You may all probably be aware that Android is a Linux based ‘distro’ though it doesn’t include or use any X-window elements. Technically it’s a huge stack of APIs, middleware while Apps run in Java-like VM called the Dalvik VM.
Android is not using a proper Linux Kernel, the current ‘thing’ used in Android is a fork of the main Linux Kernel with ARM patches and vendor specific modifications, this has long fragmented the Android kernel until progress was made to merge the Android kernel with the mainline Linux Kernel.
Android initially had a hard time with the Linux kernel and its developers including Linus Torvalds who were frustrated about Google including and submitting their own patches to the Linux mailing list, years later some of the patches were accepted(eg: wakelocks) and incorporated in the mainline linux kernel (version 3.3 onwards and later 3.5). The merge is still incomplete but Google has now opened an public repository with an experimental build of Kernel 3.8 with optimized ARM patches.
Using the very latest mainline Linux Kernel allows kernel updates to be delivered more efficiently and quicker than ever. Android currently relies a forked Kernel 3.4.0-3.6.x which is used in popular devices like the Nexus 4 and Xperia Z. Other devices like the Galaxy SIII still use Kernel 3.0.31.
via Google Source