Anders Hoveland
01-06-2015, 02:31 AM
A small amount of genetic diversity is good, too much is bad.
The Darwinian Sweet Spot: 3rd Cousin Marriages?
It's long been understood theoretically that there must exist a Darwinian fitness trade-off between too much inbreeding and too much outbreeding, but nobody knew where that was. If you marry your first cousin, you are likely to suffer a 30% higher infant mortality rate. But if you marry somebody too genetically dissimilar, you can start running into various reproductive problems as well.
"Third Cousins Have Greatest Number Of Offspring, Data From Iceland Shows." ScienceDaily. ScienceDaily, 8 February 2008
http://isteve.blogspot.com/2008/02/darwinian-sweet-spot-3rd-cousin.html
Outbreeding depression refers to cases where offspring from crosses between two different populations have a lower level of fitness than offspring from crosses between individuals from the same population.
One of the ways that outbreeding depression can occur is by the breakdown of biochemical or physiological compatibilities between genes in the different breeding populations. Within local, isolated breeding populations, alleles are selected for their positive, overall effects in complementary combination with other specific alleles. Due to nonadditive gene action, the same genes may have rather different effects in different genetic backgrounds--hence, the potential evolution of locally coadapted gene complexes.
These effects can be observed in switchgrass (Panicum virgatum). While actually a single species, switchgrass comes in many different varieties, with striking differences between the different types. This genetic diversity reflects the divergent evolution and adaptation to a wide range of different environments. The different varieties of switchgrass can generally be grouped into two distinct forms: the lowland cultivars and the upland cultivars.
The lowland variety tends to produce more biomass, and grow up to 2.7 meters high in favorable environments. The upland variety is generally of more northern origin, and is more cold-tolerant. Upland switchgrass types are generally shorter, less than 2.4 meters in height, and less coarse than lowland types. The upland types tend to have more vigorous rhizomes so they tend to be more sod-forming, whereas the the lowland cultivars may appear to have a bunchgrass habit. Lowland cultivars appear more plastic in their morphology, produce larger plants if stands become thin or when planted in wide rows, and they seem to be more sensitive to moisture stress than upland cultivars.
One study mentions potential negetive effects on native varieties on switchgrass caused by outbreeding depression, which could be a cause for concern.
"Gene flow matters in switchgrass, a potential widespread biofuel feedstock", Charles Kwit, C. Neal Stewart. Department of Plant Sciences, University of Tennessee, Knoxville, Tennessee; and BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
"The potential for genetic pollution has been investigated in switchgrass..."
"Appropriate Use of Genetic Manipulation for the Development of Restoration Plant Materials", T. A. Jones, J. G. Robins, Progress in Botany, Volume 72, Part 5, p 249-264, 2011
Different groups of humans have been separately evolving for tens of thousands of years. There has been plenty of genetic divergence over this long period of time. Could it be possible that each of these separate groups of people have achieved, through natural selection, a fine-tuned balance of hormones and subtle gene expression, which could become upset by sudden change?
Herbert Spencer and the Harvard geneticist Edward East, a pioneer in hybrid corn research, proposed that genetic crossing would disrupt the smooth operation of the physical and mental qualities which have been established in each race over hundreds of generations by natural selection.
Carleton Coon, former professor at Harvard and president of the American Association of Physical Anthropologists, wrote: "Genes that form part of a cell nucleus possess an internal equilibrium as a group, just as do the members of social institutions. Genes in a population are in equilibrium if the population is living a healthy life as a corporate entity. Racial intermixture can upset the genetic as well as the social equilibrium of a group."
An analysis of more than 3 million respondents revealed the average pay was $15.74 per hour for people of mixed race, $17.39 for black people and $22.04 for white people. This was despite the fact that 18 per cent of mixed-race people had college degrees, compared with 11 per cent of black people and 28 per cent of white people.
"Can the 'one-drop rule' tell us anything about racial discrimination? New evidence from the multiple race question on the 2000 Census", Robert W. Fairlie
University of California, Santa Cruz
A study by J. Richard Udry’s National Longitudinal Study of Adolescent Health, which sampled a random, nationally representative school-based sample of U.S. adolescents in grades 7 through 12, during 1994-1995, showed an increase in behavioral problems amongst mixed-race children, as well as significantly higher rates of asthma, and generally poorer health. Another interesting finding was that mixed children that had a black parent were significantly more likely (63% more) to have skin problems.
