If you haven't heard the comments made by David Attenborough regarding humans having stopped evolving, see this (http://tinyurl.com/khdapmd).
This post only seeks to further support comments made by prominent evolutionary biologists and anthropologists who have already pointed out the flaws in Attenborough's thinking (http://tinyurl.com/msy24eh).
As I've pointed out on this blog before, there's a gap in the understanding of human evolution - a lot of people think that only selection is acting as a force of evolution. Attenborough's comments state that humans have stopped selective forces, with the advent of medicine and birth control, etc etc.
This is why I wrote the second blog topic on understanding evolutionary and what we can infer about health - there are more forces of evolution than just selection. Evolution is, simply, the change in allele frequencies over time. Alleles are constantly under the effects of genetic drift, with an allele having the potential to drift upwards or downwards in frequency - Attenborough said that natural selection was the strongest force of evolution, but he clearly has not heard of the neutral and nearly neutral theories of molecular evolution. With the advent of modern transportation, we are seeing more gene flow than arguably ever before in all of human history - human populations that have been segregated for any number of reasons have the ability to exchange genetic information - there has also been a lessening of the effect of some of the cultural norms that kept individuals from sharing genetic information. Each individual born also has a number of mutations that his progenitors didn't have, potentially creating new alleles.
Besides the other forces of evolution, the idea that we've stopped any selective pressures is absolutely incorrect. As this nih.gov article points out, about 1/2 of all fertilized eggs are miscarried before a woman knows she's pregnant (1) - i've heard this number to be even higher. We also have a culture where individuals are having children later - this has caused concern of issues like autism, which has a genetic component and has recently increased in prevalence - Fathers accumulate more mutations in their sperm as they age(2) - this can potentially introduce new exonic alleles into the population or alter regulatory function of introns that are viable with life. It would also be difficult to quantify the effect on allele frequencies that sexual selection, changing culture perceptions of what is attractive, and effective population size (number of males and females who actually reproduce) have, but they likely have some effect on changing allele frequencies - See this article on sexual selection and human height ( http://tinyurl.com/mzdt2me). One must also address the issue of impaired fecundity - a large number of people have trouble becoming pregnant - if they are unable to reproduce, their alleles are lost from the population, also contributing to continuing human evolution.
From a nutrigenetic perspective, there are known variants of the MTHFR gene, as well as ApoE, that contribute to impaired reproductive capacity/outcomes (3, 4, 5). There is a growing body of research which shows that obesity, as well as other lifestyle factors such as smoking, alcohol and consumption (6, 7, 8) can negatively effect fecundity - particularly in the case of obesity, with rising rates of childhood obesity, the future could hold huge effects on the physiological ability to reproduce, and consequently, how static allele frequencies remain.
The comments made by Attenborough are rather ill-informed, and I can't help but see his perspective as 1st-worldly narrow minded. With natural disasters like tsunami's in India, Chinese earthquakes and mudslides, widespread wars/violence, the prevalence of starvation/dehydration and infectious disease worldwide, there are obvious selective factors that are still at play. Yes, the factors that were most prevalent in the past are not necessarily the most prominent for westernized society, but we are most certainly still seeing changes in allele frequencies - someone was hoping for Hardy-Weinberg equilibrium a bit too hard with these comments.
Evolution happens at the population level, and over a long period of time. I highly doubt in a century our descendants will be hominid creatures that we wouldn't be able to recognize, but where our allele frequencies will be in 10,000 years from now might lead to physiologically and morphologically distinct organisms from what we see today- assuming there are still descendants left to speak of *cue climate change and alien attacks* (jk about that last part).
1. http://www.nlm.nih.gov/medlineplus/ency/article/001488.htm
2. http://www.nature.com/news/fathers-bequeath-more-mutations-as-they-age-1.11247
3. http://www.ncbi.nlm.nih.gov/pubmed/23292450
4. http://www.ncbi.nlm.nih.gov/pubmed/22047507
5. http://www.ncbi.nlm.nih.gov/pubmed/20825376
6. http://humrep.oxfordjournals.org/content/22/6/1634.full
7. http://onlinelibrary.wiley.com/doi/10.1111/j.1747-0080.2010.01460.x/abstract
8. http://www.sciencedirect.com/science/article/pii/S0015028203028462
This post only seeks to further support comments made by prominent evolutionary biologists and anthropologists who have already pointed out the flaws in Attenborough's thinking (http://tinyurl.com/msy24eh).
