Minimum viable human population

Skeptical said:
To Dinosaur

If we accept the premise that one man and one woman are trying to repopulate the world,
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But we don't. What if they only have sons?

It is an interesting question though. Assuming that we could par people, and realizing that way less men are needed than women, maybe 2-3 men (1 for back up) and 8 women would do the job. This way inbreeding could be avoided for at least 2 generations and cousins marrying didn't seem to be a huge problem in the past....

Here is the coupling:

Men are called A and B, women 1-8

Man A fathers kids with 1-4 women, who later breed kids from Man B and women 5-8 kids. For faster population we throw in a more complicated version too, where both men fathers kids with all women (but we assume fatherhood can be established) and the kids marry first the unrelated kids.

Then down the line they will try to par off the less related kids.
 
Hercules

I do not know how variable the genetics are within Drosophila and zebrafish populations, but I know that Homo sapiens has a limited genomic variability from get go. I am aware that incestuous reproduction leads to a high rate of defective offspring in humans. You have told me that it is different with Drosophila and zebrafish. OK. I believe you. But that is not true for humans.
 
For a generation ship we would need about 10-20 women and a few liters of frozen sperm from 100thousand plus men. Men are not required so only females would need to be born. When you get to the destination you could then go back to having males. Also as a back up several 1000 female gametes could also be on hand in case of any genetic problems.

Why bring men to use up resources when all they are needed for are sperm donors.

Thus we can carry all races to a new world without the need for a large population on the ship.

The only problem is how long can we freeze human gametes.
 
Single sex

I don't think a single sex society is viable in a generation type ship.
 
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If you want to follow this line of logic, then why not build a ship programmed to be operated purely by robots? After all, the first interstellar ship will not be built for 500 to 1000 years, and we can expect robotics to be highly sophisticated by then. We can put artificial wombs on board (again due to the technological progress in 500 to 1000 years) and a large number of frozen embryos. The length of time to get to other stars becomes kind of unimportant when the passengers are frozen. Careful selection of the highest genetic calibre for the embryos should ensure the new colony gets off to the best start.
 
alanwc said:
I don't think a single sex society is viable in a generation type ship.
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Is it viable anywhere? Perhaps if they were all lesbians, but there's no way to guarantee that their daughters would be.

Who would sign up for a lifelong one-way voyage with the promise that there will never be anyone of the opposite sex? I'm sure out of seven billion people there actually are a few, but what other quirks do they have and would we want them in charge of galactic exploration?
Skeptical said:
If you want to follow this line of logic, then why not build a ship programmed to be operated purely by robots?
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Humans want to see it first-hand, not a video clip shot by a robot ten, twenty, a thousand years ago.
Careful selection of the highest genetic calibre for the embryos should ensure the new colony gets off to the best start.
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You're sure putting a lot of faith in those robot critters. Considering how difficult it is for humans to raise their children, are you willing to trust the future of the galaxy to a bunch of humans who were raised by machines without ever interacting with adults of their own species?

Not to mention, are you willing to trust this endeavor to a bunch of computers with no technicians around to fix their software defects? Sounds plenty scary to me. I guess those robots won't be running Microsoftware. ;)
 
Fraggle

I doubt there will ever be tourists going to other stellar systems. When the closest takes a journey of decades, it becomes rather impractical. So, for anyone other than colonists, viewing another planet around another star becomes a case of watching whatever the futuristic equivalent of a DVD might be.

Faith in robots?
Not so much that, as faith in human ingenuity. Over 500 to 1000 years, the result will be enormously sophisticated.

Do I trust them to raise kids? Why not. Considering what a hash of it human parents make, how can these incredibly intelligent and finely programmed robots do worse? At least none of those kids will be beaten up because Dad got drunk and lost his temper.

Software defects?
Some of the robots will doubtless be programmed to repair other robots, including their own kind.

Imagine how much easier it would be to send a starship with robots and frozen embryos. No difficult life support. No need for artificial gravity. No need to entertain. Radiation shielding only around the frozen embryo tanks. The robots could turn themselves off for the multi-decade voyage. The time to travel is irrelevent since the passengers will not experience it. In fact, the whole shebang could be done on a star ship a fraction of the size of an ark ship required for conscious human colonists. A fraction of the cost also.
 
Skeptical: To the best of my knowledge there have been no controlled incest experiments performed with human subjects.

Without controlled experiments statistics are unreliable. You are picking numbers out of thin air or from studies based on uncontrolled data. Your statements on this subject are no more than opinions.

At least in the Western technological nations, incest very rarely occurs in normal successful families. When you study a group of people alleged to be the result of an incestuous union, you are studying a suspect population.

In such population, you cannot be 100% sure of the identity of the father. You are probably dealing with people with less than average intelligence & inferior education.

The only valid statements you can make about incest relates to the fact that it is likely to result in the pairing/grouping of recessive genes. In most populations, recessive genes are more likely to be detrimental.

The act of incest itself does not cause faulty offspring. If you had father/daughter or brother/sister incest where the original father was a world class athlete or a genius, you would increase the chances for very good offspring. If the father & his initial spouse had few or no detrimental recessives, you would not have much chance of defective offspring & certainly little or no chance of the line dying out.

Cleopatra was an example of several generations of brother/sister marriages. She was alleged to be attractive & known to be intelligent/healthy. I am sure there are other examples involving royal families.

