It can be assumed that as the species procreates (whether with humans or other hybrids) it evolves and improves with each generation. The movies reveal numerous generations of the female species, each varying in appearance and abilities. The female of the Species is the most prominent as well as decidedly the most dangerous. The purest of the aliens seen was Sara, due to the fact that she was the daughter of the late Patrick Ross and the Sil duplicate Eve. A similar creature is born from a female human astronaut infected by the alien DNA. After a little over two minutes of life, it was killed by immolation. The alien grew so fast that it would double in size in a matter of seconds.
However, a pure form as been seen, taking the appearance of a blobby, tentacled monster with a long mouth-like appendage that lashed out at whatever was nearby. Most of the members of the Species seen are actually mutations from humans. The DNA structure of the species is extremely versatile and is constantly evolving and mutating which in turn gives them incredible regeneration abilities that render them immortal in the fact that they can only be killed by having every last bit of their body destroyed. The species also has the ability to shape shift between human and alien forms, as well as a limited ability to morph their alien forms for the purpose of adaptation to given situations. The mouth has two mandibles and they possess hair-like tentacles. Patrick Ross seems to have two types of alien forms: bipedal and quadrupedal. Both genders of the Species have chitinous, skeletal bodies which are semi-transparent. The Species basically appear to be bipedal (humanoid) forms with the exception of Patrick Ross, a male of the species. Sil was later succeeded by several more generations of the species.
Three living organisms were created, two of which were put into frozen stasis in liquid nitrogen, while the third (a female) was allowed to grow under the code-name "Sil". As the first message was seen as friendly contact, scientists went ahead and performed the fusion.
The first message contained a more efficient use of methane, while the second contained a DNA sequence along with directions on how to mix it with human DNA. Mankind's first interaction with this particular species occurred in 1994 when the SETI (Search for Extra-Terrestrial Life) project received a pair of messages from outer space. It is also stipulated that they were a "cancerous" race that visited Mars millions of years ago when its surface was similar to that of Earth, and annihilated all life on its surface before leaving remnants of their DNA in its soil. Professor Herman Cromwell claims that the original species originated in the Large Magellanic Cloud (called the Magellanic Galaxy), the only other place in the universe where carbon-based life had apparently been discovered.