by TD 77 Replies latest jw friends
bohm
I've been giving your question some thought. Here is a link that shows how complex the issue is.
http://plato.stanford.edu/entries/species/#DeaEss
While I would define myself as a type of "essentialist", and this article oversimplifies my position a little, it does show how difficult this issue is.
It really gets to the heart of this thread.
That's a bunch of bullit. You just proved you don't know what you're talking about.
Thanks for such an erudite and polite reply. Sort of what I'd expect from a middle schooler.
I got my information from a wolf rehabilitation center I recently visited. However, a little further investigation indicates that it might be way off. The closest thing to a credible source I can find is a National Geographic test where rottweilers and german shepherd averaged around 300 psi and wolves around 400. I should have been more careful with my info and for that I apologize.
However, my error in this aspect of my analogy doesn't nullify my overall point. The domestic dog, whether pit bull, rottweiler or golden retriever, is still considered a separate though closely related species. And as such, it differs from wolves in behavior and some aspects of morphology. Because of how closely they're related, they can produce fertile offspring.
Interesting excerpt from DD's stanford link:
Evolutionary theory ... tells us that the boundaries between species are vague.
Which is the point I was trying to make with my (foundering) dog analogy
And it tells us that a number of forces conspire against the existence of a trait in all and only the members of a species. From a biological perspective, species essentialism is no longer a plausible position
I think this is really a key point. Essentialism runs up against the overwhelming evidence for comment descent (which even Michael Behe, irreducible complexity's poster boy believes).
However, DD's link asserts (and I admit I've only read part of it) that there is no essential feature common to all humans and not found in other species. I have to wonder whether the innate universal grammatical capacity of humans isn't such an essential feature. Animals have varying degrees of communication and rudimentary "language" but none (to my knowledge) have the generative capacity of syntax that is unique to ALL human languages.
If that's the case, then one might suggest that the line be drawn where language ability began to manifest itself.
Cadellin
However, my error in this aspect of my analogy doesn't nullify my overall point. The domestic dog, whether pit bull, rottweiler or golden retriever, is still considered a separate though closely related species. And as such, it differs from wolves in behavior and some aspects of morphology. Because of how closely they're related, they can produce fertile offspring.
Actually you're wrong again. You can pick any behavioral trait from a wolf you like, and breeding just from dog breeds I can breed it back, in just a few generations. In fact you can see them in various breeds. It's also very easy to see that some breeds of dogs have more in comon with wolves than with other breeds of dog. Should we make each breed it's own species?
As a dog trainer for 25 years, and, Fish and wildlife officer for 20, who has worked with wolves and wolf hybrids a few times, wolf traits in dogs are very easy to spot.
Also, are you aware of how much wolves and coyotes interbreed in the wild? The eastern coyote is much more wolf like than it's western cousin. They are larger and act more wolf like.
Interesting excerpt from DD's stanford link:
Evolutionary theory ... tells us that the boundaries between species are vague.
Which is the point I was trying to make with my (foundering) dog analogy
And my point is that sometimes they are so vague they really aren't there at all, they are simply variety within a species.
Which brings us back to TDs little test.
Variety within a "kind?" (As opposed to species?)
Using a fertility-based definition of "Kind," we could say that Canis lupus and Canis latrans are the same "kind" because they can reproduce, but are either of them the same "kind" as the Black backed jackal? (Canis mesomelas) Are they the same kind as the Dhole (Cuon alpinus) or the Bush dog (Speothos venaticus) or the Gray Fox? (Urocyon cinereoargenteus)
The problem is the dog family is so big and so divergent and some branches have been separated from others for so long that the genetic information is rearranged. It's not that they are fundamentally different creatures. Chromosomal painting has confirmed that they share much of the same genetic information but that information is no longer arranged in precisely the same order from species to species.
The Golden jackal (Canis aureus) for example has 74 chromosomes instead of 78 because the information that is carried in 4 chromosomal pairs in the domestic dog is carried in 2 larger chromosomes in the Golden jackal. This doesn't make the domestic dog and the Golden jackal completely infertile, but it does reduce fertility. You don't have to be an expert in genetics to realize that the greater the mismatch in chromosomal number, the harder it will be for chromosomes in sperm and ovum to successfully pair up.
