Applicability onto humans of medical research on non-humans

As most of us are aware, due to ethical concerns, most organic and drug research has to be (at least, initially) conducted on non-humans. Research involving estimating LD50; what happens if you breed animals with genetically-engineered DNA; drug effects and experimentation of the like. Coming from a non-biological background, I’ve, doubtless, missed other types of research.

So, what I’m looking for, are texts (on or offline) and/or explanations of the various animals out there, being used for research and the justification of the confidence that at least some aspects of the research can be carried over to humans. Some other questions include, e.g. why would one use a certain rat for an experiment as opposed to a mouse or a chimpanzee? Why is the fruit fly a popular lab subject? How similar is the gorilla brain to the human brain and where is it different? What about the other organs?

I fully realize that this is a broad and complex topic. I’m just looking for some primers, presented here or elsewhere. Just to reiterate, my focus is limited to comparative analysis of those animals, who are used for research, directly or substantially, towards understanding humans. Thanks.

IANAMR (I am not a medical researcher), but I know that not all diseases can be caused in all animals. Only armadilloes and humans can get leprosy, I think, and I’m sure there’s more diseases that are more species specific.

Well, the standard laboratory rat is a strain that has been studied repeatedly, and is available to researchers all over the world, so that everyone is working with subjects that are as genetically identical as possible. Rats are bigger than mice, and easier to work with (and on). Larger animals are quite expensive, and one generally doesn’t work on them unless one must (for example, rabbits are de rigeur for ophthalmic work), or unless one has reached an advanced stage in research where a few highly appropriate subjects are better than several approximate subjects.

Fruit flies are used for genetic research because they breed really fast, mutate very visibly, and have only four chromosomes.

Your other questions will have to wait for a current biologist.

There is a huge volume of research in animals that has been later applied to humans. This knowlege gives scientists a decent approximation of how animal results will translate into humans. This is only an approximation, though, and human trials are always required to fine-tune the research to get valid results.

Right. For example, we have information about how LD50 in rats generally correlates to toxicity in humans for different sorts of compounds. If you determine an LD50 for rats, you can roughly estimate what a lethal dose would be for humans.

The basic biology of rats or other mammals is close enough to that of humans to provide useful information that can be related to humans. Knowing the similarities and differences between human biology and that of the test organism helps, although there will always be some things that don’t correlate exactly as predicted. So eventual research in humans is necessary where it’s practical and ethically appropriate (as in developing new drugs).

Genetic research concentrates on model organisms that are well understood and can be easily mutated. Fruit flies, as has been said, reproduce quickly, show obvious morphological changes when they’re mutated, and have a simple genome that’s very well understood. Plus, since both fruit flies and humans are eukaryotes (organisms that have cells with a nucleus), there’s a striking amount of similarity between genetics in fruit flies and that in humans. Everything is done essentially the same way, but with a different set of tools and different genes. Prokaryotes (single-celled organisms without a nucleus, such as bacteria) have a different genetic machinery, but there are prokaryotes that have sufficiently well understood genetics to be used as model organisms. E. coli is probably the best-known one.

If you’re questioning whether animal research provides useful information on humans, it’s simply not true that animal research is of little use in understanding humans. Such an argument starts from the conclusion that animal research is wrong, and then finds evidence to fit the conclusion, inventing or altering evidence as necessary. This is contrary to the scientific method, but it’s a technique that’s often used in politicized arguments. In reality, animal research allows us to understand many things about humans, without having to do things that are impractical (waiting 25 years for a human to reproduce) or unethical (giving someone a toxic substance or performing surgery on a healthy person). The areas where humans really are different than other animals, such as the brain, are few and known. Otherwise, the applicability of animal research to humans can usually be confirmed by comparing the data with similar data available for humans. I can’t recommend a text that explains this, though – it’s Not My Field.

Even here, the difference between a non-human ape brain and a human brain is basically that of complexity and not a fundamental difference, right?

Anyway, any comparative biology primers?