If I’m not mistaken, a lot of the relationships between different organisms (tree of life) were first established in the 19th century and were done so by looking at similarities in form and function and is the basis for scientific names. Since the development of genetic analysis, has there been an effort to go back and confirm that these educated guesses were correct? If so, were there any huge surprises? Like learning that animals that were thought to be closely related based on how they look are actually much more distant
In: Biology
Your question here is mainly about the differences between cladistics (grouping things by attributes) and phylogeny (grouping things by evolution/ DNA/ common ancestors). So, the differences between cladograms and phylograms.
The historical tree of life isn’t actually as historical as most people seem to think. While Darwin conceptualised it, it was never given a formal introduction like evolution was. Its popularity mainly spiked around the 1960s, which wasn’t too far before genetic sequencing anyway. By the 1960s we also had good non-evolutionary knowledge of most common species (e.g. we had things like skeletons of most animals, which do make certain things more obvious). We also had a lot more knowledge of common ancestors through fossil records, which had a big impact on the understanding of things like dolphins and whales.
Also worth noting: a lot of modern cladograms do cheat. They use knowledge of genetic links to make biased decisions in clade differentiation. And since cladograms can take different attributes into account, there are multiple ways of comparing groups of animals (however in functional terms, historically the most obvious differences were taken – although there are issues with bias here too).
Some big deviations between the two:
1. Cladograms usually have humans as very separate. We are bipedal, relatively bald and don’t really look like anything else. We have a lot of attributes distinct from anything else. However, we know that the evolutionary difference between a human and an ape are actually tiny. Genetic comparison between human and ape DNA did cause quite a big stir – we previously assumed we were more separated.
2. Another big difference was snakes vs lizards. Again, the observed difference here is much larger than the actual DNA-measured split – probably because of how extreme “leg vs not leg” is.
3. Splits under the hoofed mammals are pretty exaggerated. Particularly marine mammals. The evolutionary distance/ difference between a whale and a hippo and a horse is relatively small considering the massive visual differences.
4. Flight was traditionally a struggle in cladograms. Wasps and bees are very closely related to (non-flying) ants, but this evolutionary difference often wasnt reflected. The connection between bats, birds, flightless birds and dinosaurs is another very clear example of taking the wrong indicators for clades.
5. (perhaps the most important) – cladograms basically entirely ignore how horizontal gene transfer works in separating simpler organisms.
To give some credit to cladograms; they get a lot of things right, and in general tracking small changes in attributes is a good approximation of evolutionary differences. The introduction of a fossil record (although strictly speaking shouldn’t have made a big difference) did massively help steer the construction of cladograms – so a cladogram from 1910 vs 1930 vs 1950 vs 1970 would have had increasing “accuracy” or agreement with a phylogram.
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