Around the time I turned 40, I decided to address the trifecta of concerns I had about climate change, animal rights, and my health: I went hard vegan. My doctor had been warning me to cut down on red meat, and I had also moved to a rural Japanese farming village populated by farmers growing a wide variety of veggies. They were delicious.

After a while, the euphoria wore off and the culinary limitations of vegan food, especially when traveling, became challenging. I joined the legions of ex-vegans to become a cheating pescaterian. (I wonder if this article will get me bumped off of the Wikipedia Notable Vegans list.) Five years later, the great Tohoku earthquake of 2011 hit Japan, dumping a pile of radioactive cesium-137 on top of our organic garden and shattering the wonderful organic loop we had created. I took my job at the Media Lab and moved to the US the same year, thus starting my slow but steady reentry into the community of animal eaters.

Ten years after I proclaimed myself vegan, I met Isha Datar1, the executive director of New Harvest, an organization devoted to advancing the science of what she calls “cellular agriculture.” Isha is trying to figure out how to grow any agricultural product—milk, eggs, flavors, fragrances, fish, fruit—from cells instead of animals.

Art fans will remember Oron Catts and Ionat Zurr, who in 2003 served “semi-living steak” grown from the skeletal muscles of frogs as an art project called Disembodied Cuisine. Five years later, they presented “Victimless Leather” at MoMA in New York, an installation that involved tissue growing inside a glass container in the shape of a leather jacket. Protests broke out when the museum had to disconnect the life support system because the jacket grew too big.

Isha wasn’t trying to make provocative art. We now have more challenging choices to make than simply whether to be vegan, pescatarian or carnivore, thanks to technology that has given us an explosion of meat-like products that run the ethical gambit in their production processes. She was and is trying to solve our food problem, and New Harvest is supporting and coordinating research efforts at numerous labs and research groups.

Civilians often clump the alternative meat companies and labs together in some kind of big meatless meatball, but, just like different kinds of self-driving car systems, they’re quite distinct. The Society of Automotive Engineers identifies five levels of autonomy; similarly, I see six levels of cellular agriculture. Just as “driver assist” is nice, having a car pick me up and drive me home is a completely different deal, and the latter might not evolve from the former—they might have separate development paths. I think the different branches of cellular agriculture are developing the same way.

Level 0: Just Be Vegan

Some plants are very high in protein, like beans, and they taste great just the way they are.

Level 1: Go Alternative

As a vegan, I ate a lot of processed plant-based proteins like tofu that feel fleshy and taste savory. I call these Level 1 meat alternatives. Many vegan Chinese restaurants serve “fake meat,” which is usually some sort of seitan, a wheat gluten, or textured vegetable protein like textured soy. It’s flavored and has a texture similar to some sort of animal protein, say, shrimp. This kind of protein substitute is a meat alternative—a plant-based protein that starts to mimic the experience of eating meat. Veggie burgers fall into this category.

Level 2: Get Cultured

These meat alternatives are also plant-based, but they contain some “cultured” proteins that are produced using a new scientific process. Yeast or bacteria are engineered to ferment some plant substances and output products that mimic or even replicate the proteins that make a plant-based recipe taste, smell, look or feel more like meat. Impossible Foods’ Impossible Burger falls into this category because its key ingredient is a protein called heme that is produced by genetically engineered yeast. Heme imparts “bloodiness” and “meatiness” to the plant-based burger-like base. This process relies on the industrial biotechnology and large-scale fermentation systems that are already used in the food industry. JUST’s Just Scramble “scrambled eggs” uses a proprietary process to create a plant-based protein as well, combining processes used in the pharmaceutical business, food R&D labs, and chemistry labs.

Level 3: Post-Vegan

Foods at this level are made of plant-based ingredients combined with cultured animal cells (as opposed to the products of bacterial fermentation). In other words, cells as ingredient, plants for mass. The animal cells provide the color, smell, or taste of meat, but not the substance. This relies on industrial biotech and large-scale cell-culture production methods already used in the pharma industry. Level 3 is the first level that requires going beyond the tools and the science already available in the food business.

Level 4: That's a Spicy Meatball

Level 4 alternatives are pure cultured animal cells like the products Memphis Meats and others are working on. The texture and shape of a real steak comes from the muscle cells that grow around the bones and otherwise self-organize into bundles of tissue. At Level 4, we aren’t really dealing with sophisticated texture yet, so we’re pretty much turning the cells we’ve grown into meatballs. (The difference between this and Level 3 is that most of the mass of the food here is animal cells, whereas Level 3 is mostly plant-based with cells sprinkled on top.)