Answer by Diane Eager
Let’s start by asking where the figure of 49% comes from. The complete genome of fission yeast Schizosaccharomyces pombe (the yeast used in brewing) was found to have only 4,824 protein coding genes, whilst humans have over 20,000. Therefore, it cannot be a reference to 49% of the total human genome. It may mean 49% of the genes in yeasts have some similarity with human genes, but even that is probably a generous overestimation.
However, yeast does have a significant number of genes that are very similar to human genes, but that should not surprise us. There are many functions that all living cells must have in order to operate effectively, whether they exist as a single-celled organism like yeast, or are part of a large, multi-celled organism like a human being. These essential functions include: building and maintaining cell membranes and internal structures; controlling the movement of fluids and salts in and out of the cell; copying and maintaining genetic information; transferring genetic information from the nucleus to the cell and using it; controlling the process of cell division; and making new proteins and disposing of defunct proteins and other debris. As these functions are carried out in a similar way, and involve molecules with the same structure, don’t be surprised that genes that code for them will be the same or very similar.
One of the intriguing discoveries scientists made when they worked out the DNA code for yeast was the number of genes whose human equivalents can cause cancer if they are mutated. This seems rather bizarre for a single-celled organism. However, the functions of these genes are involved in processes that control cell division, and cancer is a disease of uncontrolled cell division. In their normal state, these genes are needed by both single-celled and multi-celled organisms.
Some of the other yeast genes that are similar to human genes are those involved in controlling the movement of salts across cells membranes. This is an important function for nerve and muscle cells, and mutations of these genes cause heart and brain diseases in humans. However, single-celled organisms like yeast also need to control the movement of salts across their cell membranes, so they will also have genes for them, even if they have no heart or brain to suffer as a result of such gene-breakdown.
These findings are a good reminder that mutations have been only been observed to degrade genetic information, not to improve on it. Any change in these genes renders them useless, and they would be eliminated by natural selection. This means evolution is a useless explanation for the existence of similar genes in yeast and humans. As yeast cells already have fully functioning versions of these genes, they do not provide any evidence for evolution, and will not make a single-celled organism like yeast evolve into complex multi-cellular organisms such as human beings.
So do these observations fit a Biblical framework? They certainly fit well with Genesis, which tells us that living things were separately created according to their kinds. This means the One Creator, who designed all cellular functions, has embedded the same or similar genetic information into all the cells that have a common function, regardless of the kind of creature the genes are part of. To say it another way: different kinds of unrelated creatures can be made separately and still share similar structures and functions, in the same way engineers design and build different machines, yet use many similar components because they all need them to carry out their overall function.
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