Can evolution explain rise in certain diseases? (Autism included in article)

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Any idea where they basing their conclusion for the autism idea (see subsection

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Can evolution explain rise in certain diseases?

Study: Evolutionary factors may play role in uptick of autism, some cancers

By Jeanna Bryner

LiveScience

updated 8:29 p.m. ET, Mon., Jan. 11, 2010

While natural selection is best known for weeding out the weak, it may also be

partly responsible for the apparent rise of some disorders, such as autism,

autoimmune diseases and reproductive cancers, according to researchers.

Since evolutionary factors play a role in disease, the two fields should have

some crossover, say a group of scientists who have studied various aspects of

the link between evolution and medicine.

" This work points out linkages within the plethora of new information in human

genetics and the implications for human biology and public health, and also

illustrates how one could teach these perspectives in medical and premedical

curricula, " said researcher Ellison, an anthropologist at Harvard

University.

The results, they say, could save lives.

" Evolutionary medicine got going in the '80s and early '90s, but it has been

energized in the last decade by the discovery that it really makes a

difference, " researcher Stearns of Yale University told LiveScience. " In

the last 10 years we have found out that taking an evolutionary perspective

really helps to reduce suffering and to reduce the risk of death. "

Evolution and disease

Stearns and a long list of scientists presented their findings on this

evolution-medicine link at the Arthur M. Sackler Colloquium in the spring of

2009. The results, announced publicly today, are now published in the journal

Proceedings of the National Academy of Sciences.

For example, previous work in evolutionary medicine has helped to explain some

reasons why disease is so prevalent and difficult to prevent: Natural selection

favors reproduction over health; biology evolves more slowly than culture; and

pathogens evolve more quickly than humans.

They describe these and other connections between evolution and sickness along

with possible explanations. Here are the highlights:

Humans evolved alongside beneficial bacteria and parasitic worms, and so our

ancestors built up immunity to such bugs. But nowadays with increased hygiene,

we've eliminated the bacteria and worms. The result: Since our immune systems

aren't used to these good bugs, our bodies fight them as foreigners. That can

result in allergies, asthma and autoimmune diseases, such as Graves' disease in

which a person has an overactive thyroid.

Humans have higher rates of cancer than other species. One reason: We aren't

adapted to the new risk factors of modern society, including tobacco, alcohol, a

high-fat diet and contraceptives, researchers have found.

Certain adaptations that once benefited us might be helping several ailments to

persist in spite of, or perhaps because of, advancements in modern culture and

medicine, according to researchers.

With respect to evolution and culture, here's a case in point: Harmful mutations

are often recessive, and so both parents must pass on the gene in order for the

disease to show up in offspring. And while natural selection has supported

outbreeding (breeding with people other than close relatives), culture hasn't

always followed suit. Across the globe, about 10 percent of spouses are second

cousins or closer, the researchers say, with the prevalence ranging from 1

percent to 50 percent in different cultures.

The inbreeding can cause recessive genes that should only have a small effect on

mortality to have a much larger impact.

Autism and evolution

Autism and schizophrenia also have ties with evolutionary science. Essentially,

they boil down to a battle of the sexes.

Past studies beginning in the 1960s have built on one another to suggest mom and

dad are in evolutionary conflict over investment of resources to their

offspring. A mother knows all of her babies are hers and so should give evenly

to all. But fathers only want to invest in their biological kids (not offspring

from another male) and so a father's genes will pressure mom to skew investment

toward those offspring.

Studies in genetically engineered mice have shown that when certain paternal

genes get expressed, the baby mice are 10 percent heavier than normal.

The results should translate to humans and carry into early childhood, affecting

children's behaviors, the researchers suggest.

For instance, when the paternal form of a gene on chromosome 15 gets expressed,

and not the mother's, the resulting offspring will be more demanding, sleep

poorly, want to suckle frequently and have a 40 percent to 80 percent chance of

having autism as an adult. (Humans normally have 46 chromosomes in each cell.)

While scientists think genes play a role in developing autism, the complex

causes of this disease are still unknown.

Similar findings have shown psychoses such as schizophrenia can develop when the

maternal form of certain genes gets expressed.

Educating physicians on evolution

Stearns suggests evolutionary perspectives should be integrated into curricula

as early as undergraduate school for students planning to attend medical school.

The knowledge, Stearns said, would complement traditional studies undertaken in

medical school.

We're trying to design ways to educate physicians who will have a broader

perspective and not think of the human body as a perfectly designed machine, "

Ellison said. " Our biology is the result of many evolutionary trade-offs, and

understanding these histories and conflicts can really help the physician

understand why we get sick and what we might do to stay healthy. "

The take-home message: " Evolution and medicine really do have things to say to

each other, and some of these insights actually reduce suffering and save

lives, " Stearns said.

© 2010 LiveScience.com. All rights reserved.

URL: http://www.msnbc.msn.com/id/34811171/ns/health-more_health_news/