User blog comment:Admiral Sugar/Thoughts on Devil Fruits/@comment-24529455-20140217015138

What people don't understand is that the "D" initial is taken from three brothers: Dogma, Darius, and Drake. Dogma had the power to turn into any animal he wanted, Darius could manipulate his and others' bodies in unnatural ways, and Drake could turn into any existing element. These brothers were known as the "Three Devils" and left behind a legacy greater than any before them. However, despite their power, they were not immortal, and were killed after facing the might of the World Government's Ancient Weapons, in the final battle of the Void Century. The battle took place across the entire world, shattering the land and leaving behind only small islands. As they fought, the brothers' blood spattered the Earth. The combination of the brothers' blood and the soil caused trees to grow bearing a fruit-shaped item. However, one fruit did not carry the entire power of the brother; only one part of each brother's power was bestowed on each fruit. For example, One drop of Drake's blood brought forth the Mera Mera no Mi, while another drop brought forth the Magu Magu no Mi. Thus, the classification for each fruit is based on what brother's blood it came from.

Vegapunk knows all this, and while experimenting he found something unusual. Adding a significant amount of water to the genome of the devil fruit caused the power to cancel out, as in a virus. The devil fruits taste horrible because they came from blood, of course. Finally, any attempt to gain more than a fraction of the brothers' power (e.g. eating two or more devil fruits) will fail, as most people's bodies are unable to shoulder the immense burden. Blackbeard, I believe, was blessed with a body similar to the brothers