Are red-heads going extinct?

Question

There is a widely-held belief that there will no longer be humans with red hair in the future (sometimes cited by 2060 or 2100).

For example, these Facebook groups:

• "Save the ginger kids, there going extinct D:"

  One of my teachers told me that in a couple years there wont be any ginger kids left

• "Jump on a Ginger"

  Currently, two percent of the world’s population is adorned with red hair. Scientists have speculated that this rare breed may possibly going extinct.

• Ginger Moses

  They say that 2060 will be the end of the road for Gingers

The justifications given include:

• red hair is a recessive gene (Seattle Times):

  If predictions by the Oxford Hair Foundation come to pass, the number of natural redheads everywhere will continue to dwindle until there are none left by the year 2100.

  The reason, according to scientists at the independent institute in England, which studies all sorts of hair problems, is that just 4 percent of the world’s population carries the red-hair gene. The gene is recessive and therefore diluted when carriers produce children with people who have the dominant brown-hair gene.

• climate change (The Week):

  Only 1 to 2 percent of people in the world have red hair — and that number could continue to decrease due to climate change, scientists warn.

Is this just a myth, or will ginger hair soon cease to be?

Answer 1

Some phenotypes caused by recessive genes occur in sub-populations that tend to reproduce with other members of the sub-population.

For example, Tay-Sachs disease is a recessive genetic disease caused by having two bad alleles of a gene, and mainly occurs in specific sub-populations who reproduce with each other:

Tay–Sachs disease (also known as GM2 gangliosidosis or hexosaminidase A deficiency) is a rare autosomal recessive genetic disorder.

...

who described in 1887 the cellular changes of Tay–Sachs disease and noted an increased disease prevalence in Ashkenazi Jewish people.

Research in the late 20th century demonstrated that Tay–Sachs disease is caused by a genetic mutation in the HEXA gene on (human) chromosome 15. A large number of HEXA mutations have been discovered, and new ones are still being reported. These mutations reach significant frequencies in specific populations. French Canadians of southeastern Quebec have a carrier frequency similar to that seen in Ashkenazi Jews, but carry a different mutation. Cajuns of southern Louisiana carry the same mutation that is seen most commonly in Ashkenazi Jews. HEXA mutations are rare and are most seen in genetically isolated populations. Tay–Sachs can occur from the inheritance of either two similar, or two unrelated, causative mutations in the HEXA gene.

If individuals with the alleles for red hair continue reproducing at the same rate that others are, then the frequency of the red-hair allele will remain the same.

However, if populations with a high frequency of the red-hair allele decide to stop reproducing predominantly with other members of the same sub-population, then it's possible that the overall frequency of the red hair phenotype may decrease, as the number of individuals homozygous for the red hair allele will decrease, and the number of individuals heterozygous for the allele will increase.

The section Deviations from Hardy–Weinberg equilibrium in the Wikipedia article on the Hardy–Weinberg principle also states that non-random mating, also known as inbreeding, causes an increase in homozygosity.

Interracial marriage is becoming more socially acceptable in the United States (XKCD), and is becoming more common (blog post citing Pew Center research). If the same trend is happening in Scotland and Ireland, which have a high proportion of redheads (do I really need a citation?), then this will lead to a decrease in the number of individuals homozygous for the red head allele, and therefore fewer redheads.