laptoppop said:
What is the best way to define a "kind" (as in animals)?
This should be a hard boundary that has not been observed to be crossed.
One of the difficulties in communication between creationists and evolutionists is that they use a different set of vocabulary and concepts.
Creationists typically think of evolution--especially macro-evolution--as crossing a "kind barrier". But, as you say, such a barrier ought to be a hard boundary that cannot be crossed.
The scientific vision of evolution is not one of crossing barriers, but one of establishing barriers where there were none before. As we go back in time, we see these barriers between species becoming thinner, fuzzier and eventually melting away.
Here and now we see many breeds of domestic dogs, as well as many hybrids of these breeds, but we visualize these as all variants on an original dog-species. We also see wild populations of dogs, wolves, coyotes, etc. and even a YECist sees these as all variants of a single original dog-kind. How did that original dog-kind become many different species and sub-species? By the introduction of barriers between separate populations of the original dog-kind, that resulted in the morphological differences between them.
The same occurs in bears. Today we never see a bear that is just a bear: we see brown bears, black bears, polar bears, Asian bears, etc. There are barriers between these populations that did not exist when there was a single ancestral population of bear-kind.
Now what the scientists see is that just as the current divisions within "kinds" melt away as we move back in time, we also see the current divisions between "kinds" melting away. The original dog-kind population was not the beginning of dogs. Nor was the original bear-kind population the beginning of bears. Before there were bears and dogs, there were populations of bear-dogs. So that dog and bear are each variants of the ancestral bear-dogs, just as black bears and polar bears are variants of the ancestral bear, and foxes and wolves are variants of the ancestral dog.
Go back still futher, and the current barriers between all mammalian carnivores melt away and you find nothing you can call dog, bear, cat or seal, but rather a primitive mammalian carnivore with generalized characteristics, rather than the specialized features which mark different carnivore families today.
Run this track in reverse, and you see no crossing of boundaries but rather the erection of boundaries as populations become more diverse and can be distinguished one from another by their special features.
No crossing of boundaries occurs in evolution, but rather new groups are formed within established groups. That is why we are able to classify living forms in a nested hierarchy, with the largest and most inclusive nest being life itself.
I'm wondering if it can be defined by DNA, but I don't know enough about DNA to know.
Definitely not. Some DNA sequences are almost identical in function across an immense range of species. The tinman gene which regulates heart development has already been mentioned. The pax-6 gene regulates eye development in species as diverse as fruit flies and mice. You can take the pax-6 gene from a mouse embryo and insert it in a fruit fly embryo and it will produce eye tissue. Even more amazing it produces fruit fly eye tissue, not mouse eye tissue, even though it came from a mouse embryo.
The more we study DNA, the more we see the fundamental unity of all life forms.
I believe the following have been observed for particular DNA sequences:
Cross breeding causing variations from a pool of possibilities (Mendellian variation?)
Generally speaking hybridization or cross-breeding only works when the parents of the hybrid are closely related--breeds of the same species or closely related species of the same genus. So from a YEC perspective they would already be of the same kind. When the parents are not closely related the hybrid is often infertile or inviable.
Copying of a particular sequence (polyploidy?)
Right. Polyploidy is the term used when a whole chromosome or set of chromosomes is duplicated resulting in a new chromosome number. But smaller sequences, genes, triplets or single nucleotide bases can also be duplicated.
Degradation in a given sequence (typically mutation?)
This is another case where creationist vocabulary simply does not jibe with scientific terminology, so it is difficult to know the meaning of the term. "Degradation" is not a defined term. Perhaps what you are referring to is a non-functional gene or pseudogene. For example, all mammals have a gene whose function is to produce Vitamin C. Because Vitamin C is produced internally, most mammal species do not need to ingest it via their food. This gene exists in humans, but it includes a mutation that makes it non-functional. It does not produce Vitamin C. This is also true of the living species most closely related to humans: the other species in the hominid family. This group of mammals must get their Vitamin C from their environment. Only one other mammal is not capable of producing Vitamin C. And for the same reason. It has the gene, but there is a mutation in the gene that has rendered it non-functional. Not the same mutation as found in the hominid group, but the end result is the same.
Is that an example of what you mean by degradation?
Have any other variations been observed? In particular entirely new DNA sequences resulting in changed morphology?
What do you mean by entirely new DNA sequences? Remember DNA is a quasi-alphabetic system. A DNA sequence is a sequence of nucleotide bases, and there are only four of them. These get translated via the universal DNA code into a signalling system for assembling amino acids. There are 64 possible arrangements of nucleotide bases in the code, and 20 amino acids used to build proteins. So there is even redundancy built in, such that up to six different DNA sequences can signify the same amino acid.
Twenty amino acids are not much fewer than the 26 letters of the English alphabet. And just as the alphabet can be arranged in millions of sequences, so can amino acids, to form all the variety of proteins needed to carry out the functions of the cell.
Now within this framework, what possible sequences of DNA could be identified as "entirely new"? Just what standard of "newness" are we looking for? A new "spelling", a new gene, a new protein? All of these have been observed.
We also see a whole lot of cooptation, that is the reusing of an existing structure for a new purpose. The ASPM gene in mice was named for its function in regulating the formation of the spindle when the cell is dividing. But in humans, a variation of the same gene seems to be involved in the growth of the brain. When this gene is damaged, the child is born with an abnormally small head (microcephaly) and brain, and often a degree of mental retardation.
Much morphological change is developed through coopting existing structures rather than inventing totally new ones.
For my TE brothers and sisters - consider this a thought experiment. If you WERE to try to define a "kind" -- how would YOU do it?
I would define it just as Linnaeus did: species.
"Species" is derived from the Latin translation of the Hebrew "min" which in English is translated as "kind". Since scholarly work in Linnaeus day (both scientific and theological) was done in Latin, I think it obvious that when he referred to "species" he identified them with the Hebrew "min" i.e. "kind".
Historically, it was not until the late 19th century that it was proposed that "kind" referred to a group of related species instead of each species separately.
