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University of Wisconsin-Madison: 10-Dec-2007
Modern humans in evolutionary fast lane
New research shows that humans have been evolving rapidly for the past 40,000 years.
This challenges the widespread belief that human evolution has slowed to a crawl
or even stopped.
The new study finds that modern humans' recent past has been a time of extra-fast
evolution. This has been driven by cultural changes and an explosive increase in
Data for the study came from aninternationalgenomicsproject. The work is published
in the 10 Dec issue of the Proceedings of the National Academy of Sciences (PNAS).
The research team was led by University of Wisconsin-Madison anthropologistJohn
Hawks estimates that positive selection in the past 5,000 years has been happening
roughly 100 times as fast as at any time in human evolution.
Many of the new genetic changes are linked to alterations in human diet caused by
the coming of agriculture (Note 1). Another source of change has been resistance
to diseases, says the research team. These became major killers when humans first
began to live in cities.
The findings will likely lead to a rethinking of our ideas about human evolution,
Hawks says. In particular the notion that modern culture has ended evolution in humans
does not seem to be true at all.
“We are more different genetically from people living 5,000 years ago than they were
different from Neanderthals,” Hawks says.
The research team analyseddata from the internationalHapMap project. This is a
global effort to find all the genetic similarities and differences in human beings.
It studies genes from distinctpopulations around the world.
HapMap will in time be used to identify genes that affect human health. But it can
also provide a map of genetic variation in our ancestors.
The Hapmap project has mapped roughly 4 million of these SNPs. There are estimated
to be 10 million of them in all. The project is also identifying different regions
of DNA known as haplotypes, which contain a large number of SNPs and are shared by
All this Hapmap data is being used in many ways by scientists around the world. The
research carried out by Hawk and his colleagues is using a technique called linkage
disequilibrium decay or LDD.
Human DNA is shuffled from one generation to the next. This is called 'recombination'.
But a chunk of DNA that gives its owner an advantage quickly spreads through a population.
So long, uninterruptedsegments carried by large numbers of people are strong evidence
of a fairly recent evolutionary change - recent enough for recombination not to have
broken them up again. This is what the scientists have been looking for.
Using this test, they found evidence of recent selection on roughly 1,800 genes.
This is 7% of all human genes.
Conventional wisdom is that the pressures of natural selection on humans are less
nowadays than in the past, Hawks says. But genetic changes are now being driven by
major changes in human culture
A good example is lactase, the substance that helps people digest milk. The gene for this normally stops being active when children grow up. But northern Europeans
have developed a variety of the gene that lets them drink milk all their lives. This
is a recent adaptation caused by farming and the widespread use of milk.
The biggest new pathway for selection is in resistance to disease, Hawks says. People
started living in much larger groups and settling in one place roughly 10,000 years
ago. That's when epidemic diseases such as malaria, smallpox and cholera began to
dramatically change the patterns of deaths.
Malaria is one of the clearest examples, Hawks says. Scientists have found more than
two dozen genetic adaptations related to malaria resistance. These include a whole
new blood type known as the Duffy blood type.
Another recently discovered gene, CCR5, first appeared about 4,000 years ago. It
now exists in about 10% of European people. It was discovered recently because it
makes those who have it resistant to HIV/AIDS. But its original value might have
been in fighting smallpox.
“There are many things under selection that are making it harder for pathogens to
kill us,” Hawks says.
Population growth is making these changes happen much faster than they would otherwise
have done. Charles Darwinpointed out that the size of the herd “is of the highest
importance for success”. This is because the larger the population the more genetic
variation there is in it.
It is the same for humans. The population of the world has grown very rapidly. There
were only a few million people 10,000 years ago. This had grown to 200 million people
by the beginning of the Christian era.
By the year 1700 there were 600 million people in the world. And today there are
more than 6.5 billion.
Before these times, the population was so small for so long that positive selection
happened very, very slowly, Hawks says.
Ten million single nucleotides can be different between one human and the next. But
99% of the human genome is the same for all of us. So how many single nucleotides
are there on the human genome?
What is recombination?
In your own words explain the sentence that begins "But a chunk of DNA that gives
its owner an advantage …
In your own words explain the next sentence that begins "So long, uninterrupted segments
In what fraction of human genes did the scientists find evidence of recent evolutionary
Most people believe that evolutionary pressures on humans are less now than before
we became civilised. In one sentence how is modern medicine part of
this reduced pressure to evolve?
But according to these scientists evolution in humans is happening much faster than
ever. It's just that the pressures to evolve don't come from the rigours of winter
and wild animals. They come from what?
What kind of scientific statement is the answer to the last question? Is it a new
finding, a hypothesis or a piece of existing knowledge?
Hawks provides a number of examples of recent evolutionary changes due to disease
and different ways of living. Are these part of his new findings?
Do they help to support these findings?
If you think they do support them explain why. If you think they don't explain why
not. Use no more than one sentence in either case.
In your own words and one sentence why is the rapid increase in the human population
helping to make evolution happen much faster than before?