Evolution: Descent with Modification

YourInnerFishThe debate regarding whether the Theory of Evolution is compatible with Christian belief has been driven by those who are at the extremes of the possible positions.  I have followed this debate with varying degrees of interest, attempting to understand the nuances of the issues as well as the positions of the hard core polemicists.  Neil Shubin’s book YOUR INNER FISH: A JOURNEY INTO THE 3.5 BILLION-YEAR HISTORY OF THE HUMAN BODY was recommended to me as a good book to read for understanding why so many scientists are convinced that evolution is true.  The vast majority of scientists involved in fields related to biology do accept that evolution is true, and they do think there is so much evidence supporting the Theory that they can speak about it as fact.   (see the NY TIMES Book Review “Evolution All Around” which does take scientist Richard Dawkins to task for mixing up theory and fact).

I found Shubin’s book to be an enjoyable read and comprehensible for me the non-scientist (though admittedly I have read enough in this field to be familiar with the concepts).   I would recommend this book to any who want to understand how evolution works in theory and how the current known facts about human life do give solid support to the theory.

kidsWhat Shubin does so well is to show that “evolution” fundamentally means that all living things reproduce in the same basic way: “descent with modification.”    Any of us with the most basic knowledge of genetics or DNA understand that every human child receives from his/her parents a set of genes – half from the father and half from the mother.  Every human child is thus clearly a genetic descendant of his/her parents (thus the Genesis reproduction law – according to their kind).  However no child is genetically identical to either parent – thus descent with modification.   Descent with modification is visible everywhere in which we can see life.  Even those who accept a notion that the earth is less than 10,000 years and that all humans are descendants of Adam and Eve have to admit there is tremendous variety in humanity today – not one of us is a clone of Adam or Eve, but rather we each share the genetic diversity which belongs to all humanity and makes each of us genetically unique;  in Shubin’s words: “all of us are modified descendants of our parents or parental genetic information.”

That is evolutionary fundamentalism.    Of course evolution has other ideas which are more controversial – especially speciation.   But in other works I’ve read there are known examples of biological speciation – where offspring are genetically different enough from their parents so as not to be able to reproduce with their parent’s “species.”   The offspring though sharing the genetic recombination of its parent’s genes, have such a genetic makeup that they cannot reproduce with others genetically similar to their parents but can reproduce with others genetically similar to themselves.  The offspring may even look identical to their parent but have in fact become a separate species.   And when given the millions of years which science says life has had to evolve, it is easier to understand how small changes through large periods of times can lead to speciation – where though two life forms share a common ancestor in their distant past, they no longer even look anything alike and have undergone the steps and stages macro-evolution.  Just a few examples of how long ago science is seeing significant changes in life on earth according to Shubin:

1)    Multicellular creatures first appear in the fossil record some 600 million years ago. 

darwinius2)     In fossils which are 385 million years old, we find only things that look like fish, while in fossils 365 million years old we find amphibians.  Somewhere in that time period animals with necks and ears and 4 legs emerge.

3)    The teeth structure of mammals and the mammalian way of chewing emerge in fossils between 225-195 million years ago.

4)    Structures associated with primate color vision first emerge in the fossil record 55 million years ago.

Shubin writes:

The oldest many-celled fossil is over 600 million years old.  The earliest fossil with a three-boned middle ear is less than 200 million years old.  The oldest fossil with a bipedal gait is around 4 million years old.  Are all these facts just coincidence, or do they reflect a law of biology we can see at work around us every day?”  (p 184) 

Shubin offers pretty sound evidence that if evolution theory is true regarding  human life evolving from singular cell life forms 600 million years ago then certain evidence should be found in the fossil record of specific time periods and scientists should be able to make certain predictions about when in the fossil record to look for specific physiological developments.    What Shubin shows is that in fact in both the fossil record and DNA record we find the evidence exactly where it should be if evolution is true.    This gives incredible support that the Theory of Evolution is giving us an accurate picture of how life emerged and evolved since it first appeared on earth.


If one still doubts that the complex human body could ever have emerged from a single cell, consider the following.  When in the mother’s body the fertilization of an egg takes place, the fertilized cell soon splits into two IDENTICAL cells.  These two cells then divide and form 4 identical cells.  This cellular division continues as the embryo grows into a fetus and then into a baby.  All the cells in a human body are identical, but some form into the nervous system, others into the circulatory system, others into skin, bones or other organs.   It is not the cells themselves that differ, nor does each specialized cell contain DNA unique to itself or its function in the body.  Rather in each cell genes are being turned on or off to cause different cells to specialize so that a complete human with trillions of cells can form and function.    From a one celled egg emerged a complete human being.   As Shubin notes the component parts work together to form a complete human being:  cells with no brains, containing nothing more than chemical proteins or enzymes, are able to work together to form the human.  This is a true miracle.

Shubin in his book looks at three different functions of the human body: smelling, seeing and hearing, and then traces the development in the fossil record of the corresponding human body parts (nose, eyes and ears) that make these senses possible.   In each case, the evolutionary signs indicating the development of these senses appears precisely where it should in the fossil record; again giving credence to the basic framework of the Theory of Evolution.  Shubin avoided polemics with anti-evolutionary folk.  He simply states the fossil and DNA evidence that we currently have and then shows how it does in fact fit in and support the Theory of Evolution.  It answers the questions science raises, though not necessarily the questions of philosophers or theologians.