Yea, the kernel is basically Unix and FreeBSD put together and called Darwin.
Now for a small rant about Apple.
Then they lock it in to specific apple hardware. On top of this "Darwin", they add some other technologies that just take even more resources, such as the unneccisarily heavy GUI, and some other software, a few very buggy, such as Safari, rename it as OS X and sell it for $129 as the world's most advanced operating system. Very little of it is truely Apple written code, that's why many computer veterans call OS 9 the death of the Macintosh. Every little feature of it comes from something else, such as the GUI based off of adobe's PDF format. Dashboard being a copy of confabulator. MSN and Google had desktop search before Apple had Spotlight. Hell, the hypocracy. They used to rely on Internet Explorer, and now that they have Safari, a browser which isn't that good to begin with, they down IE. They rely on Microsoft to make them an Office Suite. They openly say this in a PC bashing ad. Some mac users even say Office is better on the mac, which is complete bull, as first, it's not universal yet, second, the full office has some 20 apps, 4 of them are available on the mac platform. Third, so many of the features are cut from the mac version of the app which are included in the Windows versions. Ah, Apple and it's fanboys annoy me so much.