Have you ever had a project in school, where you had to figure out what was related and what wasn’t? Languages? Categories of literature? The blossoming of certain kinds of sports?
How would you tackle such a project? All these things that we study (from Ants to Zoophytes) are all embedded in a timeline, right? So one looks for indications of relatedness that seem to be more than just coincidence, right? And you are looking for a sequence of similarities and differences which make chronological sense!
If a Fish and a Bird share the exact same kind of cellular chemistry about a specific chemical, an Evolutionist would expect that this is a very common chemistry that would be in fact shared by much more than Fish and Birds. Why? Because there’s no evolutionary model that would predict that the body chemistry, in common between Fish and Birds, would not be shared even more widely.
But if we have a chemistry shared between Fish and Amphibians, but not with lizards, one might expect that Fish and Amphibians are more closely related than Fish and Lizards. But, at the same time, if you look at a different genetic trait, and you see similarities between amphibians and lizards, you start to think: ah, maybe the amphibians are “the middle men” between fish and lizards. And so on. This is common sense stuff, @Dredge.
You seem to think that genes acknowledge some limit to their ability to allow or enforce changes on a living thing. How would that happen? The only thing that actually does tend to slow down population wide changes is a large population of stable variants. If a mutation happens here or there in a large population, it is more likely to be drowned out by the sheer “noise” of the pre-existing genetic variability.
So speciation becomes less likely with population size. Not too surprisingly then, when a population is being decimated by a new environmental situation (either a new rival for the same food, or the extinction of a once plentiful food source), the population size begins to contract. And the smaller the population becomes, the more significant each new mutation or variant combination becomes. In a now tiny population (sometimes called a “bottleneck”), a beneficial change can explode within the ranks of the population, and come to easily predominate as the old guard genes become less and less able to perpetuate within the population.
You get this, right? So, try to imagine then, what happens if you have one large population, unified, even as members of the population range across various geographies and climates. If there is robust exchange of genetic factors throughout the range … from East to West, from North to South, and so forth, then new variants are going to have a difficult time prevailing when the “noise” of the existing variants drown them out.
But if the free flow of exchanging genetic factors becomes interrupted … by distance or by barriers … then what was once one very large population has now become 2 or 3 smaller groups. Perhaps 1 group is half the originally unified population, and a second group is one third the original population, that means the third group is a tiny fraction, about 12% of what used to be a unified population!
Over time, this 12% could do one of the following things:
- become extinct.
- eventually move back into closer contact with its original population source. Or,
- continue to change in a direction that eventually reduces reproductive compatibility with the other populations, and thus close off further external exchange of genes to virtually nothing!
When (3) happens, it means that population can start to change much more quickly than those other groups that continue to have a robust exchange of genetics!
So how would you figure out which group was the original group? Wouldn’t you look to see which odd-ball genetic factors exist in more than one group, and which factors belong to all of them? Wouldn’t you make a common sense investigation of genetic factors that indicate a straight line of change, rather than changing from “A” to “B” … and then proposing that a specific group ended up returning to “A”? One would not expect this very often, right?
In an Eskimo village where one very famous hunter had red hair, and appears to have produced a great number of children and great grand children with red hair. If you came back to the village after 50 years and you found that the one village was now four villages. Would you expect the village with mostly red-headed people in it to be unrelated to the famous hunter, but that it was the black-haired villagers who were most closely related to the red-headed hunter? Why would anyone propose a scenario like that? It could happen, I suppose, but one would find indicators for how that happened. One wouldn’t expect it to happen all the time as a general rule, right?
Here is a narrative treatment that someone must have written just for you!:
Evidence from Biochemistry
"Evidence for common descent may be found in traits shared between all living organisms. In Darwin’s day, the evidence of shared traits was based solely on visible observation of morphologic similarities, such as the fact that all birds—even those which do not fly—have wings."
"Today, the theory of common descent is supported by genetic similarities. For example, every living cell makes use of nucleic acids as its genetic material, and uses the same twenty amino acids as the building blocks for proteins. All organisms use the same genetic code (with some extremely rare and minor deviations) to specify the nucleic acid sequences that form proteins. The universality of these traits strongly suggests common ancestry, because the selection of these traits seems somewhat arbitrary."
“Similarly, the metabolism of very different organisms is based on the same biochemistry. For example, the protein cytochrome c, which is needed for aerobic respiration, is universally shared in aerobic organisms, suggesting a common ancestor that used this protein.”
"There are also variations in the amino acid sequence of cytochrome c, with the more similar molecules found in organisms that appear more related (monkeys and cattle) than between those that seem less related (monkeys and fish)."
“The cytochrome c of chimpanzees is the same as that of humans, but very different from that of bread mold. Similar results have been found with blood proteins.”
“Other uniformity is seen in the universality of mitosis in all cellular organisms, the similarity of meiosis in all sexually reproducing organisms, the use of ATP by all organisms for energy transfer, and the fact that almost all plants use the same chlorophyll molecule for photosynthesis.”
The closer that organisms appear to be related, the more similar are their respective genetic sequences. That is, comparison of the genetic sequence of organisms reveals that phylogenetically close organisms have a higher degree of sequence similarity than organisms that are phylogenetically distant."
“Comparison of the DNA sequences allows organisms to be grouped by sequence similarity, and the resulting phylogenetic trees are typically congruent with traditional taxonomy, and are often used to strengthen or correct taxonomic classifications.”
“Sequence comparison is considered a measure robust enough to be used to correct erroneous assumptions in the phylogenetic tree in instances where other evidence is scarce.” "“For example, neutral human DNA sequences are approximately 1.2 percent divergent (based on substitutions) from those of their nearest genetic relative, the chimpanzee, 1.6 percent from gorillas, and 6.6 percent from baboons (Chen and Li 2001; Cooper et al. 2003).”
"Further evidence for common descent comes from genetic detritus such as pseudogenes, regions of DNA that are orthologous to a gene in a related organism, but are no longer active and appear to be undergoing a steady process of degeneration. Such genes are called “fossil” genes. Since metabolic processes do not leave fossils, research into the evolution of the basic cellular processes is done largely by comparing the biochemistry and genetics of existing organisms."
"The proteomic evidence also supports the universal ancestry of life. Vital proteins, such as the ribosome, DNA polymerase, and RNA polymerase, are found in everything from the most primitive bacteria to the most complex mammals. The core part of the protein is conserved across all lineages of life, serving similar functions."
“Higher organisms have evolved additional protein subunits, largely affecting the regulation and protein-protein interaction of the core. Other overarching similarities between all lineages of extant organisms, such as DNA, RNA, amino acids, and the lipid bilayer, give support to the theory of common descent.”
“The chirality of DNA, RNA, and amino acids is conserved across all known life. As there is no functional advantage to right- or left-handed molecular chirality, the simplest hypothesis is that the choice was made randomly by early organisms and passed on to all extant life through common descent.”
[End of Narrative Section]