Monday, October 10, 2011

Born in Africa

Another book review.  This weekend I read Born in Africa: The Quest for the Origins of Human Life by Martin Meredith (2011, Public Affairs).  It was in the new books section of the library and I was hoping it would discuss some of the newer (past decade or so) hominid discoveries.

I found it to be mostly a review of what I already knew (or once knew and forgot) but it would be a good introductory book for those unfamiliar with the field of paleoanthropology (the study of ancient humans).  It's a field I've read quiet a bit about in the past (my first interest in college was archaeology).

Martin Meredith is an historian and journalist.  I'm always a bit skeptical of science books written by nonscientists but Meredith seems to do an OK job of summarizing the latest thinking on human evolution - his journalist side comes through, however, in his focus on the personalities of the people invovled, more than analysis of the specimens discovered and the significance of the finds.

Unfortunately, the field of paleoanthropology seems to attract people who develop emotional, and sometimes irrational, attachments to their pet hypotheses. In all accounts I've read, two of the best known leaders in the field, Richard Leakey and Donald Johanson, are both egotistical jerks. Many times, grand claims were made from discoveries that were little more than a few scraps of bone.  Rivalries between researchers in the field and irrational attachment to preconceived ideas about hominid evolutionary relationships has probably kept the field from developing as fast as it could have otherwise.

Anyway, the book starts with Darwin's ideas on the origin of man and then moves on to early discoveries in South Africa by Raymond Dart (Taung Baby) and Robert Broom.  Much of the book, quite reasonably, is devoted to the work of Louis and Mary Leaky in Olduvai Gorge in northern Tanzania and then the work of his son Richard and Donald Johanson (discoverer of "Lucy") in northern Kenya and Ethiopia (Koobi Fora; Turkana; Hadar).  Most interesting to me were accounts of more recent discoveries (1990s and 2000s) at the classic sites of Sterkfontein and Swartkrans in South Africa, the discovery of Ardipithecus ("Ardi") in Hadar, and a description of other hominids I was unfamiliar with (Kenyanthropus platyops, Sahelanthropus tchadensis, Orrorin tugensis, etc.).

The field of paleoanthropology was really turned on its head in the 1970s and 1980s by the development of molecular dating and analysis of mitochondrial DNA.  The genetic information of modern hominids (humans, chimps, gorillas, and orangutans) and other primates can be studied to show when they had a last common ancestor.  Turns out that gibbons and humans had a last common ancestor around 20 million years ago, orangutans split off from us around 16 million years ago, gorillas around 10 million years ago, and humans and chimpanzees (with whom we share 98.6% of our DNA) had a last common ancestor only around 6 million years ago.  Far more recent than paleoanthropologists had thought based solely on fossil evidence.

The big takeaway from this book is that human evolution is complicated.  Many people still have the following image of "the evolution of man" (at least those who don't hold to the Adam and Eve literalism of the Bible!).
I put a big red X through it because it's completely incorrect.  It's a 19th century idea rooted in the false concept of evolution working to produce the "crown of creation" - humans.

Evolution is like a many-branched bush and, during the last few million years, there were many hominids walking around and coexisting together.  Some became evolutionary dead ends and others led eventually to us (judging by what we're doing to our world, it's hard not to believe that in a few million years, Homo sapiens will be an evolutionary dead end as well!).  Below is one interpretation of our ancestors and possible evolutionary relationships.

Just to be clear, in the diagram above, the fossils and the age ranges are facts.  They are specimens that have been excavated and very well studied.  The age ranges may be extended with new discoveries, of course.  The interpretation comes in with the taxonomy - assigning the specimens to a particular genus and species (a man-made construct) - and the arrows showing inferred evolutionary relationships.  These are also subject to change based on new discoveries (that's how science works!).

It's an interesting and still unfolding story.

1 comment:

  1. very good.
    thanks from Brazil.
    I hope there is "born in africa" in portuguese too.