Ploy gives us a superb puzzle this week - a lovely idea well executed.
As hinted at in the preamble ("an initial line of descent") the clues contain an acrostic which spells out AND ANOTHER ANCESTOR OF THE CROSSWORD IS THE ACROSTIC. This is a strong hint that the "present descendant" is this crossword puzzle and its ancestor is another type of puzzle, to be discovered in the grid. The extra and omitted letters in wordplay spell out ERASE ALL GRID ENTRIES THAT CONTAIN NON TITLE LETTERS. Taking the title letters to be PATERSON (from Pater & Son, ignoring the ampersand) and erasing all grid entries which contain any other letters, the solver is left with the following 5x5 word square
R O T A S
O P E R A
T E N E T
A R E P O
S A T O R
This well-known word square (known as the SATOR or PATERNOSTER square) dates back to Roman times and examples in this or its mirror image form have been found in many places throughout Europe and the Middle East. It also appears in the Chambers Crossword Manual so should be readily recognised by readers (and the author!) of that esteemed tome.
In the following explanations, the modified answers (although sometimes ambiguous for anagrams) indicated by the wordplay are shown in square brackets after the answers.
ACROSS
1 A screen to subdue aphid (6, two words)
ANT COW [ANETCOW] (A + NET (screen) + COW (subdue))
5 New South Wales inundated by tide as it turns and returns (7)
ANSWERS [ANSWES] (NSW (New South Wales) inside SEA (tide) rev)
10 Doctor, taking iron, treated someone concerned with joint operation?
(11)
CO-ORDINATOR [COORDINTOR] (anag of DOCTOR IRON)
12 A strip of cloth held by Velcro's one-sided (4)
ROON [ROSON] (hidden)
14 Nag failing to start race evenly - stirrups perhaps? (4)
OSSA [OSSAE] ((HOSS (nag) minus first letter + AE (even letters of race))
16 One getting on last rode off (7)
OLDSTER [OLDSTERA] (anag of LAST RODE)
17 Twist back the spades after earth bursts out (6)
ERUPTS [ELRUPTS] (E (earth) + PURL (twist) rev + T (the) + S (spades))
18 Hoppers take single turns (4)
ROOS [ROLOS] (R (take) + SOLO (single) rev)
20 Exhausted person trails cherished girl (5)
PETRA [PETRAG] (PET (cherished) + RAG (exhausted person))
22 Removers of plunder stole nothing decrepit (7)
LOOTERS [LOOTES] (anag of STOLE + O (nothing))
24 Anger starts to rise up - Neighbours broadcast again (5)
RERUN [IRERUN] (IRE (anger) + RUN (first letters of rise up neighbours))
25 Never retiring, the English doctor cut deeper (7)
RE-ENTER [REENTEDR] (NEER (never) rev + T (the) + E (English) + DR
(doctor))
26 Colonist, perhaps travelling west in short overcoat (5)
VOTER [VOTR] (hidden rev)
27 Eros with plan taking shape for resting (7)
REPOSAL [REPOSALN] (anag of EROS PLAN)
28 Sheep initially coming after smooth bitter vetches (5)
ERSES [TERSES] (TERSE (smooth) + S (first letter of sheep))
29 Total of 200, at least, knock back a quick drink (4)
TONS [TRONS] (SNORT (quick drink) rev)
31 Obstruct middle of step with a heavy spar (6)
BARITE [BARTE] (BAR (obstruct) + TE (middle letters of step))
33 Reverse cut slice of bread with butter and salt (7)
NITRATE [NITRAT] (TARTINE (slice of bread with butter) minus last letter
rev)
34 Ohio heritage body at a former time (4)
ONST [ONT] (O (Ohio) + NT (heritage body - National Trust))
36 For instance, noise from a cannon round, right? (4)
ROAR [ROTAR] (ROTA (round) + R (right))
38 Tamper with hose in resolving seepages (11)
PERMEATIONS [PERMEATIONSH] (anag of TAMPER HOSE IN)
39 Having good prospects, gentleman secures Eastern newspaper backing (7,
two words)
SET FAIR [SETFIR] (SIR (gentleman) round E (Eastern) + FT (newspaper)
rev)
40 Enjoying robust health running around Norway a good deal (6)
HANTLE [HANLE] (HALE (enjoying robust health) round N (Norway))
DOWN
1 Confounded acrostic is one to be ignored! Super? (5)
ACTOR [ACTORC] (anag of ACROSTIC minus S (is) and I (one))
2 Rocky place, Turkey (3)
TOR [TR] (double def)
3 On upper mast, a piece of timber unstably rests on half recess
(9)
CROSSTREE [CROSSTREEN] (anag of RESTS ON REC (half of recess))
4 Stone sweepers move about in grape processing machines (11)
WINEPRESSES [WINEPRESSEST] (anag of ST (stone) SWEEPERS round IN)
5 Student research reveals sizable openings in rock (6)
ANTRES [NTRES] (hidden)
6 Waterside sedge - fish eats this regularly (4)
STAR [STIAR] (SAR (fish) round TI (alternate letters of this))
7 Own up over nothing in court (3)
WOO [NWOO] (OWN rev + O (nothing))
8 Rapid returns on US holding in rave eating places (11)
RESTAURANTS [RESTURANTS] (REST (rapid returns) + US round RANT (rave))
9 Ditch also falls in summer, perhaps (8)
SEASONAL [SEASOAL] (SEA (ditch) + anag of ALSO)
11 Inwardly ruddy fruit could be "Bologna Red" (11, two words)
BLOOD ORANGE [BLODORANGE] (anag of BOLOGNA RED)
13 Strange entities in docked boat making wine (11, two words)
PETITE SIRAH [PETITESINRAH] (anag of ENTITIES inside PRAHU (boat) minus last
letter)
15 Thinly-scattered endless grasses (6)
SPARTS [SPARS] (SPARSE (thinly-scattered) minus last letter)
19 House member's a chatterer on rising (4)
PEER [PIEER] (PIE (chatterer) + RE (on) rev)
21 Extremely rapid transport is one run floating on air (9)
AEROTRAIN [AERORAIN] (AE (one) + R (run) + anag of ON AIR)
22 Are these mass washings given by a slave left worried about body odour?
(8)
LAVABOES [LAVABOESL] (anag of A SLAVE L (left) round BO (body odour))
23 Class turns up on the first with special oils (6)
OTTARS [OTETARS] (O (on) + T (the) + RATE (class) rev + S (special))
24 Return by proxy European reference library material (4)
REPP [LREPP] (PP (by proxy) + E (European) + RL (reference library) all
rev)
27 Offcuts of polyisoprene and polyester for commercial film distributor
(6)
RENTER [RENETER] (RENE (end of polyisoprene) + TER (end of polyester))
30 See this having no completion of telestich involved! Appropriate?
(5)
SEISE [SEISET] (anag of SEE THIS minus H (last letter of telestich))
32 Tasmanian fern, broad one (4)
TARA [TARTA] (TART (broad) + A (one))
35 In Ethiopia, a cereal crop first found centrally (3)
TEF [TF] (middle letters of first found)
37 Cobblers with no tree for boot (3)
ROT [OT] (BOOT minus BO (tree))