Natural selection

Five basic components of natural selection:

1. Individuals within a population are not identical. They vary, sometimes only slightly in structure, function and behaviour.

2. Some of this variation is heritable, determined by the organism's genetic make-up, and can be passed from parent to offspring.

3. All living things have a tendency to overproduce. More offspring are produced than are required to keep the population stable.

4. Despite overproduction, populations tend to remain relatively stable. Thus many individuals fail to survive and reproduce.

5. Different individuals leave different numbers od descendants.

Natural Selection Outside the Bounds of Biota

Natural selection, a term most often associated with Darwinism and evolutionists has become common vocabulary in the economic and political sectors. Statements overheard at recent market and technology events include statements such as “they just couldn’t find their niche in the market;” “talk about bottom of the food chain;” and “it is time to find a company better suited for this environment.” Not too different from conversations going on in ecology classrooms across the great state of Georgia.

As far as a nation, company, or political figure being more or less fit in an unregulated setting, one can not simply state whether or not it is “justified.” The basis of capitalist or market economy is that anyone can compete. This is no different than an ecosystem inhabited by individuals of a population. Those able to adapt to their environment, be it a foreign trade policy change or a weather pattern, are able to thrive. The difference is the ethos of competition in a human infested ecosystem. This writer proposes that there is a basic morality in the economic and political sectors of competition; which when followed provide a basically even field for competition. The same cannot be said for ecosystems.

(**note, i am not from georgia, my ecology instructor is...this essay was part of my final in that class.)

The three basic requirements for evolution through natural selection (as told by the anthropology textbook used in ANTH 1001 at the University of Minnesota):

Genetic variation in a species

Heritability of the variation

Differential reproductive success

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This is essentially the same as what melodrame stated, but simpler.

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Contrary to popular belief, natural selection does not necessarily imply increased survivability of a species, but only a change in survivability. It works both ways, wherein a trait can be selected for or against (or have no change in the survivability of the species).

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There are three basic types of natural selection as well:
1. Directional Selection: Selecting for taller people, resulting in overall higher mean heights of a population.
2. Disruptive Selection: Selecting for either the tallest or the shortest, resulting in a similar average height, but two populations with much higher or much lower local averages.
3. Stabilizing Selection: Opposite of Disruptive selection; selection against the tallest/shortest of a population, reducing variation of that trait.

Natural selection describes how evolution works.

More organisms are produced then can possibly survive. This is best illustrated by looking at organisms with a high breeding speed. For instance common brown rats have an average litter of eight young and pregnancy takes only 21 days average. You go figure how long it takes to get one million rats if you start with only two.

(No I can’t do maths for crap, that’s what I am becoming a biologist for)

There’ll be a struggle for existence. At one point the environment will fail in supplying enough food water and space for all organisms produced. Here’s were selection comes in. Those individuals best adapted to the environment will logically manage to get the best resources, like food, water, territory, mates, you name it.

Only those best adapted to their environment will survive bad times so they can reproduce for themselves. This how ‘nature selects’ the ‘fittest’, best equipped for surviving.

So the most succesfull indivuals pass on their genes to the next generation. Hereby they spread their genes further trough the population. This happens generation after generation. After a number of generations considerable changes in physiology as a response to the selective environment can be noted.

An extreme case are our common dogs, all dogs belong to the same species, be they a poodle or a golden retriever. In this case man has selected out the dogs with traits they liked, and interbred dogs until they had the desired physical appearance.

Natural selection only works on genetically inheritable characteristics though. Simply because an non genetic adaptation cannot be inherited. A non genetic adaptation can be something an organism learned.

There are for instance chimpansees that have learned to use sticks to catch termites. When a small stick or twig is stuch into a termite hill the termites will start biting the ‘intruder’. The chimpansee can then just retract the twig and eat the bugs. They can of course teach their young this trick, but the young don’t know it by instinct or anything.

Same thing is that human babies don’t know language by instinct. The ability to speak has to do with brain, tongue and troath etc. Many genetically inheritable traits have an influence on our ability to speak. But language itself is a learning process.

