In Darwin's book "The Descent of Man" (1871), the evidence he presents for human evolution from ape-like creatures is based purely on similarities in our body form and development. He had none of the fossil evidence we take for granted today and the process of heritability was not understood at all. However his theories encouraged people to re-examine humanoid fossils and to discover that some of these were very old indeed. The original Neanderthal skull, found in 1856, had been described as being that of an old Roman, a Dutchman, or even a Central Asian soldier in the service of the Russian czar during the Napoleonic wars. We now know it dates from around 40,000 years ago. 

Darwin knew there were problems with his theory which the science of his day could not solve. In "The Origin of Species" he wrote a whole chapter pointing them out (Chapter 6 - Difficulties on Theory). He also predicted that there would be new fields of science and research which would support evolution. He was right. 

Each year there is more fossil evidence (though it is still very sketchy), and more contributions from other disciplines of science: from chemistry and physics we have carbon and radiometric dating to tell us how old rocks and fossils; Geologists reveal time-lines of climate change in geological strata and ice cores; Geneticists analyze the DNA from ancient bones and modern creatures to determine their relationships.

What can we prove?

Although biologists can demonstrate how evolution works, how characteristics are inherited, how mutations occur, we can never scientifically prove how we evolved. For example, how did we come to walk on two legs? Why did we become naked? Or to put it in a more scientific way: what survival and reproductive advantage was there for early man to walk on two legs instead of four? What survival and reproductive advantage was there for early man in not being furry? We can only speculate and suggest likely answers. Like Hercule Poirot we must use observation and the little grey cells to deduce what may have happened, but unlike Poirot we cannot reveal the whole truth.

In science, an explanation (hypothesis) should be proved by experiment. We cannot do experiments on history!  So, we are left with theories which try to incorporate all the known facts. In time, investigations and a better knowledge of how the world works gives us better clues, so that we can make better hypotheses and paint a more accurate picture.

This inability to "prove" the theory of evolution is one of the weapons used by creationists to attack it. The proponents of "intelligent design" say that living thing are beautifully adapted to their purpose, and no random process could possibly have made them. Living things can therefore only have been made by a divine engineer. The biologist's answer is that the process of evolution by natural selection is far from random. It depends upon the accumulation of tiny changes in a species' genes over many of generations, giving rise to variation between individuals. The genes dictate structure. Natural selection chooses the fittest designs and their genes are passed on. Bad designs become extinct. No divine intelligence is required.  

The evidence for evolution is overwhelming and there is no other theory which so elegantly and simply explains the diversity of life on earth:

• Fossils are always found in correctly aged rocks and their time line follows the geological time line. That is, you do not find fossilised rabbits in rocks dating from 200 million years ago -if you did, that would blow the whole of the theory of evolution to pieces-.

• Evolution can be seen at work. One famous example is that of the peppered moth which was originally light in colour, and camouflaged when resting on light-coloured trees and lichen. When the industrial revolution happened in England, the trees became darkened by soot. The light coloured moths were eaten by birds while a darker genetic variant, which could hide on blackened trunks, survived and flourished.

• The embryological development of back-boned animals is so similar, that it is impossible to distinguish between a fish and human embryo. Both start off with rudimentary gills, and the inference is that we evolved from fish-like creatures.

• At the genetic level, the Pax6 gene which controls development of the eye seems to be the same in all animals, from flatworms to fruit flies to humans, reflecting our common ancestry and a single origin for the evolution of the eye.

Still there are unbelievers

There are no observations on living things which contradict the theory of evolution. All observations support it, and yet many people are unable to accept it. In the United States a Gallup poll conducted last year found that only 14% of people agreed with the proposition that "humans developed over millions of years", which means that 86% denied human evolution.

Perhaps this denial is because evolution challenges the notion that we are different from and superior to other animals. It contradicts the biblical idea that we have been especially chosen to dominate and exploit the world we live in. It implies that there may be no such thing as progress, that there is no higher purpose in life. Above all, evolutionary theory has no place for the concept of God.

Acceptance of evolution varies around the world, with the most ardent believers being in Iceland, Denmark and Sweden (see chart). Countries with more religious influence have the lowest proportion of people who accept the theory.

Religious beliefs are common to all cultures. No doubt they provide some adaptive advantage in the evolution of our minds. But what this is remains a scientific puzzle. When we finally understand how our brains generate religious ideas, what will be left for religion?

Oxford Professor Colin Blakemore (who is becoming as publicly controversial as his colleague Richard Dawkins) asserts that the greatest threat to Christianity is the theory of evolution, and that: "Science is just one gene away from defeating religion".

However, most human beings are capable of having a split personality on how we see the world. On one level we can accept the theory of evolution and on another, believe in ghosts, after-life, and an all powerful God.

If religious belief is an adaptation to enhance survival, passed on through generations by natural selection, it is a powerful part of what makes us human and will not be extinguished so easily.

by Dr Christine Betterton-Jones BSc. (Zoology), PhD (Parasitology)

Bibliography

1. The Descent of Man - Charles Darwin 1871

http://www.darwin-literature.com/The_Descent_Of_Man/index.html

2. Dennis O'Neil - Evolution of modern humans - Behavioral Sciences Department, Palomar College, San Marcos, California. Updated January 2009. 

http://anthro.palomar.edu/homo2/default.htm

3. The Origin of Species - Charles Darwin  !879

http://www.darwin-literature.com/The_Origin_of_Species/index.html

3. El origen de las especies por medio de la selección natural Charles Darwin (trad:Antonio de Zulueta)

http://www.cervantesvirtual.com/servlet/SirveObras/13559620212026495222202/index.htm

4 Unfinished business - The Economist - Feb 5th 2009

http://www.economist.com/science/displaystory.cfm?story_id=13059028

(diagram from The Economist)

5. Science is just one gene away from defeating religion

Colin Blakemore . The Observer, Sunday 22 February 2009