‘You shouldn’t marry your cousin!’
by David Catchpoole
The alarming increase in defective births in some communities in Britain has led
to calls for marriages between cousins to be banned.1
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In Bradford, more than 75% of all marriages between people of Pakistani origin are
believed to be between first cousins. This has resulted in a dramatic increase in
the rate of genetic defects and infant mortality. Bradford’s Royal Infirmary
Hospital has identified more than 140 different recessive disorders among local
children, compared to the usual 20–30. Across Britain, the Pakistani community
accounts for 30% of all births with recessive disorders, despite representing only
3.4% of the national birth rate.
The calls to ban marriage between cousins are certainly understandable from a genetic
perspective. When first cousins marry, the chances of them both passing on just
one variant (disorder-causing) gene to a child is one in eight.2 For other couples the likelihood is estimated to
be less than one in 100.3
A recognized risk
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While suggestions to ban marriage between cousins are not yet common, prohibitions
against siblings marrying one another have long been in place in societies
around the world. It is widely understood that union between brothers and sisters
(including half-brothers and half-sisters) results in an unacceptably high risk
of their children being deformed. From genetic studies we now understand why.
The more closely related two people are, the greater the likelihood of them carrying
the same mutations—copying mistakes in their genes. Therefore a brother
and a sister are more likely to have mistakes in the same genes since these
have been inherited from the same parents. (Everyone has two sets of genes
that specify how we are put together and function—we inherit one gene of each
pair from each parent.) So the child of a union between siblings could inherit the
same mutated gene from both parents—resulting in serious defects. But where
a child’s parents are not so closely related, inheriting a bad gene from one
parent is not calamitous, because a good copy of the gene from the other parent
is there as a back-up.
We’re going downhill
Today we see a steady accumulation of the number of defective genes in both human
and animal populations.4
In other words, the accumulating mutations mean that genetically we’re going
downhill with every passing generation.
This is very confronting for evolutionary theory, but just what we’d expect
from the Bible’s account of our history. Originally, the Creation was ‘very
good’ (Genesis 1:31) but because of Adam’s disobedience,
God cursed the world, bringing death and decay to the Creation (Genesis 3:6ff; Romans 5:12, 8:22). So Adam and Eve did not have the
accumulated genetic mistakes (mutations) that we have. Their genes were perfect,
but as genes passed from generation to generation, the now imperfect copying process
in this sin-cursed world resulted in errors.
Today we see a steady accumulation of the number of defective genes in both human
and animal populations.
By the time of Moses (more than two thousand years after Creation Week), degenerative
mistakes would have built up to such an extent that it’s not surprising to
us (in light of today’s genetics knowledge) that it became necessary for God
to forbid marriage between siblings—even half-brother and half-sister (Leviticus 18:9, 20:17; Deuteronomy 27:22). Also, there were plenty of people
on Earth by now, and there was no reproductive necessity for close relatives to
marry.
In contrast, prior to Moses (before laws forbidding sibling marriage) there would
have been fewer accumulated genetic mistakes—the first few generations after
Adam and Eve would have exhibited minimal degeneration—so it makes sense that
Cain could have married his sister5
with God’s approval, without any potential to produce deformed offspring.
evolutionary theorists have got some hard thinking to do
But today, some 6,000 years later, the situation is very different. With the degeneration
in the genome all too evident, we are increasingly hearing of authorities, such
as in Bradford, wanting to go beyond the Law of Moses to institute prohibitions
against marriage between cousins.
From the standpoint of biblical history—an original ‘very good’
Creation now in ‘bondage to decay’ and which ‘waits eagerly for
the sons of God to be revealed’ (Romans 8:19–22)—the situation facing authorities,
and their suggested solution, is understandable.
In contrast, evolutionary theorists have got some hard thinking to do.6
References and notes
- Giannangeli, M., Ban Asian marriages of cousins, says MP,
news.telegraph, <www.telegraph.co.uk/news/main.jhtml?xml=/news/2005/11/16/ncous16.xml>,
22 November 2005. Return to text.
- The ‘one in eight’ chance refers to any particular
gene locus, but note that with hundreds of possible mutations there is actually
a higher chance that at least one will be inherited from both parents.
Return to text.
- Charles Darwin married his first cousin, and his descendants
have been quite successful. Return to text.
- Geneticists refer to this as a population’s ‘genetic
burden’ or ‘genetic load’. Return to text.
- Cain’s mother was named Eve (by Adam) ‘because
she was the mother of all the living’ (Genesis 3:20). Thus Cain could only have married a descendant
of his own mother (Genesis 4:17, 5:4). Return to text.
- For a detailed analysis of how this degeneration in genes
confounds evolutionary thinking, see Sanford, J.C., Genetic Entropy and the Mystery
of the Genome, Ivan Press, New York, 2005. Return to text.
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