Question about a biologos article.

[Annonymus]

http://biologos.org/blog/does-genetics- ... mal-couple

This website says that it's impossible that humanity came from two people, and they said that they proved it using the three methods in the article. To someone who knows about genetics, is it true?

[PaulSacramento]

It is impossible for humanity AS WE HAVE IT NOW, to have evolved from ONLY two people in such a short period of time.
The genetic variety present today could not have happened via only two people

[PaulSacramento]

In short, the article points out there are multiple lines of evidence ( in the case of the article they point out 3) that show that humans did NOT/could NOT come from only 2 people.

[Kurieuo]

I'm not so sure Paul that it is proven beyond doubt.

Consider an example of mouflon sheep:

In 2007 a research team reported on the genetic diversity of wild mouflon sheep on one of the islands that are part of the Kerguelen sub-Antarctic archipelago.6 This group of sheep provided researchers with an unprecedented opportunity to study the effects of population dynamics on genetic diversity in small populations.

In 1957 a male and female yearling were placed onto Haute Island (an island in the Kerguelen Archipelago). These two sheep were taken from a captive population in France. By the beginning of the 1970s, the number had grown to 100 individuals and peaked at 700 sheep in 1977. Since that time the population has fluctuated in a cyclical manner between 250 and 700 members. Given that the population began with only two individuals (the founder effect), has experienced cyclical changes in the population size, and was isolated on an island, the researchers expected very low genetic diversity (measured as heterozygosity).

Using mathematical models, the heterozygosity of a population can be computed at any point in time from the heterozygosity of the ancestral population (which was known for the original mouflon pair) and the original population size. What the researchers discovered, however, when they measured this quantity directly for the sheep on Haute Island was that it exceeded the predictions made by the models by up to a factor of 4. In other words, the models underestimated the genetic diversity of the actual population.

The researchers explained this discrepancy by speculating that natural selection drives the increase in genetic diversity, since an increase in genetic variability increases the survivability of the population.

Consequently, if these same models were used to estimate the effective sizes of the ancestral population from the measured genetic diversity at any point in time, they would have overestimated the original population size as much larger than two individuals.

Also, what are we to make of DNA sequences sampled from humans alive today being traced back to single ancestors.
Can we not understand these as reflecting an origin from a single man and single woman?

[PaulSacramento]

I'm not so sure Paul that it is proven beyond doubt.

Consider an example of mouflon sheep:

In 2007 a research team reported on the genetic diversity of wild mouflon sheep on one of the islands that are part of the Kerguelen sub-Antarctic archipelago.6 This group of sheep provided researchers with an unprecedented opportunity to study the effects of population dynamics on genetic diversity in small populations.

In 1957 a male and female yearling were placed onto Haute Island (an island in the Kerguelen Archipelago). These two sheep were taken from a captive population in France. By the beginning of the 1970s, the number had grown to 100 individuals and peaked at 700 sheep in 1977. Since that time the population has fluctuated in a cyclical manner between 250 and 700 members. Given that the population began with only two individuals (the founder effect), has experienced cyclical changes in the population size, and was isolated on an island, the researchers expected very low genetic diversity (measured as heterozygosity).

Using mathematical models, the heterozygosity of a population can be computed at any point in time from the heterozygosity of the ancestral population (which was known for the original mouflon pair) and the original population size. What the researchers discovered, however, when they measured this quantity directly for the sheep on Haute Island was that it exceeded the predictions made by the models by up to a factor of 4. In other words, the models underestimated the genetic diversity of the actual population.

The researchers explained this discrepancy by speculating that natural selection drives the increase in genetic diversity, since an increase in genetic variability increases the survivability of the population.

Consequently, if these same models were used to estimate the effective sizes of the ancestral population from the measured genetic diversity at any point in time, they would have overestimated the original population size as much larger than two individuals.

Also, what are we to make of DNA sequences sampled from humans alive today being traced back to single ancestors.
Can we not understand these as reflecting an origin from a single man and single woman?

Nothing is proven BEYOND a doubt my friend.
The article simply points out that views that carry multiple lines of evidence can not be discounted and carry more weight than those that don't.