June 20, 2013

Genetic load accumulation during range expansions

arXiv:1306.1652 [q-bio.PE]

On the accumulation of deleterious mutations during range expansions

Stephan Peischl et al.

We investigate the effect of spatial range expansions on the evolution of fitness when beneficial and deleterious mutations co-segregate. We perform individual-based simulations of a uniform linear habitat and complement them with analytical approximations for the evolution of mean fitness at the edge of the expansion. We find that deleterious mutations accumulate steadily on the wave front during range expansions, thus creating an expansion load. Reduced fitness due to the expansion load is not restricted to the wave front but occurs over a large proportion of newly colonized habitats. The expansion load can persist and represent a major fraction of the total mutation load thousands of generations after the expansion. Our results extend qualitatively and quantitatively to two-dimensional expansions. The phenomenon of expansion load may explain growing evidence that populations that have recently expanded, including humans, show an excess of deleterious mutations. To test the predictions of our model, we analyze patterns of neutral and non-neutral genetic diversity in humans and find an excellent fit between theory and data.

Link

9 comments:

apostateimpressions said...

Does this study imply that deleterious mutations accumulate when populations rapidly expand their numbers, like with industrialism, because selection is suspended? I would guess that less than optimum adaptations also increase in frequency, like low IQs.

That seems to fit with the recent study that found that the average British IQ has declined by about 15 points since the Victorians. They analysed statistics going back to them regarding reaction times, which closely correlates with IQ.

http://www.dailymail.co.uk/sciencetech/article-2323944/Were-Victorians-cleverer-Research-indicates-decline-brainpower-reflex-speed.html

Meanwhile studies show that the Flynn effect has reversed in Britain. Usually IQ scores gradually increase decade on decade as social and educational conditions improve. Figures show that, despite unprecedented wealth and educational levels, with half of youngsters going to university, the average IQ of youngsters in Britain is now lower than 30 years ago, suggesting that the genetic intelligence barrier has begun to plummet. IQs in the upper half have fallen by _six points_ in 28 years.

http://www.dailymail.co.uk/news/article-1139062/British-teenagers-lower-IQ-scores-generation-ago-new-study-reveals.html

Francis Galton is estimated to have had an IQ of 200, twice the present average, which is quite humbling for all of us.

Should the vote of someone with an IQ of 70 have equal weight as that of someone with an IQ of 150? Wherelse but politics, the most important science of all?

apostateimpressions said...

Oh I think I get what they are saying. Deleterious mutations somehow segregate when populations spacially expand and they have a higher frequency in the expanded population?

<< We investigate the effect of spatial range expansions on the evolution of fitness when beneficial and deleterious mutations co-segregate. >>

terryt said...

"We find that deleterious mutations accumulate steadily on the wave front during range expansions, thus creating an expansion load. Reduced fitness due to the expansion load is not restricted to the wave front but occurs over a large proportion of newly colonized habitats".

Almost certainly the product of reducing genetic diversity on the margin of expansion leading to increased inbreeding and survival of deleterious mutations.

Grognard said...

"Almost certainly the product of reducing genetic diversity on the margin of expansion leading to increased inbreeding and survival of deleterious mutations."

lol. Again, evolution is not random chance, it's selection. All these mutations go every which direction, they don't all go into a new direction all together for the hell of it. Only when a bottleneck occurs does selection determine which variations will survive.


"That seems to fit with the recent study that found that the average British IQ has declined by about 15 points since the Victorians. They analysed statistics going back to them regarding reaction times, which closely correlates with IQ."

More like a massive demographic shift. At the time they were pulling in the best minds from around the world, and had been for some time. Now the best and brightest are heading for other waters and being replaced by massive immigration wave of cheap laborers instead of engineers scientist statesmen etc since the empire has long since collapsed and it's not a big center of the world any more (in spite of what they seem to think).

Selection or lack of it happens over many generations, GB has declined sharply in only 20-30 years.

Fanty said...

@apostateimpressions

"That seems to fit with the recent study that found that the average British IQ has declined by about 15 points since the Victorians."