As I've pointed out on this blog before, there's a gap in the understanding of human evolution - a lot of people think that only selection is acting as a force of evolution. Attenborough's comments state that humans have stopped selective forces, with the advent of medicine and birth control, etc etc.
This is why I wrote the second blog topic on understanding evolutionary and what we can infer about health - there are more forces of evolution than just selection. Evolution is, simply, the change in allele frequencies over time. Alleles are constantly under the effects of genetic drift, with an allele having the potential to drift upwards or downwards in frequency - Attenborough said that natural selection was the strongest force of evolution, but he clearly has not heard of the neutral and nearly neutral theories of molecular evolution. With the advent of modern transportation, we are seeing more gene flow than arguably ever before in all of human history - human populations that have been segregated for any number of reasons have the ability to exchange genetic information - there has also been a lessening of the effect of some of the cultural norms that kept individuals from sharing genetic information. Each individual born also has a number of mutations that his progenitors didn't have, potentially creating new alleles.
Besides the other forces of evolution, the idea that we've stopped any selective pressures is absolutely incorrect. As this nih.gov article points out, about 1/2 of all fertilized eggs are miscarried before a woman knows she's pregnant (1) - i've heard this number to be even higher. We also have a culture where individuals are having children later - this has caused concern of issues like autism, which has a genetic component and has recently increased in prevalence - Fathers accumulate more mutations in their sperm as they age(2) - this can potentially introduce new exonic alleles into the population or alter regulatory function of introns that are viable with life. It would also be difficult to quantify the effect on allele frequencies that sexual selection, changing culture perceptions of what is attractive, and effective population size (number of males and females who actually reproduce) have, but they likely have some effect on changing allele frequencies - See this article on sexual selection and human height ( http://tinyurl.com/mzdt2me). One must also address the issue of impaired fecundity - a large number of people have trouble becoming pregnant - if they are unable to reproduce, their alleles are lost from the population, also contributing to continuing human evolution.
From a nutrigenetic perspective, there are known variants of the MTHFR gene, as well as ApoE, that contribute to impaired reproductive capacity/outcomes (3, 4, 5). There is a growing body of research which shows that obesity, as well as other lifestyle factors such as smoking, alcohol and consumption (6, 7, 8) can negatively effect fecundity - particularly in the case of obesity, with rising rates of childhood obesity, the future could hold huge effects on the physiological ability to reproduce, and consequently, how static allele frequencies remain.
The comments made by Attenborough are rather ill-informed, and I can't help but see his perspective as 1st-worldly narrow minded. With natural disasters like tsunami's in India, Chinese earthquakes and mudslides, widespread wars/violence, the prevalence of starvation/dehydration and infectious disease worldwide, there are obvious selective factors that are still at play. Yes, the factors that were most prevalent in the past are not necessarily the most prominent for westernized society, but we are most certainly still seeing changes in allele frequencies - someone was hoping for Hardy-Weinberg equilibrium a bit too hard with these comments.
Evolution happens at the population level, and over a long period of time. I highly doubt in a century our descendants will be hominid creatures that we wouldn't be able to recognize, but where our allele frequencies will be in 10,000 years from now might lead to physiologically and morphologically distinct organisms from what we see today- assuming there are still descendants left to speak of *cue climate change and alien attacks* (jk about that last part).
1. http://www.nlm.nih.gov/medlineplus/ency/article/001488.htm
2. http://www.nature.com/news/fathers-bequeath-more-mutations-as-they-age-1.11247
3. http://www.ncbi.nlm.nih.gov/pubmed/23292450
4. http://www.ncbi.nlm.nih.gov/pubmed/22047507
5. http://www.ncbi.nlm.nih.gov/pubmed/20825376
6. http://humrep.oxfordjournals.org/content/22/6/1634.full
7. http://onlinelibrary.wiley.com/doi/10.1111/j.1747-0080.2010.01460.x/abstract
8. http://www.sciencedirect.com/science/article/pii/S0015028203028462
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