Should animals be used to produce organs that could be implanted in humans?
I think that most people would consider that question to be ethically along the same lines as "Should animals be used in medical research?".
If anything, it seems ethically more "reasonable" to use their organs in transplants than to eat the animal, since eating the animal only provides fuel for a day or so, whereas an organ could give a human around 15 years of extra life (assuming the animal organs had a similar functioning life as a allograft transplant, which may prove to be a bad assumption). However some people will object to this view on the ground of "it involves genetic engineering" or "it puts the animal through unnecessary pain". Some people may just generally feel uncomfortable at the concept of having an animal organ keep them alive.
There are of course additional risks associated with xenograft transplants, however I suspect that under lab conditions necessary to perform the "humanizing" of animal organs, these risks have been accounted for. (E.g ensuring that animals are not carrying any diseases which could be spread to humans). Indeed, knowing that the animal was completely healthy is actually a huge advantage compared to trying to establish the complete medical (and sexual) history of a cadaverous human donor. The "humanizing" of the organs is designed to negate the additional rejection risks associated with "normal" xenograft transplants (i.e. non-humanized xenograft transplants).
If humanized-xenograft transplants worked as well as (or better) than allograft transplants, fewer people would die whilst waiting for a donor organ. They would also be able to schedule their surgery for a particular day. However, I have always wondered whether hospital transplant units would be able to cope if everyone waiting for a transplant were to receive one. (Even as it is, bed spaces, ITU spaces, surgeons, nurses and blood products seem to be a little stretched.) But I like to think that's just my cynicism, and I hope to be proven wrong.
No. No species on earth is closely related enough to humans to produce offspring. Although hybrid animals do exist, they are the product of very closely related animals usually in the same genus (example: horses and donkeys are bred to produce mules). We are the only living species in our genus, other members went extinct long ago.
In embryology, animals with bilateral symmetry, like arthropods (and also humans) produce three germ layers. Animals with radial symmetry like echinoderms produce two. Note that the term 'anthropod' should not be confused with 'arthropod' - anthropod is not a phylum nor taxon but is a broader term meaning human or humanoid.
animals produce energy for other animals to use. for example, when a prey animal eats, energy is stored in its tissues. when a predator animal eats the prey animal, the stored energy is "given" to the predator. Animal use this energy for everything, and this is why animals (and humans!) eat. Hope this helps!
The way I see it is that they should. Animals, in some respects, are the same as humans. How would you like it if you had to stand in a 60 cm by 60 cm cubicle and forced to do something unnecessary? You wouldn't would you? Well that's what they do to some chickens and force them to produce eggs. So if people would never do it to themselves, then why do it to chickens?