Posted on 02/24/2007 4:59:17 AM PST by Pharmboy
A male chimpanzee feeds in Kibale National Park tropical
rain forest, 354km southeast of Uganda's capital Kampala,
December 2, 2006. A new study, certain to be controversial,
maintains that chimpanzees and humans split from a common
ancestor just 4 million years ago -- a much shorter time
than current estimates of 5 million to 7 million years
ago. (James Akena/Reuters)
Chimpanzees and humans split from a common ancestor just 4 million years ago -- a much shorter time than current estimates of 5 million to 7 million years ago, according to a study published on Friday.
The researchers compared the DNA of chimpanzees, humans and our next-closest ancestor, the gorilla, as well as orangutans.
They used a well-known type of calculation that had not been previously applied to genetics to come up with their own "molecular clock" estimate of when humans became uniquely human.
"Assuming orangutan divergence 18 million years ago, speciation time of human and chimpanzee is consistently around 4 million years ago," they wrote in their study, published in the Public Library of Science journal PLoS Genetics, available online at http://genetics.plosjournals.org/perlserv/?request=get-document& doi=10.1371/journal.pgen.0030007#toclink4.
"Primate evolution is a central topic in biology and much information can be obtained from DNA sequence data," Dr. Asger Hobolth of North Carolina State University said in a statement.
The theory of a molecular clock is based on the premise that all DNA mutates at a certain rate. It is not always a steady rate but it evens out over the millennia and can be used to track evolution.
Experts agree that humans split off from a common ancestor with chimpanzees several million years ago and that gorillas and orangutans split off much earlier. But it is difficult to date precisely when, although most recent studies have put the date at somewhere around 5 million to 7 million years ago.
Hobolth and colleagues from the University of Aarhus in Denmark and the University of Oxford in Britain looked at four regions of the human, chimpanzee, and gorilla genomes.
QUICK SPLIT
They used a statistical technique called the hidden Markov model, developed in the 1960s and originally applied to speech recognition.
What they found may contradict some other recent research. They found evidence that it took only 400,000 years for humans to become a separate species from the common chimp-human ancestor.
Just last May, David Reich of the Broad Institute at the Massachusetts Institute of Technology and Harvard Medical School's Department of Genetics found evidence that the split probably took 4 million years to occur, although his team put the final divergence at just 5.4 million years ago.
"I don't think it really contradicts our paper," Reich said in an e-mail exchange.
"We were focusing on a maximum time for the common ancestor of humans and chimpanzees, while they were focusing on a best estimate," added Reich, who reviewed Hobolth's paper before it was published.
Experts have long known that humans and chimpanzees share much DNA, and are in fact 96 percent identical on the genetic level.
And one year ago, Soojin Yi and colleagues at the Georgia Institute of Technology said they found genetic evidence that chimpanzees may be more closely related to humans than to gorillas and orangutans.
Their look at the molecular clock showed humans evolved one unique trait just a million years ago -- our longer life span and our long childhood that means humans reach sexual maturity very late in life compared to other animals.
"The theory of a molecular clock is based on the premise that all DNA mutates at a certain rate. It is not always a steady rate but it evens out over the millennia and can be used to track evolution.
This theory does not seem correct on the face of it.
Aren't there bursts of evolution when climate or environments change, followed by millions of years of relative stability?
Quite a bit of the DNA code is "junk", not required for the creature to survive. Mutations in the required parts of DNA tend to be weeded out of the genome because the critter may not survive with those errors, but changes in the junk DNA happen at a relatively steady rate, and are passed down and can be measured.
The "bursts of evolution" you talk about, often associated with environment changes, exploit mutations in the non-junk DNA and result in separate species.
I think this is how it works. I don't claim to be a genetic scientist.
Mutation and natural selection are not the same thing.
Long childhood seems a strange bedfellow to traits that are beneficial for survival. If you want to stick with an evolutionary explanation, then you must embrace this. Is there a forum in FR where people calmly discuss various theories of existence?
Indeed...the species must have been able to protect and provide for these young 'uns for them to have an extended childhood.
I believe they study regions of DNA that are considered "junk;" theory has it that junk DNA doesn't code for anything particular in the phenotype, and would therefore not be subject to selective pressures, only random mutations.
And there are reasons to believe that the rate of occurrence of these mutations, due to the random processes of thermal action and ionizing radiation, is roughly constant over the long term.
Very recent research, however, is questioning just how "junky," or non-functional, this DNA actually is. One subtle use for junk DNA might be to facilitate the folding of long DNA chains into usefully compact forms. (Chromosomes are such long DNA molecules that they critically depend on a large amount of folding.)
Another interesting theory about junk DNA is that it serves to intercept ionizing events relative to its proportion in the overall DNA structure, thus reducing the probability or frequency of harmful mutations to non-junk DNA. Sort of the way a larger herd of wildebeests minimizes the chances of any particular one getting caught by a lion. < }B^)
The "junk" DNA is not junk at all. Much of it is regulatory genes and likely stuff we do not yet comprehend.
