Reply
Sat 16 Oct, 2004 04:32 am
From The new Scientist:
(Full story here
http://www.newscientist.com/news/news.jsp?id=ns99994817 )
Early humans swapped bite for brain
18:00 24 March 04
NewScientist.com news service
Humans owe their big brains and sophisticated culture to a single genetic mutation that weakened our jaw muscles about 2.4 million years ago, a new study suggests.
The slack muscles relaxed their hold on the human skull, giving the brain room to grow. Other primates remained stuck with mighty muscles that squeezed the skull in a vice-like grip.
The finding is "pretty amazing", says Peter Currie, an expert on skeletal muscle development at the Victor Chang Cardiac Research Institute in Darlinghurst, Australia: "Changes in muscle anatomy are well known to alter the bones to which they attach. The exciting part of this is the mutation in the gene dates to exactly when this transition occurs in the fossil record."
Over the past 2.5 million years, human brains have grown enormous compared to those of other primates. Human brains are now roughly three times the size of those of chimps or gorillas.
One possible reason is that changes in the environment forced early humans to invent tools, and those with the biggest brains had greatest manual dexterity, which led to yet more sophisticated tool use. Alternatively, selection may have favoured larger brains because they permitted more complex cultures.
But why did this process occur in humans and not in other primates? According to Hansell Stedman, an expert on muscle disorders at the University of Pennsylvania in Philadelphia, it was a simple mutation in a gene found in our jaw muscles...........
It is known there were two streams of hominid species around 2 million years BP(before present); Homo habilis and Australopithecus robustus, of which the latter had strong jaws.
http://www.wsu.edu:8001/vwsu/gened/learn-modules/top_longfor/timeline/timeline.html
That saying you disagree with the theory, Satt?
Thanks for the link.
The two kinds of hominids must have different genes. It must be studied further to determine whether it was due to a single gene or not.
Another interesting article - though not about the theory:
"Oldest hominid skull shakes human family tree
19:00 10 July 02
NewScientist.com news service
The wind-blown Djurab Desert of Chad has opened a new window on early human evolution - a hominid skull six to seven million years old, at least two million years older than any skull previously discovered.
The stunning find was unearthed by Michel Brunet of the University of Poitiers in France and his team. "It's a lot of emotion to have in my hand the beginning of the human lineage. I've been looking for 25 years."
The strong brow and small teeth contrast with the chimp-like size of the skull(Photo: MPFT)
Named Sahelanthropus, the new species is close to the common ancestor of humans and chimpanzees. It and other recent discoveries "strongly shake our conceptions of the earliest steps of hominid history," Brunet says. "The divergence between chimp and human must be even older than we thought."
Sahelanthropus shows the last common ancestor "did not closely resemble any modern ape," said Tim White of the University of California at Berkeley. Although its body and brain were the size of a modern chimp's, its face was quite different, with large brow ridges and much smaller canine teeth.
From the back, the skull "looks like a chimpanzee, whereas from the front it could pass for a 1.75 million year old advanced australopithicine" says Bernard Wood of the George Washington University. Such a mosaic of features is also evident in a newly discovered 1.8 million year old skull from Georgia........"
(Full story here
http://www.newscientist.com/news/news.jsp?id=ns99992533 )
The question of divergence among big apes seems very complicated:
Quote:
'New' giant ape found in DR Congo
Scientists believe they have discovered a new group of giant apes in the jungles of central Africa.
The animals, with characteristics of both gorillas and chimpanzees, have been sighted in the north of the Democratic Republic of Congo.
According to local villagers, the apes are ferocious, and even capable of killing lions.
A report about the mysterious creatures is published in this week's edition of the UK magazine New Scientist.
If they are a new species of primate, it could be one of the most important wildlife discoveries in decades.
The discovery of these apes "reveals just how much we still have to learn about our closest living relatives," New Scientist says.
'NEW' GIANT APE
Large, black faces (like gorillas)
Up to two metres tall (6.5ft)
Weigh 85kg-102kg (187lb-224lb)
Males make nests on the ground (like gorillas)
Diet rich in fruit (like chimps)
They stand up to two metres tall, the size of gorillas, and like gorillas, they nest on the ground, not in trees.
But they live hundreds of km away from any other known gorilla populations, and their diet is closer to that of chimpanzees.
