Reddit mentions of Animal Madness: How Anxious Dogs, Compulsive Parrots, and Elephants in Recovery Help Us Understand Ourselves

You may be surprised to hear this, but MS is not a hereditary disorder. Your family may be like mine, wherein autoimmune disorders, in general, run in the family, but even in my family, even that is questionable. What is significantly more likely to be happening in my family (and maybe yours) has to do with epigenetics. Go down that rabbit hole, it's fascinating. The MS center I go to has been offering my family to graduate medical researchers to study if/how epigenetics has played a role in the autoimmune diseases we all seem to have (especially because we have all spent most of our lives geographically and socio-culturally close to each other.

Mental illness in early hominids or even early H. sapiens is absolutely fascinating to me, though any information we find can only be inferred from things like endocasts, other neuro-structural elements in the fossil record, and from the behavior of mammals and primates, apes in particular. It can also be inferred from mental illnesses that are found to be caused 100% by biology. This book gives a thorough overview of mental illness in animals and the research studies she cites could be looked at in the quest for our own maladies. Other things we look at are mental health disorders that we know to be found in all current human cultures, with evidence in some past cultures. Schizophrenia is a good example.

We have to be careful of culture-specific disorders and disorders that are not considered disorders in other cultures. I'll give you some reading for thins:

This book is not directly about a mental health disorder, but it shows why medical and psychological anthropology is vital to living in a melting pot like the US. I have stories from my mentor, a forensic and bioanthropologist, that are similar.

This book is an absolutely fascinating book that talks about how the mental health framework has been exported all over the world. Again, it's not directly able to talk about mental illness in early hominid species, but I think it important to understand while we are on that search.

Hopefully those books will help you with your questions, at least until more fossil evidence is found, since endocasts are not just popping up everyday!