This evolutionary tree of life has a problem. Yes, it beautifully illustrates that we are related to all life on earth, from bacteria to plants and birds. Still. there’s something wrong with it. The problem is that it is constructed from a human viewpoint. You can see that humans occupy a special position at the top branch of the tree, to the bottom right, close to our fellow vertebrates. The more distantly related species are placed to the left. This ordering wrongly implies an (upward) direction in evolution. This was even more explicit in Häckel’s drawing of the tree of life in 1874 (below) where humans are literally placed at the crown of the tree. This is one of the oldest fallacies in evolutionary thinking, and can lead to wrong conclusions being drawn, as I experienced during a philosphy course on evolution I followed this semester.
During this course on evolution and philosophy, the teacher had posed the question whether there is any direction and progress in evolution. I naively expected that most of us would snicker and say ‘No, of course not!’. Naturally, I was wrong (you probably felt this one coming). Several students advocated the progression in evolution, pointing to humans as the greatest example of an ‘upward direction’ in evolution. Some of them even stated that ‘humans are more evolved’ than other species! Our supposed dominance over the earth and other animals was given as the principle argument for this standpoint. This kind of reasoning is so flawed, that I was cringing in my seat.
How on earth can evolution be a quantity that you ascribe to species in varying degrees? How are we ‘more evolved’ than cyanobacteria in the ocean, a panda in a bamboo forest or an earthworm in the earth? Cyanobacteria surely photosynthesize a lot better than we do! Likewise, we can better leave digesting bamboo to pandas and I doubt many people would fancy burrowing through soil like earthworms do. Each of those species has evolved to be adapted to their specific environments. All species that are alive today have the same evolutionary timespan behind them! Sure, some species resemble ancestral species more than others. Maybe they have not changed much in morphology for millions of years. But this does not mean they are more ‘primitive’ or that we are more ‘advanced’ than they are! Jonathan Eisen published an excellent blogpost on this issue here.
I will not deny that humans are unprecedented tool users who can manipulate environments like no species has done before. No cow, crustacean or squid has ever set foot on the moon. This does not mean that we should try to find biological reasons to confirm this notion of ’specialness’! People have tried, and failed time after time. Our genome is not the biggest, we are not the only tool-users and language is not unique to us.
This notion of an upward direction in evolution has deep roots, roots which seem difficult to eradicate. This is not surprising, because the word evolution itself is part of these roots! The Online Etymology Dictionary has the following entry for ‘to evolve’:
“to evolve – to unfold, open out, expand,” from L. evolvere “unroll,” from ex- “out” + volvere “to roll”
So ‘evolving’ finds its origin in ‘rolling out’ of something that was previously enclosed, the unlocking of a potential from within. The term evolution better fits a Lamarckian world view (Lamark hypothesized that an intrinsic drive to perfection caused species to evolve). Herbert Spencer, a Lamarckist, was one of the first people to refer to Darwin’s theory as a theory of ‘evolution’. Because of the great differences between Darwin’s theory and the Lamarckian background of the word ‘evolution’, Darwin was extremely hesitant to use the word evolution to describe his theories. He much preferred ‘descent with modification’. He only introduced ‘evolution’ in the very last paragraph of the sixth edition of ‘the Origin of Species‘! Even though Darwin tried his best to avoid this confusion, the misunderstanding persists up to this day.
I am by no means an expert in evolution. Evolution is a beautiful and complex, with many intricacies and subtleties. What I do know is that sponges are not ‘primitive’ and that humans are definitely not ‘more evolved’.
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Darwin himself is not totally innocent in this regard, in the conclusion of The Origin he writes:
Amazingly, there are contemporary evolutionary biologists like Dale Russell and Simon Conway Morris that make similar arguments.
@Neil: Thanks for that quote, I never saw it before! It is good to realize that this argument was, for a long time, the most prevalent and accepted opinion.
@Doug: There’s nothing wrong with playing devil’s advocate: it keeps one sharp ;).
