Has human evolution stopped.pdf

Rambam Maimonides Medical Journal, 2010

It has been argued that human evolution has stopped because humans now adapt to their environment via cultural evolution and not biological evolution. However, all organisms adapt to their environment, and humans are no exception. Culture defines much of the human environment, so cultural evolution has actually led to adaptive evolution in humans. Examples are given to illustrate the rapid pace of adaptive evolution in response to cultural innovations. These adaptive responses have important implications for infectious diseases, Mendelian genetic diseases, and systemic diseases in current human populations. Moreover, evolution proceeds by mechanisms other than natural selection. The recent growth in human population size has greatly increased the reservoir of mutational variants in the human gene pool, thereby enhancing the potential for human evolution. The increase in human population size coupled with our increased capacity to move across the globe has induced a rapid and ongoing evolutionary shift in how genetic variation is distributed within and among local human populations. In particular, genetic differences between human populations are rapidly diminishing and individual heterozygosity is increasing, with beneficial health effects. Finally, even when cultural evolution eliminates selection on a trait, the trait can still evolve due to natural selection on other traits. Our traits are not isolated, independent units, but rather are integrated into a functional whole, so selection on one trait can cause evolution to occur on another trait, sometimes with mildly maladaptive consequences.

Proceedings of The National Academy of Sciences, 2007

Genomic surveys in humans identify a large amount of recent positive selection. Using the 3.9-million HapMap SNP dataset, we found that selection has accelerated greatly during the last 40,000 years. We tested the null hypothesis that the observed age distribution of recent positively selected linkage blocks is consistent with a constant rate of adaptive substitution during human evolution. We show that a constant rate high enough to explain the number of recently selected variants would predict (i) site heterozygosity at least 10-fold lower than is observed in humans, (ii) a strong relationship of heterozygosity and local recombination rate, which is not observed in humans, (iii) an implausibly high number of adaptive substitutions between humans and chimpanzees, and (iv) nearly 100 times the observed number of highfrequency linkage disequilibrium blocks. Larger populations generate more new selected mutations, and we show the consistency of the observed data with the historical pattern of human population growth. We consider human demographic growth to be linked with past changes in human cultures and ecologies. Both processes have contributed to the extraordinarily rapid recent genetic evolution of our species.

eLS, 2013

Regions of the human genome that have been subject to past positive selection contain patterns of genetic variation that are markedly different in specific ways from regions that have not experienced positive selection. By uncovering these so-called signatures of positive selection in the genome we can discover the unique ways in which humans have evolved.

Hacettepe journal of biology and chemistry, 2010

Humans are genetically little diverged from their closest living relatives, chimpanzees. However, human anatomy, physiology and behavior show substantial divergence from those of chimpanzees and other primates. The evolutionary processes that generated this phenotypic divergence are still debated. Given the incomplete state of the hominid fossil record, genetic information is indispensible for studying human evolution. Recently, data from genome sequencing projects, gene expression profiling, and large-scale genotyping across multiple populations, has significantly improved our understanding of human origins, as well as the forces of selection, adaptation, and demographic forces that shaped human evolution. Recent multispecies comparative genomic studies indicate that random genetic drift, i.e. neutral evolution, is a leading evolutionary mechanism in shaping human protein coding sequences, as well as gene expression patterns. Still, there is also compelling evidence that a large number of human genes were affected by adaptive evolution. Genes involved in immunity, sensory perception, reproduction, and apoptosis appear among the most frequently positively selected classes. Likewise, comparative transcriptome studies indicate adaptive expression changes in human brain gene expression. Importantly, variants of both positively and negatively selected genes are frequently found to be responsible for human genetic diseases. Comparison of genetic diversity within and between human populations suggests that humans have been a relatively small, homogeneous species. Accordingly, patterns of genetic diversity are to large extent shaped by neutral, demographic processes. Meanwhile, genome scans and functional studies identify pathogens, diet, and environmental conditions as major selective forces driving genetic diversity in humans. These results portray human evolution as a complex process, simultaneously affected by forces of selection and drift.

Evolution, 2007

Starting with "mitochondrial Eve" in 1987, genetics has played an increasingly important role in studies of the last two million years of human evolution. It initially appeared that genetic data resolved the basic models of recent human evolution in favor of the "out-of-Africa replacement" hypothesis in which anatomically modern humans evolved in Africa about 150,000 years ago, started to spread throughout the world about 100,000 years ago, and subsequently drove to complete genetic extinction (replacement) all other human populations in Eurasia. Unfortunately, many of the genetic studies on recent human evolution have suffered from scientific flaws, including misrepresenting the models of recent human evolution, focusing upon hypothesis compatibility rather than hypothesis testing, committing the ecological fallacy, and failing to consider a broader array of alternative hypotheses. Once these flaws are corrected, there is actually little genetic support for the out-of-Africa replacement hypothesis. Indeed, when genetic data are used in a hypothesis-testing framework, the out-of-Africa replacement hypothesis is strongly rejected. The model of recent human evolution that emerges from a statistical hypothesis-testing framework does not correspond to any of the traditional models of human evolution, but it is compatible with fossil and archaeological data. These studies also reveal that any one gene or DNA region captures only a small part of human evolutionary history, so multilocus studies are essential. As more and more loci became available, genetics will undoubtedly offer additional insights and resolutions of human evolution.

Proceedings of the National Academy of Sciences, 2010

This paper results from the Arthur M. Sackler Colloquium of the National Academy of Sciences, "Evolution in Health and Medicine" held April 2-3, 2009, at the National Academy of Sciences in Washington, DC. The complete program and audio files of most presentations are available on the NAS web site at www.nasonline.org/Sackler_Evolution_Health_Medicine.

Nature Genetics, 2008

The considerable range of observed phenotypic variation in human populations may reflect, in part, distinctive processes of natural selection and adaptation to variable environmental conditions. Although recent genome-wide studies have identified candidate regions under selection 1-5 , it is not yet clear how natural selection has shaped population differentiation. Here, we have analyzed the degree of population differentiation at 2.8 million Phase II HapMap single-nucleotide polymorphisms 6 . We find that negative selection has globally reduced population differentiation at amino acid-altering mutations, particularly in disease-related genes. Conversely, positive selection has ensured the regional adaptation of human populations by increasing population differentiation in gene regions, primarily at nonsynonymous and 5¢-UTR variants. Our analyses identify a fraction of loci that have contributed, and probably still contribute, to the morphological and disease-related phenotypic diversity of current human populations.

Among the several main reasons for the present gradual demise of the hitherto dominant hypotheses of 'modern' human origins, the replacement or 'out of Africa' models, are the issues of genetic drift and introgression. The operation and consequences of genetic drift are considered, especially in terms of their effects on the evolution of the human species during the Late Pleistocene period. The complexity of the subject is reviewed in the light of several relevant frames of reference, such as those provided by niche construction, gene-culture co-evolutionary theories, and by the domestication hypothesis. The current cultural, genetic and paleoanthropological evidence is reviewed, as well as other germane factors, such as the role of neurodegenerative pathologies, the neotenization of humans in their most recent evolutionary history, and the question of cultural selection-based self-domestication. This comprehensive review leads to a paradigmatic shift in the way recent human evolution needs to be viewed. This article explains fully how humans became what they are today.

Encyclopedia of Global Archaeology, 2014