Primatologist Shelly Williams is thought to be the only scientist to have seen the apes.
During her visit to DR Congo two years ago, she says she captured them on video and located their nests.
She describes her encounter with them: "Four suddenly came rushing out of the bush towards me," she told New Scientist.
"If this had been a bluff charge, they would have been screaming to intimidate us. These guys were quiet. And they were huge. They were coming in for the kill. I was directly in front of them, and as soon as they saw my face, they stopped and disappeared."
Mystery
The discovery has baffled scientists. There are three controversial possibilities to explain the origin of the mystery apes:
They are a new species of ape
They are giant chimpanzees, much larger than any so far recorded, but behave like gorillas
They could be hybrids, the product of gorillas mating with chimpanzees.
So far, researchers have little to go on, but they now plan to return to northern DR Congo to study the apes further.
In the meantime, there are fears that unless measures are taken to protect them, poaching could threaten this new group of primates before the mystery of their identity is resolved.
"This is a lawless area," says Kenyan-based Swiss photographer Karl Ammann, who tipped Ms Williams off about the apes.
"The government has practically no control over hunting. If we found something interesting it would attract more investment. People would be more interested in conserving it."
source BBC
Heehee - I and walter have threads on that.
Fascinating! Any ideas where one could find out more????
Thanks satt! More very welcome.
I am reading and learning. Thanks, folks.
I like it. We knew that arliest of the homo and late pithecenes were contemporary with fossil bone piles that suggested that our ancestors were meat scavengers. They would sneak up to a kill and smash the bones to extract the marrow. The benefit of a meat diet was the extraa B and amino acids were stimulating brain growth. Now , if the actual mutation date could be pinned down to , say the laetolli ash falls or the CobbHill event, then there would be something more than an educated "guess".
im dubious of the date for the mutation. its all done by cladistics and we dont have all the species in the clades yet.
its neat but not ready for prime time yet.
I've got a book on the bedside table that argues that the common ancestor of the great apes was more hominid-like than "ape"-like. Prolly won't get to it for months, though. Heard anything about this, f-man?
Cladistics. Family bushes that go back a really long way.
Arrrrrrrrrr.....
Or: cladistics
Noun
1. a system of biological taxonomy based on the quantitative analysis of comparative data and used to reconstruct cladograms summarizing the (assumed) phylogenetic relations and evolutionary history of groups of organisms
(synonym) cladisitic analysis
(hypernym) taxonomy
Yeah, but my answer is in good old Ainglish...
Oh? I thought you spoke 'Murrican?
heeeheeheheheheeheheehhehehhheee .......ahem.....
Ok - I got interested - ad for anyone else who is, too:
http://en.wikipedia.org/wiki/Cladistics
Excerpt:
"Cladistics
From Wikipedia, the free encyclopedia.
This cladogram shows the relationship among various insect groups. In some cladograms, the length of the horizontal lines indicates time elapsed since the last common ancestor.Cladistics or phylogenetic systematics is a branch of biology that determines the evolutionary relationships of living things based on derived similarities. It forms the basis for most modern systems of classification, which seek to group organisms by evolutionary relationships. In contrast, phenetics groups organisms based on their overall similarity, while more traditional approaches tend to rely on key characters. Willi Hennig is widely regarded as the founder of cladistics.
Introduction
Based on a wide variety of information, which includes genetic analysis, biochemical analysis, and analysis of morphology, treelike relationship-diagrams called "cladograms" are drawn up to show different possibilities.
A vertical orientation yields a cladogram reminiscent of a tree. All plants in this diagram descend from ferns.In a cladogram, all organisms lie at the leaves, and each inner node is ideally binary (two-way). The two taxa either side of a split are called sister taxa or sister groups. Each subtree, whether it only contains one item or a hundred thousand, is called a clade. A correct cladogram should have all the organisms contained in any one clade share a unique ancestor for that clade, one which they do not share with any other organisms on the diagram. Each clade should be set off by a series of characteristics that appear in its members but not in the other forms it diverged from. These identifying characteristics of a clade are called synapomorphies (shared, derived characters). For instance, hardened front wings are a synapomorphy of beetles, while circinate vernation, or the unrolling of new fronds, is a synapomorphy of ferns......"
Stumble It!
Tweet This
Bookmark on Delicious
Share on Facebook
Share on MySpace