Musings on evolution, observations of the evolved

Evolution in action

When is a species not a species? It might seem that all living things are neatly divided into separate types and each is distinct from all others, but the boundaries are actually much more blurry than this. A fascinating example is shown by what are called ring species and there are two types of gull in the northern hemisphere that provide a classic case.

gull

Two of the gulls occurring in Britain are the herring gull and lesser black backed gull. They are quite distinct from each other. They do not interbreed with one another and they look quite different – herring gulls have light grey backs and black backs have, er well, very dark grey backs. If you now take a quick trip round the world, first you will find that in North America there are herring gulls but no lesser black backs. Then as you journey round you will notice that these gulls look progressively less like herring gulls and more like lesser black backed gulls. Adjacent populations are mixing and interbreeding as they are virtually identical. But as you go round the world through Russia and back to Europe, the population has now become fully lesser black backed gull and does not breed with the herring gulls there. As you travelled round the ‘ring’ one species ever so gradually morphed into the other until you get back to the start where they exist together as two separate species.

This is showing two interesting things. Firstly it’s a great example of evolution in action – one species is splitting into two in front of our eyes. For a dichotomy to occur a population needs to be physically divided into two to prevent genetic mixing so that evolution will take each of them off in their own independent direction. In the case of these gulls the populations have not been fully isolated so the genetic mixing that is happening over part of the range is blurring the concept of species. The other thing it does is give a superb insight into the gradual nature of evolution. Here we can see a gradual transition over a geographical range, but exactly the same thing happens over time as well. As things evolve the changes taking place are incredibly gradual – at no point does a species suddenly leap from being one into being another. It’s a little like counting. If we define 5 as a small number and 1000 as a large number, when we count from 5 to 1000, at what point does the number become large? It’s impossible to define, and so is the change from species to species in evolution.

There is a natural desire to define things and to put them in different boxes, but the nature of evolution tends to make this a difficult and rather artificial task. Another area which tends to confound the desire for strict definitions is that of grouping and classifying living things. Seeking to put everything into it’s own neat little box is always going to lead to problems – but I’ll probably come back to that in another post.

darwin2

Well it might be a bit of a cliche to bring up the great man in my first post, however it seems as good a place to start as anywhere. But of course Darwin was not the discoverer of evolution. His original idea was the theory of change by natural selection as an explanation of how evolution happens. By amassing such a huge amount of detailed research and explaining every step of his thinking in great detail, he finally put evolution into the minds of the general public and caused a fuss and fascination that continues to this day.

The first ideas about evolution date back even as far as the ancient Greek philosophers. There were a few suggestions about how animals may have come about and that they might undergo change, but they don’t bear much comparison to modern science. It was not until the 17th and 18th Centuries that some clearer ideas about the gradual change of species began to arise, but an explanation of how it might happen was still elusive. Then in 1809 the Frenchman Jean-Baptiste Lamarck put forward one of the most important theories of the time. He considered that characteristics acquired during the lifetime of an individual would be passed on to it’s offspring. So, for example, if an animal used a particular muscle to a great extent and built this muscle up very strongly, this larger muscle would then be passed on to the next generation. Modern genetics, of course, tells us this is not true.

Then came Darwin’s Origin of Species, or, to give it it’s full title – On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life – in 1859. Note the lack of the word evolution, and it is a word he uses very few times throughout the book. I don’t know if he did this on purpose, but it does seem a little strange.

Very briefly, his argument was this. He noted that all individuals within a species showed variations from each other. He also noted that there were far more offspring than could possibly survive, and so there would be a struggle for existence. He therefore concluded that those varieties with beneficial traits within a particular environment were more likely to survive and prosper in the population, so giving rise to gradual change and eventual extinction of the less favoured variety. Given enough time and enough generations the changes would be sufficient for a new species to come into being.

There is a beautiful simplicity to the theory, but given the immense amount of time that life has existed, there is also a beautiful complexity and variety to the life forms that we see today as a result of evolution. I’ll leave the last word to the man himself. This is the closing sentence from The Origin of Species, and I find the last word a little ironic.

There is a grandeur in this view of life, with its several powers, having been originally breathed into a few life forms or into one; and that, whilst this planet has gone on cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

darwin1

Welcome!

Welcome to my new blog. My fascination is the natural world and evolution in particular. If something amazes, informs or amuses me – that’s what I’ll write about. Through little blog sized pieces I’d like to say something about the processes of evolution and maybe also a bit about the history of it’s discovery and some of the incredible things that have evolved. I might even digress into other areas of science as well, astronomy is something that tends to fire my imagination too.

Whenever I learn something new about the workings of the natural world I tend to think ‘wow, that’s fascinating, I never knew that’. I hope you do too.