Natural Selection is a modification for the
video game Half-Life.
Its concept is a mixture of the first-person
shooter and real-time strategy game genres.
The game was created by Charlie "Flayra" Cleveland,
who later founded the company Unknown Worlds
Entertainment.
Natural Selection v1 was first publicly released
on Halloween 2002, and is now at version 3.2.
Natural Selection 2 was released in late 2012.
The game features two teams: Kharaa (alien
species) and Frontiersmen (human space marines).
The visible Kharaa "units" are actually simply
the spawn of the real Kharaa (aliens) which
are microscopic life-forms according to the
storyline.
The game was, in 2008, one of the ten most
played Half-Life modifications in terms of
players, according to GameSpy.
On January 22, 2014 Unknown Worlds released
the source code for download on a GitHub repository
under GPLv3.
== Gameplay ==
Natural Selection is a hybrid FPS/RTS that
pits Marines against Aliens ("the Kharaa"),
played primarily in the first-person perspective,
within the confines of large atmospheric maps
of spaceships or space stations, which have
been invaded by the Kharaa.
There are two game modes in Natural Selection:
Classic and Combat.
Classic is the original Natural Selection
game, mixing FPS and RTS elements.
Natural Selection was one of the first multiplayer,
first-person shooters to incorporate a "Commander",
whose view of the battlefield was essentially
2-D, from a strictly top-down perspective.
One member of the marine team must enter the
"command chair" to lead the team, and thus
become the "Commander".
From here, he can purchase upgrades, issue
movement orders and drop supplies - all from
an overhead perspective, as in many RTS games.
The commander can also place buildings, although
these are inactive until built by players
in the field.
The role is somewhat similar to the Intelligence
Officer of Global Operations in that it is
provided an overview of the map, though the
ability to place objects and control is much
more extensive.
A similar 'commander' mode can also be seen
in Starsiege:Tribes (1998), Battlefield 2
and the Empires modification for Half-Life
2.
This mechanic is also the centerpiece of the
Savage and Savage 2 games or Rainbow Six.
The alien team has no defined leader, and
so it must communicate and co-operate to ensure
different roles are fulfilled as needed.
There is only one "Builder Class", the Gorge
which can be used to build a multitude of
structures.
Gorges can choose to build three different
"upgrade" chambers: Movement, Defense, and
Sensory, each providing three distinct abilities
each alien can get.
Gorges can also build Offense chambers which
damage Marines from a distance, and resource
towers.
When a resource nozzle is capped, the resources
gained are split evenly among all aliens.
Each alien can choose how he wants to use
his own personal reserve of resource points
: building structures (as a gorge), or gestating
into higher lifeforms.
On death of the lifeform or structure, there
is no refund on the resource points spent.
Kharaa "Hive Sight" reveals teammates through
the walls and structures of the map, this
was originally their answer to the commander
with his top-down overview of the game.
However, in later versions both teams have
gained substantial advantage from the addition
of a map hotkey.
This overlays the whole level, showing teammates
and friendly structures; plus enemies and
structures currently in view of comrades,
and areas under attack.
The aliens start with one active hive, randomly
chosen from the 3 hive spots of the map.
Active hives heal damaged aliens and respawn
dead players.
Marines initially spawn in a set location
on the map, and after that spawn from Infantry
Portals, which can be built in a set radius
of the Command Chair.
Healing and ammunition can be dropped by the
commander in 'packs' (at a cost) or obtained
free from an Armoury.
The teams compete for territory, and critically
for the resources ('res') it offers.
The currency for both sides, resources are
obtained by building resource towers to tap
the nozzles sited around the map.
This is another area where the teams have
a key difference - while marines draw on a
common pool of resources, each alien accumulates
a personal store.
This further increases the requirement for
teamwork on the alien side, to achieve the
right balance of hives, lifeforms, resource
towers and chambers.
The game ends when either all the marines
or aliens are dead, and have no means to respawn.
For the Frontiersmen (marine) side, this entails
destroying all alien hives, ensuring no further
alien players may respawn, and then hunting
the rest down.
For the Kharaa (alien) side, winning requires
destroying all marine "Infantry Portals",
ensuring that they do not respawn, and then
eliminating the rest of the marines.
Other possibilities exist such as destroying
the command chair, or destroying all finished
hives, and killing the whole alien team before
the remaining hive is fully grown.
Game duration and game balance has been continually
addressed by Unknown Worlds Entertainment
throughout each of their releases with extensive
changelogs describing these issues.
In v1, games were slower and often measured
in hours.
One of the stated aims of v2 was to address
this, by introducing a broad range of changes
to abilities, structures, etc.
In current releases (v3), a typical game lasts
5–15 minutes, but can run over an hour,
with both sides vying for control over strategically
important Hive Rooms and Resource Nodes.
Combat is the team deathmatch, or beginner
mode of NS.
It was introduced in NS 3.0 to help new players
learn how to play alien lifeforms in an easier
environment.
Neither team can build structures, the marines
do not have a commander, and aliens have only
one hive.
Each player has an individual experience meter,
increased by killing enemies; dealing damage
to the enemy hive/command chair or healing/repairing
their own hive/command chair.
When the experience meter reaches maximum,
the player gains a level and it resets.
There have been various changes to the spawn
system in the various betas to try to make
matches more interesting and more winnable
but also without making it such that a team
that suffers a major loss of players can still
come back.
An admin configurable time limit (default
15 minutes) was introduced in beta 5 which
remains in the final version.
With the time limit, Marines are usually on
the attacking side and Kharaa are on the defending
side.
Failure of the attacking side to win within
the time limit results in a victory for the
defending side.
== Reception ==
GameSpy hailed Natural Selection as "possibly
the most ambitious user-made modification
ever brought to fruition.
This multiplayer-only mod somehow manages
to transform the aging Half-Life into a seemingly
brand-new, atmospheric, and surprisingly deep
action-strategy game, pitting hive-minded
aliens against resourceful space marines,"
and "Natural Selection's innovations are too
numerous to list, but the marine's "commander"
mode deserves special mention.
Playing as the marine commander, you can order
and re-supply other marines in an RTS-style,
top-down perspective."
FiringSquad : "The way all these details boil
down in gameplay is simply amazing, and occasionally
fascinating to just watch unfold," and "is
probably one of the most creative and well
thought out shooters we’ve played in a very
long time."
== 
Sequel ==
Natural Selection 2 is the sequel to Natural
Selection.
Natural Selection 2 started development using
the Source Engine, however their development
blog later announced [1] that Unknown Worlds
had moved to the Spark engine, an engine they
created themselves.
Natural Selection 2 has the same basic gameplay
as Natural Selection, but with new weapons
and abilities.
It was released commercially on Steam.
According to an interview with the game director,
Charlie Cleveland (Flayra), the sequel continues
where the original left off and features environments
that are dark and denser.
Several gameplay modes once available only
as community-developed mods (such as Marines
vs. Marines) became officially supported.
In addition, a major new feature of Natural
Selection 2 is dynamic infestation [2], released
in December 2006.
The proposed feature would dynamically generate
bacterial infestation based on what areas
of the map the alien team controlled.
The alpha testing of Natural Selection 2 began
on 26 July 2010.
The game was released on October 30, 2012
