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 distant a species is related to use, the more it is placed to the left. Such an 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. The idea that evolution has a direction is one of the oldest fallacies in evolutionary thinking, one that has persisted for over 150 years of evolutionary researched. I experienced this first hand 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 that there was progress 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. If LUCA lived 3.8 billion years ago, all species on this planet have been evolving for 3.8 billion years. 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 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’. In fact, 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’, we are simply different.
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