Some European royal family had recessives for hemophilia & frequent marriages of cousins, which resulted in a lot of early deaths in that family. It was not the incest that caused the hemophilia. It was the pairing of detrimental recessives.
 
I think most of the numbers quoted for the minimum number of mating pairs relate to primitive environments.

A generation starship would provide a better environment & the crew/passengers could be selected based on genetic analysis. The required number of mating pairs would be minimal for a generation starship.
 
Dinosaur

The genetics of incest are well understood. Related to the problems of incest are the problems of inbreeding. Also well understood. If you want to pretend that there are no problems, then I cannot convince you.

Certainly there are no controlled experiments on reproduction from human incest. There are no controlled experiments on how dioxins poison people either. These are things that are not done because they would be totally unethical. Instead, we look to uncontrolled events and their results. Such small scale studies show that incestuous reproduction leads to a high rate of defects in resultant offspring.

Cleopatra may have been beautiful. or she may have had a face like a draft horse. We do not actually have a credible source from the time. The closest thing is a silhouette of her face from coins of the time. However, that tells us nothing. Shakespeare called her beautiful, but good old Willy knew no more than I do about her looks. Important men wooed her, but that was just as likely to be from a desire for power and wealth as anything else.

Here is the abstract of a study that shows incest leads to a high rate of mental deformity.
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2788.1990.tb01560.x/abstract

However, I am aware that there are people who, for whatever reason, refuse to believe that incest is bad, and no matter how many references I post, I will not convince those people.
 
There is a huge difference between the starship and repopulating Earth idea. For the starship, we only need a few generations, after that we can go back to normal breeding.
To repopulate Earth, all the genetic problems will be carried down forever to further generations.

Now I looked at the question that common sense allowed in the experience, but no complicated scientific tools. So you can look at kids and determine whom they belong but you can't make genetic tests with them or DNA sequencing or sperm freezing.

Assuming no natural disaster whipping out the colony, I think a relative small number is sufficient for the spieces to survive. 4 men and 16 women (all healthy) max. but probably less.
 
"Minimum viable population is usually estimated as the population size necessary to ensure between 90 and 95 percent probability of survival between 100 to1,000 years into the future. The MVP can be estimated using computer simulations for population viability analyses (PVA). PVA models populations using demographic and environmental information to project future population dynamics. The probability assigned to a PVA is arrived at after repeating the environmental simulation thousands of times.

For example, for a theoretical simulation of a population of 50 giant pandas in which the simulated population goes completely extinct, 30 out of 100 stochastic simulations projected 100 years into the future are not viable. Causes of extinction in the simulation may include inbreeding depression, natural disaster, orclimate change. Extinction occurring in 30 out of 100 runs would give a survival probability of 70%. In contrast, in the same simulation with a starting population of 60 pandas, the panda population may only become extinct in four of the hundred runs, resulting in a survival probability of 96%. In this case the minimum viable population that satisfies the 90- to 95% probability for survival is between 50 and 60 pandas. (These figures have been invented for the purpose of this example.)" off wiki "Minimum viable population"
 
Skeptical:From your Post #10
A brother/sister mating results in offspring with about a 50% chance of serious - not necessarily fatal - defect.
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The above is incorrect.
There will be no problem if neither sibling has a detrimental gene. If both have one detrimental gene the following is applicable.
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If the detrimental gene is dominant, 75% of the children will have the defect.

If the detrimental gene is recessive, only 25% will have the defect.​
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Skeptical: From your Post #31
The genetics of incest are well understood. Related to the problems of incest are the problems of inbreeding. Also well understood. If you want to pretend that there are no problems, then I cannot convince you.
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I doubt that you know much about genetics.​

If you understood genetics you would realize the following
Incest increases the probability of a pair of matched recessive genes being inherited.

There is a tendency for recessive genes to be detrimental. The basic reason is that a detrimental gene which is also dominant gene is highly likely to be eliminated from the gene pool. A recessive gene can last for quite a few generations.

If a brother mates with his sister, there will only be a problem if they both carry the same detrimental recessive gene. In this case, 25% of their children are expected to inherit that gene from each parent & suffer the detrimental trait; 25% are expected to not have a detrimental gene; & 50% are expected to have exactly one detrimental gene.

If neither or only one of the siblings carry the recessive detrimental gene, there will be no problem.
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Cleopatra was the result of several generations of brother/sister matings (I think 6 generations). Id est: her parents, grandparents, great grandparents, et cetera were brother/sister matings.

History indicates that she was intelligent (at least not retarded) & attractive. This indicates that incest is not detrimental in the absence of detrimental genes. Id est: It is not incest itself which causes a problem; It only causes a problem if recessive detrimental genes become paired.

BTW: There are some interesting Situations involving detrimental genes. Consider the following.

A gene for Sickle cell anemia is recessive. It also has the trait that it prevents a lethal form of some disease (malaria, I think). Prior to modern medicine, some African populations were almost 100% carriers on exactly one sickle cell gene. The situation was as follows
Matings tended to result in 25% of the children having no sickle cell gene: Almost all of these died of malaria prior to adulthood.

25% with two sickle cell genes: Almost all of these died of sickle cell anemia.

50% with exactly one sickle cell gene: All of these had neither sickle cell anemia nor malaria.
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The gene for Tay Sachs (?spelling) in Jewish populations has an interesting history. One such gene confers immunity for some disease prevalent in European ghettos.
 
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