Cytochrome-C
Cytochrome-c is a protein that is found in most organisms; it is involved in electron transport in mitochondria.
About 70% of its 104 amino acid sequence is set in stone - if it changes, the protein does not work. A mutation that leads to such a change will lead to an organism that does not survive, will not reproduce and so the mutation is quickly lost.
The other 30% does not matter so much, and a change in one position can lead to a functional protein (though I would guess it is still restricted to a subset of amino acids), and so to an organism that survives, produces and passes on the mutation. Nevertheless, such mutations are very rare events for cytochrome-c, which means the variations between species are minimal, and this gives us a great insight into how they evolved, confirming the nested hierarchy indicated by morphology and genetics.
Here is a list of species (from here) indicating the number of differences in the amino acid sequence compared to that of humans.
- Chimpanzee 0
- Rhesus monkey 1
- Rabbit 9
- Pig 10
- Dog 10
- Horse 12
- Penguin 11
- Moth 24
- Yeast 38
What this means is that since chimp and human lineages diverged, they has not been a single change in the cytochrome-c amino acid sequence. However, go back a bit further, 40 million years, when monkeys and primates split. At some point in one lineage a mutation caused a change, and we see one difference between us and Rhesus monkeys. At the other end of the scale, looking at yeast, we can see there are 38 difference, because there has been so much longer since humans yeast diverged. Those difference will be split down the two lineages; there are perhaps 25-30 mutations between us and the common ancestor.
The penguin result is interesting as it is so low, given how long ago we split from penguins? There is a consistent pattern across all birds that the rate of mutation is slowed, not just in cytochrome-c. The reasons for this are not clear, but this paper gives one view.
Look at table 3 in this paper, which goes beyond the simple list above, and shows difference between all the species, not just compared to humans. We can see that the three birds in the table have very few differences between them, and are clustered together.
In fact, we can see that for any group, animals in the group have small difference, and have large differences with animals outside it.
It exactly matches what we would expect from the nested hierarchy of evolution.
See also here:
https://www.biology-pages.info/T/Taxonomy.html
https://content.csbs.utah.edu/~rogers/evidevolcrs/lectures/molevol-2x3.pdf
This post is all about whether the molecular evidence in the structure of cytochrome-c supports common descent or special creation.
Comparing Cytochrome-c Between Species
Added 10/Dec/25 from something I wrote long ago....
Scientists have collected data on the cytochrome-c of numerous species, and compared them against each other. Some of this is presented at this web site. Here is a snippet of data.
Horse Dog Penguin Pigeon Sunflower Horse 0 6 12 11 41 Dog 6 0 10 9 39 Penguin 12 10 0 4 41 Pigeon 11 9 4 0 39 Sunflower 41 39 41 39 0
At first glance the data is pretty straightforward. Horses are closely related to dogs (according to the theory of Common Descent), so have similar cytochrome-c - only 6 differences. Penguins are closely related to pigeons, so have only 4 different amino acids in their cytochrome-c. Sunflowers are distantly related to all of them, and so we see about 40 differences.
The problem is that some people believe the results are too good. We are talking about random mutations here, and yet look at that last column; the values for the sunflower are all 40, give or take one. What gives? Is this "perfectection" a sign of a Designer, a biotic message from God?
Let us consider the horse, the dog and the sunflower. According to Common Descent, the dog and the horse had a common ancestor a few million years ago, which I will call the horse-dog precursor. The sunflower had a common ancestor with the other about a billion years ago; call it the plant-animal precursor.
We could guess at how many changes there have been in Cytochrome c over the billion years from plant-animal precursor to sunflower, or from plant-animal precursor to horse, but we have no way of knowing. Here are a couple of possibilities:
P~A / \ / \ 30 / \ 7 / \ / H~D / 4 / \ 2 Sunflower Horse Dog
P~A / \ / \ 12 / \ 25 / \ / H~D / 4 / \ 2 Sunflower Horse Dog
In the first one there were 30 mutations on the way to the sunflower, and only 11 (=7+4) to the horse. In the second there were 12 mutations to the sunflower, and only 29 to the horse. In either case, the total number of differences between the sunflower and the horse is 41, so either might be right, or neither.
Note that the only bit that is the same is from the horse-dog precursor and down. The data says there are six differences between the horse and the dog, and two more when you go from the sunflower to the horse compared to the sunflower to the dog, so I was obliged to use 4 and 2 there.
Hopefully it is clear that a whole set of diagrams are possible of the form:
P~A / \ / \ a / \ b / \ / H~D / 4 / \ 2 Sunflower Horse Dog
... where a + b = 37, and a >= 0, b >= 0.
So what about this divine perfection? The prefection is simply an artefact of the diagram. When you consider the sunflower to the horse difference compared to the sunflower to the dog difference, 37 of the changes are the same. It is like two people driving from a house in one city to different houeses in a second city being surprised that 90% of their routes were the same.
The only difference is the short bit from the horse-dog precursor to either the dog or the horse. When you go to the horse there are 4 mutations, and when you go to the dog there are 2. There is a two fold difference in the mutation rate along the only part of the diagram where they are different.
I suggest that a two fold difference is more indictative of random mutation than of "divine perfection".
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