not other races, these sons of God refers here, some people
refer them as fallen angels (that is in some translation, will need
to do some check on this) 
Gen 6:1-6 (NKJV)
Now it came to pass, when men began to multiply on the face of the
earth, and daughters were born to them, that the sons of God saw
the daughters of men, that they were beautiful; and they took wives
for themselves of all whom they chose.
And the LORD said, My Spirit shall not strive with man forever,
for he is indeed flesh; yet his days shall be one hundred and
twenty years. There were giants on the earth in those days, and
also afterward, when the sons of God came in to the daughters of
men and they bore children to them. Those were the mighty men who
were of old, men of renown.
Then the LORD saw that the wickedness of man was great in the
earth, and that every intent of the thoughts of his heart was only
evil continually. And the LORD was sorry that He had made man on
the earth, and He was grieved in His heart.
