Occasionally, I'll read about an animal that is said to be "unchanged for millions of years" in evolving. How do scientists know that an animal hasn't (or barely) changed for millions of years? Is it simply because their makeup is similar to ancient organisms?
1) Often it's the journalist writing the article that uses this kind of clickbait vocabulary, not the scientists he's reporting on.
2) Some animals are apparently the same size, shape and have the same skeletal structure as fossils that are millions of years old. For example, sharks and maybe scorpions.
Originally posted by vivify How do scientists know that an animal hasn't (or barely) changed for millions of years?
I agree with AThousandYoung on this one. If the fossil evidence shows a very similar structure, then people often make the error of assuming they animal is genetically identical to its ancestor. In reality it is probable that significant genetic change has taken place but not dramatically affected the observable body structures.
I haven't studied the topic, but genetic change over time is probably mostly a direct function of population size and generation length. Some genes are strongly conserved regardless of the environment. Other genes constantly drift. Dramatic changes in the observable parts of an organism are usually a result of a very small number of genes.
[edit]I have to add that it isn't only journalists that go for clickbaity statements. Scientists do it too. They do it a lot.
Originally posted by twhitehead [b]I agree with AThousandYoung on this one. If the fossil evidence shows a very similar structure, then people often make the error of assuming they animal is genetically identical to its ancestor. In reality it is probable that significant genetic change has taken place but not dramatically affected the observable body structures.
Why would that be probable?
If a species is well-adapted, the conditions should select against any significant genetic changes. Modern genomic sequencing is often used to assess evolution, but the technique lacks clarity as to what single mutations do to change species. There are literally millions of so called "incidental mutations" that have no known functional significance. Structural changes to species are considered more concrete evidence of evolution.
Originally posted by wildgrass Why would that be probable?
If a species is well-adapted, the conditions should select against any significant genetic changes.
Firstly, the abundance of life demonstrates that for any given environment many possible forms can be 'well-adapted' to the conditions. Genes come in all shapes and sizes. Some are highly conserved because even minor changes are catastrophic, others may have many variants without causing major problems. Genetic drift is normal for a large proportion of the genome.
Even if basic appearance of an animal doesn't change significantly, minor changes exist and more subtle changes happen too, ones that cannot be seen from fossilized remains.
Lets take the crocodile that some might say has been around for millions of years relatively unchanged. Yet look around the world and you will find many different species of crocodile, and as you look closer you will find very significant differences between them. Some for example are adapted to saltwater living. You will probably find that crocodiles are as genetically dissimilar from each other as the great apes.
26 Mar '17 19:28
"Unchanged" for millions of years
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