Discussion on debate between Esquilax and His_Majesty.

[Mystical]

You have it exactly except that 100 or more generations would be better.

There's another way too. Sometimes a population gets split by a geographical barrier-- a landslide separates one population/species into two. Both sides continue breeding, and for several generations if you removed the barrier there would still be one species, but there would come a time when they could no longer breed even if you lifted the barrier.

The barrier can be social too. Change one bird's mating song and he and his off-spring might become a new breeding population.

Thank you for the taking the time to critique this Jenny. I have more to say, but I don't want to derail this thread, so, for now, just know I appreciate the help.

Considering I had a creationist upbringing/education, my introduction to evolution has been like that of a child. I'd say what helped me to understand this subject was the concept of ring species (finches on island A can breed with B and B with C, but A and C cannot), and looking with my own eyes at the evolution of Skinks in Australia transitioning from egg birth to live birth (they can currently do both) in response to its' change in environment from temperate climate to mountain climate. I do believe Esquilax linked to the skinks in his opening statement. Lastly, transitional fossils like this one:

This ancient creature was undoubtedly a fish, possessing gills, scales and fins. However, it also had features seen in modern tetrapods — four-limbed creatures like amphibians, reptiles, birds and mammals — such as a mobile neck and robust ribcage.

This extinct fish had large forefins and shoulders, elbows and partial wrists, enabling it to support itself on ground. This makes it the best-known example of an intermediate between finned animals and limbed animals marking the evolutionary leap from water to land for vertebrates, or creatures with backbones.
The scientists discovered the rear portion of Tiktaalik, which contained hips as well as partial pelvic fin material. This made a direct comparison of the front and rear appendages of the animal possible. [10 Useless Limbs (and Other Vestigial Organs)]

Unexpectedly, the researchers found Tiktaalik had big, strong pelvic bones with similarities to early tetrapods.

"I was expecting to find a diminutive hind fin and pelvis,"study lead author Neil Shubin, a paleontologist at the University of Chicago,told LiveScience. "Seeing the whopping pelvis set me back a bit — I looked at it again and again, because I was quite surprised."

The pelvic girdle of Tiktaalik was nearly identical in size to its shoulder girdle, a tetrapodlike feature that would help support strong rear appendages. It also possessed a deep ball-and-socket hip joint that connected to a highly mobile femur — analogous to a tetrapod thighbone — that could extend beneath the body.

It remains uncertain how the hind appendages of the earliest limbed vertebrates were used. "Were they used to walk, swim or both?" Shubin asked.

The scientists detailed their findings online today (Jan. 13) in the journal Proceedings of the National Academy of Sciences.

http://m.livescience.com/42525-early-fis...-legs.html

There's lots of examples of species alive who are obvious in transition.

Phylogenic taxonomy (DNA) has also undoubtedly connected land mammals to ocean mammals. The transitional fossils are impressive.
http://evolution.berkeley.edu/evolibrary...vograms_03