UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934

                               (AMENDMENT NO. 4)*

                          Alnylam Pharmaceuticals, Inc.
--------------------------------------------------------------------------------
                                (Name of Issuer)


                                  Common Stock
--------------------------------------------------------------------------------
                         (Title of Class of Securities)


                                    02043Q107
--------------------------------------------------------------------------------
                                 (CUSIP Number)


                                DECEMBER 31, 2006
--------------------------------------------------------------------------------
             (Date of Event Which Requires Filing of this Statement)


Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

[ ]  Rule 13d-1(b)

[x]  Rule 13d-1(c)

[ ]  Rule 13d-1(d)


*The remainder of this cover page shall be filled out for a reporting
person's initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which could
alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be
deemed to be "filed" for the purpose of Section 18 of the Securities Exchange
Act of 1934 ("Act") or otherwise subject to the liabilities of that section of
the Act but shall be subject to all other provisions of the Act (however, see
the Notes).



                               Page 1 of 8 Pages



                                      13G
CUSIP NO.  02043Q107

                                  SCHEDULE 13G

Item 1(a). NAME OF ISSUER: Alnylam Pharmaceuticals, Inc. (the "Issuer").

Item 1(b). ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES: 300 Third Street,
     Cambridge, Massachusetts 02142.

Item 2(a).  NAMES OF PERSONS  FILING:  ARCH Venture Fund V, L.P.  ("ARCH Venture
     Fund V"); ARCH V Entrepreneurs  Fund,  L.P. ("ARCH V Entrepreneurs  Fund");
     ARCH Venture  Partners V, L.P. ("AVP V LP");  ARCH Venture  Partners V, LLC
     ("AVP V LLC")  (collectively,  the "Reporting  Entities" and  individually,
     each a "Reporting Entity"); and Steven Lazarus ("Lazarus"),  Keith Crandell
     ("Crandell"),   Robert  Nelsen   ("Nelsen")  and  Clinton  Bybee  ("Bybee")
     (collectively,  the "Managing Directors" and individually, each a "Managing
     Director").  The Reporting Entities and the Managing Directors collectively
     are referred to as the "Reporting Persons".

Item 2(b). ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE: 8725 W.
     Higgins Road, Suite 290, Chicago, IL 60631.

Item 2(c). CITIZENSHIP:  ARCH Venture Fund V, ARCH V Entrepreneurs Fund, and AVP
     V LP are  limited  partnerships  organized  under  the laws of the State of
     Delaware. AVP V LLC is a limited liability company organized under the laws
     of the State of Delaware. Each Managing Director is a US citizen.

Item 2(d).  TITLE OF CLASS OF SECURITIES:  Common  Stock,  $.01 par value (the
     "Common Stock").

Item 2(e). CUSIP NUMBER: 02043Q107

Item 3. IF THIS  STATEMENT IS FILED PURSUANT TO SS.SS. 240.13d-1(b) OR
        240.13d-2(b) OR (c), CHECK WHETHER THE PERSON IS A:

        Not applicable.

Item 4. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS.

        Each reporting person has ceased to own  beneficially  more than 5% of
        the outstanding Common Stock of the Issuer.

Item 5. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON.

        Not Applicable.


                             Page 2 of 8 Pages

                                      13G
CUSIP NO.  02043Q107


                                   SIGNATURES
                                  ------------
        After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

Dated: February 13, 2007

                                ARCH VENTURE FUND V, L.P.

                                By:     ARCH Venture Partners V, L.P.
                                        its General Partner

                                        By:     ARCH Venture Partners V, LLC
                                                its General Partner

                                                By:           *
                                                   ---------------------------
                                                   Keith Crandell
                                                   Managing Director

                                ARCH V ENTREPRENEURS FUND, L.P.

                                By:     ARCH Venture Partners V, L.P.
                                        its General Partner

                                        By:     ARCH Venture Partners V, LLC
                                                its General Partner

                                                By:           *
                                                   ---------------------------
                                                   Keith Crandell
                                                   Managing Director


                                ARCH VENTURE PARTNERS V, L.P.

                                By:     ARCH Venture Partners V, LLC
                                        its General Partner


                                      By:            *
                                           ---------------------------
                                           Keith Crandell
                                           Managing Director

                                ARCH VENTURE PARTNERS V, LLC

                                By:            *
                                     ---------------------------
                                     Keith Crandell
                                     Managing Director


                                                  *
                                -----------------------------------
                                Steven Lazarus



                               Page 3 of 8 Pages



                                      13G
CUSIP NO.  02043Q107


                                                  *
                                -----------------------------------
                                Keith Crandell

                                                  *
                                -----------------------------------
                                Robert Nelsen

                                                  *
                                -----------------------------------
                                Clinton Bybee


* By: /s/ Mark McDonnell
      ------------------------
        Mark McDonnell as
        Attorney-in-Fact


------------------------------------------------------------------------------

This Schedule 13G was executed by Mark McDonnell pursuant to Powers of Attorney
attached hereto as EXHIBIT 2 and incorporated herein by reference.


