It is becoming clear that primate
speciation or something like that produced huge diversity among primates world
wide during the hundreds of thousands of years preceding the emergence of an
effective sub class of tool makers that began to modify their environment. It appears then that cross breeding subsumed
a wide range of local characteristics into the emerging dominant modern human
strain.
Understand though that all these
sub populations numbered in the thousands at best. This is well illustrated by gorillas and the
sasquatch who arguably have populations in the thousands but certainly not an
order of magnitude greater.
An emergent human tribe was
itself a different matter. It could easily
out mass any stray hunting band it encountered and simply absorb the females
into the tribe. Thus it is rather
plausible that all the local variations that arose world wide were largely
subsumed into the more populous human stock and troublesome anomalies slowly
weeded out.
A good example of that occurring is
the low brow ridge sported by the Neanderthals that simply disappeared in the
larger gene pool, although we can be sure it is hidden away in case it is ever
important again. This is also one more
reason to recall that conscious choice by humanity will select fashionable
features. Your idea of beauty does matter to your children.
The big error is the bias toward
the apparent extinction of older genetic choices in the literature. My argument is that females of child bearing
age are conserved and especially so in an expanding population. At worst they are slaves. Thus genetic loss is unlikely but
homogenization is not as the tribe enlarges.
African fossils put new spin on human origins story
By Jonathan AmosScience correspondent, BBC News
8 September 2011 Last updated at 10:00 ET
Professor Chris Stringer, with the help of a cast of a fossil skull,
describes the similarities that this species has with modern humans
The ancient remains of two human-like creatures found in South Africa
The 1.9-million-year-old fossils were first described in 2010, and
given the species name Australopithecus sediba.
But the team behind the discovery has now come back with a deeper
analysis.
It tells Science magazine that
features seen in the brain, feet, hands and pelvis of A. sediba all
suggest this species was on the direct evolutionary line to us - Homo sapiens.
"We have examined the critical areas of anatomy that have been
used consistently for identifying the uniqueness of human beings," said
Professor Lee Berger from the University of the Witwatersrand in Johannesburg
"Any one of these features could have evolved separately, but it
is highly unlikely that all of them would have evolved together if A.
sediba was not related to our lineage," the team leader informed BBC
News.
The female's right hand is missing only a few bones
It is a big claim and, if correct, would sideline other candidates in
the fossil record for which similar assertions have been made in the past.
Theory holds that modern humans can trace a line back to a creature
known as Homo erectuswhich lived more than a million years ago. This
animal, according to many palaeoanthropologists, may in turn have had its
origins in more primitive hominins, as they are known, such as Homo
habilis or Homo rudolfensis.
The contention now made for A. sediba is that, although older
than its "rivals", some of its anatomy and capabilities were more
advanced than these younger forms. Put simply, it is a more credible ancestor
for H. erectus, Berger's team claims.
The sediba specimens were unearthed at Malapa in the
famous Cradle of
Humankind World Heritage Site, just to the northwest of Jo'burg.
They were pulled from a pit - a depression left in the ground by a cave
complex that had lost its roof through erosion over time.
Identified as an adult female and a juvenile male, the two individuals
were quite possibly mother and son. What seems certain is that they died
together in some tragic accident that saw them either fall into the cave
complex or become stuck in it. After death, their bodies were washed into a
pool and cemented in time along with the remains of many other animals that got
trapped in the same way.
In the months since their 2010
announcement, Professor Berger and colleagues have subjected the remains to
further detailed assessment.
Age: The latest dating technologies were applied to the sediments
encasing the fossils. Whereas original estimates had put the age of the remains
at somewhere between 1.78 and 1.95 million years old, the new analysis has
narrowed this window of uncertainty to just 3,000 years. The new age is now
between 1.977 and 1.98 million years old. The refined dating is important, says
the team, because it puts A. sediba deep enough in time to be a
realistic ancestor to H. erectus.
Dr Robyn Pickering, from the University of Melbourne, Australia, who
led the dating, told BBC News: "This is a very interesting time in human
evolution because it is when we think we should be seeing the beginnings of our
genus,Homo. Previously, we've had very few fossils from this time period, so
thesediba fossils are remarkable in that they are so complete."
Brain: A high-resolution X-ray scan of the male specimen's skull
has produced a virtual cast of its braincase. This was carried out at the
European Synchrotron Radiation Facility in Grenoble
It would appear from these fossils that hip evolution was not linked to
an increase in brain size
Pelvis: The pelvis is short and broad like a human pelvis. A more
ancient creature like Lucy has a flatter and more flaring pelvis. A popular
idea has been that the modern human pelvis evolved in tandem with the gradual
growth in brain volume - facilitating the birth of babies with bigger
heads. A. sediba gives the lie to this theory, says the team, because
it had a modern-looking pelvis while possessing a small brain.
Hand: The right-hand of the female is very nearly complete. It is
looks far more like a modern human hand than an ape hand. Its fingers are
shorter relative to the thumb than in a chimpanzee. And yet, it appears to have
possessed powerful muscles for grasping, suggesting A. sediba spent a
lot of time clambering through the branches of trees. The team also argues that
the dexterity would have been there to make simple tools.
Foot: The ankle joint is mostly human-like in form and there is
some evidence for a human-like arch and Achilles tendon. But A.
sedibapossessed an ape-like heel and lower tibia, or shin bone. The scientists
think this combination may have led to a distinctive type of walk when the
creature was not climbing in trees.
Whatever the correctness of the analysis, the creature certainly has a
fascinating mix of features - some archaic, some modern.
Independent scientists describe the fossils as exquisite and utterly
fascinating.
Dr William Harcourt-Smith from the American Museum of Natural History
in New York, commented: "One lineage of Australopithecusalmost
certainly led into the first member of our own genus called Homo, and from
then eventually emerged modern humans.
"But some of them are side branches, and we're trying to work out
which ones are and which ones aren't - and that's why this finding is so
important. In many ways, these fossils are the 'smoking gun' just before the
emergence of our own genus."
And Professor Chris Stringer, from London 's
Natural History Museum
"The question now is to pull out of this mess which one is really
the ancestor of the genus Homo. We know there are more remains to come
from this incredible site. Let's see if other individuals also show this mix of
features."
No comments:
Post a Comment