The Collaborative International Dictionary of English v.0.48:

Selection \Se*lec"tion\, n. [L. selectio: cf. F. s['e]lection.]
   .
   The act of selecting, or the state of being selected; choice,
   by preference.
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   2. That which is selected; a collection of things chosen; as,
      a choice selection of books.
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   Natural selection. (Biol.) See under Natural.
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The Collaborative International Dictionary of English v.0.48:

Natural \Nat"u*ral\ (?; 135), a. [OE. naturel, F. naturel, fr.
   L. naturalis, fr. natura. See Nature.]
   1. Fixed or determined by nature; pertaining to the
      constitution of a thing; belonging to native character;
      according to nature; essential; characteristic; innate;
      not artificial, foreign, assumed, put on, or acquired; as,
      the natural growth of animals or plants; the natural
      motion of a gravitating body; natural strength or
      disposition; the natural heat of the body; natural color.
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            With strong natural sense, and rare force of will.
                                                  --Macaulay.
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   2. Conformed to the order, laws, or actual facts, of nature;
      consonant to the methods of nature; according to the
      stated course of things, or in accordance with the laws
      which govern events, feelings, etc.; not exceptional or
      violent; legitimate; normal; regular; as, the natural
      consequence of crime; a natural death; anger is a natural
      response to insult.
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            What can be more natural than the circumstances in
            the behavior of those women who had lost their
            husbands on this fatal day?           --Addison.
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   3. Having to do with existing system to things; dealing with,
      or derived from, the creation, or the world of matter and
      mind, as known by man; within the scope of human reason or
      experience; not supernatural; as, a natural law; natural
      science; history, theology.
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            I call that natural religion which men might know .
            . . by the mere principles of reason, improved by
            consideration and experience, without the help of
            revelation.                           --Bp. Wilkins.
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   4. Conformed to truth or reality; as:
      (a) Springing from true sentiment; not artificial or
          exaggerated; -- said of action, delivery, etc.; as, a
          natural gesture, tone, etc.
      (b) Resembling the object imitated; true to nature;
          according to the life; -- said of anything copied or
          imitated; as, a portrait is natural.
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   5. Having the character or sentiments properly belonging to
      one's position; not unnatural in feelings.
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            To leave his wife, to leave his babes, . . .
            He wants the natural touch.           --Shak.
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   6. Connected by the ties of consanguinity. especially,
      Related by birth rather than by adoption; as, one's
      natural mother. "Natural friends." --J. H. Newman.
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   7. Hence: Begotten without the sanction of law; born out of
      wedlock; illegitimate; bastard; as, a natural child.
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   8. Of or pertaining to the lower or animal nature, as
      contrasted with the higher or moral powers, or that which
      is spiritual; being in a state of nature; unregenerate.
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            The natural man receiveth not the things of the
            Spirit of God.                        --1 Cor. ii.
                                                  14.
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   9. (Math.) Belonging to, to be taken in, or referred to, some
      system, in which the base is 1; -- said of certain
      functions or numbers; as, natural numbers, those
      commencing at 1; natural sines, cosines, etc., those taken
      in arcs whose radii are 1.
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   10. (Mus.)
       (a) Produced by natural organs, as those of the human
           throat, in distinction from instrumental music.
       (b) Of or pertaining to a key which has neither a flat
           nor a sharp for its signature, as the key of C major.
       (c) Applied to an air or modulation of harmony which
           moves by easy and smooth transitions, digressing but
           little from the original key.
       (d) Neither flat nor sharp; -- of a tone.
       (e) Changed to the pitch which is neither flat nor sharp,
           by appending the sign [natural]; as, A natural.
           --Moore (Encyc. of Music).
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   11. Existing in nature or created by the forces of nature, in
       contrast to production by man; not made, manufactured, or
       processed by humans; as, a natural ruby; a natural
       bridge; natural fibers; a deposit of natural calcium
       sulfate. Opposed to artificial, man-made,
       manufactured, processed and synthetic. [WordNet
       sense 2]
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   12. Hence: Not processed or refined; in the same statre as
       that existing in nature; as, natural wood; natural foods.
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   Natural day, the space of twenty-four hours. --Chaucer.
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   Natural fats, Natural gas, etc. See under Fat, Gas.
      etc.

   Natural Harmony (Mus.), the harmony of the triad or common
      chord.

   Natural history, in its broadest sense, a history or
      description of nature as a whole, including the sciences
      of botany, Zoology, geology, mineralogy,
      paleontology, chemistry, and physics. In recent
      usage the term is often restricted to the sciences of
      botany and Zoology collectively, and sometimes to the
      science of zoology alone.

   Natural law, that instinctive sense of justice and of right
      and wrong, which is native in mankind, as distinguished
      from specifically revealed divine law, and formulated
      human law.

   Natural modulation (Mus.), transition from one key to its
      relative keys.

   Natural order. (Nat. Hist.) See under order.

   Natural person. (Law) See under person, n.

   Natural philosophy, originally, the study of nature in
      general; the natural sciences; in modern usage, that
      branch of physical science, commonly called physics,
      which treats of the phenomena and laws of matter and
      considers those effects only which are unaccompanied by
      any change of a chemical nature; -- contrasted with
      mental philosophy and moral philosophy.

   Natural scale (Mus.), a scale which is written without
      flats or sharps.

   Note: Model would be a preferable term, as less likely to
         mislead, the so-called artificial scales (scales
         represented by the use of flats and sharps) being
         equally natural with the so-called natural scale.

   Natural science, the study of objects and phenomena
      existing in nature, especially biology, chemistry, physics
      and their interdisciplinary related sciences; natural
      history, in its broadest sense; -- used especially in
      contradistinction to social science, mathematics,
      philosophy, mental science or moral science.

   Natural selection (Biol.), the operation of natural laws
      analogous, in their operation and results, to designed
      selection in breeding plants and animals, and resulting in
      the survival of the fittest; the elimination over time of
      species unable to compete in specific environments with
      other species more adapted to survival; -- the essential
      mechanism of evolution. The principle of natural selection
      is neutral with respect to the mechanism by which
      inheritable changes occur in organisms (most commonly
      thought to be due to mutation of genes and reorganization
      of genomes), but proposes that those forms which have
      become so modified as to be better adapted to the existing
      environment have tended to survive and leave similarly
      adapted descendants, while those less perfectly adapted
      have tended to die out through lack of fitness for the
      environment, thus resulting in the survival of the
      fittest. See Darwinism.

   Natural system (Bot. & Zool.), a classification based upon
      real affinities, as shown in the structure of all parts of
      the organisms, and by their embryology.

            It should be borne in mind that the natural system
            of botany is natural only in the constitution of its
            genera, tribes, orders, etc., and in its grand
            divisions.                            --Gray.


   Natural theology, or Natural religion, that part of
      theological science which treats of those evidences of the
      existence and attributes of the Supreme Being which are
      exhibited in nature; -- distinguished from revealed
      religion. See Quotation under Natural, a., 3.

   Natural vowel, the vowel sound heard in urn, furl, sir,
      her, etc.; -- so called as being uttered in the easiest
      open position of the mouth organs. See Neutral vowel,
      under Neutral and Guide to Pronunciation, [sect] 17.
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   Syn: See Native.
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WordNet (r) 3.0 (2006):

natural selection
    n 1: a natural process resulting in the evolution of organisms
         best adapted to the environment [syn: survival, survival
         of the fittest, natural selection, selection]