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Humans Evolved From a Single Origin In Africa
Invisible Pink Unicorn writes "Researchers at the University of Cambridge have combined studies of global human genetic variations with skull measurements worldwide to show conclusively the validity of the single origin hypothesis. The alternative hypothesis contended that different populations independently evolved from Homo erectus to Home sapiens in different areas. The lead researcher explains, '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. However, 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.' The article abstract is available from Nature."
A bit off-topic, I know, but what often puzzles me is that all living things basically work with the same chemistry. All have DNA, and there are many proteins that are physically very similar between different species, even between animals and plants. This leads me to conclude that all life must have come form one ancestor that materialized somewhere on the planet. But the earth is a big place. To me it seems very unlikely that life hasn't occurred in more than one place and more than one time. So how is it possible that all life, on a chemical level, is more or less the same?
-- Cheers!
Just FYI, Hawks has an interesting blog at http://www.johnhawks.net/weblog
I think it's down right now, but I'd recommend it!
"1. Dark pigmentation is a protection against the sun.
2. When people migrate north were the sun is weaker, over time, the need for sun protection disappears and people lose the pigmentation, hence becoming lighter."
Close, but not quite right. Sun + skin = creation of vitamin D, very important to the human body. Dark-skinned people created less vitamin D in this manner than light-skinned people, but also have better protection from the sun. A good trade-off in equatorial plains regions. As people migrated north they had less exposure to sun and therefore had less natural vitamin D so the sun-blocking benefits of dark skin became a negative to their survival. Lighter-skinned people could create more vitamin D in the northern regions so that became a plus for their survival - so skin became lighter over time in those regions. (Lighter-skinned people lived longer to reproduce.)
At least according to most programs I've caught on the Discovery Channel.
Your mind looks a little cramped. Why don't you stretch it a little?
I remember hearing that it's been proven genetically that there is one common male ancestor and one common female ancestor for humans. the problem was, they were about 100,000 years apart.
It was on television, so no reference.
Rational thought is the only true freedom
The Multiple Origin Hypothesis is really misnamed, if you ask me. The model states that H. erectus migrated out of Africa, and that populations of H. erectus interbred, keeping variation down, or at least keeping interbreeding possible. Thus, modern H. sapiens evolved all over the place, in a direct line from the H. erectus ancestors already in place.
The Single Origin or Out of Africa Hypothesis states that H. sapiens evolved in Africa, and migrated out from there.
In both cases, there is an acknowledgeable that human ancestors first evolved in Africa, then moved out from there. The difference, as I see it, is really the time at which this happened. Out of Africa is much more recent than Multiple Origins.
Rhapsody in Numbers
Typical anthropology major (I kid, I kid. I have a degree in anthropology, too).
I believe I've read the same or similar material. Here is a little more detailed explanation:
Population geneticists have observed more genetic variability within the African population than in other areas. This by itself doesn't mean anything, though. It could just be that the environment in Africa in the old days was pleasant enough that mutant genes had a decent chance of survival, while harsher environments in paleolithic Europe, Asia, etc could weed out genes much more efficiently through very vigorous natural selection.
There is another piece to the puzzle, though. Not only does Africa have a huge amount of variability, but that variability encompasses nearly all the variability found in other places as well. That is, the gene pools of Europe, Asia, etc are basically sub-sets of the African gene pool. Consider the following scenarios that could explain this:
If think if you put this into mathematical language, you'd find option #3 is definitely the most likely. I wouldn't call it conclusive, though. After all, options #1 and #2 could be correct, if we discover some unknown processes that make them work without resorting to blind luck. In the meantime, though, my bet is on #3.
"Any fool can make a rule, and any fool will mind it."
--Henry David Thoreau
Scientists, as you point out, often have a 'religious' view of certain theories. We saw it back when the Big Bang theory was first proposed; the scientists of the day saw it as 'thinly veiled creationism'. What drives science forward, though, is when you have two groups of fanatics screaming at each other, the non-fanatics generally cluster to the side with the better arguments and better evidence. That's why the Big Bang theory is now taught in schools, and the various steady state theories are discarded, as are most of the 'Big Crunch' ideas.
Anyway, as far as your 4 theories go:
1. The Universe came into existence completely from nothing, by itself. There was nothing, then everything over time. Start with nothing & work forward.
I believe that Hawkings is actually espousing this idea. It seems highly unlikely to me, since it violates the First Law of Thermodynamics, without which all Chemistry, Physics, and Biology is meaningless.
2. The Universe always existed
Seems highly unlikely, given that a) the universe is expanding with no sign of collapsing and b) the Second Law of Thermodynamics.
3. The Universe is an illusion
Possible, but a pointless theory. Even if true, the universe behind the illusion still has to follow one of the other 3 possibilities (but #1 and #2 might be possible in a universe with different laws)
4. The Universe was created.
Almost certainly the case, the question is just by what. Perhaps another universe is unaffected by the Second and/or First law of Thermodynamics, and our universe was created there as an experiment/toy/prop. Perhaps our Universe was born from a black hole in another universe- and the black holes in our universe are also creating more universes. God creating this universe seems at least as likely as anything else, but that merely tells us he's insanely smart and/or powerful. He may care about our universe, but not care about us.
Our best science tells us that we can't know how the universe was created. Unless we get the opportunity to witness another Big Bang or talk to God, it seems likely we will never even have that good of an idea.
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