Dan,
My bad. Now it's just a strawman. Because I was asking about the sperm and egg.
No strawman here. A zygote is the single cell that results from the union of the sperm and egg (and a human zygote has the full human genome--or complete human DNA code--if I understood my high school biology correctly). Sperm and egg cells each contain only HALF of the parents' chromosomes (DNA codes). When the two combine, the resulting cell, the zygote, has a full set of chromosomes (a full DNA code). A human zygote has a full human DNA code.
Even the BSBC approved, chock-full-o-evolution high school biology text book, Heath's 1990 edition of
Biological Science: A Molecular Approach says on page 248:
quote:
New individuals begin at fertilization, when the nuclei of two cells--one from each parent--unite. If these cells contained the same number of chromosomes as the rest of the cells of each parent...the [chromosome] number would double...
--emphasis theirs to indicate the word can be found in the book's glossary
Human body cells contain 46 chromosomes (the full human DNA code). Sperm and egg cells only get 23 chromosomes (half the human DNA code--sort of). When the sperm and egg unite, the resulting zygote has 46 chromosomes (the full human DNA code). The text book, which is NOT pro-life, by any stretch of the imagination, actually states that the "new individuals begin at fertilization."
The Literalist asks:
1) What changes of complexity occur in the evolutionary process when going from that hypothetical first cell to humans? How do these changes in complexity occur?
2) What changes of complexity occur in embryogenesis when going from a human zygote to a human baby? How do these changes in complexity occur?
Dan Carroll responds:
Take a gander at a single-celled organism, take a look at a human, and see for yourself. Do you really not see any differences?
If I were to compare a typical, non-human single-celled organism to a human, I would see giant differences in body form AND giant differences in DNA structure. However, if I were to compare a human zygote to a human, I would see giant differences in body form, but I would NOT see giant differences in DNA structure. A human zygote has human DNA. The hypothetical first cell would NOT have human DNA.
The mechanisms of evolution that cause the hypothetical first cell to develop into humans involves changes not only in body form but also in DNA structure. The body becomes more complex but so does the DNA.
Differentiation, the process that a human zygote undergoes in developing into a human baby, results in a change in body form, but the DNA does not change.
Changing the complexity of body form has not, as I recall, been an issue in the evolution versus creation debate. Rather, complexity debates normally revolve around the DNA code and how changes to it could have occurred since a creature's body form is an expression of the creature's DNA sequences. Even the various differentiation processes of various creatures are expressions of the various DNA codes.
In other words, while I find the development from human zygote to human baby marvelous, I understand that the instructions for such development exist in the zygote's human DNA. This is simply different from the evolution process, which must first change the first cell's DNA into human DNA.
Your opening post appears to be using the following reasoning:
COMMONLY KNOWN BIOLOGICAL FACT:
All humans develop from single cells
CONCLUSION BASED ON ABOVE FACT:
Therefore, development from a single cell to a human is possible
CONCLUSION BASED ON ABOVE CONCLUSION:
Therefore, evolution from the hypothetical first cell to humans over billions of years is possible.
Here is my reasoning:
PREMISE BASED ON MY UNDERSTANDING OF EVOLUTION THEORY:
Evolution from hypothetical first cell to humans involves tremendous changes to DNA sequences through random mutations and natural selection.
PREMISES BASED ON MY UNDERSTANDING OF HUMAN BIOLOGY:
1)The single cell that a human develops from is a human zygote (the resulting cell of the union of a human sperm and a human egg). A human zygote has a human genome (complete human DNA sequence).
2)When a human zygote differentiates into a human baby, tremendous changes to the zygote's DNA do not occur.
CONCLUSION BASED ON ABOVE 3 PREMISES:
Zygote differentiation, since it doesn't involve tremendous changes to DNA sequences, cannot indicate that evolution is possible.
Your reasoning overlooks the DNA issue. I still see it as apples and oranges.
The issue was whether it was possible to go from so very simple to so very complex, not what means are used for it to happen. If you'd like to say that the mechanisms of evolution themselves are unlikely, go start a topic.
Human zygote development goes from simpler body form to more complex body form while DNA complexity remains unchanged. Evolution of the hypothetical first cell into humans involves changes in both body form and DNA structure.
Your opening post mentions evolution and describes, in a general way, the differentiation process a zygote undergoes. You attempt to compare the two processes. I see nothing off-topic by examining not only the actual changes that occur in both processes but also the mechanisms involved in both processes.
I also don't recall indicating, in this thread, whether the mechanisms of evolution are unlikely or not. I have tried to focus on simply comparing evolution's proposed mechanisms with embryogenesis's actual mechanisms.
™ Version 4.2