A masterful, epic overview of the intellectual history of evolutionary biology as it pertains to the concept of "P/progress", as the author likes to put it. "Progress" with a capital "P" refers to cultural progress, while a lower case "p" refers to biological progress (i.e., evolution manifesting progress in some form: complexity, biodiversity, adaptability, etc.) As such, it is also a superb biographical history from Lamarck's day to the mid-nineties.