Question: "Does the Bible say anything about a pre-Adamic  race?"
Answer: The concept of a Pre-Adamic race is the idea that  God created a race of humans who lived on the Earth before He created Adam, the  first man. This hypothesis has been promoted by various scholars at various  times throughout history. Roman Emperor Julian the Apostate (circa 331–363 AD)  and Calvinist Theologian Isaac de La Peyrère (1596-1676) are two notable  examples.
We will look at two popular facets of the Preadamite  Hypothesis: the hypothesis as it was proposed by Isaac de La Peyrère, and the  form which it takes in the “Gap Theory” (also known as the Ruin-Reconstruction  interpretation). According to La Peyrère, God created the Gentiles on the sixth  day when He said, “Let us make man in our image” (
Genesis 1:26). He did not create the Jews  until after the seventh day, His day of rest. At some point after the seventh  day, God created Adam, the father of the Jews.
La Peyrère cited Scripture  to support his hypothesis. Cain’s fear of being lynched, his marriage to an  unknown woman and the fact that he founded a city (
Genesis 4:14-17) are all interpreted as  evidence that another race of men coexisted with Adam and his family.
La  Peyrère subsequently reinterpreted other passages of Scripture in light of his  peculiar understanding of the Genesis account. Consider a very familiar passage,  
Romans 5:12-14: “Therefore,  just as through one man sin entered into the world, and death through sin, and  so death spread to all men, because all sinned—for until the Law sin was in the  world, but sin is not imputed when there is no law. Nevertheless death reigned  from Adam until Moses, even over those who had not sinned in the likeness of the  offense of Adam, who is a type of Him who was to come.”
This passage is  traditionally interpreted as meaning that death began with Adam’s sin and  reigned unchecked among men (even among those who haven’t actually eaten the  forbidden fruit, those who have sinned but not “in the likeness of the offense  of Adam”) until the Law was given to Moses. La Peyrère interpreted this passage  another way. According to La Peyrère, the Pre-Adamic Gentiles sinned against  God, but in a manner less egregious than Adam (which is why Adam’s sin brought  death while theirs didn’t). They merely sinned against God’s moral will, while  Adam sinned against His Law. Adam disobeyed God’s prohibition by eating the  forbidden fruit. He broke what La Peyrère called the Law of Paradise. Thus,  according to La Peyrère, the Pre-Adamic Gentiles were those who “had not sinned  in the likeness of the offense of Adam.”
By now it’s obvious how  misinterpreting one or two passages of Scripture can lead to all kinds of warped  perceptions. The Scriptural problems with La Peyrère’s interpretations are  numerous.
First, Adam is called the “first man” (
1 Corinthians 15:45). This is  inconsistent with the idea that God created men before Adam. Second, according  to La Peyrère the Gentiles were to live outside of the Garden of Eden while Adam  enjoyed paradise (a privilege which came with the responsibility of obeying the  Law of Paradise—not eating the forbidden fruit). 
Genesis 2:5-8, however, says quite plainly  that before God created “the man whom He had formed,” the very same man which He  placed in the garden, there were no men upon the Earth to cultivate the ground.  Third, God created Eve for Adam because he was alone, there was no one else like  him around (“It is not good for the man to be alone… but for Adam there was not  found a helper suitable for him” 
Genesis 2:18, 
20). Fourth, Adam named his wife Eve  “because she was the mother of all the living” (
Genesis 3:20). The list goes on but these  passages should suffice to refute La Peyrère’s misinterpretation.
As for  Cain’s fear of being lynched, his marriage to an unknown woman and the fact that  he founded a city (
Genesis 4:14-17), Adam was almost 130  years old by the time that Cain killed Abel (Adam had Seth, his next son after  Abel’s death, at about 130; 
Genesis 4:25; 
5:3). And we know that Adam had sons and  daughters (
Genesis 5:3). At 130 he could  have had grandkids and great-grandkids by the time that Cain killed Abel. Cain  had plenty of family members to be afraid of after killing his  brother.
He apparently married a family member (a necessity back then) at  some point before Abel’s murder. It seems odd to us today but incest wasn’t  outlawed by God until the Law of Moses. It may have been around that time that  generations of degenerative genetic mutations began to take a toll on our DNA.  God outlawed incest for our protection. It became (and remains) dangerous for  close relatives to procreate because of shared genetic defects which become  expressed in their children causing severe deformities and other  problems.
As for Cain founding a city, if he lived to be the average age  back then, he probably lived to be about 900 years old. By the time he died his  family would have been a small city. If Cain had a child at the age of 30, and  his child had a child at the age of 30 and so on, Cain could have produced 30  generations by the time he died (30 generations times 30 years each equals 900  years).
The Ruin-Reconstruction interpretation takes a somewhat different  approach to the Pre-Adamic race theory. According to the Gap Theory, an  unspecified amount of time passed between 
Genesis 1:1 and 
1:2, during which God created a Pre-Adamic  race of men who lived upon the Earth until God destroyed them in judgment. Other  extinct creatures, like the dinosaurs for example, are said to have also lived  during this time. Afterwards, the theory goes, God remodeled the Earth in six  days. He created Adam on the sixth day and the rest is history. Some say that  Satan’s fall occurred at some point during the ambiguous gap.
A  “mistranslation” has contributed to the case for this misinterpretation. In the  King James Version of the Bible, God says to Adam, “Be fruitful, and multiply,  and replenish the earth.” Proponents of this view emphasize the word  “replenish.” They interpret the text as saying that Adam and Eve were to refill  the Earth. They were to fill it again. The problem with this view is that,  regardless of what it says in English translations, the Hebrew word is male’ and  it simply means to fill or to be full. Moreover, the English translators of the  King James Version knew the word means to fill. They chose “replenish” because  in 17th century Elizabethan English “replenish” meant “to fill” (similar to how  in modern English the word “replete” doesn’t mean to “abound again,” it simply  means “abundant” or “abounding”). Language is not static, but dynamic. Words  change meaning over time. Today “replenish” means “to fill again.” It didn’t  mean the same thing in 17th century England. Nearly all modern translations  translate male’ as simply “fill” in the passage in question (
Genesis  1:28).
Proponents of this view respond by pointing that God said to  Noah after the flood, “Be fruitful and multiply, and fill [male’] the earth” (
Genesis 9:1). It is evident that Noah was  meant to refill the Earth after the flood. Can’t we then interpret the same  command to Adam to mean the exact same thing—that Adam was to repopulate the  Earth after God’s judgment? The fact is that regardless what the condition of  the planet was before Noah’s flood, God didn’t tell Noah to “refill” the Earth.  He simply said to fill it. God chose the words He chose and no others. If He  said “refill” that would have been something, but since He just said “fill” that  argument falls flat.
The real problem with the Gap Theory is that it  places human mortality (Pre-Adamic human mortality) before Adam’s sin. The Bible  is quite clear that death entered in through Adam’s sin. “For since by a man  came death, by a man also came the resurrection of the dead. For as in Adam all  die, so also in Christ all will be made alive” (
1 Corinthians 15:21-22).  Regardless of whether or not we believe in animal mortality before sin, the  Bible is quite explicit about human mortality before Adam’s sin. There wasn’t  any. To deny this is to deny a central Christian doctrine.