Variations on a theme

Can anyone explain to me why the fruits on one single plant can be so very different?

This is a photo of some fruits on a "Russian Black" tomato plant:

So is this. On the same plant, I emphasise.

And what about this for a wierdo?

As you can see, it is not just one fruit that is so deeply ribbed; it is the whole truss.

In the catalogue from which I bought the seeds, the fruits are shown as smooth, like those in the first picture above. Presumably therefore something has gone wrong. Are the wierdly-shaped fruits perhaps a throwback to one of the plant's ancestors? Maybe this is a hybrid variety artificially bred from different types? Or could unusual weather conditions be the cause? This year we had a very cold Spring, but now we have had a long spell of exceptionally hot dry weather.

But variations in weather have evidently not affected the regularity of these "Orkado" tomatoes:

Or these "Sungold" ones:

And these "Zapotec Pleated" ones are supposed to be deeply ribbed:

I'm thinking now about how the "Russian Black" toms will look when they are ripe. Like something from a science fiction film, I expect!

Finally for today, here is a pic of my first ripe tomatoes of the year - two of the little "Maskotka" ones. The plants are heavily laden with fruit now, so hopefully there will be many more of these to harvest in the near future.