This is a basic principle of war, and so it is implied through this that necromorphs have some shred of human-like intelligence and/or learning capabilities. Strategies, tactics, and techniques must change as people learn to counter you. This is evidenced by multiple Slashers throughout the series sort of 'playing dead', then jumping up right in front of you, indicating that they must either already know or be learning how to attack humans more effectively. Thus, since they evolve from HUMANS, it can be inferred that at least some shred of human-like intelligence, learning capacity, or instinct is left.

Infectors kill humans, and the marker signal permeates the dead flesh, reanimating it and carrying out the will of the marker(s). Necromorphs seemingly evolve into their current states from dead humans. By the way, I recommend stasis and a ripper. They're difficult to defeat, because, obviously, they're pregnant, and thus they can eviscerate themselves and release a Swarm on you, which, on a harder difficulty in the games, can VERY easily kill you. Pregnants can move around just the same as Slashers. In the same way, yellow infected flesh is weaker, and this makes it easier to dismember, for example, brutes, who have evolved into largely shielded creatures with toughened flesh. It's sort of like when you skin your knee or get shot in the shoulder. Yellow weak spots are particularly infected flesh. It's a cross-meaning phrase, referring to the death in space that occurs throughout the series and the field of dead space around the markers, inside of which people are affected directly by the dementia-like signals which the markers emit.

'Dead Space' as a title is a play on words, I believe.

Dead space wiki convergence