Data, metadata, and metametadata.
That's why evolution turns on when needed, and then turns off.
LOL!!!
I had to share this post (#30) with you two!!
LOL!!!
"Hair: everywhere" LOL.
Here's a composite of theories I have heard that make some sense to me.
Humans have long lives and long maturation periods. Part of the long development from birth is due to the exeptionally helpless condition of human babies.
This latter condition may be due to the collision of two physical evolutionary trends.
First, we have the biggest brains for our size (among land mammals, anyway). Clearly, there is (or was!!) an evolutionary advantage to this.
At the same time, we developed uniquely dextrous hands; probably in a synergy with our big brains. That allowed, or encouraged, us to evolve to walk upright so that we could make maximum use of our hands and retain good mobility.
But walking fully upright led to a change in the shape of our pelvis. It became narrower. Now there's a problem for females of the species to give birth to those big-headed human babies. Notice how much more difficult it is for the average woman to give birth than it is for your dog, cat, or any other mammal? It's the collision of the big head (brain) with the narrow birth canal.
The compromise worked out by Mother Nature was (1) To make it a bitch (no pun intended!) for human females to give birth, and (2) for human babies to be much less developed at birth so that their proportionally gigantic heads can still (just barely) fit through the birth canal.
The long ensuing childhood is IMHO due to the extreme emphasis that Mother Nature has placed on our brains for us to survive. Lord knows we're not the strongest or the fastest or most physically ferocious of beasts. (Mentally, well that's another matter.) It just plain takes a lot of years, a uniquely long fraction of our lifetimes, to acquire the learning we need to survive. You might say that the ratio of learning to instinct given to a species determines the ratio of childhood to adulthood.
Human-Chimp Gene Gap Widens from Tally of Duplicate Genes (Not as similar as previously thought)
Scientific American | December 19, 2006 | JR Minkel
Posted on 12/21/2006 11:35:52 AM EST by DaveLoneRanger
http://www.freerepublic.com/focus/f-news/1756846/posts
"Researchers studying changes in the number of copies of genes in the two species found that their mix of genes is only 94 percent identical. The 6 percent difference is considerably larger than the commonly cited figure of 1.5 percent."
[the commonly cited figure is all over the place, and was based on a superficial comparison of dark and light bands on the chimp's 24 chromosome pairs and humans' 23]
Scientists Find Evolution Clue in Chimp DNA
Digital Chosun Ilbo /Nature
Posted on 01/02/2006 6:08:53 PM EST by MRMEAN
http://www.freerepublic.com/focus/f-news/1550799/posts
"It is well known that we share more than 98 percent of our DNA and almost all of our genes with the chimpanzee."
Study: Primates may have come along earlier than thought
The Gainesville Sun | 16 Jan 2007 | JACK STRIPLING
Posted on 01/16/2007 3:19:26 PM EST by ASA Vet
http://www.freerepublic.com/focus/f-news/1768502/posts
'Original' great ape discovered [New genus "Missing Link" found!]
BBC | 2/18/07 | Paul Rincon
Posted on 02/19/2007 2:40:54 AM EST by LibWhacker
http://www.freerepublic.com/focus/f-news/1787210/posts
Psych Prof Advocates Human/Chimp Hybrids – But only to Offend Christians
Lifesite | July 28, 2006 | Hilary White
Posted on 07/31/2006 10:49:24 AM EDT by NYer
http://www.freerepublic.com/focus/f-news/1675094/posts
"Assuming orangutan divergence 18 million years ago, speciation time of human and chimpanzee is consistently around 4 million years ago," they wrote in their study...Heh...
The Scars of Evolution"The most remarkable aspect of Todaro's discovery emerged when he examined Homo Sapiens for the 'baboon marker'. It was not there... Todaro drew one firm conclusion. 'The ancestors of man did not develop in a geographical area where they would have been in contact with the baboon. I would argue that the data we are presenting imply a non-African origin of man millions of years ago.'"
by Elaine Morgan
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Nope--our hands are pretty much generalized primate hands. Evolved >50 million years ago (likely) for two main purposes: grabbing branches and picking up insects. The latter is thought to be the reason that we have nails instead of claws--easier to pick up the little buggers. And nails rather than claws is one of the special traits that defines primates.
Why are there still apes then? wouldnt they "evolve" too?
YEC INTREP
For example, hypothesize for a moment that a great earthquake occurred in Africa which caused chasms in land that was occupied by an animal. Now , however, the chasms kept individuals from that group isolated from others (there are many ways in which isolation can occur, for example, merely through one group moving away, or isolation through flooding).
At any rate, this second population will never breed with the first group again. Different environmental pressures on the second group now pick out certain individuals for reproductive success based on changes in their genes. None of these pressures were present on the original group (on the OTHER side of the chasm). After hundreds of thousands and millions of years a new species may now arise, while the original group is unchanged.
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