                               Page 4 of 8 Pages


                                       13G
CUSIP NO.  02043Q107

                                                EXHIBIT 1

                                    AGREEMENT
                                    ---------


     Pursuant to Rule  13d-1-(k)(1)  under the Securities  Exchange Act of 1934,
the undersigned hereby agree that only one statement  containing the information
required by Schedule 13G need be filed with respect to the  ownership by each of
the undersigned of shares of stock of Alnylam Pharmaceuticals, Inc.

     This Agreement may be executed in any number of counterparts, each of which
shall be deemed an original.

Dated: February 13, 2007

                                ARCH VENTURE FUND V, L.P.

                                By:     ARCH Venture Partners V, L.P.
                                        its General Partner


                                        By:     ARCH Venture Partners V, LLC
                                                its General Partner

                                                By:          *
                                                   ---------------------------
                                                   Keith Crandell
                                                   Managing Director

                                ARCH V ENTREPRENEURS FUND, L.P.

                                By:     ARCH Venture Partners V, L.P.
                                        its General Partner

                                        By:     ARCH Venture Partners V, LLC
                                                its General Partner

                                                By:          *
                                                   ---------------------------
                                                   Keith Crandell
                                                   Managing Director

                                ARCH Venture Partners V, L.P.

                                By:     ARCH Venture Partners V, LLC
                                        Its General Partner

                                        By:           *
                                           ---------------------------
                                                Keith Crandell
                                                Managing Director


                                Page 5 of 8 Pages


                                       13G
CUSIP NO.  02043Q107

                                ARCH VENTURE PARTNERS V, LLC


                                By:           *
                                    ------------------------------
                                     Keith Crandell
                                     Managing Director

                                              *
                                -----------------------------------
                                Steven Lazarus

                                              *
                                -----------------------------------
                                Keith Crandell

                                              *
                                -----------------------------------
                                Robert Nelsen

                                              *
                                -----------------------------------
                                Clinton Bybee


* By: /s/ Mark McDonnell
      -----------------------
        Mark McDonnell as
        Attorney-in-Fact

------------------------------------------------------------------------------

This Schedule 13G was executed by Mark McDonnell pursuant to Powers of Attorney
attached hereto as EXHIBIT 2 and incorporated herein by reference.


                               Page 6 of 8 Pages


                                       13G
CUSIP NO.  98411C100

                                                                       EXHIBIT 2
                               POWERS OF ATTORNEY
                              --------------------

     KNOW ALL MEN BY THESE PRESENTS,  that each person whose  signature  appears
below  hereby  constitutes  and  appoints  Mark  McDonnell  his true and  lawful
attorney-in-fact,  with  full  power  of  substitution,  to  sign  any  and  all
instruments,  certificates  and documents  that may be  necessary,  desirable or
appropriate  to be  executed  on behalf of  himself as an  individual  or in his
capacity as a general partner of any partnership, pursuant to Sections 13 and 16
of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), and any
and all  regulations  promulgated  thereunder,  and to file the  same,  with all
exhibits  thereto,  and any other  documents in connection  therewith,  with the
Securities and Exchange  Commission,  and with any other entity when and if such
is mandated by the Exchange Act or by the By-laws of the National Association of
Securities  Dealers,  Inc., granting unto said  attorney-in-fact  full power and
authority to do and perform each and every act and thing necessary, desirable or
appropriate,  fully  to all  intents  and  purposes  as he  might or could do in
person, thereby ratifying and confirming all that said attorney-in-fact,  or his
substitutes, may lawfully do or cause to be done by virtue hereof.

     IN WITNESS  WHEREOF,  this Power of Attorney has been signed as of the
8th day of June, 2004

                                ARCH VENTURE FUND V, L.P.

                                By:     ARCH Venture Partners V, L.P.
                                        its General Partner

                                        By:     ARCH Venture Partners V, LLC
                                                its General Partner


                                                By: /s/ Keith Crandell
                                                   ---------------------------
                                                   Managing Director

                                ARCH V ENTREPRENEURS FUND, L.P.

                                By:     ARCH Venture Partners V, L.P.
                                        its General Partner


                                        By:  ARCH Venture Partners V, LLC
                                             its General Partner


                                             By: /s/ Keith Crandell
                                                 ---------------------------
                                                 Managing Director



                                Page 7 of 8 Pages


                                      13G
CUSIP NO.  98411C100

                                ARCH VENTURE PARTNERS V, L.P.


                                By:     ARCH Venture Partners V, LLC
                                        its General Partner

                                        By: /s/ Keith Crandell
                                           ---------------------------
                                           Managing Director

                                ARCH VENTURE PARTNERS V, LLC

                                By: /s/ Keith Crandell
                                    ----------------------
                                    Managing Director

                                /s/ Steven Lazarus
                                -----------------------------------
                                Steven Lazarus

                                /s/ Keith Crandell
                                -----------------------------------
                                Keith Crandell

                                /s/ Robert Nelsen
                                -----------------------------------
                                Robert Nelsen

                                /s/ Clinton Bybee
                                -----------------------------------
                                Clinton Bybee


                               Page 8 of 8 Pages