What is a theory in biology?

OED writes: HYPOTHESIS1. A subordinate particular thesis involved in a general thesis; a particular case of a general proposition. In quot. 1596, a particular or detailed statement. Cf. F. hypothse (sense 3 in Littr). Obs.

1596 EARL OF ESSEX in Ellis Orig. Lett. Ser. III. IV. 137 If I be commaunded to sett doune the Hypothesis, or to descend into particulars. 1620 T. GRANGER Div. Logike 10 note, The compound Theme is also (a) speciall, or (b) generall: (a) Hypothesis; (b) Thesis. Ibid. 204 To amplifie a speciall or particular sentence, called hypothesis. 1638 BAKER tr. Balzac's Lett. (Vol. III.) 24 Without descending from the thesis to the hypothesis. a1647 FILMER Patriarcha i. 1 (1884) 13 If the thesis be true, the hypothesis will follow. a1721 J. KEILL Maupertius' Diss. (1734) 49 Whence it is plain that there is no Hypothesis wherein the Spheroid is not flat at the Poles.
b. A proposition laid down; a thesis. Obs.

1669 GALE Crt. Gentiles I. Introd. 1 Endeavoring to promote this Hypothesis. 1678 Ibid. III. Pref., It is..impossible..demonstratively to discusse such an hypothesis without some opposition against such as defend the antithesis.
2. A proposition or principle put forth or stated (without any reference to its correspondence with fact) merely as a basis for reasoning or argument, or as a premiss from which to draw a conclusion; a supposition. In Logic, the supposition or condition forming the antecedent or protasis of a conjunctive or conditional proposition (e.g. If A is B, C is D): cf. HYPOTHETICAL 1b.

1656 BLOUNT Glossogr., Hypothesis, a supposition or condition; sometimes it is taken for a Position of something, as it were demonstrated, and granted by another. 1657 J. SMITH Myst. Rhet. 263 Hypothesis is an argument or matter whereon one may dispute; or it is a conditional proposition. 1660 BARROW Euclid I. xxvii. (1714) 23 Which being supposed, the outward angle AEF will be greater than the inward angle DFE, to which it was equal by Hypothesis. 1827 HUTTON Course Math. I. 3 An Hypothesis is a supposition assumed to be true, in order to argue from, or to found upon it the reasoning and demonstration of some proposition. 1837 BABBAGE Bridgew. Treat. App. E. 196 Collusion being, by hypothesis, out of the question. 1885 C. LEUDESDORF Cremona's Proj. Geom. 67 The hypothesis is satisfied in the particular case where the rays a and a coincide.
b. An actual or possible condition or state of things considered or dealt with as a basis for action; one of several such possible conditions, a case or alternative (cf. 1).

1794 BURKE Corr. IV. 217 The other hypothesis, upon which the war ought ‘to be carried on with vigour’, though last put, must be preliminary to the other. 1803 WELLINGTON Let. to Col. Stevenson in Gurw. Desp. I. 545 In each of these last hypotheses, you will observe the necessity that we should be within reach of each other. 1876 MOZLEY Univ. Serm. v. 119 Christianity..only sanctions war..upon the hypothesis of a world at discord with herself.
3. A supposition or conjecture put forth to account for known facts; esp. in the sciences, a provisional supposition from which to draw conclusions that shall be in accordance with known facts, and which serves as a starting-point for further investigation by which it may be proved or disproved and the true theory arrived at.

1646 SIR T. BROWNE Pseud. Ep. II. ii. 60 Irons doe manifest a verticity not only upon refrigeration..but (what is wonderfull and advanceth the magneticall hypothesis) they evidence the same by meer position according as..their extreams [are] disposed..unto the earth. 1660 R. COKE Power & Subj. 265 By a perpetuall motion of the Earth from West to East according to the new Hypotheses in Astronomy, or of the Sun from East to West, after the former Hypotheses. 1664 POWER Exp. Philos. 82 To make good the Atomical Hypothesis. 1674 BOYLE Excell. Theol. I. v. 207 One of the conditions of a good hypothesis is, that it fairly comport..with all other phnomena of nature, as well as those 'tis framed to explicate. 1774 WARTON Hist. Eng. Poetry (1775) I. Diss. i. 22 A late ingenious critic has advanced an hypothesis, which assigns a new source, and a much earlier date, to these fictions. 1843 MILL Logic III. xiv. 4 It appears..to be a condition of a genuinely scientific hypothesis, that it be not destined always to remain an hypothesis, but be of such a nature as to be either proved or disproved by that comparison with observed facts which is termed Verification. 1862 HUXLEY Lect. Wrkg. Men 67 Do not allow yourselves to be misled by the common notion that a hypothesis is untrustworthy simply because it is a hypothesis. 1893 SIR R. BALL In High Heav. ix. 212 The celebrated nebular hypotheses of Herschel and of Laplace.
4. A supposition in general; something supposed or assumed to be true without proof or conclusive evidence; an assumption.

