Evolution: Evidence and "Gaps"
I am not the original author of this piece. The true credit goes to ZomgItsCriss on youtube, so if you'd rather here these words from an attractive woman sitting on her bed, here's the link. I thought she was brilliant in her presentation and thus transcribed it so it can exist on the 'net in another format, granting more people access. For the most part I stayed true to her original words, but made small changes, mostly to sentence structures for reasons of grammar and flow when reading. Also at the 5:31 mark on her video she says that the Ambulocetus's ___ bones are like whale's and I couldn't figure out what that word was for the life of me, so I cut that sentence out. (If anyone can figure it out, I'll happily put it back in)
Natural Selection
The main mechanism of evolutionary change is natural selection, which was first proposed by Charles Darwin. The idea of evolution existed before him but nobody managed to present a plausible mechanism for it.
In the natural world there is a constant undeniable fight for survival and the organisms that have the most suited for survival traits will be the ones to pass those traits to the next generation. As such the average characteristics of a population will change over time. Given a very long period of time this can result in very dramatic changes. That is natural selection in a nutshell and there is evidence of it all around nature.
To give an example, some microbes have evolved resistance to certain antibiotics. This is because every once and a while there are a few microbes that either have already, or develop later due to a mutation, a genetic difference that makes them resistant to the drug. They pass this trait to the next generation, so the resistance to the drug spreads through the population. And we learned this the hard way because the cost in human life is very high due to infections caused by bacteria that evolved resistance to one antibiotic or another.
Natural selection is also self evident to those who observe speciation.
For instance, the California salamander which became separated geographically and evolved to adapt to different environments. The salamanders on the forest region relied on camouflage, while the ones on the coast adapted to display a coloration of dangerously poisonous newts to keep predators away. The salamanders are now so different that they're on their way of becoming separate species.
Homology
Homology is a refer to similar structures in different organisms. For instance, the forelimb in tetrapods which is made from the same set of skeletal bones. We have a long bone in the upper arm, than two bones in the lower arm than a bunch of small bones in the wrist than a set of five digits.
If you look at any other tetrapod, even if their forelimb is used for different things, be it the wing of a bat or the flipper of a whale, they all have the same bone structure as our forearm. Some of those animals lose some of those digits in various stages of development like we see in birds.
This would make no sense unless you consider a common ancestor. Otherwise, why would it be that way? Why would birds initially develop five digits if they only needed three?
Embryology
This is very evident with embryology.
For instance the presence of limbs in dolphin embryos which are virtually identical with arm and leg buds in developing humans.
These species are normally observed in later development but the fact is that embryos display traits of characteristics found in their ancestors. Again, this makes no sense except in an evolutionary context.
Why do birds have genes for making teeth? Why do dolphins have genes for making legs? And since we're talking about this, why do we have a muscle to move a tail (just like monkeys do) if we don't have a tail?
Atavisms
Which brings us to atavisms. An atavism is the reappearance of a vestigial feature that disappeared generations ago. For instance,
Chickens born with teeth
Hind legs in snakes
Humans born with tails.
Atavisms don't happen often but these anomalies occasionally occur because the ancestral genes are still present.
The Fossil Record
At the time that the origin of the species was published, Darwin admitted there were some gaps in his theory, for instance there were not that many known fossils to support it. Indeed, the fossil record in Darwin's time was quite limited and the dating was imprecise. However, the fossil record grew significantly since than and new fossils are found every day. We can now accurately date them and put them in very precise periods of time.
Creationists love to throw around the very famous and overly debunked claim that there are no intermediate fossils, often naming them missing links. Such a claim is ignorant on its own because every fossil is, in fact, a transitional form. These are is fossils that present clear features found in both classes of animals they are transitioning.
This is Archeopteryx
Archeopteryx very primitive bird which lived in the late Jurassic. Actually it's the oldest bird known so far, and it shows clear transitional characteristics from dinosaurs to birds. In some fossils, we can actually see the presence of feathers, clear indication that this animal was a bird. In addition to the feathers there are also reptilian characteristics including the long boney tail, clawed fingers and teeth which none of the modern birds have.
This is Ambulocetus
Ambulocetus is a transitional form from land mammals to whales. An animal that could swim but also walk. From the nose adaptation we could see that it could swallow underwater and the teeth are very similar to those of whales.
This is Tiktaalik
Tiktaalik is a beautiful transitional form from primitive fish to early tetrapods and there are plenty, plenty of other examples, but what I must stress again is all fossils are transitional forms.
These are Human
We have also many fossils of evolutionary intermediates of hominids showing gradual change from Lucy three million years ago to other species of australopithecus... to homo habilis... to homo erectus... to archaic homo sapiens... to modern homo sapiens which is us and anyone can read and learn about them, even see them for themselves in museums, provided of course they are willing to.
