The tiny islet of ball’s Pyramid lies 600 kilometers to the East of Australia in the South Pacific ocean, Vipera from the sea as a piece of glass. And there were — sloped cliff, hiding under a spindly Bush — last. Two escaped, and only nine years later there were 9000, children and grandchildren children and grandchildren of Adam and eve.
No, it’s not a fun interpretation of the history of the creation of man. These happily were three lobster Dryococelus australis, arthropods are the size of a human fist. They were considered extinct soon after black rats have invaded their native Lord Howe island in 1918, but was found on the Pyramid ball 83 years later. This species owes its miraculous restoration of the team of scientists who braved 130 vertical feet of rock to find their hiding place in 2003. Lobster named Adam and eve and sent to breeding program in the Melbourne zoo.
To save animals from Armageddon. Three female lobster lays 10 eggs every 10 days and are capable of parthenogenesis; they do not need the male for reproduction. The colonization of the Earth people again — is another matter. Will we be able to do it? How long will it take?
The answer to this question is more than idle interest. It is a question worthy of international attention, important and relevant, and engage them in NASA, and the pioneers of moving to another planet.
Let’s fast forward to 100 years ahead. Then the case of humanity gone horribly wrong, and the machines have destroyed the Earth’s population — as predicted by Stephen Hawking in 2014. There are only two left. I can’t help it: the first generation will be presented to brothers and sisters.
Sigmund Freud considered incest is the only universal human taboo, along with the murder of his parents. This is not only horrible, but dangerous. A study of infants born in Czechoslovakia between 1933 and 1970, showed that close to 40% of those whose parents were relatives of the first degree, were disabled, and 14% died.
Recessive risks
To understand why inbreeding is so dangerous, we need to become a little familiar with genetics. We all have two copies of each gene, one from each parent. But some gene variants are not shown if you do not have two the same. Most genetic diseases are caused by these “recessive” variants that have slipped past the radar of evolution, being essentially harmless. According to statistics, the average person has one or two recessive lethal mutations in the genome.
If the pair will be in a relationship, it will manifest relatively quickly. Take achromatopsia, a rare recessive disorder that leads to complete color blindness. Studies have shown that 1 of the 33,000 Americans it manifests itself, and 1 out of 100 carries. If one of our post-apocalyptic survivors will be a one in four chance that the child will copy. Yet such is not terrible. After one generation of incest increases the risk of a one in four chance that the children will have two copies. A chance of 1: 16 that the first grandchild of the original couple will have the disease.
Such was the fate of the inhabitants of Pingelap, an isolated Atoll in the Western Pacific ocean. All of its population descended from 20 survivors of a Typhoon that covered the island in the 18th century, including the carrier of achromatopsia. With such a small genetic pool, today one tenth of the population suffers from color blindness.
Even having in mind those terrible risks if the survivors will leave enough children, chances are high that some of them will be healthy. But what if inbreeding will continue for hundreds of years? You do not need to be stuck on the island to learn, because there is a society that just can’t get enough of close relatives: a European monarchs. And after nine generations of strategic marriages between cousins, sisters, uncles and nieces, for 200 years, the Spanish Habsburgs naturally conduct a similar experiment.
Charles II was the most famous victim of the family. Born with a whole set of physical and mental disabilities, the monarch learned to walk only to eight years. In adulthood infertility it meant the disappearance of the whole dynasty.
In 2009, a group of Spanish scientists has found out why. Ancestors of Karl so confused that his “coefficient of inbreeding” — a figure reflecting the proportion of inherited genes that are identical in both parents was higher than if he was born of twins.
The same measure is used by ecologists to estimate the genetic risks faced by endangered species. “When the small size of the population, sooner or later everyone will be related, and with increasing connectivity, the effects of inbreeding are manifested all the stronger,” explains Bruce Robertson from Otago University. It examines new Zealand’s giant, flightless parrot, named kakapo, of which there are only 125 on the planet.
Of particular concern are the effects of inbreeding on sperm quality, they increase the proportion of infertile sperm from 10% to 40%. This is an example of inbreeding depression, says Robertson, is caused by the impact of recessive genetic defects in the population. Despite the abundance of food and protection from predators, the kakapo can not cope.
Immune blend
Endangered species may be affected and long-term risks. Although they may be well adapted to the environment, genetic diversity allows species to pave the way through future challenges. This is especially important for immunity. “This is probably the most calls for diversity, even people. We choose partners with a very different immune composition, so that our descendants have a wide array of immune protection,” says Dr. Philip Stephens from the University of Durham. Sometime in our evolutionary past, mating with Neanderthals could give our immune system the genetic push.
Even if our species can get through this, it will become unrecognizable. When a small group of people remain isolated for too long, they become vulnerable to the founder effect, due to which loss of genetic diversity increases the genetic oddities of the population. New people will not only look and hearing the other — it could be a whole new look.
How much diversity do you need? Disputes on this subject have roots in the 80 years, Stevens says, when an Australian scientist has proposed a universal rule of thumb. “In fact, you have 50 breeding individuals to avoid inbreeding depression and 500 to adapt,” he says. This rule is still used today although this number was increased to 5000 to account for random loss of genes in the transmission from generation to generation — to inform the IUCN red data book, which collects the catalogue of species under threat of extinction.
All this leads to a revised policy of preservation of the species, to focus on the “most endangered” species, those that increasingly are under threat of extinction. “This is a saving feature in the context of the sort — you sift the threats and ask the question, is there any chance to save them. In other words, you can say, “okay, can we forget about the form”?
And yet, one scholar aptly remarked that we are living proof of this concept inherent disadvantages. According to the anatomical and archaeological evidence, our ancestors are unable to perform our own population problem, and approximately 1000 individuals has existed for a million years. And about 50 000-100 000 years ago we reached a new level when our ancestors migrated from Africa. As expected, we were left with extremely low genetic diversity. The study of genetic differences between neighbouring groups of chimpanzees from 2012 revealed more diversity in one group than among all seven billion people living today.
The study of our ancestors can be our best choice. Anthropologist John Moore in 2002 published its assessment, which led to the base of a small migratory groups of early humans — about 160 people. It’s recommended to begin with young childless couples and look out for the presence of potentially harmful recessive genes. Alas, Moore was assessed a long-term space travel, and not repopulating the planet. His numbers were built around two hundred years of isolation, before the pioneers will return to Earth.
So what about the last man and last women? It’s hard to say with some confidence, but Stevens looks optimistic. “Evidence of short-term effects of low genetic diversity is very strong, but all these things are purely probabilistic. There are many stories of incredible journeys from the end of the world — everything is possible”.
While the Apocalypse did not shake the foundations of modern civilisation, humanity can recover surprisingly quickly. At the turn of the 20 century North American society of Hutterites — very inbred, by the way — has reached the highest level of population growth for all time, doubling every 17 years. And if every woman gave birth to eight children, we would come to a seven billion population and the modern crisis of overpopulation in just over 556 years.