thanks for your hard work on this wondeful site.

i can't really get my head around evolution, I suppose I should have listened a bit more in school :)

i except evolution is fact, as the evidence points to it etc, but how do scientists know what caused it and why, how do you know for sure that natural selection and chance mutation are the reason?

i'm not disputing evolution, but because I'm an average Jo, with just GCSEs, I can't get my head around how a mutation can give us eyes, organs etc, it's mind blowing.

is the evidence undeniable?


Hi Lian,

We know that mutation and selection leads to evolution because it can (and has been) conclusively demonstrated both in the lab under controlled conditions and in real-world field studies.

For example, development (ie natural selection in favour of) of antibiotic resistance in pathogenic mircobes can be directly linked to a mutation, or series of mutations. In the lab, the Lenski experiments on citrate metabolism illustrates the concept very well indeed.


In a more general sense, physical characteristics are the basis of selection (the "phenotype") and your genes (the "genotype") are the heritable basis of phenotype. There is variation in the genotype, which occurs naturally (think how many different types of human there are!) by accumulating mutations in individuals. Selection happens when the environment puts a bias on a particular kind of variation, favouring one over the other through greater success in breeding over all in a population. This results in an increase in the population of the favoured ones and decrease of less favoured or harmful variations. Subsequent generations have more of these favoured genes, and they also have a new set of variations, which can be re-selected again. Over many generations in this way, the population can change a great deal by this gradual biased selection. If you give it long enough, the changes can be MASSIVE, eventually producing all of the structures you mentioned; eyes, ears, etc.

Eyes are actually a great example, because it appears that eyes independently evolved multiple time in different animals through this same process of selection from variation. Tetrapods (like us humans) have one kind of eye, cephalopods (like squid) have a completely different kind, and arthropods (insects, spiders, crabs) have yet another different kind. In fact, virtually all animal groups have some kind of light-sensitive organ that could be called an eye-like structure. Each of these have entirely separate and in dependant evolutionary origins, produced by selection from variation over many, many generations.

One of the most convincing pieces of evidence for the validity of evolution by common descent I have personal experience with is ancestral enzyme reconstruction. Common descent is the notion that species diverge from a parent species, and our genes reflect that in both their similarities and differences with other species.

The idea is; if we build phylogenetic trees (a tool for figuring out possible patterns of evolution) of a particular family of enzyme proteins based on their genotype, it is possible to statistically infer the probable sequences of the ancestral enzymes by assuming common descent. And we are talking a divergence that happened up to 800 million years ago. The incredible part is that this approach does work, it can produce functional enzymes with different characteristics. If common descent were not true, I don't believe this approach would work nearly as well, if at all.


Last edited by John Steemson (11th Oct 2014 01:51:33)