The Evolution of Xenomorph

The original Alien film (1979) depicts the Xenomorph beginning it's life cycle as a Fleshy Egg, which, when approached, releases a crab-like Facehugger that attaches itself to a human face. Eventually, the Facehugger lets go, and the slithering Chestburster breaks through from the chest of the host. Within a few hours, the Chestburster grows into the bio-mechanical looking Xenomorph, with a translucent domed head and an extra-snapping jaw.

The sequel, Aliens (1986), features Xenomorphs with ridged heads and extra defence appendages on their arms. A Queen Alien is also depicted in this film - she's much larger, and produces a fleshy egg every few seconds.

In Alien 3 (1992), a Facehugger uses a dog (or an Ox) as a host, resulting in a quadrupedal Xenomorph. This Xeno is the first to appear noticeably less bio-mechanical, and for this film only, is lacking it's back dorsal tubes. The domed head, while less translucent, makes a reappearance.

Alien: Resurrection (1997) depicts Xenomorphs with longer tails and arms, perfect for swimming. As a result of DNA splicing, a pale Alien-Human-Clone-Hybrid is born... but not even a mother could love it.

In the first Alien vs Predator (2004) film, Xenomorphs appear similar to those from Resurrection, aside from the Alien that dons an artful Grid on it's skull. This time, Xenomorphs go face to face with Predators, culminating in the birth of a Predalien Chestburster.

In the sequel, Alien Vs Predator: Requiem (2007), Xenomorphs have ridged heads again. The Predalien Chestburster from the previous film matures, resulting in an Alien with Predator traits. It's stated in these crossover films that there has been an ongoing fight between Predators and Aliens since Egyptian times, which contradicts the following film's time-line, so, uh... let's forget about that.

The prequel, Prometheus (2012), introduces god-like beings called Engineers, who with the power of black-goo can alter DNA in mysterious ways. An android called David gets a hold of the goo and uses it to infect a scientist, who gets busy with his girlfriend and creates the premature squid-like Trilobite. The Trilobite grows, and uses an Engineer as a host, producing a smooth alien called a Deacon.

The prequel-sequel, Alien: Covenant (2017), depicts fungus-type plants being affected by the black-goo, creating tiny egg-sacks. When the sacks are disturbed, tiny spores are released and enter a human through any orifice. Once a host is infected the spiky-backed Bloodburster will burst out, first in quadrupedal form, then evolving into the bipedal standing Neomorph.

Meanwhile, the android David continues experiments with the goo, mixing it with human cells and other mystery pieces to make a Xenomorph egg-sac and Facehugger.

He finds a human host, and soon a tiny nearly fully-formed version of the Xenomorph bursts out of the human experimentee. It grows into a thin and more organic looking Xenomorph, leading many to call this a Proto-morph – but whether David was working from a blueprint or his own invention isn't known. What we do know is that Ridley Scott will surely release another Alien film that changes the life-cycle yet again, rendering this entire video completely worthless.