First, it was really fun to hear Darwin refer to his contemporary scientists. Alfred Russell Wallace, Charles Lyell, Jean-Baptiste Lamark, James Hutton, Carl Linnaeus, and Frederic Cuvier were all mentioned as either contemporaries or relatively recent scientists. Many of these guys who's ideas are reviewed in most modern high school and college science classes were known by and sometimes pen-pals with Darwin. It kind of made them all seem a bit more real.
Second, this is a small thing, but I was surprised at how ambiguous the term "species" was. He talked frequently about how a species is supposedly a group animals that won't interbreed with an outcome of fertile offspring with another species. This is a definition we use today in introductory science classes. He then went on to say, that that definition is bogus. Fertile and sterile offspring happen within species sometimes (look at bees), and not between supposed species in other cases. He spent a long time explaining how the "definition" is wrong but we don't have a better one. The inaccuracy of the species definition is taught today in upper division science classes.... So if Darwin, back in the early 1900s, was talking about how the definition of species is bogus and we still agree... why do we ever even use that definition?
Third, science was done differently back then. It was fascinating to hear of some of the "experiments" that Darwin or his contemporaries enacted. They were mostly more anecdotal and qualitative rather then quantitative facts. But with that being said you could tell that in experiments like these is where modern science has its roots. Also I was struck with the diversity of Darwin's knowledge. He is one smart dude. He talked in an informed way and often with first hand knowledge about geology, paleontology, biology, botany, entomology, husbandry etc. His examples to fortify his theory of natural selection ranged from ancient gastropods to parasitic ants to mule, pigeon, and plant husbandry to geologic strata. One of the more random but fascinating experiments was on seed germination, when the seeds are collected from dirt that was either attached to logs floating in the ocean, or mud caked onto duck's feet. The range of knowledge was phenomenal... Nowadays, scientists, by necessity a lot more specialized, but it was really cool to hear him talk about it.
Finally, how Darwin approached religion in the actual text was fascinating, especially because of all the hype about "Darwinism" and religion. He was always super respectful of religion, and when he did talk about it, mostly in the final chapters of his book, he focused on how his theory of natural selection really should not be conflicted with religion. I felt like he tried really hard to separate them. However he did make some cool comparisons. He talked about how gravity, perhaps the greatest natural law, is amazing and if God into that into place, why could he not have started natural selection. And if God started the process of natural selection and allows it to continue, and if we look at everything that has happened because of that, why is that not equally awesome, or even more awe inspiring then immutable creation? I agree! Another point he brought up, was that Galileo was persecuted severely be the Catholic Church for proposing a sun-centered universe, but in Darwin's day believing in heliocentrism and religion, even Catholicism, isn't a big deal. Darwin proposed that even if the doctrines or cultures of organized religions at his time sometimes seemed at odds with the idea of natural selection that someday they could be reconciled.
I'm not sure I'm going to make Origin of Species one of those books I reread every couple of years, but I definitely am glad I listened to it once. It gave me a better understanding of the history of science, as well as the implications of the theory of natural selection. It also made me respect Darwin and his struggle with organized religion, and it made me more grateful for the reconciliation I understand between religion and science, particularly evolution.
