Ben Fry:

We often think of scientific ideas, such as Darwin's theory of evolution, as fixed notions that are accepted as finished. In fact, Darwin's On the Origin of Species evolved over the course of several editions he wrote, edited, and updated during his lifetime.

Using the six editions as a guide, we can see the unfolding and clarification of Darwin's ideas as he sought to further develop his theory during his lifetime.

See also, the Darwin Correspondence Project:

The main feature of the site is an Online Database with the complete, searchable, texts of around 5,000 letters written by and to Charles Darwin up to the year 1865. This includes all the surviving letters from the Beagle voyage - online for the first time - and all the letters from the years around the publication of Origin of species in 1859.

Lee Alan Dugatkin:

It began as a small difficulty with honeybees. At first glance, it did not seem like the sort of complication that could sink a theory that many have characterized as the most important one that biology has ever produced. But it turned into a problem that troubled biologists, fascinated naturalists, engaged popular writers and the general public, and even worked its way into political discourse for the next 145 years.

From The World in 2009:

Someone once accused Craig Venter of playing God.

His reply was, "We're not playing."