Of course there are demented creationists who think Adam and
Allah are real and the planet only 6000 year old , but we scientists
know what is true and based on evidence.

excerpt

http://news.independent.co.uk/sci_tech/article2782518.ece

The skulls that prove we all came from Africa
By Steve Connor, Science Editor
Published: 19 July 2007
The human population arose from a single migration out of Africa
55,000 years ago, which replaced all other humans in Europe and Asia,
a study shows.

Scientists have confirmed the "out-of-Africa" model of human origins
with a study that combines genetic evidence with physical data from
more than 6,000 skulls around the world.

The twin approach has delivered what may turn out to be the killer
blow to the rival theory that humans evolved in several regions of the
world, said Andrea Manica of the University of Cambridge, who led the
study, published in the journal Nature.

"We are convinced of the out-of-Africa hypothesis because the way we
did this study gives us an edge we didn't have before," Dr Manica
said. "We looked at the genetics and we looked at the skulls and I
cannot see what other arguments you can come up with to explain what
we have observed."

Studies of DNA and the physical differences between skulls show that
human variation diminishes the greater the distance from Africa. This
confirms the view that after originating in Africa about 200,000 years
ago, anatomically modern Homo sapiens lived on the continent for about
150,000 years before beginning the long trek to Asia, Australia,
Europe and finally the Americas.

Other species of humans, such as Homo erectus and Neanderthal man, had
already migrated from Africa much earlier in history, but they all
became extinct after modern humans arrived in their areas.

The study appears to confirm that interbreeding between modern Homo
sapiens and other human species did not occur, or, if it did, it was
not on a scale that resulted in any living descendants.

The study also strongly suggests the cradle of modern humanity lies in
central or southern Africa, where Homo sapiens arose and spent
three-quarters of its history before migrating to the four corners of
the globe.

"The origin of anatomically modern humans has been the focus of much
heated debate," Dr Manica said. "Our research shows the further modern
humans have migrated from Africa, the more genetic diversity has been
lost within a population. Some have used skull data to argue that
modern humans originated in multiple spots around the world. We have
combined our genetic data with new measurements of a large sample of
skulls to show definitively that modern humans originated from a
single area in sub-Saharan Africa."

Indigenous people living in Australia and South America show the
lowest amount of genetic variation as well as differences between the
shapes and sizes of their skulls. Meanwhile, the genetic and physical
variation between people living in Africa is the greatest anywhere in
the world.

This is precisely what is predicted from the out-of-Africa hypothesis,
according to Dr Manica. "The origin of anatomically modern humans has
been the focus of much heated debate. Our genetic research shows the
further modern humans have migrated from Africa the more genetic
diversity has been lost within a population," he said.

http://news.independent.co.uk/sci_tech/article2782482.ece

One of the ways to visualise this is to imagine a large glass bowl
full of different coloured beads, representing genetic variation. This
equates to our ancestral population of H. sapiens who evolved some
200,000 years ago and had lived in Africa for 150,000 years,
accumulating genetic variation along the way, without straying outside
the continent.

However, some of these "beads" then went on a migratory journey out of
Africa, taking only a small portion of the total amount of genetic
variation from the ancestral stock (as measured in the total variety
of colours in the original glass bowl). As each subsequent migration
occurred, smaller amounts of variation were taken with each migrant
group. This would mean that the further people moved from their
African homeland, the less genetic variation there is among them
today. This is precisely what the researchers found when they studied
human genetic variation.

What about the physical variation in the skulls?

The same thing was found here too. The further from Africa the skulls
were, the less variation the scientists found in terms of the physical
features they measured.

It was thought that this might not be the case even if the
out-of-Africa hypothesis were correct because skull shape and
dimensions are subject to natural selection, whereas the genetic
variations measured by the scientists were in the "neutral", non-gene
part of the DNA, which varies simply by random chance.

However, it became clear that - just like DNA - the amount of
variation between skulls depended on the distance from Africa, with
African skulls showing the greatest variety.

As Dr Manica said: "Some have used skull data to argue that modern
humans originated in multiple spots around the world. We have combined
our genetic data with new measurements of a large sample of skulls to
show definitely that modern humans originated from a single area in
sub-Saharan Africa."

Why is this important?

One of the reasons is that we are still unsure about what happened to
other species of more ancient humans, such as Neanderthals and H.
erectus. We know they went extinct, of course, but was it possible
that they interbred with anatomically modern H. sapiens?

Genetic studies suggest that this was not the case, or at least that,
if there was some interbreeding, the offspring did not manage to leave
any detectable genetic signal in their descendants living today