Misconceptions of Evolution Part I February 1, 2009Posted by Ian in Science.
This is the first in an open-ended series of posts I plan on making highlighting common misconceptions and misinterpretations on evolution by natural selection and its implications. Most of them are ones that I have held at some point before coming to realise it just isn’t the case while others are things I commonly hear from people who don’t get it. Some of them may be obvious, others more subtle, but hopefully they are of interest.
They are in no particular order other than the order I thought of them. Here are the first two:
1. Macroscopic animals dominate evolution
I’ll let Stephen Jay Gould (from Life’s Grandeur, 1996, pp 176) start this one:
On any possible, reasonable, or fair criterion, bacteria are – and always have been – the dominant forms of life on earth. Our failure to grasp this most evident of biological facts arises in part from the blindness of our arrogance, but also, in large measure, as an effect of scale.
I’ll paraphrase some of the criteria he then goes on to discuss:
- Time: Multicellular animals have only existed for 1/6 of the history of life. Bacteria have been there essentially from the start.
- Dependency: Bacteria don’t need any other form of life to exist; the same cannot be said of more complex beings which all heavily depend on bacteria for a lot of different functions.
- Numbers: “One fact will suffice: during the course of life, the number of E. Coli in the gut of each human being far exceeds the number of people that now live and have ever inhabited the earth.”
- Places: Bacteria colonised far more environments on earth than any other kind of organism. Hotter temperatures, more extreme pH levels, deeper in the earth etc.
- Utility: Bacteria can do many more different things than other organisms.
- Mass: While impossible to know for sure, it seems likely that bacteria outweigh all the other biomass on earth. Opinions vary on this but if it isn’t the case they are probably in the same order of magnitude. It is interesting to know about 10% of a humans dry body mass is bacteria!
One thing is clear. In the grand system of life, large animals do not dominate things. Humans are just a part of the picture, not the main event. And this also has another consequence: the reliance of macroscopic organisms on bacteria means that their evolution has in many ways been shaped by the evolution of bacteria. One example is the bacteria within the gut of an organism. They are not capable of digesting everything that comes their way so their diet is restricted quite aside from what their genes would like to achieve.
2. Evolution is about progress
We tend to look at things that fit an environment or situation well and presume the main driving force behind their was targetted to get them to that state. This means we quite naturally see progress as the goal or purpose of evolution. However it seems much more likely that there is no goal or purpose driving any of the changes in species over time and I will explore two reasons why not:
Firstly most people tend to think of evolution as operating directly on an animal, such that if the environment gets colder, an animal will get a longer coats (often known as Lamarkian evolution). However it doesn’t take much thinking to realise that there is no direct mechanism for this to happen.
DNA and genes determine what an organism looks like but they are actually much more than that – they are the only connection between an organism and its descendents. It makes no difference whether an organism has long hair or not, it only matters that it can survive well enough to pass on the genes for long hair. Therefore we have this interesting situation where the genes that code for animals that are more likely to do well are more likely to be represented in future generations which leads to apparent progress but is not driven by it. Richard Dawkins explains this in considerable detail in The Selfish Gene.
The significance of this is that evolution is not trying to produce animals that fit their environment perfectly, but rather that animals that fit their environment are a consequence of gene propagation. Thus progress is the result of evolution, not the driving force of it.
There is another powerful argument for this (discussed in Life’s Grandeur) which is that life has no option but to get more complex. There is generally a limit to how simple it can be in that there are minimum requirements for replication etc. Over time there will be various changes in the complexity coded for by the replicators and this would be the case purely due to random changes. However if a replicator gets too simple it ceases to replicate and this means there is a limit on the simple side of things. There is no such limit on the complex side of things (life can probably get as complex as it likes) so over time increasing complexity is almost a certainty for no other reason that statistics, over time, it must happen.
There is a good statistical analogy to this called the drunkards walk which explains this well and without the complications of biology. I’ll paraphrase Life’s Grandeur again to explain: Imagine there is a drunk man who left a bar and is walking down the footpath. On his left is a wall which he would bounce off and keep going; and on his right is a gutter which he would fall into. He stumbles randomly down the path randomly shifting left, right. or staying the same direction each step. If the footpath is long enough what will happen? Every single time he will fall into the gutter. Why? Because he can only go so far left, then he just stays there against the wall. But eventually he would move right again which means eventually he must hit the gutter because it is the only way his walk can stop in this scenario.
Remove the gutter and replace it with an infinitely wide footpath and you have a drunk that moves randomly but over time gets further and further away from the wall (even if he returns towards it for a while). Call the left simplicity (an absolute limit) and the right increased complexity (unlimited) and you can see why logically life should more complex over time with no target or driving force pushing it that way. In other words “progress” becomes a statistically very likely.
Well that’s the first two. There are more to come!