"Natural Selection" is the title of the fourth chapter of On the Origin of Species by Means of Natural Selection. The first major new ideas of the book come in this chapter. Natural selection, to Darwin, was the "preservation of favourable variations and the rejection of injurious variations." To put it another way, any plant or animal is mostly similar to its parents, but has a certain amount of random variation. If this variation is useful, it is more likely than most to survive to have children of its own. If this variation is harmful, the plant or animal is less likely than most to pass on its genes. Useful variations spread throughout a species, as descendants continue to be successful, while harmful ones quickly go away, as their possessors die.

Natural selection does not make up evolution by itself, but without natural selection evolution would not produce better organisms. In Darwin’s Ghost, Steve Jones recounts the classic example of natural selection: As factories sprung up in England, the peppered moth, a gray animal, seemed to turn black. This was natural selection at work. The newly-built factories spewed black smoke into the air. Gray moths, which had been well camouflaged in the past, were now visible to birds while sitting on filthy trees. Many of these moths were killed. Darker moths more often survived to reproduce, and became more and more common. By 1900, in some parts of England, just one peppered moth in fifty was of the gray variety.

This is an example of natural selection that did not progress to speciation, and it is often challenged for this reason. Creationists and others who oppose evolution say things like, "Evolution can make small changes like that, but it can’t create a new species." Darwin argues, however, that no "extreme amount of variability is necessary; as man can certainly produce great results by adding up in any given direction mere individual differences, so could Nature, but far more easily, from having incomparably longer time at her disposal." As humans breed dogs through selection of preferred traits, so does nature evolve all species.

As mentioned in the last chapter, this is done in part through the deaths of animals that do not have the traits needed to survive. It is also done through another mechanism: sexual selection. Jones describes evolution as "an examination with two papers." He continues, "The first involves staying alive long enough to have a chance to breed, while the mark in the second depends on the number of progeny." The second is as important as the first.

In some species, such as giraffes, sexual selection takes place through fighting among the males for the rights to the females. (As Jones explains, the length of giraffes’ necks is primarily due to their use as clubs; males hit each other with their heads when fighting. This explains why the giraffe’s neck is long rather than its legs, which would be just as good for reaching high leaves.) In other species, one gender or the other has a song or plumage that it uses to impress the other. In either case, the result is that animals with certain traits pass on their genes more often than those with other traits, and those genes, and the traits they carry, spread throughout a population.

Natural selection and sexual selection are sometimes in conflict with each other. To quote Jones, "In Uganda in the 1930s, almost every male elephant had tusks, structures evolved (at least in part) as statements of reproductive excellence. Sixty years later, ivory poachers had greatly reduced the number of animals, with those with the largest tusks at greatest risk. Now, a third of adults are tuskless, because the negative effects of ivory on survival outweighed its role in allure." For these elephants, there is a constant balancing act between survival and reproduction.

Natural selection also works against humanity sometimes. Old collections of bacteria, kept in suspended animation, exist going back to 1914. When these bacteria are reanimated, they are susceptible to every antibiotic used today. Contemporary bacteria, however, are not nearly as easy to destroy. Through natural selection, they have evolved resistance to antibiotics. "Twenty years ago," Jones writes, "the drug [penicillin] could kill the bacterium which causes meningitis. In many places—the United States and France included—three quarters can now defy it." At the same time as being a lesson in biology, this is a lesson in caution; if we had not overused antibiotics, this problem would not be nearly so great. Throughout the rest of his chapter, Jones uses examples like this.

Darwin ends his chapter on natural selection by explaining the principle of divergence of character. This section explains several of the toughest parts of the theories of evolution. For instance, why do we get new species at all? Why do perfectly successful species go extinct? The answer to these questions is that, as new varieties of a species evolve through natural selection, they compete vigorously with their parent species for resources. Because the varieties are so similar, they have similar survival needs, and there is simply not enough to go around between the old species or variety and the new one. To quote Darwin, "Hence, all the intermediate forms between the earlier and later states, that is between the less and more improved state of a species, as well as the original parent-species itself, will generally tend to become extinct."

This tendency of newer species to compete with and destroy older species also explains the "family tree" sort of branching chart that is often drawn to explain evolution. If you look at one of these trees, you’ll notice that species generate other species, but that individual species do not appear to survive the entirety of the chart. This type of chart makes sense only if the earlier species die out.

As a result of this constant natural selection, only one in a thousand species that have ever existed are alive today. This is a shocking number when one considers the vast number of species that exist now, but not so shocking when one considers the length of time species have had to evolve and extinguish.

