I’d like to add another comment to Craig’s talk to show why I was so excited about it when Craig told me about it. Or, more accurately, when I finally understood it.
For me, the example of the immune system is a terrific analogy to the basic theory of evolution. It helped me understand evolution and finally realize that it really is an excellent description of the origin of species. Let me explain.
As Craig told us, our bodies have many types of cells, almost all with nearly identical DNA. One exception to this is the cells that make antibodies. How does that happen?
First, he said there are special stem cells in the blood whose job it is to make B cells which produce antibodies. While the stem cells all have the exact same DNA, each B cell is different in one special way. The genes for creating an antibody have a portion of their DNA scrambled. This is called the VDJ variability region and certain rules apply as a different selection of V and D and J regions is selected at random for each B cell. The human body typically makes millions of new B cells every day. Every single one is unique.
In my opinion, those stem cells are analogous to our last universal common ancestors. These ancestral cells reproduced with variability to generate a variety of life forms that are analogous to the B cells. This is the random mutation part of evolution and it continues to this day.
Next is the natural selection part. The B cells (a kind of lymphocyte) travel through the blood. If a B cell never encounters a virus or germ cell or any kind of antigen, then it dies in a few months. That particular DNA sequence will never be made again. But, if it encounters foreign (bacterial, viral) molecules that stick to the antibody to some degree, then that B cell will be activated to reproduce itself and generate more B cells almost like itself but again with some random variation. These will all be much more similar to the parent B cell than to other B cells. So most will also stick to the antigen and reproduce themselves, generating a diversity of B cells that stick to the antigen. Those that don’t stick as well will soon disappear while those that stick the most will survive and soon dominate. In a short amount of time, there is a large army of B cells making antibodies for the invading antigens. I see this as the same as natural selection. Of the variety of organisms produced by mutations, some won’t find the resources to survive while those who do will reproduce more successfully and live, becoming the dominant species.
Why is this happening? Why didn’t God just make all the antibodies we would ever need to begin with? Craig pointed out that the number of possible antigens is so vast that our bodies aren’t big enough to store all the antibodies that would be necessary to defend against any invasion. The diversity of antigens we encounter is changing constantly throughout our lives and can’t be predicted in advance. So the scheme of starting with only a few (a couple of hundred billion is just a few in this process!) which are enough so that at least some will be close enough to any antigen to get the process going, is a far more efficient way of solving the problem. I see this as analogous to God desiring to create a large set of organisms than can survive in any possible environment. Instead of creating all species at once that could endure in all environments, he created a starting point which would generate a wide variety of species that could respond to whatever environment they encountered. Those are the species that survived and they changed in response to a changing environment. What an efficient process! And we can see it working as we study the vast spectrum of species that has lived over the last nearly four billion years.
So to me, I find this immunology example to be an exciting process of evolution occurring over a period of days and months and years. It reflects what goes on at the species level over a period of hundreds of millions of years and more. What a marvelous method of creation God has chosen. Praise God!
