Neuroscientist, Stanford University, Author, A Primate's Memoir

Well, my biggest change of mind came only a few years ago. It was the outcome of a painful journey of self-discovery, where my wife and children stood behind me and made it possible, where I struggled with all my soul, and all my heart and all my might. But that had to do with my realizing that Broadway musicals are not cultural travesties, so it's a little tangential here. Instead I'll focus on science.
I'm both a neurobiologist and a primatologist, and I've changed my mind about plenty of things in both of these realms. But the most fundamental change is one that transcends either of those disciplines — this was my realizing that the most interesting and important things in the life sciences are not going to be explained with sheer reductionism. 

A specific change of mind concerned my work as a neurobiologist. 

This came about 15 years ago, and it challenged neurobiological dogma that I had learned in pre-school, namely that the adult brain does not make new neurons. This fact had always been a point of weird pride in the field — hey, the brain is SO fancy and amazing that its elements are irreplaceable, not like some dumb-ass simplistic liver that's so totally fungible that it can regrow itself. And what this fact also reinforced, in passing, was the dogma that the brain is set in stone very early on in life, that there's all sorts of things that can't be changed once a certain time-window had passed. 

Starting in the 1960's, a handful of crackpot scientists had been crying in the wilderness about how the adult brain does make new neurons. At best, their unorthodoxy was ignored; at worst, they were punished for it. But by the 1990's, it had become clear that they were right. And "adult neurogenesis" has turned into the hottest subject in the field — the brain makes new neurons, makes them under interesting circumstances, fails to under other interesting ones. 

The new neurons function, are integrated into circuits, might even be required for certain types of learning. And the phenomenon is a cornerstone of a new type of neurobiological chauvinism — part of the very complexity and magnificence of the brain is how it can rebuild itself in response to the world around it. 

So, I'll admit, this business about new neurons was a tough one for me to assimilate. I wasn't invested enough in the whole business to be in the crowd indignantly saying, No, this can't be true. Instead, I just tried to ignore it. "New neurons", christ, I can't deal with this, turn the page. And after an embarrassingly long time, enough evidence had piled up that I had to change my mind and decide that I needed to deal with it after all. And it's now one of the things that my lab studies.

The other change concerned my life as a primatologist, where I have been studying male baboons in East Africa. This also came in the early 90's. I study what social behavior has to do with health, and my shtick always was that if you want to know which baboons are going to be festering with stress-related disease, look at the low-ranking ones.  Rank is physiological destiny, and if you have a choice in the matter, you want to win some critical fights and become a dominant male, because you'll be healthier. And my change of mind involved two pieces.

The first was realizing, from my own data and that of others, that being dominant has far less to do with winning fights than with social intelligence and impulse control. The other was realizing that while health has something to do with social rank, it has far more to do with personality and social affiliation — if you want to be a healthy baboon, don't be a socially isolated one. This particular shift has something to do with the accretion of new facts, new statistical techniques for analyzing data, blah blah. Probably most importantly, it has to do with the fact that I was once a hermetic 22-year old studying baboons and now, 30 years later, I've changed my mind about a lot of things in my own life.