To end our look at this chapter with one more description of natural selection by Darwin, "Natural selection can act only by the preservation and accumulation of infinitesimally small inherited modifications, each profitable to the preserved being; and as modern geology has almost banished such views as the excavation of a great valley by a single diluvial wave, so will natural selection, if it be a true principle, banish the belief of the continued creation of new organic beings, or of any great and sudden modification in their structure."

< Struggle for Existence | Laws of Variation >

Works Cited

• Darwin, Charles. On the Origin of Species by Means of Natural Selection. London: John Murray, 1859.
• Jones, Steve. Darwin's Ghost. New York: Random House, 1999.

Natural Selection is a mod for Half-Life released on Halloween of 2002 that incorporates elements of real-time strategy into the normal first-person shooter action.

Essentially there are two teams: humans (space marines) and aliens (Kharaa). The human team gets a commander that plays the game from a top-down perspective much like an RTS giving orders that are then carried out by players as well as building structures and keeping track of things. All the other players function a lot like they do in most shooters except they build the buildings the commander places as well as fighting aliens. Aliens, on the other hand, do not have any commander. They get something called hive sight which lets them see each other as well as various buildings and enemies at all times through walls and such (basically sprites marking relative position and color-coded with some text as well).

The overall goal is to destroy the other team and their ability to keep coming back. For humans this means all the aliens and all three of their hives, for aliens all of the humans and the command console inhabited by the commander. In the intervening time there are resources to be gained, area to control, new forms for aliens to evolve into, new weapons and armor for humans to research and purchase, evolutionary traits for aliens to select and so on. In the later stages of the game it's very likely to be fighting cloaking, regenerating, silent aliens shooting acid bombs at you or marines with jetpacks or power armor carrying heavy machine guns and laying waste to all you hold dear. Teamplay is thus an essential component and without it you're toast.

Even an exhaustive writeup would fail to capture all that there is to see and do in this mod. The main site is located at http://www.natural-selection.org

Natural Selection, the mod for Half-Life, has some variations inherent to its gameplay that can be fairly confusing to somebody new to it. One of these frustrations is the fact that both sides play very differently from each other, and as such the strategies for one side will get you turned into space goo when playing the opposite side. Here's a quick rundown of some elements in the game:

-Marines(Frontiersmen)

• Have a commander that plays from an RTS perspective
• Structures are placed by the commander, and built by normal marines (in practice, this means that the commander places a non-operational building, and the marines must build it by walking up and "using" it)
• Weapons, armor and upgrades are all researched/given by the commander
• Without a commander, your team is screwed

-Kharaa(Aliens)

• Can have up to three hives, at pre-determined locations around the map
• No commander; every alien is responsible for their own upgrades
• Each alien has an allotment of resources to spend
• Buildings are built by an alien species called Gorges

Marine detail:

Each marine is spawned at base equipped with a Light Machine Gun (LMG), a pistol, and a knife. This loadout is only effective against lower level Kharaa, and even then it's wise to travel in numbers. To acquire better weapons, the team must first build the buildings required, then upgrade to the weapons. At various points, the following weapons become available: Shotgun, Grenade Launcher, Heavy Machine Gun (HMG). In addition, the general effectiveness (read: damage) of the weapons can be upgraded.

In addition to better weapons, it is also possible to get Heavy Armor, which gives a large armor bonus to the marine wearing it, but also slows them down. Both Regular and Heavy armor benefit from overall armor upgrades (functions the same way as general weapon upgrades do). Also useful: welders, which replace the pistol in weapons slot 2, are for repairing buildings and repairing your teammates' armor; jetpacks, which are mutually exclusive with Heavy Armor (i.e. can't use both at once and blast around the map laying waste to everything in sight) and function pretty much how you'd expect a jet pack to function. There are also various fun items, such as Laser Tripmines.

Kharaa detail:

The Kharaa do not have a commander, therefore the individual must be able to access resources to be able to evolve. Resources are automatically distributed among the team. However, the number of Hives that exist affect the total number of resources each alien can have available. With one hive, the resource cap for all but the Gorg is set at 33/100, and the next highest forms, the Fade and Onos, require 54 and 70 resources, respectively. With two hives, the resource cap rises to 66/100, and with all three hive locations filled with a hive, the cap reaches 100/100. (the Gorg is an exception to this resource cap, because they must be able to build; however, switching to a Gorg and then evolving to a Fade without having two hives doesn't work.)