DNA
Another problem Darwin saw in his theory was heredity. In his times it was thought that the traits from both parents blended in the offspring. This would present a problem because if a certain advantageous trait was appear in an individual, it wouldn't be passed on as it is, but it would blend in with the traits from the other parent. It would fade away over generations and the species would remain fairly stable. Again, this is what was thought of heredity at the time. Now we know this is incorrect
The discovery of DNA in 1953 has demonstrated that heredity fits evolution perfectly. Now we know exactly how it works, while some of the traits are blended, many are not. Furthermore, along the way in the process of reproduction, DNA is subjected to mutations. Some of those mutations produce traits that are benign.
Some of them are even harmful, for instance, a shorter tail in a feline that needs a long tail for balance.
Occasionally some of the traits are beneficial to survival, for instance, the variation of spots in the coloration of a feline that provides better camouflage and those traits are passed on.
Genetics explain how the new traits appears. Darwin did not know that and he had no idea how they were passed on. Yet with the discovery of DNA his theory is stronger than ever.
What's more, genetics prove beyond doubt that we do share a common ancestor with the great apes
While the cells of all great apes contain 24 pairs of chromosomes...
...the human cells contain 23 pairs.
If we do have a common descent we would find in our genome a fusion between a pair of primate chromosomes.
On the end of every chromosome we find genetic markers called telomeres.
In the middle there are different genetic markers called centromeres.
If a mutation caused a pair of chromosomes to fuse we should find telomeres not only on the ends but also in the middle of the chromosome, and not just one, but two centromeres.
That's what we find in our chromosome number two. All the markers indicate that it was formed by the fusion of two primate chromosomes.
This is the nail in the coffin proving the common descent.
Time
There's one more “gap” in Darwin's theory. At the time that he wrote the book something that troubled him was that if there had been enough time for all this variety and diversity of life to have evolved. You see, in the times of Darwin the estimated age of the earth was about twenty to two hundred million years. He expressed his worries that this probably wasn't nearly enough time for natural selection to do all we see. This problem has now been solved. We now know that the age of the earth is about 4.5 billion years and living things have probably been on earth for 3.8 billion years. That's plenty of time.
To sum all this up, since Darwin's death the fossil record grew and improved with each new discovery to further confirm evolution. With the discovery of genetics we learn that heredity works exactly as needed to support his theory. We learned that the earth is old enough for natural selection to introduce all the diversity of life seen today . Now we even have the technology to study natural selection as it happens. In all this time not one piece of evidence was found to contradict evolution. Still there's so many people that just won't accept it.
And I know why. Because for most of them accepting that all the life there is today came about through a natural process implies that there is no need for a creator god. That evolution takes God out of the picture. If you feel that way it's too bad, but it doesn't change the facts genetic evolution makes you, as Richard Dawkins put it, a history denier.
Natural Selection
The main mechanism of evolutionary change is natural selection, which was first proposed by Charles Darwin. The idea of evolution existed before him but nobody managed to present a plausible mechanism for it.
In the natural world there is a constant undeniable fight for survival and the organisms that have the most suited for survival traits will be the ones to pass those traits to the next generation. As such the average characteristics of a population will change over time. Given a very long period of time this can result in very dramatic changes. That is natural selection in a nutshell and there is evidence of it all around nature.
To give an example, some microbes have evolved resistance to certain antibiotics. This is because every once and a while there are a few microbes that either have already, or develop later due to a mutation, a genetic difference that makes them resistant to the drug. They pass this trait to the next generation, so the resistance to the drug spreads through the population. And we learned this the hard way because the cost in human life is very high due to infections caused by bacteria that evolved resistance to one antibiotic or another.
Natural selection is also self evident to those who observe speciation.
For instance, the California salamander which became separated geographically and evolved to adapt to different environments. The salamanders on the forest region relied on camouflage, while the ones on the coast adapted to display a coloration of dangerously poisonous newts to keep predators away. The salamanders are now so different that they're on their way of becoming separate species.
Homology
Homology is a refer to similar structures in different organisms. For instance, the forelimb in tetrapods which is made from the same set of skeletal bones. We have a long bone in the upper arm, than two bones in the lower arm than a bunch of small bones in the wrist than a set of five digits.
If you look at any other tetrapod, even if their forelimb is used for different things, be it the wing of a bat or the flipper of a whale, they all have the same bone structure as our forearm. Some of those animals lose some of those digits in various stages of development like we see in birds.
This would make no sense unless you consider a common ancestor. Otherwise, why would it be that way? Why would birds initially develop five digits if they only needed three?
Embryology
This is very evident with embryology.
For instance the presence of limbs in dolphin embryos which are virtually identical with arm and leg buds in developing humans.
These species are normally observed in later development but the fact is that embryos display traits of characteristics found in their ancestors. Again, this makes no sense except in an evolutionary context.