J. Richard Udry, Janet Hendrickson-Smith, Carolina Population Center, University of North Carolina at Chapel Hill, 2003
The Darwinian Sweet Spot: 3rd Cousin Marriages?
It's long been understood theoretically that there must exist a Darwinian fitness trade-off between too much inbreeding and too much outbreeding, but nobody knew where that was. If you marry your first cousin, you are likely to suffer a 30% higher infant mortality rate. But if you marry somebody too genetically dissimilar, you can start running into various reproductive problems as well.
"Third Cousins Have Greatest Number Of Offspring, Data From Iceland Shows." ScienceDaily. ScienceDaily, 8 February 2008
http://isteve.blogspot.com/2008/02/darwinian-sweet-spot-3rd-cousin.html
Outbreeding depression refers to cases where offspring from crosses between two different populations have a lower level of fitness than offspring from crosses between individuals from the same population.
One of the ways that outbreeding depression can occur is by the breakdown of biochemical or physiological compatibilities between genes in the different breeding populations. Within local, isolated breeding populations, alleles are selected for their positive, overall effects in complementary combination with other specific alleles. Due to nonadditive gene action, the same genes may have rather different effects in different genetic backgrounds--hence, the potential evolution of locally coadapted gene complexes.
These effects can be observed in switchgrass (Panicum virgatum). While actually a single species, switchgrass comes in many different varieties, with striking differences between the different types. This genetic diversity reflects the divergent evolution and adaptation to a wide range of different environments. The different varieties of switchgrass can generally be grouped into two distinct forms: the lowland cultivars and the upland cultivars.
The lowland variety tends to produce more biomass, and grow up to 2.7 meters high in favorable environments. The upland variety is generally of more northern origin, and is more cold-tolerant. Upland switchgrass types are generally shorter, less than 2.4 meters in height, and less coarse than lowland types. The upland types tend to have more vigorous rhizomes so they tend to be more sod-forming, whereas the the lowland cultivars may appear to have a bunchgrass habit. Lowland cultivars appear more plastic in their morphology, produce larger plants if stands become thin or when planted in wide rows, and they seem to be more sensitive to moisture stress than upland cultivars.
One study mentions potential negetive effects on native varieties on switchgrass caused by outbreeding depression, which could be a cause for concern.
"Gene flow matters in switchgrass, a potential widespread biofuel feedstock", Charles Kwit, C. Neal Stewart. Department of Plant Sciences, University of Tennessee, Knoxville, Tennessee; and BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
"The potential for genetic pollution has been investigated in switchgrass..."
"Appropriate Use of Genetic Manipulation for the Development of Restoration Plant Materials", T. A. Jones, J. G. Robins, Progress in Botany, Volume 72, Part 5, p 249-264, 2011
Different groups of humans have been separately evolving for tens of thousands of years. There has been plenty of genetic divergence over this long period of time. Could it be possible that each of these separate groups of people have achieved, through natural selection, a fine-tuned balance of hormones and subtle gene expression, which could become upset by sudden change?
Herbert Spencer and the Harvard geneticist Edward East, a pioneer in hybrid corn research, proposed that genetic crossing would disrupt the smooth operation of the physical and mental qualities which have been established in each race over hundreds of generations by natural selection.
Carleton Coon, former professor at Harvard and president of the American Association of Physical Anthropologists, wrote: "Genes that form part of a cell nucleus possess an internal equilibrium as a group, just as do the members of social institutions. Genes in a population are in equilibrium if the population is living a healthy life as a corporate entity. Racial intermixture can upset the genetic as well as the social equilibrium of a group."
An analysis of more than 3 million respondents revealed the average pay was $15.74 per hour for people of mixed race, $17.39 for black people and $22.04 for white people. This was despite the fact that 18 per cent of mixed-race people had college degrees, compared with 11 per cent of black people and 28 per cent of white people.
"Can the 'one-drop rule' tell us anything about racial discrimination? New evidence from the multiple race question on the 2000 Census", Robert W. Fairlie
University of California, Santa Cruz
A study by J. Richard Udry’s National Longitudinal Study of Adolescent Health, which sampled a random, nationally representative school-based sample of U.S. adolescents in grades 7 through 12, during 1994-1995, showed an increase in behavioral problems amongst mixed-race children, as well as significantly higher rates of asthma, and generally poorer health. Another interesting finding was that mixed children that had a black parent were significantly more likely (63% more) to have skin problems.
J. Richard Udry, Janet Hendrickson-Smith, Carolina Population Center, University of North Carolina at Chapel Hill, 2003