genetic predispositions

true

true, these mutations are rarely passed down across multiple generations, so they tend to be rare and recent in origin.

false, most gene mutations do not strongly affect reproductive success. they are mostly neutral. these gene mutations might only be harmful in some environments or only when they occur alongside other gene mutations.

true

The genomes of unrelated people tend to be 99.9% identical; about 1 DNA letter in every 1,000 differs across unrelated people.

a distinct version of a gene. A common allele is one that is present in at least 1% of people. We have identified hundreds of common alleles in the human gene pool that confer an increased risk of developing a disorder. Other alleles are protective.

Every common, harmful allele, on its own, is only associated with a very small statistical increase in the risk of developing a disorder. These mutations do not cause disease on their own. They have no effect in most people.

If a gene mutation clearly boosts reproductive success, the prevalence of it increases across generations until everyone gets it. At that point, we say the gene has gone to fixation.

– If a mutation increases reproductive success by 1%, it is expected to spread to the entire population and go to fixation in about 100 generations (a few thousand years for humans). – Likewise, if a mutation decreases reproductive success by 1%, it is likely to get eliminated from the gene pool in 100 generations or so

There are often clear signs of evolution when the environment of a species changes. – The people who moved out of Africa 60,000 years ago encountered new environments. They also experienced generational changes in skin color, facial characteristics, body shapes, and hair types. – These alterations and the alleles associated with them went to fixation (in local geographic regions) over the span of 10,000 to 30,000 years.

Even if a gene mutation is mostly neutral – neutral in almost all contexts – it is still not technically neutral, and it will be eliminated from the gene pool over evolutionary time. Modern humans evolved 300,000 years ago, so there has been about 13,000 generations of humans. That is more than enough time for natural selection to remove slightly bad genes. Some gene mutations are completely neutral no matter the context. These mutations are common, and the prevalence of them drifts randomly across generations. it has no effect on reproductive success.

it means the alleles were equivalent in terms of reproductive success in ancestral environments.

true, Since our environment has changed dramatically in the last few hundred years, we expect some alleles that were neutral 10, 50, 100 generations ago are no longer neutral.

If an allele is neutral in one environment but not another, we say there is a gene-environment interaction. Many of the common alleles that are currently associated with disease show the classic hallmarks of gene-environment interactions. The prevalence of the associated diseases vary widely across cultures and recent history, and there is a straightforward environmental explanation for the variability.

-> obesity and diabetes (access to a large variety of cheap, unnaturally delicious food) -> respiratory disease and asthma (changes in air quality, new pollutants and antigens) -> drug addiction (access to highly purified synthetic drugs) -> heart disease, strokes and cancer (changes in lifespan, diet, and lifestyle). -> neurodegenerative disorders (changes in lifespan, diet, and lifestyle). -> depression and anxiety (changes in lifestyle) The alleles associated with these conditions were likely neutral in ancestral environments.

It is not exactly random who has children and who doesn’t. Physical and mental health issues clearly impact people’s likelihood of having kids.

– Many of the good, protective alleles in the human gene pool would spread to everyone and go to fixation as bad alleles got selected out. – These changes in the human gene pool would dramatically reduce the prevalence of heart disease, strokes, cancer, obesity, neurodegenerative disorders, diabetes, respiratory disease, asthma, drug addiction, depression, and anxiety. – These diseases and disorders were not nearly as prevalent in ancestral conditions. They are common now because of changes in our environment, lifestyles, and lifespans. There is now strong evolutionary pressure acting on the associated alleles.

no, many mental illnesses do not show the classic hallmarks of gene-environment interactions. • Prevalence rates do not vary widely across cultures or recent history (as far as we can tell). • It is hard to imagine these disorders were completely neutral in ancestral environments, given that they make it hard for people to thrive outside of particular contexts. • There are no obvious environmental triggers for these disorders beyond having a traumatic childhood and complications during pregnancy or birth. Our ancestors must have experienced these environmental triggers as well.

true, about 4% of the populations has a debilitating mental illness.

true, researchers estimate that people who have a severe mental illness have half as many children as other people do, on average.

true, these disorders run in families and most of the variance in who develops them is explained by genetics.

The average person has less than a 1% chance of developing schizophrenia. A person’s risk of developing schizophrenia increases to… – 8% if they have a sibling who has it. – 13% if one of their parents has it. – 50% if both of their parents have it. – 50% if they have an identical twin who has it.

true, these data suggest that environmental risk factors have minimal influence.

– Not necessarily. – It is possible for a gene mutation to create only a little ambiguity in the genetic instructions. Whether cells respond one way or another might be completely random. The cause of schizophrenia (and many other mental disorders) is mostly an unfortunate combination of relatively common but slightly harmful gene mutations. We have identified many of the key gene mutations. In fact, we have identified hundreds of them, and each one individually confers a very small statistical increase in the risk of developing schizophrenia. These mutations are relatively common. Given the debilitating nature of severe mental illness, there must now be strong evolutionary pressure acting on these gene mutations, and there surely always has been throughout human history.