Posts Tagged ‘Evolution’

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What is evolutionary selection now selecting for?

November 14, 2012

What are the genetic characteristics that are effectively being “selected for” today?

Evolutionary selection is a result not a cause. It is a result describing the genetic change of a population not of an individual. But all genetic change in a population comes about only through the procreation of new generations of individuals.

Evolution then is the result of the survival, success and reproduction of organisms within an environment which is changing. By environment I mean all surrounding factors whether geologic or climatic or of competition within the species or with other species. In a population of organisms the relative success of and subsequent reproduction of those better suited to the environment begets a gradual change in the  characteristics of the surviving organisms.  It is because of the environmental changes in the first place that there is a subsequent change in the characteristics of the organism best suited to that environment. It is this gradual change of the surviving characteristics that we call evolution and we say that the resultant, surviving characteristics have been “selected for”. If the environment did not change and if an organism was suited to its environment, the genetic make-up of the organisation would always tend back to its stable equilibrium position. Any mutational changes would provide no benefit and would just die away. Without environmental change there would be no evolution to report. Over long stretches of time and many thousands of generations, these gradual changes of environment have been sufficient to have created all the species of living things that have ever existed and to have eliminated all the non-viable species that have gone extinct.

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Is human intelligence declining?

November 13, 2012

There is as yet no evidence, no hard data, no way of testing his speculation but Gerald Crabtree, a genetics Professor at Stanford University, believes that human evolution no longer selects for or favours intelligence. Our intelligence may have peaked as hunter-gatherers.

He has a point.

The intricacies of modern, “civilised”, human society where “weak” members of society are cared for by others, are such that many genetic characteristics have effectively been decoupled from survival and reproduction. “Intelligence” as one such genetic charateristic is no longer something that affects survival or reproduction. In fact from the fertility rates around the world today it is already apparent that the greater the wealth (GDP) the lower the reproduction rate. I am not sure if it can be shown explicitly but I suspect that a similar relationship may apply and that the greater the “intelligence” the lower the reproduction rate.

Crabtree has published 2 papers in Trends in Genetics

  1. Gerald R. Crabtree. Our fragile intellect. Part I. Trends in Genetics, 2012; DOI: 10.1016/j.tig.2012.10.002
  2. Gerald R. Crabtree. Our fragile intellect. Part II. Trends in Genetics, 2012; DOI: 10.1016/j.tig.2012.10.003

Science Daily: 

Human intelligence and behavior require optimal functioning of a large number of genes, which requires enormous evolutionary pressures to maintain. A provocative hypothesis … suggests that we are losing our intellectual and emotional capabilities because the intricate web of genes endowing us with our brain power is particularly susceptible to mutations and that these mutations are not being selected against in our modern society.

“The development of our intellectual abilities and the optimization of thousands of intelligence genes probably occurred in relatively non-verbal, dispersed groups of peoples before our ancestors emerged from Africa,” says the papers’ author, Dr. Gerald Crabtree, of Stanford University. In this environment, intelligence was critical for survival, and there was likely to be immense selective pressure acting on the genes required for intellectual development, leading to a peak in human intelligence.

From that point, it’s likely that we began to slowly lose ground. With the development of agriculture, came urbanization, which may have weakened the power of selection to weed out mutations leading to intellectual disabilities. Based on calculations of the frequency with which deleterious mutations appear in the human genome and the assumption that 2000 to 5000 genes are required for intellectual ability, Dr. Crabtree estimates that within 3000 years (about 120 generations) we have all sustained two or more mutations harmful to our intellectual or emotional stability. Moreover, recent findings from neuroscience suggest that genes involved in brain function are uniquely susceptible to mutations. Dr. Crabtree argues that the combination of less selective pressure and the large number of easily affected genes is eroding our intellectual and emotional capabilities.

If “intelligence” is an inherited characteristic – as it seems at least partially to be –  then it is only a matter of simple arithmetic that unless the “more intelligent” reproduce at a higher rate than those of “less intelligence” then the “average intelligence” of the population will inevitably decrease.

Related:

http://en.wikipedia.org/wiki/Dysgenics

Where Dysgenics Goes Wrong:

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The origins of counting

November 11, 2012

Before an intelligence can turn to counting it must first have some concept of numbers. When and how did our ancient ancestors  first develop a concept of numbers and then start counting?

What led humans to counting and when?

…  the increasing complexities of co-operation and their requirements for communication was what drove the parallel – and inter-linked – development of speech and numerology starting some 150,000 years ago.

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Out of Africarabia

November 9, 2012

There has been a gap of 50-65,000 years between the genetic time-line of the Out-of-Africa theory and archaeological indications of the earlier presence of anatomically modern humans outside of Africa. But the genetic evidence is now going back in time and approaching the archaeological time-line. “Out-of-Africa” is beginning to look much more like “Out-of-Africarabia”.

“Out-of-Africa” is morphing into “Out-of Africarabia” as genetic and archaeological time-lines converge

Out of Africarabia

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Before we were apes we were sharks

June 14, 2012

A new paper in Nature suggests that before we were apes we were fish and not just any old fish. The primitive fish which predates the split between sharks and bony fish, Acanthodes bronni was the common ancestor of all jawed vertebrates on Earth – including mankind, according to the paper. The split with bony fish occurred some 420 million years ago and Acanthodes bronni disappeared some 250 million years ago.