What?

That does not fit to the IQ variations in the 20th century.

The average IQ of 18 year old people, in "Western oriented countries" did INCREASE by 40 points between 1920 and 1990. (test calibrated for 1920, thats why the IQ levels it detects today are extremely high)

Usual explaination: better food

1990 was the turning point in IQ development in the western world.

Since 1990 the 18 year old people lost about 30 points.

In the 1990s this effect was detected first and called "MTV Effect". In the early 2000s it was renamed to "Digital Dementia", because the latest theory was, that computers and cellphones would make brains weaker like other mashines made the muscles weaker.

Suposed drop-speed:
1990-2000: Loss of 1 IQ point per year (in 18 year olds)
2000:2010: Loss of 2 IQ points per year (in 18 year olds)

Wich means, the currently "early 40s" are the most intelligent humans that live, while the latest youngsters and 90 year olds are the most stupid humans.

Fanty said...

Oh wait, ddnt completely read to the end. You did talk about the 20 century effect and the drop too.

I am still not conviced about "estaminated IQs" of people who lived several centuries ago.

"Francis Galton is estimated to have had an IQ of 200, twice the present average"

Well, Bethoven is estaminated 180.

I doubt all these estaminations...

What do they estaminate about Da Vinci? 5000? ;-P

Fanty said...

Also, 200 must be much more "powerfull" than just "twice 100".

I recall a German TV documentation about "Hochbegabung" ("gifted" or whatevcer the English term is). Means higher or euqal to IQ130.

They described the performance of 130 compared to 100 as: To make oneself a picture of how much more performance a 130 has compared to a 100, once needs to imagine a person who would learn and think about 4 times as fast and solves problems in a quarter of the time that a 100 would need, then you roughly understand te performance difference between 100 and 130.

There is of course the question how this is for even higher IQs. Is 160 = 4x4 (16 times as fast?) and 190 = 64x as fast?

Sure is, 200 is not just "twice 100".

apostateimpressions said...

Fanty, the researchers compared reaction times, which correlates with genetic-g. It has been demonstrated that the Flynn effect does not correspond to the g factor but merely to improved social, dietry and educational conditions. Thus the study shows that Britain has experienced a genuine and serious decline in general intelligence equivalent to about 14 IQ points. The Flynn effect does not contradict the findings of the study and indeed the Flynn effect is not really relevant to that study.

The news article says at the end: "In conclusion however these findings do indicate that with respect to 'genetic g' [general intelligence] the Victorians were indeed substantially cleverer than modern populations."

I have seen no proof that the ongoing decline in British IQ is explained, partly or entirely, by the Ipad factor. The Victorian comparison shows that Britain has suffered a rapid and likely ongoing decline in g factor.

"200, twice 100". Thank you for your interesting observations on that point. It indicates that a decline in g factor is exponentially more significant than the raw IQ stats might indicate to the casual eye.

Grognard, you make a good point about mass low-grade immigration from generally low IQ populations, which will certainly impact the host IQ. I should mention that eugenic theory postulates that low IQ sections of the population breed at a significantly higher rate than higher IQ sections. That phenomenon, long statistically observed, continues to this day and can reshape the national distribution of g factor generation by generation. Thus Britain suffers a double dysgenic whammy.

That is what I meant when I said that a rapid expansion in population, like farming or industrlialsm, could be a factor in the accumulation of deleterious mutations, if lower quality biological specimens tend to breed faster in times of population growth, when the normal selective factors that lead to a high death rate among the less well adapted are suspended. In other words a spacial expansion may accompany a population growth characterised by dysgenic breeding. (I do not claim to be an expert in any of this, just an interested casual observer. :)

The OP paper seems to talk about a "wave front" that statistically contains more deleterious mutations. I am not sure that I understand that paper and the mechanism that it describes from a brief read and I may give it a longer read next week. Hopefully an English translation or at least a summary will appear lol.

cosegration, I had to look that one up lol

terryt said...

"Again, evolution is not random chance, it's selection".

Mutations are random. Selection acts on those mutations, and is not random.