Each alien is spawned at base (base being the first, initial, hive) as a Skulk, the lowest rung on the alien evolutionary ladder. They are fast, dog-sized creatures able to climb up walls and leap out at unsuspecting marines with a fury. Their bite attack is useful against marines wearing regular armor, but fairly ineffective in small numbers against marines in Heavy Armor. Their secondary attack is ranged, and implants a parasite in the targeted Marine, making them show up on Hive Sight at all times. With two hives, a skulk can use the Leap ability, which propels them a distance at great speed, very useful for getting from A to B. The final Skulk ability, coming along with three hives existing, is Xenocide, which explodes and kills the Skulk, but dealing damage to everything caught in the blast radius.

Initially available evolutions, if you have enough resources, are the Gorg and the Lerk. The Gorg is a slow creature, slightly larger than a Skulk, that is the "builder" of the Kharaa. Their primary slot is a projectile: they shoot a blob of slime at enemies. They are capable of building structures, repairing structures, and healing teammates. These latter two take up the second weapon slot, being a healing spray with a close range. With two hives, a Gorg's third slot is the capability to place Webbing. This ensnares any enemy that touches it, immobilizes them momentarily, and disables their weapons. The fourth and final Gorg ability is to create Babblers, which are weaker, computer-controller versions of Skulks, and they automatically attack enemies nearby and self-destruct after a short amount of time. The Lerk is the only flying Kharaa, and its primary slot is a bite attack, much like the Skulks. Their second slot is a ranged spine weapon, shooting spikes at opponents from a distance. Coming with two hives, a Lerk's third slot is a cloud called Umbra, which slows down any bullets entering it, effectively reducing the likelihood that any alien within the cloud is going to be hit with a bullet. This does not hinder any other type of weapon, however, so they are still susceptible to things such as knives and grenades. With three hives comes the fourth slot ability: a ranged attack that shoots a slow-moving spore that explodes on impact, spraying a cloud of corrosive particles into the air, damaging all organic matter within the explosion zone.

The Fade is the most powerful commonly used Kharaa unit (this is because by time the Onos comes around, the game is pretty much over). It becomes available with the construction of two hives. Standing taller than a Marine, it has powerful claws used in its primary, swiping attack. Its second slot attack is a projectile; missile-like, that explodes releasing splash-damage acid on targets near the blast point. It's third slot is a short-range teleportation ability called Blink, useful for getting out of situations in which the Fade is overpowered. With three hives, the Bile Bomb ability becomes available. It's a heavy, arcing projectile that explodes and does massive damage to everything within the blast area.

The final evolution that a Kharaa can undergo is that to the Onos, the most powerful alien unit available. This requires that all three hive locations be occupied. With massive hitpoints and massive armor, it is a tank on four legs. Its first slot ability is Gore, which is a melee attack that does a considerable amount of damage to a single enemy target. The second is Paralyze, which is a close-range attack that prevents the victim from moving, though they can still aim and fire a weapon. The Onos's third slot attack is Charge, which rams enemies and deals massive damage to both Marines and structures. The fourth and final Onos ability is Primal Scream, which is a benefical area-of-effect capability that boosts energy recovery in the Onos and nearby aliens in much the same way as the Adreneline upgrade does, albeit for a short amount of time.

In addition to these major evolutions, there are also "Chambers" which allow minor upgrades and enhancements. There are three total available: Defense, Movement, Sensory. (There is also an Offense chamber, but these can always be built. They attack nearby enemies with a projectile attack.) Only one type can be built with a single hive; two hives allow two kinds to be built; three hives lets all of them be built. Each also has a special function of greater or lesser import that it can perform. The Defense chamber heals nearby units and buildings. The Movement chamber allows instanteneous teleportation from the chamber itself to the furthest hive. The Sensory chamber reveals any hostiles it can "see" on Hive Sight, and marks nearby enemies in much the same way the Skulk ability of Parasite does.

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Work in progress, still have to add: marine buildings, kharaa buildings, more specific damage, armor and health amounts.