As I stated at the event, B12 is actually not made by plants or animals, but rather by bacteria. When animals eat plants with soil still adhering, they may consume some B-12 containing bacteria. When they drink from water containing bacteria, they may also obtain B12. Animals eating unhygienically can thus concentrate B-12 in their bodies -- and this is the source of B-12 in animal products. Humans long ago likely obtained B-12 like this too -- prior to our chlorinating water, and attempting to thoroughly clean all our vegetables.
As we age, there are many things that can diminish our ability to obtain B-12 from food -- including, reduced stomach acid, leaky gut, and some autoimmune diseases, but taking B-12 as a sublingual (under the tongue) can bypass these absorption problems. Because a B-12 deficiency puts us at greater risk of dementia and other neurological problems and cardiovascular events, without any other obvious symptoms, this is something we want to make sure we are adequately supplied with. the Institute of Medicine actually recommends that ALL PEOPLE OVER THE AGE OF 50 supplement B-12 -- so its not just those on plant-based diets that need to pay attention to B-12.