Here Darwin seems to be talking about beneficial mutations that randomly occur. If these "slight modifications" allow an individual to become successful and pass on their genetic material, then this small difference will also be passed down. It is amazing to ponder how even the most minuscule of mutations can make a large difference in the survival of a single individual, or even species! If a single trait is so beneficial and passed down through generations then the trail will become very numerous.

I believe here he may be talking about invasive species; such species outcompete the native flora and fauna. This poses a problem in every part of the world. Often times you see a species monopolizing resources in an ecosystem.

Initially it seems odd to think that such destructive events could be beneficial to species diversity, considering so many individuals are killed off. I remember talking in my Intro to Ecology course about periodical disturbances, and how they are highly beneficial for species diversity; this is also known as the intermediate disturbance hypothesis. It's definitely interesting to hear Darwin introducing a similar idea here. He says that disturbances bring forth struggles, and from what I've learned, that isn't necessarily a bad thing.

This is definitely a statement that comes close to a universal truth. All life struggles to exist and pass on their genes to become 'successful'. This is very evident to us, scientists and the idea that the natural world is harsh and competitive, is not a very controversial statement.

Science is not without discussion. When putting forth a statement, one must be prepared to face the opinions and criticisms of others! In order to reach the truth, a statement must be supported and backed up, otherwise it will be almost immediately debunked. Even this book, which is seen as the manuscript of many biologists, has its own flaws.

I have found that humans love to place things into categories, but as a whole, we cannot agree on how to do so. It fascinates me how this is a trait that is nearly universally human. Before the proper technologies were created to show that two animals were genetically different species, the system of species categorization mainly depended on morphology, not phylogenies. It's just very interesting to consider how science used to be compared to what the scientific community knows today! However, our ideas in science today are not all that new; in only about 100 years, so much has changed and developed. It's excited to know that every day science is evolving just like the species on this Earth are!