There have been many articles and books written about Linux; where it came from, how it got where it is today, the whole "Who's Who" list... A good google search or some time spent on sites such as the Linux Documentation Project and Linux Journal will tell you more than you could ever wish to know. But there is little information on the history and evolution of Linux distributions. As of this writing, there are 303 Linux distributions according to DistroWatch. It would seem that everyone and his dog has a distribution available. This hasn't always been the case.
Back in late 1991, when Linux first hit the 'Net, there were no distributions per se. The closest thing was HJ Lu's Boot/Root floppies. They were 5.25" diskettes that could be used to get a Linux system running. You booted from the boot disk and then, when prompted, inserted the root disk. After a while you got a command prompt. Back in those days if you wanted to boot from your hard drive you had to use a hex editor on the Master Boot Record of your HD. Something that was definitely not for the faint of heart. I remember when Erik Ratcliffe wrote the first instructions (this was long before HOWTO files) on how to do just that. It wasn't until later that anything you could call a real distribution appeared.
The first such thing was from the Manchester Computing Centre. Known as MCC Interim Linux, it was a collection of diskettes that, once installed on your system, let you have a basic UNIX environment. It was console only, no X. Shortly after that there was a release out of Texas A&M University called TAMU 1.0A. This was the first one that let you run X, though the method they used to configure it occasionally allowed the magic smoke to escape from your monitor. Both of these were developed for their universities' in-house use. They were also released to the world for anyone to use.
The first commercial, in the sense that it was developed for public consumption rather than in-house use only, Linux distribution was Yggdrasil. This also had the distinction of being the first "Live" Linux CD. You could boot from a diskette and run everything off the CD. This was back in days of 1x and 2x CD-ROM drive speeds so it wasn't exactly setting the world on fire. You could start X then literally go get a cup of coffee before it finished coming up. Yggdrasil had some nice features dealing with configuration, though, especially for the time.
On the heels of that came the first widely recognized and used Linux distribution, SLS Linux. It was put together by Soft Landing Systems, hence the name, and came in a handful of files that you would unzip and copy to floppy disks. This was Linux's first big breakthrough. SLS dominated the market until the developers made a decision to change the executable format (if you remember the a.out to ELF conversion you'll remember this). This was not well received by the user base. Just around the time this happened Patrick Volkerding had taken SLS and adapted, modified, tweaked and cleaned it up making it a different thing all together. He called it Slackware. With the unpopular direction SLS had taken, Slackware quickly replaced it and became the dominant distribution used by nearly everyone. In fact it's still in use today.
Now, all of this took place in the span of about 3 years. In those days the speed with which changes happened was unbelievable. By the time '94/'95 came around you started seeing more distributions popping up. Familiar names like Red Hat, Debian, Caldera, TurboLinux, SuSE and Mandrake were becoming popular. There were also a few other distributions that came and went between '91 and '95. However, they had little impact on the overall direction that Linux distributions would take. If you search the 'Net you can still find references to these early distributions, and possibly even some archives of the releases themselves. If you have some free time you should look at these old releases. Not only will you be able to see how far Linux has come, you'll also see what life was like in the early days of Linux distributions.