Species have a genotype and a phenotype.<quoted text>
Excuse me, sir.
If I may be able to offer some small contribution?
Somewhere in my memory there is a study of some cheetahs that have
"changed their spots" so to speak.
I guess some of the spots on some of the cheetahs
have merged or fused together to form a slightly different pattern
on the top anterior area of the body ( the rump I think?).
The scientists had been studying the cheetahs for some
time when they noticed the mutation in a few of the specimens.
They were going to continue the study to see how far the mutation
would carry on into the population over time to study the process of "natural selection"
in a present-day context to see of course, if current experience would verify assessments made of fossil remains. A "reality check" on evolution theory. I don't know what the
study revealed later as I never kept up on it. I was younger and had
many other interests at the time.
Pardon my nom d' plume,
it has a certain purpose
as a sort of 'tool'
for a certain job.
The genotype comprises all the genetic traits observed, the phenotype is the composite of an species' observable characteristics and traits, such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior (such as a bird's nest). Of course those two connect: the phenotype always is the result of the genotype to a major extent.
The problem with fossils is that they only allow (partial) determination of morphology and physiological appearance. Development may only be determined if we find specimen of both infants and adults of the same species. Sometimes we find evidence of behavior (like the fossilized nests of dinosaurs). Also SOME biochemical analysis is possible and only to a very restrict degree. But, moreover, we almost never can determine the genotype out of fossils, but in very rare and rather recent fossils.
In biology the main criterion to distinguish between related species is genetic isolation: when two (sub)populations cannot interbreed successfully (any more), they are called different species. But we do not have the genotypes of fossils. Because DNA deteriorates rather fast, even when preserved well.
But there IS a strong relationship between genotype and phenotype.
For instance, we know that if species have different procreative strategies (like live-birth and milk feeding in contrast to egg-laying), they inevitably belong to different species (and even to different classes).
If we study the precise relationship between phenotype and genotype of extant species and are able to establish statistically strong correlation, we may use this relationship to interfere form the fossil evidence (which tells a lot of phenotype but almost nothing of genotype) a better phylogeny. Which means: we are better capable of determining distinct species in fossils when lacking their genome.
The notion "species change into other species" is wrong. And not a little bit wrong but a major flaw. It leads to the utter ridiculous and stupid questions like "when humans evolved from apes, why are there still apes"? You really can't get it any more stupid than that.
The answer lays in an analogy: "when Americans are descendants from Europeans, why are there still any Europeans"? Stupid you find? Stupid it is, indeed.
New species arise as SUB-POPULATIONS from their ancestral species.
If humans descended from a Pithecus species, then chimps, gorillas and orang utans are the OTHER descendants ("Pithecus" = "ape", but MIND that apes are EXTANT species, hence the different name "Pithecus"). That ancient Pithecus species did not "change" into Homo Sapiens but gave rise to different daughter species, among those Homo Sapiens.