Nick Kitchener wrote:Interesting topic, and something that has crossed my mind a few times.
On the surface, these laws do seem to contradict what is happening in the natural world. In situations like this, the best practice is to look at the interpretation of the law and re assess it. The number of rules (interpretations of scripture by man) far outweigh the actual rules God laid down, and many of these were unfortunately made with alternative motives in mind.
The context of a prohibition on mixing seed I believe comes from Genesis 6. When the watchers descended on Mt. Hermon, they imparted certain knowledge to mankind, one of which is referred to as "the cutting of roots". This is generally interpreted as pharmakea, as it is mentioned in the same sentence as enchantments in the book of Enoch. However, a literal interpretation of this applies equally well to grafting.
The whole action by the watchers was an attempt to draw mankind away from God, and corrupt the human genome. With a corrupted genome, it would be impossible for Eve's seed to crush the head of the serpent as prophesied by God in the garden. If the prophesy could not come to pass then the word of God is fallible. As Genesis 6 points out, they succeeded in corrupting the seed, and it took the flood to cleanse not only the human genome but the genomes of the animals too. Following the flood, there was a huge effort to wipe out the nephilim tribes that contained remnants of this genetic corruption in their population and that of their livestock.
With this in mind, I can see why the Levitical laws regarding "mixing seed of different types" was enacted, and I strongly believe that this doesn't apply to polycultures because genetic material is not altered or mixed. You aren't "mixing seed", but rather cohabiting plants IMHO. Mixing seed would involve artificial genetic modification, hybridisation that doesn't occur in nature, and grafting.
It wasn't until very recently that our technology has enabled true "mixing of seed", so it's understandable that the religious rules that formed around these scriptures developed the way they did.
Hopefully this sheds a new light on the subject and helps in some way.