I think a lot of it boils down to what the evolutionary pressures (defn: [1]) on another planet might look like. If we discover life on another planet, it wouldn't surprise me if some of the organisms we find resemble organisms in some branches of the "tree of life" on Earth, but I think it would be unlikely that there would be so many similar evolutionary pressures that we would see something particularly similar to ourselves.

For example, life has been around for at least 3.5 billion years on this planet[2]. At this point in time, there is no evidence that any other species on this planet has ever had a technological civilization that would be of particular interest to us in the way that is often envisioned for hypothetical alien visitors. This isn't for lack of different species[3] or for insufficient genomic complexity[4] in other species. In other words, there's nothing about the human genome that represents a "pinnacle" of evolution, as much as we tend to hold ourselves in pretty high regard among other species.

As another example, let's walk the tree of life (http://tolweb.org/Life_on_Earth/1) to get a ballpark idea of how many different features we run into before encountering homo sapiens:

1. Eukaryotes (organisms with nucleated cells) http://tolweb.org/Eukaryotes/3

2. Animals (multicellular, heterotrophic, lack rigid cell walls, motile, most have embryonic blastula stage) http://tolweb.org/Animals/2374

3. Bilateria (bilateral symmetry with three germ layers) http://tolweb.org/Bilateria/2459

4. Deuterostomes (blastopore becomes the anus during development) http://tolweb.org/Deuterostomia/2466

5. Chordates (animals possessing a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail for at least some period of their life cycles) http://tolweb.org/Chordata/2499

6. Craniata (have hard bone or cartilage skull) http://tolweb.org/Craniata/14826

7. Vertebrata (have backbones) http://tolweb.org/Vertebrata/14829

8. Gnathostomata (have jaws) http://tolweb.org/Gnathostomata/14843

9. Sarcopterygii (lobe-finned fish & terrestrial vertebrates. I am not an evolutionary biologist but it seems like this roughly corresponds to the evolution of limb-like structures) http://tolweb.org/Sarcopterygii/14922

10. Tetrapods (more properly terrestrial vertebrates, but to simplify things a little. Basically 4 limbs) http://tolweb.org/Terrestrial_Vertebrates/14952

11. Amniota (have eggs equipped with an amnios) http://tolweb.org/Amniota/14990

12. Synapsids (have a temporal fenestra) http://tolweb.org/Synapsida/14845

13. Therapsids (have particular skeletal and muscular structures) http://tolweb.org/Therapsida/14973

14. Mammals (hair, three middle ear bones, mammary glands, and a neocortex) http://tolweb.org/Mammalia/15040

15. Eutheria (have particular skeletal structures--not strictly placental) http://tolweb.org/Eutheria/15997

16. Primates http://tolweb.org/Primates/15963

There are several more branches before getting to homo sapiens.

I think the big remaining questions are:

1. What features of an organism are necessary for that species to develop a technological spacefaring civilization?

2. Are evolutionary pressures that support the development of those features likely to appear eventually on life-bearing planets similar to Earth? (I think this assumes that abiogenesis on other planets would be likely to produce simple cellular structures with similar capacities for evolution.)

3. Are we in a simulation created by another species in a "real" universe to answer similar questions? :)

I'd guess...

1. Limbs (and the supporting underlying physical structures) with significant capacity for manipulating objects, terrestrial-dwelling (as opposed to living in the sea), a advanced neocortex, and way too much free time, along with very difficult-to-impress mating prospects.

2. Depends on how similar to earth (a waterworld would be unlikely to have any species developing advanced technology, I think... maybe I'm not being imaginative enough). Also depends on how many of the evolutionary pressures that got us to this point were more or less inevitable as opposed to random. It seems that even if it's relatively likely that a species similar to humans will evolve on planets similar to Earth, there are still numerous additional hurdles in the development of different kinds of societies that could make or break the whole spacefaring thing. Even now, humans are not a spacefaring species, and the odds that we nuke ourselves out of existence or create a genetically engineered superbug that wipes us all out are relatively high considering we have absolutely no backup plan as a species for either of those events (or any number of other catastrophic global events). So maybe my answer to #1 is insufficient because we're not really a spacefaring species yet.

3. If they have that kind of computing power, I would've expected something more interesting. Maybe they're trying to predict the odds of encountering other species like themselves during a galactic collision? :) https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_co...

[1]: https://en.wikipedia.org/wiki/Evolutionary_pressure

[2]: https://en.wikipedia.org/wiki/Abiogenesis

[3]: There are approximately 10 million species currently alive on Earth (more or less a minimum bound, the actual number may be much higher). http://www.nytimes.com/2011/08/30/science/30species.html?_r=...
At least 99% of all species to have ever lived are extinct now: http://www.physicalgeography.net/fundamentals/9h.html

[4]: http://en.wikipedia.org/wiki/Genome#Genome_size