Milan Ćirković of the Astronomical Observatory of Belgrade, and one of
the world’s leading authorities on astrobiology and the evolution of
galaxies and baryonic
dark matter, has outlined along with philosopher Robert Bradbury the
six great mega-trajectories of the biological evolution on Earth:
1. From the origin of life to the "Last Common Ancestor”
2. Prokaryote diversification
3. Unicellular eukaryote diversification
4. Multicellularity
5. Invasion of the land
6. Appearance of intelligence and technology.
The
authors suggest a “postbiological” seventh mega-trajectory
triggered by the emergence of artificial intelligence “at least
equivalent to the biologically-evolved one. (Bradbury is the inventor
of the matrioshka brain -a hypothetical megastructure, based on the
Dyson sphere, of immense computational capacity).
In a fascinating discovery that counters a common theory that human
evolution has slowed to a crawl or even stopped in modern humans, a
recent study examining data from an international genomics project
describes the past 40,000 years as a time of supercharged evolutionary
change, driven by exponential population growth and cultural shifts.
The
findings may lead to a very broad rethinking of human evolution,
especially in the view that modern culture has essentially relaxed the
need for physical genetic changes in humans to improve survival.
A
team led by University of Wisconsin-Madison anthropologist John Hawks
estimates that positive selection just in the past 5,000 years alone
-dating back to the Stone Age - has occurred at a rate roughly 100
times higher than any other period of human evolution. Many of the new
genetic adjustments are occurring around changes in the human diet
brought on by the advent of agriculture, and resistance to epidemic
diseases that became major killers after the growth of human
civilizations.
“In evolutionary terms, cultures that grow
slowly are at a disadvantage, but the massive growth of human
populations has led to far more genetic mutations,” says Hawks. “And
every mutation that is advantageous to people has a chance of being
selected and driven toward fixation. What we are catching is an
exceptional time.”
While the correlation between population size
and natural selection is nothing new - it was a core premise of Charles
Darwin, Hawks says - the ability to bring quantifiable evidence to the
table is a new and exciting outgrowth of the Human Genome Project.
In
the hunt for recent genetic variation in the genome map the project has
cataloged the individual differences in DNA called single nucleotide
polymorphisms (SNPs). The project has mapped roughly 4 million of the
estimated 10 million SNPs in the human genome. Hawks’ research focuses
on a phenomenon called linkage disequilibrium (LD). These are places on
the genome where genetic variations are occurring more often than can
be accounted for by chance, usually because these changes are affording
some kind of selection advantage.
The researchers identify
recent genetic change by finding long blocks of DNA base pairs that are
connected. Because human DNA is constantly being reshuffled through
recombination, a long, uninterrupted segment of LD is usually evidence
of positive selection. Linkage disequilibrium decays quickly as
recombination occurs across many generations, so finding these
uninterrupted segments is strong evidence of recent adaptation, Hawks
says.
Employing this test, the researchers found evidence of
recent selection on approximately 1,800 genes, or 7 percent of all
human genes.
This finding runs counter to conventional wisdom in
many ways, Hawks says. For example, there’s a strong record of skeletal
changes that clearly show people became physically smaller, and their
brains and teeth are also smaller. This is generally seen as a sign of
relaxed selection - that size and strength are no longer key to
survival.
But other pathways for evolution have opened, Hawks
says, and genetic changes are now being driven by major changes in
human culture. One good example is lactase, the gene that helps people
digest milk. This gene normally declines and stops activity about the
time one becomes a teenager, Hawks says. But northern Europeans
developed a variation of the gene that allowed them to drink milk their
whole lives - a relatively new adaptation that is directly tied to the
advance of domestic farming and use of milk as an agricultural product.
The
biggest new pathway for selection relates to disease resistance, Hawks
says. As people starting living in much larger groups and settling in
one place roughly 10,000 years ago, epidemic diseases such as malaria,
smallpox and cholera began to dramatically shift mortality patterns in
people. Malaria is one of the clearest examples, Hawks says, given that
there are now more than two dozen identified genetic adaptations that
relate to malaria resistance, including an entirely new blood type
known as the Duffy blood type.
Another recently discovered gene,
CCR5, originated about 4,000 years ago and now exists in about 10
percent of the European population. It was discovered recently because
it makes people resistant to HIV/AIDS. But its original value might
have come from obstructing the pathway for smallpox.
“There are many things under selection that are making it harder for pathogens to kill us,” Hawks says.
Population
growth is making all of this change occur much faster, Hawks says,
giving a tribute to Charles Darwin. When Darwin wrote in “Origin of the
Species” about challenges in animal breeding, he always emphasized that
herd size “is of the highest importance for success” because large
populations have more genetic variation, Hawks says.
The
parallel to humans is obvious: The human population has grown from a
few million people 10,000 years ago to about 200 million people at A.D.
0, to 600 million people in the year 1700, to more than 6.5 billion
today. Prior to these times, the population was so small for so long
that positive selection occurred at a glacial pace, Hawks says.
“What’s really amazing about humans,” Hawks continued, “that is not
true with most other species, is that for a long time we were just a
little ape species in one corner of Africa, and weren’t genetically
sampling anything like the potential we have now.”
The recent changes are especially striking.
“Five thousand years is such a small sliver of time - it’s 100 to 200
generations ago. That’s how long it’s been since some of these genes
originated, and today they are in 30 or 40 percent of people because
they’ve had such an advantage. It’s like ‘invasion of the body
snatchers.’
Posted by Casey Kazan.
Related Galaxy posts:
Is the Human Species in Evolution’s Fast Lane? -A Galaxy Classic
Bringing Ancient Human Viruses Back to Life: A Jurassic Park or Salvation?
Loren Eiseley on Evolution: Transcending the Cosmos -A Galaxy Insight
Study Source: University of Massachusetts Amherst
Source: http://www.centauri-dreams.org/?p=1471
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