With that in mind, the Hoary fox (Lycalopex vetulus) and the Crab eating fox (Cerdocyon thous) also have 74 chromosomes. The Maned wolf (Chrysocyon brachyurus) has 76. The Fennec fox (Fennecus zerda) has 64. The Kit Fox (Vulpes velox) has 50. The Chinese Racoon Dog (Nycteruetes procyonoides) has 42. The Red fox (Vulpes vulpes) has 36. Yet these are all members of the dog family.
Interesting.
'
Humans have one fewer pair of chromosomes than other apes, since the ape chromosomes 2 and 4 have fused into a large chromosome (which contains remnants of the centromere and telomeres of the ancestral 2 and 4) in humans. [ 3 ] Having different numbers of chromosomes is not an absolute barrier to hybridization. Similar mismatches are relatively common in existing species, a phenomenon known as chromosomal polymorphism.
The genetic structure of all the great apes is similar. Chromosomes 6, 13, 19, 21, 22, and X are structurally the same in all great apes. 3, 11, 14, 15, 18, and 20 match between gorillas, chimpanzees, and humans. Chimps and humans match on 1, 2p, 2q, 5, 7–10, 12, 16, and Y as well. Some older references will include Y as a match between gorillas, chimps, and humans, but chimpanzees (including bonobos) and humans have recently been found to share a large transposition from chromosome 1 to Y that is not found in other apes. [ 4 ]
This level of chromosomal similarity is roughly equivalent to that found in equines. Interfertility of horses and donkeys is common, although sterility of the offspring (mules) is nearly universal. Similar complexities and prevalent sterility pertain to horse-zebra hybrids, or zorses, whose chromosomal disparity is very wide, with horses typically having 32 chromosome pairs and zebras possessing between 44 and 62 depending upon species. In a direct parallel to the chimp-human case, the Przewalski horse (Equus przewalskii) with 33 chromosome pairs, and the domestic horse (E. caballus) with 32 chromosome pairs, have been found to be interfertile, and produce semi-fertile offspring, where male hybrids can breed with female domestic horses. [ 5 ] ).'
http://en.wikipedia.org/wiki/Humanzee
S
A new study has found that we humans are actually physically evolving at an increasing rate. We're not talking about cultural evolutionhere. We're talking about physical mutations.
For decades the conensus view - among the public as well as the world's preeminent biologists - has been that human evolution is over. Since modern Homo sapiens emerged 50,000 years ago, "natural selection has almost become irrelevant" to us, the influential Harvard paleontologist Stephen Jay Gould proclaimed. "There have been no biological changes. Everything we've called culture and civilization we've built with the same body andbrain." This view has become so entrenched that it is practically doctrine.
So to suggest that humans have undergone an evolutionary makeover from Stone Age times to the present is nothing short of blasphemous. Yet a team of researchers have done just that. They find an abundance of recent adaptive mutations etched in the human genome; even more shocking, these mutations seem to be piling up faster and even faster, like an avalanche. Over the past 10,000 years, their data show, human evolution has occurred a hundred times more quickly than in any other period in our species' history.
The new adaptations, some 2,000 in total, are not limited to the well-recognized differences among ethnic groups in superficial traits such as skinand eye color. The mutations relate to the brain, immunity to pathogens, sperm production, and bones - in short, virtually every aspect of our functioning.
Why might evolution be picking up speed? What could be fueling the trend? "Well, there's a lot more people on the planet in recent times. In a population you dont have to wait so long for the rare mutation that boosts brain function or does something else desirable." Says John Hawks of the University of Wisconsin at Madison and Gregory Cochan, a physicist and adjust professor of anthropology at the University of Utah.
Ten thousand years ago, there were fewer than 10 million people on Earth. That figure soared to 200 million by the time of the Roman Empire. Since around 1500 the global population has been rising exponentially, with the total now surpassing 6.7 billion. Since mutations are the fodder on which natural selection acts, it stands to reason that evolution might happen more quickly as our numbers surge. Cochran notes, "Darwin himself emphasized the importance of maintaining a large herd for selecting favorable traits."
Perhaps the most incendiary aspect of the fast-evolution research is the evidence that the brain may be evolving just as quickly as the rest of the body. Some genes that appear to have been recently selected influence the function and development of the brain. Other fast-changing genes - roughly 100 - are associated with neurotransmitters, including serotonin, glutamate (involved in general arousal), and dopamine. According to estimates, fully 40 percent of these neurotransmitter genes have been selected in the past 50,000 years, with the majority emerging in just the past 10,000 years.
So, it's likely that, as time goes on, we will evolve even faster.
S
