my favourite books as a child was a huge volume devoted to the
natural history of dinosaurs. It was especially fascinating
as it included a brief section towards the end about life after
the dinosaurs, and it was from this that I first learnt about
our own evolution.
time, it all seemed wonderfully simple. Our own species, Homo
sapiens , evolved over many thousands of years from the more
brutish Homo neaderthalensis , which in turn evolved from the
smaller Homo erectus , which in turn evolved from the even smaller
Homo habilis , which in turn evolved from a much more primitive
ancestor known as Australopithecus , so far removed from ourselves
that it did not even deserve the title Homo , the poor thing.
traditional view of human evolution as one of linear progression
is still popular today at least, among the general public.
And also, I have no doubt, among a fair number of philosophers
as well. There is something very attractive about the idea that
we, Homo sapiens or Wise human with our science,
philosophy and art, are the pinnacle of evolution; that a natural
progression has taken place from brutish ape to modern wise
human, each one replacing the last until we reach the final,
simplistic view of human evolution is seriously flawed. In the
first place, there are not just a few species of humans, but
numerous species. It is becoming ever more apparent that human
evolution is like a bush, not a ladder. Secondly, the idea that
human evolution always involves progress, in that
primitive humans are permanently replaced by more advanced humans,
has been put in serious doubt by recent research.
view of human evolution began to be abandoned in the 1970s as
different species of humans were discovered that made the linear
concept increasingly unlikely. More recent discoveries have
only strengthened this position and indicate that not only is
human evolution a bush, it is an unruly bush. The four Homo
species mentioned above have been joined by H. ergaster , H.
antecessor , H. heidelbergensis , H. georgicus , H. rudolfensis
and, most recently, H. floresiensis , not to mention numerous
specimens which have yet to be properly classified. As the anthropologist
Ian Tattersall says of the numerous examples of H. habili- related
humans that have been discovered, The latest suggestion
is to remove most or all of them from Homo and to place them
into Australopithecus instead. I'm happy to go along with this,
although I must note that, while tidying up the concept of Homo
, this makes the notion of Australopithecus even messier than
it was before.
that human evolution is linear is clearly wrong, but what about
the idea that human evolution involves progress? The idea is
that, numerous though they may have been, primitive humans have
always been replaced by more advanced humans until we reached
the final, perfect form the modern human.
it may at first seem obvious after all, here we are,
modern man, the sole human species the idea that human
evolution is progressive has in recent years been increasingly
undermined by the evidence. But it is the publication of two
very different pieces of scientific research in the last few
months that has been most decisive. The first of these involved
the genetic analysis of lice, which sounds unremarkable, but
has extraordinary implications. The second involves one of most
astounding scientific discoveries in the last fifty years, a
new species of human quite unlike any other.
evolve in tandem with their host, lice, like many parasites,
can be used as unique markers to investigate their host's evolutionary
history, something which can be very useful in the absence of
any host data.
two types of lice found on humans today, one lives on the body
or the head of people all around the world, while the other
is found only on the head and is unique to the Americas.
Reed of the Florida Museum of Natural History and colleagues
analysed the genetic differences between the two and found that
they were so large that they must have diverged some 1.18 million
years ago, around the same time that our ancestors diverged
from an archaic H. erectus species.
and his team believe that the louse found only in the Americas
was the one that evolved on H. erectus while the worldwide louse
evolved on the population that eventually became H. sapiens
. As both lice are now found on H. sapiens, at some point in
the recent past the two species must have made direct contact
again (human lice cannot survive off the body of a host for
more than 24 hours) and the H. erectus louse jumped back onto
a population of H. sapiens which subsequently colonised America.
The question is, when?
to Reed, the evidence suggests that H. erectus was contemporaneous
with modern H. sapiens in eastern Asia, as suggested by Swisher
is a reference to Carl Swisher of the Berkeley Geochronology
Center who dated the soil in H. erectus skulls from Java in
1996 and proposed that H. erectus survived in Java up until
53,000 to possibly 27,000 years ago, give or take a couple of
thousand years. In other words, H. erectus may have survived
on Java at least 250,000 years longer than on the Asian mainland,
and perhaps 1 million years longer than in Africa. Swisher raised
the possibility that H. erectus overlapped in time with modern
humans in Southeast Asia, but he lacked any evidence of direct
interaction. This evidence has now been tentatively provided
by Reed at al.
from being replaced by more advanced species, such
as H. neaderthalensis and H. sapiens , it would appear as if
H. erectus flourished for thousands of years after the appearance
of these species and was walking the earth until perhaps 25,000
that were not incredible enough, it was recently announced by
Peter Brown of the archaeology and palaeoanthropology department
of the University of New England that a new species of human
has been discovered in Southeast Asia, on the island of Flores.
The evidence suggests that H. floresiensis , as it has been
named, may have lived up until some 14,000 years ago. To put
this in perspective, that is some 3000 years after the caves
were painted at Lascaux by modern humans and some 25,000 years
after modern humans first reached Australia.
is thought to have descended from an ancestral H. erectus population.
More significantly, as it was only one metre tall, and slightly
built, it represents an example of dwarfing in human evolution.
According to the authors of the research: H. floresiensis
shows that the genus Homo is morphologically more varied and
flexible in its adaptive response than previously thought.'
this tells us is that only 30,000 years ago there may have been
four distinct human species walking the planet. Not one, as
there is now, not two, as was thought to be the case up until
very recently ( H. neaderthalensis and H. sapiens ), but certainly
three, and very possibly four human species walking the earth
at the same time. And yet over the next 15,000 years all but
one of them died out.
not wish for a clearer indication of the role of chance in the
survival of our species. If things had gone only slightly differently
in the recent past then modern humanity might not have been
represented by H. sapiens , but instead by H. neaderthalensis
or by H. floresiensis or possibly even H. erectus .
there would have been no representative at all.
new small-bodied hominin from the Late Pleistocene of Flores,
Indonesia,' P Brown et al, Nature, volume 431 (28 October 2004)
Analysis of Lice Supports Direct Contact between Modern and
Archaic Humans,' Reed et al, PLoS Biol (November 2004, www.plosbiology.org)
in the Mirror (Essays on the Science of What Makes Us Human)
, Ian Tattersall (Oxford University Press)