Further to slcrazy,
All the life forms we see on earth have the morphology, anatomy, chemistry etc specifically determined to thrive under earth's atmospheric conditions.Science we worship a lot keeps changing every moment.
For example most of the living organisms consume oxygen for their survival, in order to exploit that each life form has developed some sort of "lung" system. But if there wasnt oxygen on earth the physiology of the beings and the way they break down food in their cells through respiration would have been completely different.
Scientists today think that you should necessarily have a earth-like atmosphere for life to exist, but who knows, life on other planets may be using some other constituent (probably abundant) for the survival, for example in deep sea thermal vents or black smokers, temperature rises upto 400 degrees Celsius, however, still in that environment where toxic gases such as hydrogen sulfide and sulfur dioxide dominating, bacteria such as Archae grow.Tube worms populate. In this habitat the intense water pressure can crush u down, however life exist..so few decades back if u told these things in public, they would call u were a fool..science is something like that.
Of course our genomes can have similarities, and Darwin developed his theory upon phenotypic characteristics of the animals he saw in Galapagos.We all have the basic skeleton for our body to stand upright against the earth's gravity.So we all living under same earth conditions so we necessarily have similarities, this doesnt mean we all are coming from the same distant ancestor.
Phynotypic or morphological caharacteristics are not reliable today, therefore they have gone for genetic code level.But the same principle is applicable to here.
Science talks about only what u can prove, only things the modern equipments can measure/track down..so we dont know when we will stop, when will be able to go for the maximum state...hm am sleepy..