It is clear that evolutionary rates may differ. After all, homologous proteins may be under different selection pressures in different species. This has oft been misinterpreted as ‘more or less evolved’. Two years ago, it was found that chimpanzees had more fast-evolving protein sequences than humans did. Media quickly picked this up as ‘Chimps are more evolved than humans, OMG!’ (apart from the headline, this piece from Discovery covered the research fairly well). If one would follow this kind of reasoning, bacteria and viruses would be the most evolved species on earth, since their sequences change the fastest in the living world!
Your last example is a great one! The whale clearly underwent more morphological changes than the shark underwent, since it adapted to extremely different environments in its evolutionary history. But I’m hesitant to say that the whale ‘evolved more’, precisely because it implies that whales are more advanced somehow. For the shark too, is a highly derived form from the common ancestor of sharks and whales..
I’d like to call the ‘something’, ‘complexity’. I can fully agree with the statement that mammals are more complex than bacteria. Being multicellular (to name one thing) requires division of tasks, detailed regulation of gene expression (when and where) etc. The regulatory networks are more complex than in bacteria, who primarily change gene expression when environmental conditions change.
I hope this somewhat addresses the valid points that you raised!
Of course I agree with you on the most basic level. But to play devil’s advocate a bit: One reason why this concept is so hard is because while cyanobacteria and humans have indeed been evolving for the same amount of time, the rate of change in measurable phenotypes is much greater for humans. Does this mean that we are more evolved because we are evolving faster? There is the concept that some protein sequences change faster than others over time. So even different parts of an organism can be said to be evolving faster than others. So I think that there is room to put a finer point on the argument. Humans may not be more evolved but we are definitely more “something” than bacteria. What do we call that, “differentiated”? “phenotypically changed”?
Just to show that I can be a complete smart Alec, how would one describe the relative evolvedness or phenotypic change of a whale? A creature that has gone from a water dwelling species, evolved phenotypes to enable land dwelling and then evolved back to water. Is a whale more phenotypically changed than a shark?
Have you read “Wonderful Life” by Stephan Jay Gould? He addresses this problem wonderfully (There should be a book review of it appearing on my blog on Tuesday!).
In terms of the ‘relative phenotypic changes’ arguement, it all depends on what you see as a more interested phenotypic change. Humans obviously look a lot more different from the blobs that they came from, but bacteria have adapted so many more varieties in genetic sequence, even though they look somewhat the same. And as you point out in your comment, bacteria are capible of much quicker genetic change; antibiotic resistance spreads through bacterial populations much quicker than bacteria/viral resistance spreads through human populations.
Funny that you mention Stephen Jay Gould! I received ‘The Richness of Life’ as a gift during the holidays, which is a collection of Gould’s essays. I was smiling from ear to ear when I read his essay “The Evolution of Life on Earth” that was published in Scientific American. I found an online version here. More eloquently than I ever could, he already argued against a progressive view of natural history 15 years back :).
Hi, I’ve just found this post while browsing through the site. You say that “language is not unique to us”, and provide a link to the story on Campbell’s Monkeys and their calls. I’ll have to stop you right there. Language, as understood in its technical sense (which is what we should be using if we are going to claim that other species have it), is indeed (so far) unique to us. Animal communication systems, amazing and complex as they are (bee dances, monkey calls, birdsong) are not language.
As Geoff Pullum, a very distinguished linguist, put it on Language Log:
This is not to say that only humans can have language, but we can say quite authoritatively that all the research done to date in the field of animal communication has provided no evidence that animals have anything like it.
Thanks for your comment Szwagier!
Your point is well taken, and (as the non-expert of linguistics that I am) I have to agree with you that human language is unprecedented in the natural world. My (bold) statement that ‘language is not unique to us’ could’ve maybe better been written as ‘complex communication systems are not unique to us’.
The point that this doesn’t place us at the crown of evolution still stands of course, especially because language as we find it in humans doesn’t seem to be a logical or necessary outcome of evolution. But a wonderful ‘coincidence’, of course!