Why do birds have genes for making teeth? Why do dolphins have genes for making legs? And since we're talking about this, why do we have a muscle to move a tail (just like monkeys do) if we don't have a tail?
Atavisms
Which brings us to atavisms. An atavism is the reappearance of a vestigial feature that disappeared generations ago. For instance,
Chickens born with teeth
Hind legs in snakes
Humans born with tails.
Atavisms don't happen often but these anomalies occasionally occur because the ancestral genes are still present.
The Fossil Record
At the time that the origin of the species was published, Darwin admitted there were some gaps in his theory, for instance there were not that many known fossils to support it. Indeed, the fossil record in Darwin's time was quite limited and the dating was imprecise. However, the fossil record grew significantly since than and new fossils are found every day. We can now accurately date them and put them in very precise periods of time.
Creationists love to throw around the very famous and overly debunked claim that there are no intermediate fossils, often naming them missing links. Such a claim is ignorant on its own because every fossil is, in fact, a transitional form. These are is fossils that present clear features found in both classes of animals they are transitioning.
This is Archeopteryx
Archeopteryx very primitive bird which lived in the late Jurassic. Actually it's the oldest bird known so far, and it shows clear transitional characteristics from dinosaurs to birds. In some fossils, we can actually see the presence of feathers, clear indication that this animal was a bird. In addition to the feathers there are also reptilian characteristics including the long boney tail, clawed fingers and teeth which none of the modern birds have.
This is Ambulocetus
Ambulocetus is a transitional form from land mammals to whales. An animal that could swim but also walk. From the nose adaptation we could see that it could swallow underwater and the teeth are very similar to those of whales.
This is Tiktaalik
Tiktaalik is a beautiful transitional form from primitive fish to early tetrapods and there are plenty, plenty of other examples, but what I must stress again is all fossils are transitional forms.
These are Human
We have also many fossils of evolutionary intermediates of hominids showing gradual change from Lucy three million years ago to other species of australopithecus... to homo habilis... to homo erectus... to archaic homo sapiens... to modern homo sapiens which is us and anyone can read and learn about them, even see them for themselves in museums, provided of course they are willing to.
DNA
Another problem Darwin saw in his theory was heredity. In his times it was thought that the traits from both parents blended in the offspring. This would present a problem because if a certain advantageous trait was appear in an individual, it wouldn't be passed on as it is, but it would blend in with the traits from the other parent. It would fade away over generations and the species would remain fairly stable. Again, this is what was thought of heredity at the time. Now we know this is incorrect
The discovery of DNA in 1953 has demonstrated that heredity fits evolution perfectly. Now we know exactly how it works, while some of the traits are blended, many are not. Furthermore, along the way in the process of reproduction, DNA is subjected to mutations. Some of those mutations produce traits that are benign.
Some of them are even harmful, for instance, a shorter tail in a feline that needs a long tail for balance.
Occasionally some of the traits are beneficial to survival, for instance, the variation of spots in the coloration of a feline that provides better camouflage and those traits are passed on.
Genetics explain how the new traits appears. Darwin did not know that and he had no idea how they were passed on. Yet with the discovery of DNA his theory is stronger than ever.
What's more, genetics prove beyond doubt that we do share a common ancestor with the great apes
While the cells of all great apes contain 24 pairs of chromosomes...
...the human cells contain 23 pairs.
If we do have a common descent we would find in our genome a fusion between a pair of primate chromosomes.
On the end of every chromosome we find genetic markers called telomeres.
In the middle there are different genetic markers called centromeres.
If a mutation caused a pair of chromosomes to fuse we should find telomeres not only on the ends but also in the middle of the chromosome, and not just one, but two centromeres.
That's what we find in our chromosome number two. All the markers indicate that it was formed by the fusion of two primate chromosomes.
This is the nail in the coffin proving the common descent.
Time
There's one more “gap” in Darwin's theory. At the time that he wrote the book something that troubled him was that if there had been enough time for all this variety and diversity of life to have evolved. You see, in the times of Darwin the estimated age of the earth was about twenty to two hundred million years. He expressed his worries that this probably wasn't nearly enough time for natural selection to do all we see. This problem has now been solved. We now know that the age of the earth is about 4.5 billion years and living things have probably been on earth for 3.8 billion years. That's plenty of time.
To sum all this up, since Darwin's death the fossil record grew and improved with each new discovery to further confirm evolution. With the discovery of genetics we learn that heredity works exactly as needed to support his theory. We learned that the earth is old enough for natural selection to introduce all the diversity of life seen today . Now we even have the technology to study natural selection as it happens. In all this time not one piece of evidence was found to contradict evolution. Still there's so many people that just won't accept it.
And I know why. Because for most of them accepting that all the life there is today came about through a natural process implies that there is no need for a creator god. That evolution takes God out of the picture. If you feel that way it's too bad, but it doesn't change the facts genetic evolution makes you, as Richard Dawkins put it, a history denier.
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