One of the questions I have recently been thinking about is the degree to which veganism is science based. Many people try to dismiss veganism because they think of humans as omnivores, that there is scientific evidence we have evolved to eat me. To me this argument is fundamentally mistaken, but to begin I think its important to ask in what ways is veganism science based.
Veganism is scientific in the sense that it is based on the idea that both we and animals are evolutionary cousins, and in contrast to the religious beliefs that we are made in the image of god, humans are in fact not inherently special, we have no more inherent worth than any other animal. Any favour towards humans over animals then has to be the result not just of species, but on ethically relevant characteristics, such as our capacity to suffer, or intelligence or capacity for language. Since we give rights to humans who are far more lacking in these areas than animals, eg when we give rights to infants or people with severe mental disabilities who don't have moral agency, to be consistent with this we should also give rights to animals.
If we look at the arguments against this though, I think there are good reasons to reject the types of arguments I mentioned some meat eaters make about the implications of humans evolved adaptations to a eat meat. This starts with the idea that just because we have evolved to be able to do something this does not mean we should. Evolution merely selects for characteristics that promote for reproductive success within certain environmental contexts. For us, we evolved in tribal societies, and we evolved the capacity for tribal violence. But this does not mean violence right. We were also selected to be able to have as many children as possible, but that does not mean we should, particularly given our over population crisis. Humans have also discriminated against those with disabilities, and indeed many animals do this too. Should we discriminate because is natural too?
Evolution is just this impartial process, it does not dictate what is or is not ethical behaviour. We should not copy lions behaviour when they kill infant lions in completion for mates. And also remember that one of the things that made us so successful as a species is our ability to reason. If we look at how the context has changed since we lived in tribes, we no longer need to eat meat to survive, but rather eating meat puts the environment at risk. A vegan diet could reduce dietary GHG emissions by 70%, and reduces the risk of further deforestation using just half the crop land(as so much crops are inefficiently fed to animals). So when we think of the harm it causes to animals, the harm it causes to the environment and to our health, the reasonable and science based thing to do is to go vegan.