1654 H. L'ESTRANGE Chas. I (1655) 182 The Romanists..began..to cry him [Laud] up for their Proselyte. Upon this hypothesis..they grew excessive proud and insolent. 1665 SIR T. HERBERT Trav. (1677) 352 That no other place in the East-Indies produces Gold..An Hypothesis found mistaken by such as drive a Trade for Gold..towards Cochin-China. 1827 JARMAN Powell's Devises II. 353 The gift should first be read on the supposition that it is intended to embrace legitimate children, and if there be nothing in the terms..or..context, incompatible with this hypothesis [etc.]. 1868 GLADSTONE Juv. Mundi iii. (1870) 76 The hypothesis that the Pelasgians were the base of the Greek nation.
b. Hence spec. A groundless or insufficiently grounded supposition; a mere assumption or guess.

1625 N. CARPENTER Geog. Del. I. iv. (1635) 87 Which later Astronomers..haue derided, or at least omitted as Hypotheses or suppositions. 1747 WESLEY Prim. Physic (1762) p. ix, To build Physick upon Hypotheses. 1827 SCOTT Surg. Dau. vii, Your reasoning..seems plausible; but still it is only hypothesis. 1865 SEELEY Ecce Homo v. (ed. 8) 46 The statement rests on no hypothesis or conjecture; his [Paul's] Epistles bear testimony to it. 1876 E. MELLOR Priesth. i. 14 This explanation of Bellarmine..is a pure hypothesis, for which there is not a shadow of evidence in the New Testament itself.
Hence hypothesist, one who forms a hypothesis.

1788 T. JEFFERSON Writ. (1859) II. 431 The blank..must remain for some happier hypothesist to fill up.

OED writes: THEORY1. A sight, a spectacle. Obs. rare.

1605 BP. ANDREWES Serm., Passion (1631) 365 Saint Luke..calleth the Passion a Theory or Sight... Of our blessed Saviour's whole life or death, there is no part but is a Theorie of it selfe, well worthie our looking on.
2. Mental view, contemplation. Obs.

[1598-1611 FLORIO, Theora, contemplation, speculation, deepe study, insight or beholding.] 1611 COTGR., Theorie, theorie, contemplation, deepe studie; a sight, or beholding, speculation. 1643 SIR T. BROWNE Relig. Med. I. 45 Nor can I thinke I have the true Theory of death when I contemplate a skull, or behold a Skeleton with those vulgar imaginations it casts upon us. 1646 Pseud. Ep. VII. xix. 385 As they encrease the hatred of vice in some, so doe they enlarge the theory of wickednesse in all. 1653 W. HARVEY Anat. Exercit. Pref. v, All their theory and contemplation (which they count Science) represents nothing but waking mens dreams, and sick mens phrensies. 1710 NORRIS Chr. Prud. ii. 65 Speculative Knowledge contemplates Truth for itself, and accordingly stops and rests in the Contemplation of it, which is what we commonly call Theory.
3. A conception or mental scheme of something to be done, or of the method of doing it; a systematic statement of rules or principles to be followed.

1597 HOOKER Eccl. Pol. V. xxix. 8 If they had been themselves to execute their owne Theorie in this Church. 1643 BP. HALL Devout Soul i, It will hardly be believed, how far some of their contemplative men have gone in the theory hereof. 1674 DRYDEN Prol. Univ. Oxford 11 Your theories are here to practice brought, As in mechanic operations wrought. 1798 MALTHUS Popul. III. ii. (1806) II. 103 A theory that will not admit of application cannot possibly be just. 1832 AUSTIN Jurispr. (1879) II. 1133 Theory of what is and theory of what ought to be are perpetually confounded. 1853 BRIGHT Sp. India 3 June (1876) 4 The theory of the old Government of India was one which could not be defended. 1879 M. PATTISON Milton xiii. 219 Even the calm and gentle author of the Christian Year..deliberately framed a theory of Poetic for the express purpose, as it would seem, of excluding the author of Paradise Lost from the first class of poets.
4. a. A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment, and is propounded or accepted as accounting for the known facts; a statement of what are held to be the general laws, principles, or causes of something known or observed.

1638 SIR T. HERBERT Trav. (ed. 2) 127 Or whether from subterranean fires,..I dare not conclude, but leave such theories to those that study Meteors. 1684 BURNET (title) The Theory of the Earth. 1706 PHILLIPS (ed. Kersey), Theories of the Planets, certain Hypotheses, or Suppositions about the Motions of the Heavens, according to which, Astronomers explain..the Phnomena or Appearances of the Planets. 1727-41 CHAMBERS Cycl. s.v., We say..theory of the rainbow, of the microscope..the motion of the heart, the operation of purgatives, etc. 1812 PLAYFAIR Nat. Phil. (1819) I. 3 A theory is often nothing else but a contrivance for comprehending a certain number of facts under one expression. 1850 GROVE Corr. Phys. Forces (ed. 2) 105 Were a theory open to no objection it would cease to be a theory, and would become a law. 1879 M. PATTISON Milton xiii. 180 The Copernican theory, which placed the sun in the centre of our system, was already the established belief of the few well-informed. 1890 A. R. WALLACE Darwinism 7 The truest and most complete theory would not enable us to solve all the difficult problems which the whole course of the development of life upon our globe presents to us.
b. That department of an art or technical subject which consists in the knowledge or statement of the facts on which it depends, or of its principles or methods, as distinguished from the practice of it.

