard Dawkins has a really good way of explaining it:  There are a lot more ways to be dead than there are ways to be alive.  In other words, most changes to a gene will be negative.  Only a very few changes turn out to be beneficial.

What is good for a Liger?  The same thing that's good for any other animal.  It wants to eat, sleep, and avoid pain.  It's just my opinion, but if scientists are treating the animals well and not unnecessarily making them uncomfortable, it seems just fine to me.  There's no magic to evolution.  It's just math.  We're just tinkering with the math.  Think about it this way.  Whenever you have sex with another human, you're doing the same thing.  Do you have any idea how many babies are born deformed?  Humans regularly come out with dwarfism or infertility.  Every mating is a rolling of the genetic dice.  Humans who are crossbreeding other animals are just rolling the dice in the context of a scientific experiment.

Don't misunderstand me -- I'm not saying we have no ethical obligations to animals.  I believe we do.  I just can't find any reason at all to think that we shouldn't try to learn as much as we can about genetics through crossbreeding.

Very cool.  I like the Dawkins quote. 

It appears that evolution has allowed current living species to develop a successful pattern of staying alive.  If you mix up the genes and crossbreed too much you may change their dna so profoundly that they loose their precise ability to function in the wild.

I am thinking about wolves.  They function fine in the wild.  But dogs on the other hand have been cross bread to such a degree that some (I can imagine) are only really able to survive as human house pets.  They could not make it in the wild.  I heard that our cows produce so much milk, that if we didn't milk them constantly they would be in great pain from overfilling their bladders with milk. 

Some animals have been cross bread to such a degree that they can only survive with our help and we did that for our own benefit.  I always figured that cross breading would be only beneficial. 

Do you think it is any advantage for different human groups to inter marry?  It may sound like a stupid question, but I always figured that it would spice things up genetically.  Humans have developed different immunities and skin colors that resist against sun burn etc.  I always figured a good mixing of genes from opposite parts of the world might be a way to give people a more varied set of advantages.  Plus I personally think mixed people look cool.  Exotic.

Is that non-scientific or un realistic?

There are a LOT of food products that need constant human supervision to keep reproducing (or keep being grown.)  Yes, many milk cows would have severe (probably fatal) problems if they weren't constantly milked.  They've been bred to produce far more milk than they would ever need in the wild.  Pigs have been bred to be HUGE compared to their undomesticated ancestors.  The list is very long.

In evolution, most changes are bad.  It's a cruel system, but that's one of the proofs that it wasn't designed by a benevolent deity.  If someone actually cared about individuals, he wouldn't have invented a system where the way to a small advancement is thousands or even millions of "mistakes."

In most circumstances, it doesn't matter much either way.  There are some populations that have minor adaptations which could be beneficial to other populations.  For instance, Native Americans and other groups who only recently adopted European diets high in complex sugars could mate with a Western European and pass on genes slightly better at processing french fries.

Some ethnic groups have particular susceptibilities to various diseases or drugs.   For example, People of Mediterranean or African descent often suffer from hemolytic anemia when taking primaquine (a drug for malaria).  I don't know specifically whether this is the presence of a particular gene or absence of it, but the point is still clear.  Mixing genetic lines could well negate or at least lessen this effect in several generations.

Any kind of diversification is generally good in the long run but you have to remember that natural selection doesn't care about you specifically.  It cares (in a metaphorical sense... of course it's not conscious) about the broad results.  It's like playing blackjack.  You don't care if you win any individual hand.  You care if your strategy works in the long run.

Racial differences are (mostly) not really differences at all.  They're just "alternate expressions" of existing alleles.  That is, if you took a bunch of caucasians and put them in the tropics for a thousand generations, you'd have black people, and if you put blacks in Antartica for the same time (what a horrible thought!) you'd get pasty white people.  I said the differences are mostly not real because as I mentioned, there are some minor adaptations that have kept themselves somewhat localised in populations, mostly dealing with things like digestion of starches or lactose.  It appears that some of these may be new adaptations that have appeared in the last 4000 years or so.  Really, though, with global travel as easy as it is now, we shouldn't expect these kinds of adaptations to stay localised for long.

Slightly.  I hope I've helped clear it up just a little.