The researchers  re-examined fossils of Acanthodes bronni, the best-preserved acanthodian species. They created highly detailed latex moulds of specimens revealing the inside and outside of the skull, generating a  new data set for assessing cranial and jaw anatomy as well as the organizations of sensory, circulatory and respiratory systems in the species. The analysis of the sample combined with recent CT scans of skulls from early sharks and bony fishes led to the reassessment of what Acanthodes bronni tells us about the history of jawed vertebrates.

Acanthodes bronni : Wikipedia

Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes

(more…)

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A special gene for camouflage

November 1, 2010

C. Zhang, Y. Song, D. A. Thompson, M. A. Madonna, G. L. Millhauser, S. Toro, Z. Varga, M. Westerfield, J. Gamse, W. Chen, R. D. Cone. Inaugural Article: Pineal-specific agouti protein regulates teleost background adaptation. Proceedings of the National Academy of Sciences, 2010; DOI: 10.1073/pnas.1014941107

Science Daily

 

Like other bony fish, the peacock flounder can change the color and pattern of its skin to blend into the sea floor. (Credit: Photo by Jimmie Mack)

 

Researchers led by Vanderbilt’s Dr. Roger Cone have discovered a new member of a gene family that has powerful influences on pigmentation and the regulation of body weight.

The gene is the third member of theagouti family. Two agouti genes have been identified previously in humans. One helps determine skin and hair color, and the other may play an important role in obesity and diabetes. The new gene, called agrp2, has been found exclusively in bony fish, including zebrafish, trout and salmon. The protein it encodes enables fish to change color dramatically to match their surroundings, the researchers report this week in the early edition of theProceedings of the National Academy of Sciences (PNAS).

“When my graduate student, Youngsup Song, discovered a third agouti protein in the fish pineal gland, an organ that regulates daily rhythms in response to light, we initially thought we had found the pathway that regulates hunger diurnally,” said Cone, chair of the Department of Molecular Physiology & Biophysics and director of the Vanderbilt Institute for Obesity and Metabolism.

“That is the mechanism that makes you hungry during the day, but not at night,” he continued. “However, Chao Zhang, a graduate student who followed up the study, ultimately discovered that this agouti protein … is involved in the rapid pigment changes that allow fish to adapt to their environment.”

This phenomenon, called background adaptation, also has been observed in mammals. The coat of the arctic hare, for example, turns from brown in summer to white camouflage against the winter snow.

In contrast to mammals that have to grow a new coat to adapt to a changing environment, fish, amphibians and reptiles can change their skin color in a matter of minutes. The first agouti gene, which produces the striped “agouti” pattern in many mammals, was discovered in 1993. The same year, Cone and his colleagues at Oregon Health Sciences University in Portland reported the discovery of the gene that encoded the melanocortin-1 receptor, a key player in the pigmentation story.

In the current paper, Cone’s group reports that the newly discovered protein, AgRP2, regulates expression of the prohormone genes pmch and pmchl, precursors to melanin-concentrating hormone, which has a pigment-lightening effect. “Together, the versatile agouti proteins and melanocortin receptors are responsible for regulation of body weight, the banded patterns of mammalian coats, and even red hair in most people,” Cone said. The current work shows that agouti proteins are also involved in the camouflage mechanisms used in thousands of fish species.

Read the article.

If only the gene could be activated in humans as well!!!

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The ongoing evolution of humans

October 23, 2010

DNA. image ichromatography.com

 

The Yoruba of West Africa have been exposed, historically, to the dry conditions of the Sahel on the edge of the Sahara desert. To find out whether they had evolved to cope, Andres Moreno at Stanford University in California and colleagues looked at the variation of a gene known to be involved in water retention in the kidney, called FOXI1, in DNA samples from 20 Europeans, 20 east Asians and 20 Yoruba.

(BMC Evolutionary Biology, DOI: 10.1186/1471-2148-10-267).

The team found that 85 per cent of the Yoruba had an identical sequence of genetic information that was longer than it would have been if it was produced by random recombination and genetic shuffling. Instead, they suggest that it had been naturally selected.The length of the genetic signature suggests that the change occurred in the last 10,000 to 20,000 years, which could have coincided with the initial stages of the desertification of the Sahara. They also analysed a region of the gene in 971 samples from 39 human populations around the world, including the Yoruba, and found that the same genetic sequence was found at higher frequencies in lower latitudes. Since lower latitudes are more likely to be regions of water-stress, this suggests that the selection pressure was climate-related, says Moreno.

Humans are still evolving: the evidence

“Over the long term, if the Earth keeps warming, I would not be surprised to see genetic shifts,” says anthropological geneticist Anne Stone at Arizona State University in Tempe.

While we may look like the finished article, there is plenty of evidence that humans are still evolving. John Hawks at the University of Wisconsin-Madison even argues that population explosions and rapidly changing lifestyles are causing humans to evolve faster now than ever before. Evidence includes:

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