An outline of my possible (lightly pencil in the MacGregor connection; DNA results may exclude a MacGregor connection) Greer ancestors who originated in Scotland (I have not verified many of the more distant ancestors):
Malcolm, 11th of Macgregor [perhaps a son of Malcolm's was Gilbert Grierson's father - or no MacGregor at all?]
Gilbert Grierson, 1st of Lag m. Janet Glendinning
Gilbert Grierson, 2nd of Lag m. Isabel Kirkpatrick
Vedast Grierson, 3rd of Lag m. Margaret Glyndonwen
Roger Grierson of Lag m. Isabel Gordoun
Roger Grierson m. Agnes Douglas
Sir John Grierson of Lag m. Egidia Kennedy
Roger Grierson of Lag m. Helen Douglas
William Grierson m. Nicola Maxwell
James Greer m. Mary Browne
James Greer m. Ann Taylor
John Greer m. Sarah Day
Aquilla Greer m. Elizabeth Lowe*
Aquilla Greer, Jr. m. Elizabeth Bandy
Asa Greer m. Rebecca Neighbors
Mary (Polly) Greer m. John Johnson
James Johnson m. Nancy Graves
James D. Johnson m. Katie Rice
Katherine Johnson m. James H. Garrett
Living m. Richard N. Powers
Me [Cathy (Powers) Palm]
*AQUILLA 3 GREER born ca. 1716-19; married Elizabeth whose name has been variously said to be Lowe, Smith, Haynes or Bandy. Since they married ca. 1739, it seems more logical that she was Elizabeth Lowe. Two of his brothers married Lowe sisters thought to be the daughters of William Lowe, Jr.
From "The Peerage" :
Sir James Grierson b. circa 1604, d. 1666
Born circa 1604 at Capenoch, Dumfries-shire, Scotland. He married Mary Browne, daughter of Reverend John Browne. He lived at Rock Hall, Northumberland, England. Son of Sir William Grierson, 9th of Lag and Nicola Maxwell. [See Sir James Grierson's lineage at The Peerage site]
Thoughts about the Grier/Grierson family from Letters From And To Charles Kirkpatrick Sharpe:
It is possible that DNA eliminates McGregor origins..... . However there are American Greers with DNA that indicates a "Lag" relationship. More DNA here.
A comment to the James Grear Comes To America article:
...I think there is little doubt about the relationship of Aquilla Greer elder and younger to the Lag family. This is born out by the DNA test results, which show they carried all the specific Grierson differences from the majority of members of the same haplogroup.
[written by David Grierson]