Thursday, March 30, 2006

Income and reproductive success in the US

A paper looking at sex differences in the effect of income on reproductive success, with implications for understanding the demographic transition:

Sex, status, and reproductive success in the contemporary United States
- Rosemary Hopcroft

Evolution and Human Behavior, March 2006, 27:104-120

Abstract: This paper reexamines the relationship between status and reproductive success (at the ultimate and proximate levels) using data on sex frequency and number of biological children from representative samples of the U.S. population. An ordered probit analysis of data from the 1989–2000 General Social Survey (GSS) shows that high-income men report greater frequency of sex than all others do. An OLS regression of data from the 1994 GSS shows that high-income men have more biological children than do low-income men and high-income women. Furthermore, more educated men have more biological children than do more educated women. Results also show that intelligence decreases the number of offspring and frequency of sex for both men and women.

Recent Selection in the Human Genome

A new paper in PLoS Biology by Voight, Pritchard et al.

A Map of Recent Positive Selection in the Human Genome B. Voight et al.


Briefly, this paper uses the fact that favored alleles can be expected to lie in longer haplotypes than expected based on the rest of the genome (background). 800, 000 SNPs are examined in 309 individuals divided into 3 major population groups (AF, EU, AS). The authors point out that the signals of selection in this test are for markers that are at an intermediate frequency, and most of the signals of selection are presumed to have arisen after the three goups split off.

Types of genes under selection:

- chemosensory perception/olfaction
- carbohydrate metabolism
- fertility/reproduction/spermatogenesis (why????)
- skin pigmentation
- skeletal development/morphological features
... and a few others...

NOTE: There is also a paper in this same issue that discusses the need for more stringent measures and standards for reporting "selection" from genetic data.

Thursday, March 23, 2006

The emergence of Homo and the African "carnivore guild"

This is something that I haven't heard of before and seems to be of great relevance to the emergence of Homo, with its' increased stature and brain size.

Out of Africa 1: Who, where, and when?, by J.J. Shea
Evolutionary Anthropology, Jan/Feb 2006, 15:1-2

Passage of interest:

"There has been a growing consensus in the paleo-anthropological literature that the increases in stature among early Homo erectus fossils over earlier and contemporary hominins reflects an increase in higher-quality food sources in their diets, most likely meat or fat, either scavenged or hunted. Meave Leakey, in her presentation, noted correlated shifts in the African carnivore guild that coincided with the emergence of Homo. The major such shift was a decline among large carnivorans of specialists and an increase in generalists across the Plio-Pleistocene. Increased hominin carnivory, in the context of what was almost certainly a flexible, situationally variable, omnivorous diet may have been a factor in these changes."

Friday, March 17, 2006

MC1R functional variants in Asia

The authors find functional variants (pharmacologically tested) mainly in high altitude Asian/Oceanian populations.

Identification of novel functional variants of the melanocortin 1 receptor gene originated from Asians.

Kazuhiro Nakayama et al.

Human Genetics, April 2006, 119:322-330.

Abstract: Human melanocortin 1 receptor (MC1R) is a seven transmembrane G-coupled protein receptor that upregulates the cAMP pathway. Several functional variants of MC1R that show an impaired ability to activate the cAMP pathway are strongly associated with fair skin and red hair in Europeans and European descendants. The sequence variations of the MC1R gene were repeatedly investigated against worldwide populations; however, there was no evidence that functional variant of MC1R exists in non-European descendants. We report the presence of novel functional variants of MC1R with Asian origins. Three novel variants of MC1R, Phe147Δ, Thr157Ile, and Pro159Thr, were identified in our screening for the sequence variations of the MC1R gene against 995 individuals from 30 Asian and Oceanian populations; there was a single case for the Pro159Thr variant allele and two instances of Phe147Δ and Thr157Ile variant alleles. Our pharmacological assay revealed that Phe147Δ, Thr157Ile, and Pro159Thr variant showed similar or more dramatically impaired activities in comparison with Arg151Cys, which is a major functional variant of MC1R in Europeans. These functional variant alleles were geographically localized in relatively high latitudes, which suggest that the adaptation to ambient UV light intensity may play an important role in shaping the geographical distribution of MC1R alleles in Asia and Oceania.

Monday, March 06, 2006

Population substructure due to assortative mating

The authors of this paper find that even in an ethnically homogeneous population, stratification can occur due to assortative mating.

The Effect of Assortative Mating upon Genetic Association Studies: Spurious Associations and Population Substructure in the Absence of Admixture

David T. Redden and David B. Allison

Behavior Genetics, Online First

: Spurious associations due to confounding factors are an often cited and intensely debated concern for genetic association studies. Great attention has been focused upon the specific threat of confounding due to population stratification. This emphasis has spurred the development of many statistical genetic methods to detect and correct for the potentially confounding effects of admixture. Unfortunately, this emphasis on admixture has led some authors to suggest that if ethnically homogenous populations are used, spurious associations are unlikely to occur. We show that under small and realistic degrees of assortative mating over time, spurious associations arise even in ethnically homogeneous populations. We demonstrate that structured association and genomic control tests can, under certain conditions, correct for these spurious associations. We conclude that investigators should not assume spurious associations will not occur in association studies using ethnically homogenous populations and recommend the use of genomic control methods and/or family-based association tests within genetic association studies.
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