Interesting stuff about the science of evolution and the natural world

Archive for April, 2014

Family tree – literally

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Researching family history is very popular these days. With a bit of luck you might be able to go back a few generations and maybe find out who your four times great grandparents were and what they did. Going back any further begins to get a bit tricky, but I guess it’s possible to indulge in a bit of imagination. We could think of our ancestors from a thousand years ago working the land to put food on the table, or from 20,000 years ago, before farming, living as hunter gatherers with very simple tools. At around 100,000 years ago, our ancestors are a relatively small population existing only in Africa, and amongst them will be our approximately 5,000 times grandparents.

Now we get to the bit that needs the mind to take a slightly bigger leap in imagination. If we could find our 250,000 times grandparents they would be apes, also living in Africa, some 6 million years ago. OK, granted this is nothing new – ever since the famous cartoon of the head of Darwin on the body of an ape, from 1871 – but it’s quite sobering to remind ourselves of the closeness we share with the rest of the natural world, and the fact that we are not so different from other animals.

So we can keep going back through our direct ancestors – to a primitive primate, then the first shrew-like mammal, an early reptile (or synapsid, to be correct), the first land vertebrate, a fish, a marine worm, a very simple multicellular animal, a single celled animal and right back to bacteria.

But with ancestry, you’re not restricted to direct ancestors, you could also consider other branches to your family tree – your cousins. First cousins share the same grandparents, second cousins great grandparents, and so on. Using these links we can begin to find our relationships to other animals not within our direct ancestry. But now comes the bit that gets a bit more weird, to me anyway, but still doesn’t cross the line into fiction. If we go back to a linking ancestor way back in the time of single celled life and follow a different lineage to the present we would find that, for example, our cousin was an oak tree – in fact all oak trees and all plants. It’s impossible to know the correct numbers but I guess it could be something like a 100 billionth cousin many million times removed. And this means an actual cousin, not using it as a metaphor for species evolution. All individual oak trees are our literal cousins, albeit somewhat distant.

I think I have a new found respect for the tree huggers.

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Archaeopteryx at the museum

Not much to say here really, just a bit of a plug for the Natural History Museum in London. One of it’s most treasured displays is the very first Archaeopteryx fossil which was found in Germany in 1861, giving Darwin and Wallace some timely evidence for their newly published theory. And they show the genuine fossil, not a cast.

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I think I love the building nearly as much as the exhibits.

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Inside and out, everywhere you look, there are carvings of creatures weird and wonderful.

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Bigging up Wallace

Alfred Russel Wallace (1823-1913) certainly doesn’t deserve to be forgotten. He came up with an identical theory for the mechanism of evolution at the same time as Darwin, but how many people now would know his name?

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Fortunately things are changing a little and he is being brought out of the shadows to take his place in history once again. This is largely down to the work of George Beccaloni of the Natural History Museum, London who has been campaigning to give him the credit he is due. The campaign was given a huge boost by comedian Bill Bailey’s programmes on the BBC last year when he retraced Wallace’s steps in the jungles of Borneo.

Wallace was a dedicated and adventurous naturalist and spent his life studying the distribution of life around the globe and attempting to unravel the mysteries of evolution. He had two major trips to collect and study wildlife. The first was a four year exploration of the Amazon Basin. Unlike Darwin, he was not from a wealthy privileged background so needed to generate funds for himself and he did this by selling samples that he collected. The South American trip was a great success, but soon after they sailed for home a fire broke out in the ship and it was sunk. Luckily all on board were saved in the life boats, but a large part of Wallace’s samples and notes from the trip was lost.

His other major exploration was an eight year trip to the Malay Archipelago. It was during this trip in 1858 that his theory on evolution suddenly came to him – apparently when he was laid up in bed with a fever. He wrote up his ideas in a paper and sent it to Darwin back in Britain to see what he thought, asking him to pass it on to the eminent geologist Charles Lyell if he felt it was worthy. In Wallace’s absence, they decided to present the paper, along with some of Darwin’s writing on the same subject, at a meeting of the Linnean Society in London. Initially there was not a huge amount of interest, but Darwin was now spurred on. He had been developing his own ideas for some years but had been reluctant to publish, wishing to amass as much evidence as possible for what he knew would be a controversial theory. But now the cat was out of the bag, so to speak, and he rushed out his first edition of The Origin of Species the following year.

Wallace and Darwin deserve equal credit for natural selection in my view. Wallace was a modest man from a modest background and perhaps that is largely why he has become sidelined in history – but it’s good to see him getting a little of the limelight once again. A painting of him was donated to the Natural History Museum in 1923 and displayed on the stairs at the head of the Central Hall, but it was removed in 1971. Last year it was restored to the same position and it was unveiled by Bill Bailey.

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The Museum is also home to an ongoing project to digitise and make available online approximately 5000 letters to and from Wallace.

We now also have for the very first time a statue of Wallace. His grandson gave a speech at it’s unveiling at the Natural History Museum, which was performed by David Attenborough.

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The statue captures the moment when he first saw what is now called Wallace’s Golden Birdwing butterfly. In his book he says “On taking it out of my net and opening the glorious wings, my heart began to beat violently, the blood rushed to my head, and I felt more like fainting than I have done when in apprehension of immediate death. I had a headache the rest of the day, so great was the excitement produced by what will appear to most people a very inadequate cause.”

Wow, he was certainly a dedicated and enthusiastic naturalist.

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.

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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.

Darwin didn’t discover evolution

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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.

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