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So, Craig, as you requested, here are my thoughts, as a biologist, on the biology of the Universe. Please note that these are my thoughts are quite obviously not related to any direct observation leading to hypothesis etc, merely my own personal thoughts. Some is based on observation etc.
Reviewing what I have written below, I guess I need to point out that when I refer to "life", I am mostly referring to "animal" like life as compared to plants, algae etc.
The Earth is in the "so called" Goldilocks zone. Goldilocks for life on Earth, but not Goldilocks for life on, say Eridanus. One would imagine that life on Eridanus, if it did exist, may well have trouble in surviving on Earth. Or, maybe not. There may well be life forms in the Universe that could not possibly survive on Earth or survive in a different planet in the same zone as Earth.
I think (would like to believe, but being a very non-religious type, I steer away from the concept of evidence free belief) that life is, more likely than not, common throughout the Universe. But not to the extent of occurring on, say, even 0.001% of planets.
I think that if there is a planet on which conditions are suitable, life will, at some point in that planet's life, arise and evolve. This thought is based, to an extent, on Paul Davies' suggestion that it seems possible that life may have arisen and become extinct a number of times during the "early period of bombardment". If life arose on Earth on more than one occasion, it would therefore appear that life will form if conditions are suitable.
I think that life throughout the Universe (given the existence the same set if Laws of Physics throughout the Universe) is likely to have certain similarities. For example, what is the prime aim of a living organism? Answer; to reproduce more organisms similar to itself. Therefore a reproductive system is required. Asexual reproduction is inherently a poor form of reproduction due to the lack of mixing of genetic information. Life on Earth consisted of simple, single celled organisms with very little variety for a very long time. The lack of genetic variation leads to a reduced ability to adapt to changes in the local environment, and hence reduced survival ability. It was only once sexual reproduction with sharing of genetic information appeared in life on Earth that life was able to firstly improved its survivability and also to develop into far more complex, multicellular life forms. Therefore, while I think that the majority of life in the Universe is likely to be quite simple, I believe that any complex, multicellular and, by extension, any "intelligent" life is likely to use some form of sexual reproduction associated with some sort of genetic information sharing.
Similarly, the complex life form needs a mode of getting from A to B. Getting from A to B therefore requires some sort of rigid body structure such as a bony (on Earth at least) internal skeleton or a chitin (on Earth at least) external skeleton. Then a means of causing the rigid support structure to move (called muscles on Earth) is required. Using muscles requires energy, so a means of capturing, ingesting and metabolising food into useable energy is also required. I'm not saying that these systems must be exactly as they are on Earth, but the basic set of plans requires what I have described above in order to work.
All up, I would not be surprised at all to see that a complex, multicellular life form in another part of the Universe has numerous basic similarities to life on Earth.
Of course, I could be very, very wrong. In fact, if someone was to discover life elsewhere that did prove me very, very wrong, I would be ecstatic.
Regarding Earth; there are some important things that make Earth a suitable place in which life might arise.
The 23 and a bit degree tilt of the Earth's axis is very important for life on Earth as it leads to us having seasons. The resulting change in weather patterns though the course of a year and also the continually changing day lengths in turn leads to the pituitary glands of pretty much every mammal, and quite a few non-mammals, to produce the hormones essential for effective reproduction. If the Earth had zero axial tilt, would reproduction be possible? I imagine, based on the "life will find a way" theory, that, yes, it would. But would reproduction be as efficient as it is here on Earth?
Having the Moon be the mass that it is, the distance from Earth that it is and having the 29 day lunar cycle that it does leads to tides here on here. Tides lead to the existence of an intertidal zone which may very well have played a major part in complex life being able to leave the oceans and colonise the land.
And of course, orbiting the Sun is far better for us than orbiting many other kinds of stars.
Anyway, Craig, you asked for my biologist's view. Here it is. And again, I am very happy to be proven wrong in any of the above thoughts as said proof will mean we have discovered life elsewhere. I just hope that happens in my life time.
Stuart
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