Download What is evolution?

Evolution talk – February 2016
Marge and David Rose
Marge offered this talk because someone asked for the subject but she knows nothing about it so it
was a bit of a challenge. Dave did Biology so he was roped in to answer questions that she couldn’t.
While researching this talk (and before) they were both astonished by the number of times creationist
websites would be listed whatever particular aspect of evolution was being investigated.
‘On the Origin of Species’ is the classic book but a lot of it is out of date now, however ‘Why Evolution
is True’ by Jerry Coyne is much shorter and current so the talk has been written around it. It is a simple
talk because it reflects Marge’s understanding, not because the subject is simple.
What is evolution? It’s the theory that life on Earth evolved gradually, beginning with one primitive
species that lived more than 3.5 billion years ago, called the last universal ancestor (LUA). There are
several components to the theory and the book cites six so here they are:
Evolution, Gradualism, Speciation, Common Ancestry, Natural Selection and Genetic Drift.
Evolution is the process whereby genetic changes happen over time which we now know are due to
mutations in the DNA.
Evolution is generally very slow. This is Gradualism – in fact some forms of life have hardly evolved at
all. It’s important to realise that evolution is not about individuals, it is about groups.
Speciation is the splitting of one species into two. A speciation event is generally only identifiable
after a very long time. The definition of a species is a group of individuals that actually or potentially
interbreed in nature. A tree diagram that shows the common ancestry of all life on Earth is called a
phylogenetic tree. Beware of simple examples that can give the wrong impression – it has never been
a straightforward process and resembles a very complicated bush with pruned branches rather than
a simple tree. All life is categorised into three domains – Archaea – single-celled micro-organisms that
have no cell nucleus, Bacteria and Eukarya (which includes humans).
Modifications of the DNA occur in individuals but it is natural selection that determines whether or
not the modification is passed widely through the group or species. Natural selection works because
certain mutations of the DNA confer evolutionary advantage and are therefore passed on to
subsequent generations.
It’s said quite often that the existence of the human eye cannot be explained by evolution because it
works as a whole. David Attenborough refutes this so eloquently in his series “Charles Darwin and
the Tree of Life”. See http://www.bbc.co.uk/programmes/p005lnm7
Natural selection is a tinkerer rather than a master engineer.
Genetic drift is a non-selective mechanism that is most likely to make a big difference in a short period
of time in small isolated communities like remote islands.
According to Jerry Coyne, the evidence that we need to gather to prove that evolution is ‘true’, falls
under the following headings, one for each of the main planks of the theory as detailed above:
1. evidence of evolutionary change in the fossil record
2. evidence of one species dividing into two in the fossil record
3. examples of species that link together the major groups thought to have common
ancestry e.g. amphibians with fish, birds with reptiles
4. genetic variation for many traits
5. examples of imperfect design
6. natural selection acting in the wild
Going through these one by one, we find that there are many examples of evolutionary change in the
fossil record. One of the ways in which we could confirm evolution is if the fossils of simpler creatures
were found deeper than the more complex ones and this is indeed what is found. The nomenclature
of the strata can be confusing because it was only standardised not long ago – for the definitive names
see http://www.stratigraphy.org/icschart/chronostratchart2015-01.pdf
This diagram is the best I found to give an idea
of the layers and how the simpler creatures
are found deeper. It’s been reproduced all
over the internet but it took me ages to track
down the original source which was a book
that I then bought and heartily recommend –
‘Cruising the Fossil Freeway”. The whole book
is fun and the tone enthusiastic and scientific.
One of the best examples of fossils confirming
evolution is the one found by Mary Anning, a
non-scientist who lived on the Dorset coast in
the 19th century. She found the skeleton of a
creature that had a back-bone and could fly
but it looked nothing like anything alive today
so it helped to convince the scientists of the
time that it wasn’t true that since God had
created everything it must all be perfect and
a species could not die out.
Dating of fossils is done by radiocarbon analysis, the ratio of lead to uranium (which can reach further
back right to the formation of the Earth) and counting the growth rings on ancient corals.
The splitting of one species into two is impossible to pin down because evolution happens so gradually.
At one time, the talk was of a ‘missing link’ but nowadays the term ‘transitional form’ is used and there
are loads of them. There are fossils showing the evolution of the whale from a land-based animal to a
sea-based one. Another example is the fossil of a species that links amphibians with fish – called the
Tiktaalik. The way that fossils are produced tends to favour sea-based creatures so many of the
examples are of animals that lived in water.
Only 0.1% of the human genome exhibits variation but that is what makes us all unique, whether in
terms of hair colour, skin colour or even the shape of our faces. These are traits. If evolution is to
work, then you need these variations to occur for different traits so that natural selection has
something to work with to effect evolution in response to prevailing conditions.
If there was an intelligent designer then we would expect perfection but imperfect design is the mark
of evolution. There are many examples of non-optimum design from the ridiculously long recurrent
laryngeal nerve of mammals which is a legacy of our fishy ancestors and birth through the pelvis, a
particular problem for humans because they are habitually bipedal.
And for an example of genetic drift see https://www.youtube.com/watch?v=gugY9C6
Finally on the radio programme ‘The Infinity Monkey Cage’, Robin Ince suggested that you could only
disprove evolution by finding something like a Pre-Cambrian rabbit!