Isn't it possible that other people could have come over after the flood to intermarry with Book of Mormon people?

I responded:

Glen, I see that you're still thinking like a Mormon.  You're using circular
reasoning---you're using one unproven premise (the literalness of the global
flood) to support another unproven premise (the authenticity of the BOM). 
For us to even entertain your theory, you must first prove that the global
flood which killed every human on earth even happened.

But for the sake of discussion, let's assume that the flood did happen
exactly as Mormon doctrine mandates.  The problems here as they concern the
BOM's claims are ones of chronology and archaelogical evidence.

To explain:  One popular pro-Mormon work which some apologists use as a
reference is Joseph Allen's "Exploring the Lands of the Book of Mormon" (BYU
Print Services, 1989.)
In his book, Allen uses dates from the Mayan calendar and other material to
attempt to give a beginning date for civilization in Mesoamerica.  On page
14, Allen states on a timeline:

"3114 BC---Calendar base date/Proposed flood date

2700 BC---Arrival of first settlers to Mesoamerica/Arrival of Jaredites to
Promised land/Tower of Babel--Iraq"

Allen then states on page 16:  "the Maya used a base system that, when
correlated with our calendar, dates to August 13, 3114  BC.  We do not know
to what event, if any, the 3114 BC date is attached.  However, the date
apparently is associated with some great event, such as the great flood or
the arrival of the first settlers in Mesoamerica."

It's obvious that Allen is trying to suggest that the "Jaredites" were the
first settlers of America, just as passages in the BOM and statements of LDS
leaders including Joseph Smith also do.  To quote Smith:

"In this important and interesting book, the history of America is unfolded,
from its first settlement by a colony that came from the Tower of Babel, at
the confusion of languages to the beginning of the fifth century of the
Christian era.  We are informed by these records that America in ancient
times has been inhabited by two distinct races of people.  The first were
called Jaredites and came directly from the Tower of Babel.  The second race
came directly from the city of Jerusalem, about six hundred years before
Christ.  They were principally Israelites, of the descendants of Joseph. The
Jaredites were destroyed about the time that the Israelites came from
Jerusalem, who succeeded them in the inheritance of the country.  The
principal nation of the second race fell in battle towards the close of the
fourth century.  The remnent are the Indians that now inhabit this country."
(Joseph Smith Jr., published in Times and Seasons March 1, 1842 and in
History of the Church, Vol 4).

Note that Smith did not mention any Asians nor anyone else inhabiting the
Americas before the "Jaredites."  In keeping with LDS belief in the
"young-earth" theory, which holds that humans have only existed for about
5000 or so years, LDS apologists like Allen above date the flood at circa
3000 BC.  The problem with that is that the archaelogical and DNA evidence
demonstrate that human civilization in the Americas is thousands of years
older than that, and there has never been a break in the chain of continuous
human habitation in the Americas such as a catastrophic flood which killed
everyone.  For example, In his 1954 "The Rise and Fall of Maya Civilization,"
noted archaelogist Eric Thompson wrote:

"Considerable evidence of early hunters has been found recently in a district
a few miles north of Mexico City, once the swampy fringe of Lake Texcoco.  At
Itzapan the remains of a young mammoth were found in 1952 with a flint point
lodged between two of the ribs and with other implements of flint and
obsidian mixed with the bones.  The beast had been butchered after apparently
being driven into the sticky soil of the so-called Upper Becerra formation,
dated about *nine to ten thousand years ago.*  Bones of another mammoth found
two years later under similar conditions had clearly been moved around by
human agency, and again points were associated with them.  Some of the bones
showed deep cuts made by the hunters as they chopped up the beast.  At
Tepexpan, only one and one-half miles away, and in a similar formation were
the remains of a woman of about thirty, the only human so far associable with
those early hunters.  *Her bones did not differ noticeably from those of the
general run of present-day Indians of Mexico;* there was nothing primitive
about her, although she was buried when mammoth still roamed the land."

Note that Thompson dated human remains at circa 9,000-10,000 years ago (many
centuries before the alleged global flood), and yet the remains were similar
to modern-day Mesoamericans which inhabited the same region---the point
being, that modern-day Amerinds are descended from those 10,000-year-old
mammoth hunters---and that means that no global flood interrupted human
culture or activity in Mesoamerica during or after the time in which it
allegedly occurred.  The alleged global flood did not interrupt human
civilization in other areas around the world either.  Archaelogical and DNA
Evidence of unbroken human culture abounds in Egypt, Israel, Malaysia, and
Australia, to name a few.  Study the info at
http://dsc.discovery.com/convergence/realeve/realeve.html

Thus, the ancient inhabitants of America did not arrive after the time of the
alleged flood to intermarry with the "BOM people," as you hypothesize.   They
were already in America centuries before the alleged flood, and they never
ceased to exist at any time.  But that is only half of the BOM's problem in
this area.  The other half is the DNA evidence which does not support the
idea of ANY ancient Americans being descended from Semite stock beginning
circa 2500 BC (the alleged "Jaredites") or 600 BC (the alleged "Lehites.")  
Also, the population figures of the "Jaredites" as stated in the BOM---which
alleges that at least two million of them were killed in battles circa 600
BC---mandate that the Jaredites and their enemies would have necessarily been
the dominant culture in the region, rather than just a small minority which
intermarried with, and were swallowed up, by a larger population of alleged
Asian-descended peoples.  That being the case, then we should be able to find
"Jaredite" (Semite) DNA relationships in spades among modern Amerinds, if the
"Jaredites" existed as recently as 2600 years ago.  But we don't.

The final nail in the coffin of your premise is that IF any "non-BOM people"
settled in the Americas sometime between the flood of circa 3000 BC and the
"Jaredite" crossing circa 2500 BC, those people would have necessarily been
closely related to Noah---a Semite.  Since, according to LDS doctrine, only
eight humans survived the flood circa 3000 BC, then all humans who migrated
to the Americas after the flood should show a close relationship with a
common, small group of ancestors beginning some 5000 years ago.  But they
don't.  So your premise is destroyed from four directions: 

*The lack of evidence for the global flood

*The archaelogical evidence which shows the Americas to have been
continuously inhabited for at least 10,000 years

*The DNA evidence which shows a close relationship between Amerinds and
Asians

*The DNA evidence which does not support the Semite origins of Amerinds in
the timeline necessary for us to accept the BOM's claims.

Conclusion:  The Book of Mormon has no basis in historical or scientific
fact.  It is soundly refuted by everything we know about ancient American
history, anthropology, archaelogy, and by DNA research.

Randy J.