Claim 5 - The Eye is too complicated to have evolved

Many creationists quote outright the above 'fact' without ever actually investigating the assumed principles behind the growth of the human eye. The fact is that the human eye is an extraordinarily complex organ, but to say therefore that it did not evolve is unscientific. One must prove that it cannot have evolved, or else the argument is utterly invalid.

How does evolution claim the eye evolved?

Early primitive organisms were aware of their surroundings, just like primitive organisms today, in very simple ways. Firstly they would be able to sense physical contact, and they would be able to sense chemical inbalances in the water surrounding them. Clearly an advantage would be gained by any creature that could develop some sort of accurate sensory apparatus with which it could analyse its surroundings.

From the first primitive organisms whose central nervous systems managed to tune slightly more into the reception of light from certain slightly more sensitive cells, these cells would them become more sensitive because they gave the animal possessing them a slight advantage over his peers - he had a slightly heightened sense of danger. These primitive cells would then evolve into clusters of cells, and so on up to the eyes we see today. We are not proposing that the eye suddenly appeared out of nowhere - we are claiming that it evolved gradually over time from something much more primitive.

Is this plausible?

Many very tiny organisms today possess eyes. They are not an exclusive property of mammals. For example, most insects possess eyes, some of which are extremely tiny. The function of such eyes is significantly more primitive than those of a human being, but they are still eyes. Study of the various types of life on Earth tell us that the eye has evolved totally separately several dozen times, suggesting that the process can't really be all that complex or unlikely.

Evolution tells us that large changes can occur over extremely long periods of time, but in tiny steps. The change from a primate's eye to that of a human isn't a very big step. The change from the eyes of common farmyard animals aren't really all that different either. What about rodents? Well they see too, though obviously with a lower resolution and sensitivity than humans. Is it such a big claim to say that an eye the size of a rat's can evolve into one the size of a chimpanzee's? Evolution shows us a way by which that could happen. It might only be a very tiny change at a time.

The diameter of the human eye is approximately 2.4cm (1 inch). According to this page, the eyeball of a human being grows considerably over the course of a human's life. We don't see that as being remarkable at all. We could investigate the change in size required to grow a rat's eye up to the size of a human's eye over a hundred million years, which is a typical evolutionary timespan. A rat has an eyeball around 4mm in diameter. This is a factor of 6 increase in size.

A little mathematics shows us that this change of a factor of 6 over 100 million years, assuming geometric growth, corresponds to an increase of 0.0018% in every thousand years. That's not really a remarkable change, is it? If we assume linear growth then we need to increase the diameter of the eye by 0.0002mm (200 nanometres) every thousand years. That's an increase about 500 times thinner than the width of a human hair!

So we can easily evolve from a rodent's eye to a human's eye in a mere 100 million years, probably significantly less. Remember that we have much longer than this to carry out our entire evolutionary sequence - perhaps twenty or thirty times longer. Is it that much to claim that the eye can develop from a primitive single receptor cell through a slightly more complicated row or receptor cells, through a cluster of cells, right up to a tiny spherical adornment and to the kind of eyes you see in tiny marine animals, all the way up to that of a tiny land animal such as an insect, and through to rodents and humans? I don't think so.

Remember - all we have to do is to prove that there is a series of small, gradual changes that could lead from a primitive, light-sensitive cell right the way up to the modern eye. We are not claiming that the eye sprang into being fully-formed!

Evolutionary timescales

Evolutionary timescales are really surprising, mainly because they are so counterintuitive. You'd be amazed how long a billion years really is! Human beings are used to thinking about things from human perspectives. A human lives about 70-80 years on average, so we consider 100 years to be a long time. In our everyday life, an hour is a long time. Any task which is likely to take an hour to complete we might see as being lengthy. Those who disagree should try doing the washing up at my house after one of my house mate's parties!

Many people use human arguments to try to disprove evolution, but they are really not disproofs at all. In fact, they contain no logic or reasoning. All they are is supposition. Supposition without factual backing is utterly worthless. In order for an argument to be considered in the scientific world it must be associated with logic and evidence. You can't simply claim things and appeal to reason - you must provide evidence.

A billion years is a truly enormous time span. There are currently six billion people alive on the Earth. Each one has, on average, 80,000 hairs on their head. You could count all their hairs at a rate of 1 per second in a mere 15 million years. In a billion years you would have the time to go off and rest for a minute between each hair, or alternatively count the hairs on every single human being 66 times! Just imagine what amazingly complicated changes could occur in such a long time.

Experiments

Richard Dawkins says the following;

"Thus the creationist's favourite question "What is the use of half an eye?"
Actually, this is a lightweight question, a doddle to answer. Half an eye is
just 1 per cent better than 49 per cent of an eye, which is already better
than 48 per cent, and the difference is significant."

In 1994, Dan-Eric Nilsson and Susanne Pelger presented the results of the experiments that they had been running on the evolution of the eye. They wrote computer simulations in order to analyse the rate at which such a complicated optical organ could evolve from a simple initial condition. The abstract of their paper contains the following description;

"Theoretical considerations of eye design allow us to find routes along which
the optical structures of eyes may have evolved.  If selection constantly
favours an increase in the amount of detectable spatial information, a
light-sensitive patch will gradually turn into a focused lens eye through
continuous small improvements of design.  An upper limit for the number of
generations required for the complete transformation can be calculated with
a minimum of assumptions.  Even with a consistently pessimistic approach the
time required becomes amazingly short: only a few hundred thousand years."

Nilsson & Pelger used a few simplifying assumptions in order to carry out this modelling technique. Whenever they were required to make any important assumptions in terms of figures, timescales, rates etc. they always chose the most pessimistic value. That is, the value which would cause the estimated timescale for evolution to be the longest. Even through this technique they discovered that the timescale was of the order of 400,000 years, assuming generations of one year each, i.e. for fish.

This experiment is available in "Nilsson, D.-E., and Pelger, S. 1994. A pessimistic estimate of the time required for an eye to evolve. In Proc. Royal Soc. London, vol. 256 of Series B, 53--58". It can be downloaded from the following site.

Is this a fair representation? If not then drop me an email. Address below.

This page maintained by Colin Frayn. Email

Last Update : 22nd April, 2005