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Q: Evolutionary science ( Answered,   0 Comments )
Subject: Evolutionary science
Category: Science > Biology
Asked by: aquinas-ga
List Price: $5.00
Posted: 03 Aug 2003 04:59 PDT
Expires: 02 Sep 2003 04:59 PDT
Question ID: 238414
(i)  How is the age of fossil bones determined, apart from using their
local environmental evidence? (2) What connection can be made between
Orrogin tugenensis and homo sapiens?  (3) What place does DNA analysis
have in establishing the age and composition of fossils, and their
connection to homo sapiens?
Subject: Re: Evolutionary science
Answered By: knowledge_seeker-ga on 03 Aug 2003 10:35 PDT
Hi aquinas-ga, 

In keeping with the pricing of your question, I will answer all 3
parts briefly and provide you with search information to do your own
follow up.

1 ------------------------------

There are two traditional methods used to estimate the age of rocks
and the fossils contained in them – one, as you mentioned is "Relative
Dating" – based on the study of rock strata and the order of
appearance of the fossils contained in them.

The other is Absolute (Radiometric) Dating which is based on the rate
of decay of radioactive elements in rocks.  Since the radioactive
decay of large numbers of radioactive atoms follows a predictable
pattern, scientists can measure the age of an object (e.g. a mineral
in a rock) if they can work out how many radioactive atoms were
originally present. For bones, the presence and decay rate of 
Carbon-14 atoms are used. This is commonly called Carbon Dating.

Determining the age of rocks and fossils

Newer methods include Thermoluminesence and Mitochondrial DNA (mtDNA)
testing, neither of which is an exact science.

Thermoluminesence is not used for bones but is well suited to the
dating of archaeological remains:  ceramics and brick, hearths, fire
pits, kiln and smelter walls, heat treated flint or other
heat-processed materials, the residues of industrial activity such as
slag, incidentally fire-cracked rocks, and even originally unfired
materials such adobe and daub if they had been heated in an accidental

Thermoluminescence (TL):

"…mtDNA dating is based on the assumption (debated by geneticists)
that mutations occur at a constant rate. The accumulated mutations in
DNA can be measured, and the time necessary for them to occur
calculated. The amount of difference between Neandertal and human DNA
suggests that our common ancestor existed about 550,000 to 690,000
years ago. Although this date must be qualified (it is based on one
specimen only, and the DNA clock may or may not be as accurate as we
assume), it is in accord with the fossil record…"



The connection between Orrorin tugenensis and homo sapiens is scanty
and hotly contested.  Fossil evidence for this species from western
Kenya  includes only 13 fossils, including a partial femur, bits of a
lower jaw, and several teeth.  Those who believe that O. tugenensis is
"the missing link" cite similarities in tooth structure and the
presence of grooves in the femur which indicate bipedalism.

"One of the few things about O. tugenensis that is not controversial
is its age. Sediments in which the bones were found have consistently
been dated at 6 million years old, making O. tugenensis the oldest
hominid by far, if in fact the species is a hominid."

The origin of human kind

Hominid species


The role of Mitochondrial DNA (mtDNA) studies in both living humans
and in fossilized remains of human ancestors is to help establish (or
refute) the continuity of the ancestral line from the former species
to ours.

Most analysis involves testing living populations and establishing
"gene flow" maps which allow researchers to see how populations have
moved and spread across the earth over time. These studies are being
used to both support and refute the "out of Africa" theory of human



Some testing however, has also been done on fossil bones, in order to
help establish homo sapiens genetic relationship with ancestral

In 1997  Svante Pääbo of the Max Planck Institute for Evolutionary
Anthropology in Leipzig, Germany, and his colleagues retrieved and
sequenced for the first time mitochondrial DNA (mtDNA) belonging to a

Their results seemed to refute the idea that modern humans stemmed
from Neandertals.

"The team found that the difference between the Neandertal and modern
mtDNA was more than three times that observed between any two living
humans.  Moreover, the Neandertal DNA didn't show any special
similarity to DNA from living Europeans, which one might expect if the
Neandertals, who occupied Europe for more than 200,000 years,
contributed to the modern human gene pool. For many researchers, the
Cell study put a serious, if not fatal, dent in the multiregionalists'
argument that Neandertals were among our ancestors. And last year DNA
from two other Neandertal specimens yielded similar results, further
strengthening the Out of Africa replacement case."

The Modern Human Origins Morass

However, these results are contested as well ---

"Gregory J. Adcock of the Australian National University and his
colleagues retrieved and studied mtDNA from the fossilized remains of
10 ancient but anatomically modern Australians, including a
60,000-year-old specimen known as Lake Mungo 3 (LM3). Intriguingly,
like the Neandertal mtDNA studies, analysis of the LM3 sequence
revealed an mtDNA lineage that no longer exists as such in living

This suggests then, that the absence of Neandertal mtDNA in living
humans does not reject the possibility of some genetic continuity with
modern humans."

So the battle rages on. 

I trust what I've given has answered your question. Please use my
search terms below to find further information.

Thanks for your question!


determining  fossil age
Orrorin tugenensis and homo sapiens
fossil DNA analysis
fossil DNA analysis human origin
scientific american DNA human origin
Mitochondrial DNA testing fossil bones
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