Consider this case:
Planaria is a flatworm with a network of nerves and just the beginnings of the brain. Professor James V. McConnell of the University of Michigan as well as other scientists have carried out interesting experiments with these worms.
This rather is a set of cruel experiments sadly but the results are interesting to study. The worms were subjected to electric shocks which they did not like and wriggled every time the current passed through them. Then shortly before the shocks the experimenters warned the planarian worms of what was coming by a flash of a light bulb. Soon the worms “got wise” that every time the lamp flashed they could expect a nasty shock, and they started wriggling. Obviously the worms learned to associate light flashes with electrical impulses. But that is not all. The scientists made a stew of these educated planarians and fed it to other new worms. When this second different group of worms was experimented with, they learned the lesson of linking the flash of the light bulb to the shocks in half the length of time it had taken the eaten group. How is this possible? It appears the knowledge gained by the stewed worm victims was transferred to the new worms through the digestive tract instead of genes.
Evidence for Lamarckism?
Not taking into account the possibility of exaggeration/faulty experiment design/observation, this is an evidence for what it is described, the events, not for an underlying mechanism, which at this point is just a guess. "Lamarckism" is a bit broader and even if such experiments were impeccable and outstanding in its results, it may still be quite specific to these conditions rather than a more general phenomenon.
For example, perhaps those worms, as they pass through the experience, produce some chemistry that has the sole effect of improving their general ability to learn, and this product either remain intact through digestion, or to the degree that it's decomposed it's still more ready to be reconstructed. Or yet, perhaps morel likely, as the worms pass through such situation, they do not simply learn it "for themselves", but they may also release some environmental pheromone which then affects the next generation of worms. So the next generation is not inheriting the "knowledge" from the previous one, but rather some chemistry that signals that they're in an environment with some form of danger, where learning is more crucial.
It could even be something a bit more specific than a "general ability to learn" that is passed on pheromonally or otherwise, like some nearly-specific "fear of light" neurotransmitter. The odds are that this is something that cannot be generalized to something like that it's possible to become smarter/more intelligent/knowledgeable by cannibalizing brains (no caricature intended). Oddly enough, I think that somewhat similar and even more grotesque experiments where animals are induced to cannibalize brains are somewhat likely to yield results that also bring some resemblance to lamarckism -- things that could be interpreted as the animals behaving somewhat more intelligently in general -- but then it would be only because brains are specially nutritious (not only for zombies), and that could be an advantage over the previous generation. It didn't occur to me initially, but it's another possibility for the experiment with the worms, perhaps cannibalism is just specially nutritious and produces worms that are able to learn at a faster pace.
With these attempts to explain it with other things than "knowledge inherited through ingestion" I do not intend to deny that there are instances of lamarckian-like inheritance (like epigenetics, thrift genotype and other cool stuff), but rather to find more parsimonious, mundane alternatives. There's a fringe biologist who I guess would be happy to suggest that this experiment could be explained by
telepathy. I think it's more prolific to try to explain things with ordinary phenomena we know to be true rather than coming up with new, extraordinary phenomena. "Eating knowledge" may not be as far-fetched as telepathy, but I think we can come up with considerably more trivial explanations.
