- Cheetahs. From Wikipedia (with a Scientific American citation):"The cheetah has unusually low genetic variability and a very low sperm count, which also suffers from low motility and deformed flagellae. Skin grafts between non-related cheetahs illustrate this point in that there is no rejection of the donor skin. It is thought that it went through a prolonged period of inbreeding following a genetic bottleneck during the last ice age."
- The present-day population of cheetahs is low enough to put them into this category again. So it's good to know that this endangered species has survived such a problem in the past.
- Northern elephant seals, which had a population that fell to a number somewhere in the 30s during the 1890s but now are no longer endangered (residing in the "least concern" category). However, it should be noted that male elephant seals are able to impregnate up to 50 females every mating season.
- The stereotypical hamster (the golden/Syrian) is actually endangered in the wild. Virtually every domesticated Hamster is descended from a single litter captured in the 1930s.
- Genetic studies trace the native fruit flies of Hawaii to a single gravid female, which was probably blown there by a storm.
- In some areas, humans. Although there was never a colony or town that came entirely from a single couple, there is what is called the "Founder Effect", where having a overly small gene pool increases hereditary traits, usually leading to a higher rate of certain diseases or disorders. For example:
- For centuries, Martha's Vineyard had an abnormally large number of deaf people. This was because up until the 20th century, there were rarely any outsiders (read: tourists) showing up so it was rare for any new genes to be introduced into the pool.
- Polydactyly (having more than 5 fingers) is more common in the Amish than elsewhere, for similar reasons (endogamy means small gene pool).
- 75-80% of Fundamentalist Mormons (not to be confused with the 'regular' Mormons) are related in some way to Joseph Smith or John Barlow. There is also an unusual amount of fumarase deficiency in Mormon populations, the result of Fundamentalists continuing to practice polygamy and endogamy.
- The royal houses of Europe and other places developed recurring issues because of the massive inbreeding in the second millennium. Notable occurrences include hemophilia (through the descendants of Queen Victoria, currently recessed in living population), prognathism (the famous Habsburg lip; culminated in Charles II of Spain, whose jaw was so deformed he couldn't chew), various problems (including club foot, scoliosis, and cleft palates) in the Greek-descended Ptolemaic Dynasty of Egypt (who preferred brother/sister marriages).
- While outbreeding has been specifically practiced in the last century, other lesser traits are still endemic to certain royal families (large jaw in Spanish, large ears and premature balding in English).
- In 1775, a giant typhoon hit the Micronesian Island of Pingelap. Only 20 people survived. One of them was a carrier for achromatopsia — "total color-blindness". Since achromatopsia is a recessive genetic disorder, over time more and more islanders have inherited the gene, and thus also a greater number have inherited color-blindness. Today, 10% of the population is completely color-blind, and 30% more of the population carries the alleles that could cause their children to be color-blind.
- The modern day inhabitants of Pitcairn Island, all descendants of the Bounty mutineers, are subject to a variety of genetic defects associated with several generations of inbreeding.
- The CCR5-Delta 32 mutation is descended from Europeans during the time of the Black Death. It's theorized that those that had the mutation then were immune to the disease, thus after it passed, a significant number of Europeans left had the mutation. It's almost unknown in African and indigenous American populations, but about 10% of European-descended humans have the mutation. It would be unremarkable now, except that if you have two parents with the mutation, you have immunity to some strains of HIV, for now. (Wikipedia has more under http://en.wikipedia.org/wiki/CCR5#HIV .)
- 5-alpha-reductase deficiency, a very rare genetic condition where a child is born with a female appearance but develops male genitalia at age 12, has a very high incidence rate in areas of the Dominican Republic, where nearly everyone with the condition is descended from a single colonist dating from the days of Columbus.
- The high proportion of people suffering from Huntington's disease (a disease that is hereditary but doesn't have major negative effects until after reproductive age) in the Lake Maracaibo region of Venezuela is believed to be a result of one of the ten or so women who first immigrated there from Europe having the disease.
- Geneticists have posited that all modern day Homo sapiens were descended from one woman dubbed as the Mitochondrial Eve who lived in Africa around 200,000 years ago. But this is really a subversion as all scientists are very certain that she is in no sense of the word comparable to the biblical Eve: she was not the first woman, she is simply the earliest woman to which geneticists can trace, and she just happen to be lucky enough that her daughters were able to produce an unbroken line of descendants to the present day while the offspring of her contemporaries died out in the interim.
- "Died out", in this context, could mean "produced only male offspring for a generation", not actual extinction of the bloodline. As mitochondria are inherited solely through the female line, having sons doesn't do anything to preserve these organelles' genes.
- In fact, the Y-Chromosomal Adam was dated to live about 130,000 years before Eve.
- The Toba catastrophe theory, called so after a volcanic eruption some 75,000 years ago, states that humans themselves suffered a severe population bottleneck (down to some two or ten thousand of humans on Earth) due to aforementioned volcano. Not exactly Adam and Eve Plot, but as close as we ever got.
- There are some (hotly debated) theories that say after this eruption, for a short time there were as few as thirty some-odd breeding human females on the planet. Most estimates put the count as higher, but still considerably low.
- This is touted as an actual newspaper headline, in the vein of the stuff sent in to The Tonight Show With Jay Leno for his "headlines" segment: Panda Mating Fails; Veterinarian Takes Over.note
- Biology classes introducing evolution use this trope to describe Malthusian population growth, explaining how a mated pair of sparrows (or whatever) could hypothetically produce enough descendants to cover the Earth within a shockingly short period of time.
- Similar examples of a pregnant cat or dog producing thousands of descendants are used by animal welfare groups, to encourage spaying or neutering of pets.
- This has happened with more than one endangered species. The California Condor was down to 22 birds by the time all birds left in the species were captured and taken to zoos. There are just over 400 alive today, about half in the wild.
- The population of Przewalski's Horse, the only truly wild horse in the world, is descended from nine horses held in captivity in 1945. 1500 horses are alive today in zoos and in the wild of Mongolia.
- On Île Haute, in the Kerguelen Islands, a male and female mouflon sheep were introduced in 1957. The current population, descended only from that pair, fluctuates between 250 and 700 individuals, and shows far more genetic diversity than had been expected.
Adam And Eve Plot / Real Life