1613 R. CAWDREY Table Alph. (ed. 3), Theorie, the contemplation, or inward knowledge of any art. 1626 BACON Sylva 327 The means, hitherto propounded, to effect it, are in the practice, full of error and imposture, and in the theory, full of unsound imaginations. 1660 R. COKE Power & Subj. Pref. 5 A Musitian, who Composes well, yet under~stands but little in the theory of Musick. 1795 HUTTON Math. Dict. s.v., To be learned in an art, &c., the Theory is sufficient; to be a master of it, both the Theory and practice are requisite. 1827 WHATELY Logic (ed. 2) 205 Logic being concerned with the theory of Reasoning. 1828 J. S. MILL in Westm. Rev. IX. 155 A prodigious step in the theory of naming. a1854 Early Draft Autobiogr. (1961) 135, I pushed on..to try whether I could do anything further to clear up the theory of Logic generally. 1884 GROVE Dict. Mus. IV. 101/1 Theory, a term often used..to express the knowledge of Harmony, Counter-point, Thorough~bass, etc., as distinguished from the art of playing, which is..called ‘Practice’. 1885 Encycl. Brit. XVIII. 793/2 Epistemology (theory of knowledge, Erkenntnisstheorie). 1927 B. RUSSELL Outl. Philos. xxiii. 248 Descartes..inaugurated two movements, one in metaphysics, one in theory of knowledge. 1966 R. M. CHISHOLM (title) Theory of Knowledge.
c. A systematic statement of the general principles or laws of some branch of mathematics; a set of theorems forming a connected system: as the theory of equations, of functions, of numbers, of probabilities.

1799 W. FREND (title) The Principles of Algebra..; or the true Theory of Equations established by mathematical demonstration. 1806 [see THEOREM 1a]. 1811 P. BARLOW (title) An Elementary Investigation of the Theory of Numbers. 1838 [see PROBABILITY 3]. 1893 FORSYTH (title) Theory of Functions.
5. In the abstract (without article): Systematic conception or statement of the principles of something; abstract knowledge, or the formulation of it: often used as implying more or less unsupported hypothesis (cf. 6): distinguished from or opposed to practice (cf. 4b). in theory (formerly in the theory): according to theory, theoretically (opp. to in practice or in fact).

1624 T. MACARNESSE in Capt. Smith Virginia Pref., That thou mightst read and know and safely see, What he by practice, thou by Theoree. 1692 SIR W. HOPE Fencing-Master (ed. 2) 164 Theorie without Practice will serve but for little. 1769-72 Junius Lett. Pref. (1820) 17 Theory is at variance with practise. 1776 J. ADAMS Wks. (1854) IX. 375 It is certain, in theory, that the only moral foundation of government is, the consent of the people. 1821 J. Q. ADAMS in Davies Metr. Syst. III. (1871) 175 A compromise between philosophical theory and inveterate popular habits.
6. In loose or general sense: A hypothesis proposed as an explanation; hence, a mere hypothesis, speculation, conjecture; an idea or set of ideas about something; an individual view or notion. Cf. 4.

1792 BURKE Corr. (1844) IV. 13 Whether I am right in the theory or not,..the fact is as I state it. 1794 PALEY Evid. (1825) II. 347 Theories which have, at different times, gained possession of the public mind. 1829 JAS. MILL Hum. Mind (1869) II. xxv. 403 The word theory has been perverted to denote an operation..which..consists in supposing and setting down matters supposed as matters observed. Theory in fact has been confounded with Hypothesis. 1864 BOWEN Logic xi. (1870) 375 A Theory, sometimes incorrectly used as a synonyme for Hypothesis. 1867 M. E. HERBERT Cradle L. iii. 95 So varied are the theories as to the origin of these wonderful sepulchres. 1880 T. A. SPALDING Eliz. Demonol. 35 This was not a mere theory, but a vital active belief.
7. Comb., as theory-making adj. and n., -building, -monger, -spinning; theory-bigoted, -mad, -ridden adjs.; theory-blind a., (a) blinded by a theory, so as to be unable to see the facts truly; (b) blind to a theory, i.e. unable to see or apprehend it (cf. colour-blind); theory-laden a., applied to a term, statement, etc., the use of which implies the acceptance of some theory; contrasted with theory-free, -neutral adjs.; theory-man (nonce-wd.), a theorist; theory-tailor, contemptuously for a shaper of theories.

1884 Q. Rev. Apr. 337 More *theory-bigoted than Mr. .

Would you care to comment on the statement that "Darwinism" (or the modern theory of evolution) is not a scientific theory? What, in your opinion, makes people issue such a statement?