[extropy-chat] Recent evolution

[Keith Henson]

There have been comments here about recent evolution.  Below is a most 
interesting study of the evolution of lactose-tolerant mutation--several of 
them it seems.  Another example is the several genes conferring malaria 
resistance (malaria seems to have become a problem only after people 
started farming).  Another possible example is the "famine" genes being 
weeded out (some researchers claim the genes cause people to die early when 
they are well fed).

But the thing that is common to all these is high pressure.  As mentioned 
in the article, "Genetic evidence shows that the mutations conferred an 
enormous selective advantage on their owners, enabling them to leave almost 
10 times as many descendants as people without them."

Behaviors are biased by gene-constructed brain mechanisms.  I have no doubt 
that the genes behind behavior bias would undergo rapid evolution if some 
of them gave the kind of selective advantage in a new situation the lactose 
tolerant gene did.

I can think of one example.  Behavior genes for sex would undergo heavy 
selection if HIV was a problem for many generations.

It is *possible* we are less susceptible to fatal cult memes than our 
European ancestors were if the most susceptible of them died in crusades 
and other such disruptions in historical times.  But I kind of doubt the 
weeding was intense enough to change gene frequencies to a significant extent.

Any other examples you can think of?

Keith

********

Study Detects Recent Instance of Human Evolution

Does the EEA extend right into the neolithic?

http://www.nytimes.com/2006/12/10/science/10cnd-evolve.html?ex=1323406800&en=6576a01a1bb4ce31&ei=5090&partner=rssuserland&emc=rss 



Study Detects Recent Instance of Human Evolution


By NICHOLAS WADE


Published: December 10, 2006


A surprisingly recent instance of human evolution has been
detected among the peoples of East Africa. It is the ability to
digest milk in adulthood, conferred by genetic changes that
occurred as recently as 3,000 years ago, a team of geneticists has
found.

The finding is a striking example of a cultural practice -- the
raising of dairy cattle -- feeding back into the human genome. It
also seems to be one of the first instances of convergent human
evolution to be documented at the genetic level. Convergent
evolution refers to two or more populations acquiring the same
trait independently.

Throughout most of human history, the ability to digest lactose,
the principal sugar of milk, has been switched off after weaning
because there is no further need for the lactase enzyme that
breaks the sugar apart. But when cattle were first domesticated
9,000 years ago and people later started to consume their milk as
well as their meat, natural selection would have favored anyone
with a mutation that kept the lactase gene switched on.

Such a mutation is known to have arisen among an early
cattle-raising people, the Funnel Beaker culture, which flourished
some 5,000 to 6,000 years ago in north-central Europe. People with
a persistently active lactase gene have no problem digesting milk
and are said to be lactose tolerant.

Almost all Dutch people and 99 percent of Swedes are
lactose-tolerant, but the mutation becomes progressively less
common in Europeans who live at increasing distance from the
ancient Funnel Beaker region.

Geneticists wondered if the lactose tolerance mutation in
Europeans, first identified in 2002, had arisen among pastoral
peoples elsewhere. But it seemed to be largely absent from Africa,
even though pastoral peoples there generally have some degree of
tolerance.

A research team led by Sarah Tishkoff of the University of
Maryland has now resolved much of the puzzle. After testing for
lactose tolerance and genetic makeup among 43 ethnic groups of
East Africa, she and her colleagues have found three new
mutations, all independent of each other and of the European
mutation, which keep the lactase gene permanently switched on.

The principal mutation, found among Nilo-Saharan-speaking ethnic
groups of Kenya and Tanzania, arose 2,700 to 6,800 years ago,
according to genetic estimates, Dr. Tishkoff's group is to report
in the journal Nature Genetics on Monday. This fits well with
archaeological evidence suggesting that pastoral peoples from the
north reached northern Kenya about 4,500 years ago and southern
Kenya and Tanzania 3,300 years ago.

Two other mutations were found, among the Beja people of
northeastern Sudan and tribes of the same language family,
Afro-Asiatic, in northern Kenya.

Genetic evidence shows that the mutations conferred an enormous
selective advantage on their owners, enabling them to leave almost
10 times as many descendants as people without them. The mutations
have created "one of the strongest genetic signatures of natural
selection yet reported in humans," the researchers write.


The survival advantage was so powerful perhaps because those with
the mutations not only gained extra energy from lactose but also,
in drought conditions, would have benefited from the water in
milk. People who were lactose-intolerant could have risked losing
water from diarrhea, Dr. Tishkoff said.


Diane Gifford-Gonzalez, an archaeologist at the University of
California, Santa Cruz, said the new findings were "very exciting"
because they "showed the speed with which a genetic mutation can
be favored under conditions of strong natural selection,
demonstrating the possible rate of evolutionary change in humans."


The genetic data fitted in well, she said, with archaeological and
linguistic evidence about the spread of pastoralism in Africa. The
first clear evidence of cattle in Africa is from a site 8,000
years old in northwestern Sudan. Cattle there were domesticated
independently from two other domestications, in the Near East and
the Indus valley of India.


Both Nilo-Saharan speakers in Sudan and their Cushitic-speaking
neighbors in the Red Sea hills probably domesticated cattle at the
same time, since each has an independent vocabulary for cattle
items, said Dr. Christopher Ehret, an expert on African languages
and history at the University of California, Los Angeles.
Descendants of each group moved southward and would have met again
in Kenya, Dr. Ehret said.


Dr. Tishkoff detected lactose tolerance among both Cushitic
speakers and Nilo-Saharan groups in Kenya. Cushitic is a branch of
Afro-Asiatic, the language family that includes Arabic, Hebrew and
ancient Egyptian.


Dr. Jonathan Pritchard, a statistical geneticist at the University
of Chicago and the co-author of the new article, said that there
were many signals of natural selection in the human genome, but
that it was usually hard to know what was being selected for. In
this case Dr. Tishkoff had clearly defined the driving force, he
said.


The mutations Dr. Tishkoff detected are not in the lactase gene
itself but a nearby region of the DNA that controls the activation
of the gene. The finding that different ethnic groups in East
Africa have different mutations is one instance of their varied
evolutionary history and their exposure to many different
selective pressures, Dr. Tishkoff said.


"There is a lot of genetic variation between groups in Africa,
reflecting the different environments in which they live, from
deserts to tropics, and their exposure to very different selective
forces," she said.


People in different regions of the world have evolved
independently since dispersing from the ancestral human population
in northeast Africa 50,000 years ago, a process that has led to
the emergence of different races. But much of this differentiation
at the level of DNA may have led to the same physical result.


As Dr. Tishkoff has found in the case of lactose tolerance,
evolution may use the different mutations available to it in each
population to reach the same goal when each is subjected to the
same selective pressure. "I think it's reasonable to assume this
will be a more general paradigm," Dr. Pritchard said.


----------------------


Related Web Link
Convergent Adaptation of Human Lactase Persistence in Africa and
Europe (Nature Genetics)
http://www.nature.com/ng/journal/vaop/ncurrent/abs/ng1946.html




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"The end of cheap oil and the collapse of empire are not problems
to be solved, they are solutions to be savored." -- Me.