Numbers404
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In the United States, there has been a significant push from policiticians to either teach creationism along with evolution or to remove evolution from public education altogether. Many supporters of this movement claim that the evidence for evolution is lacking.
This article will look at the scientific evidence for a claim that creationists often have the hardest time accepting. The claim that humans and monkeys have a common ancestor.
For a more comprehensive source of the evidence for common descent in general, and the source of much of this article, please visit "29+ Evidences for Macroevolution The Scientific Case for Common Descent." http://www.talkorigins.org/faqs/comdesc/
I. Fossil evidence
There is a widespread misconception that there is a single "missing link" that, if found, would connect humans with apes. In fact, many fossils have been found that are intermediate in morphology (including the morphology of jaws, skulls, legs, and hips) between humans and apes. Creationists often contradict each other or even change their positions on which fossils are "completely human" and which fossils are "completely ape" because some fossils are so strongly intermediate in their morphology.
I will look at brain sizes in particular. As you can see from the following chart, the brain sizes of fossil hominids run the spectrum between those of Australopithecines (which creationists consider to be apes) and modern humans. The fossils intermediate in morphology between Australopithecines and modern humans are also intermediate in chronology.
Name - Brain size in cubic centimeters - Age
Australopithecines - 375 to 550 cc - 2,500,000-4,200,000 years old
Homo habilis - 500 to 800 cc - 1,500,000-2,400,000 years old
Homo georgicus - 600 to 680 cc - 1,800,000 years old
Homo erectus - 750 to 1225 cc - 300,000-1,800,000 years old
Homo heidelbergensis (aka Homo sapiens archaic) - 1200 cc average - 800,000-200,000 years old
Homo sapiens sapiens - 1400 cc average - 0-200,000 years old
( Source: http://www.talkorigins.org/faqs/homs/species.html )
[ Note: Creationists often disregard radiometric dating techniques, but the evidence for their accuracy is very compelling. For more information you can go to http://www.asa3.org/ASA/resources/Wiens.html ]
Many creationists have drawn the line between "completely human" and "completely ape" between Homo habilis and Homo erectus, with disagreement over some Homo habilis fossils. However, the Homo georgicus fossils found in 2002 are intermediate in morphology between Homo habilis and Homo erectus and it is still uncertain whether most creationists will classify them as apes or humans.
In this image you can visually see the evolutionary progression of hominids from our ape-like ancestors to modern humans. Skulls B-N proceed in choronological order, with skull B being the oldest and skull N being the youngest. Skull A is that of a modern chimpanzee for comparison. You can see why creationists have such a hard determining whether these fossils are "completely ape" or "completely human."
For more information about fossil hominids, you can go to http://www.mnh.si.edu/anthro/humanorigins/index.htm or
http://www.talkorigins.org/faqs/homs/
II. Genetic evidence
A. Pseudogenes
A pseudogene is a defective segment of DNA that is very similar to or identical to a gene but either cannot be transcribed or cannot be translated. Because pseudogenes are largely non-functional and their sequences are complex, it is highly unlikely that two or more species would have identical psuedogenes if they are unrelated.
An example of a pseudogene is the L-gulano-gamma-lactone oxidase gene, the gene required for L-ascorbic acid (Vitamin C) synthesis, found incapable of functioning in humans, apes, and monkeys. This pseudogene is also found in guinea pigs, but the mutations that rendered it functionless are very different from the mutations that caused the pseudogenes in humans, apes, and monkeys to become functionless ( http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=10572964&dopt=Abstract ).
Another example is the 21-hydroxylase pseudogene. Humans and chimpanzees, who are our closest relatives, share the same eight base-pair deletion in this pseudogene ( http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1550121&dopt=Abstract ).
III. Anatomical Vestiges
A vestige is "a degenerate anatomical structure or organ that remains from one more fully developed and functional in an earlier phylogenetic form of the individual" (Dictionary of Bioscience, 1997). An example of an obvious vestige is the eye that remains in blind species. This indicates that the ancestors of these species were able to see and this ability has since been lost. In the same way, vestiges found in humans provide evidence of our own evolutionary history.
A. Arrectores pilorum
Arrectores pilorum are tiny muscles under the skin that cause hair to become erect. Our fur-covered ancestors would have used these in the same way that modern primates use them: to make themselves appear larger and more frightening. Modern humans do not have enough body hair for this to be effective.
B. The Appendix
The appendix is a vestige of the end of the large cecum of our herbivorous ancestors. The large cecum found in many herbivorous animals contains specialized bacteria that secrete cellulase, an enzyme that digest cellulose (which is a common plant molecule). However, the cecum of hominoid apes (including humans) has lost this function and the appendix and the cecum remain as a rudiment of our evolutionary history.
For a comprehensive look at the vestigial nature of the appendix, you can go to http://www.talkorigins.org/faqs/vestiges/appendix.html
B. Endogenous retroviruses
Endogenous retroviruses convert their RNA into DNA and insert this DNA into their host's genome. This retrogene can be inherited if it happens to a sperm or an egg cell. Because this process is rare and somewhat random, two or more species having genomes with the same retrogenes in the same location strongly suggests that the two species have a common ancestor. There are many known instances of retrogene insertions that are common between humans and monkeys (and several that are common only among humans and chimpanzees) ( http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=10655035&dopt=Abstract ).
IV. The Human tail
A normal human embryo develops a tail after about 4 to 5 weeks of age, as you can see:
This tail is composed of complex tissues, including developing vertebrae, notochord, and mesenchyme. Normally, this tail is removed through a process of apoptosis (programmed cell death). However, in rare cases, it is retained and humans are born with tails. This tail "contains adipose and connective tissue, central bundles of striated muscle, blood vessels, and nerves and is covered by skin" and "can move and contract." ( http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=6373560 )
Here are a few pictures of a baby born with a functioning tail:
In biology, this reappearance of a characteristic found in an evolutionary ancestor is known as an atavism. Another extraordinary case of atavisms is living whales found with legs.
The muscle which enables these people to contract their tails is the extensor cocygis. This muscle has no practical purpose in normal humans and it is not always present. http://education.yahoo.com/reference/gray/subjects/subject?id=115
If humans and monkeys were unrelated, we certainly wouldn't expect any humans to be born with functioning tails. Nor would we expect to find human embryos developing complex tails only to later destroy them.
http://www.talkorigins.org/faqs/comdesc/
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This article will look at the scientific evidence for a claim that creationists often have the hardest time accepting. The claim that humans and monkeys have a common ancestor.
For a more comprehensive source of the evidence for common descent in general, and the source of much of this article, please visit "29+ Evidences for Macroevolution The Scientific Case for Common Descent." http://www.talkorigins.org/faqs/comdesc/
I. Fossil evidence
There is a widespread misconception that there is a single "missing link" that, if found, would connect humans with apes. In fact, many fossils have been found that are intermediate in morphology (including the morphology of jaws, skulls, legs, and hips) between humans and apes. Creationists often contradict each other or even change their positions on which fossils are "completely human" and which fossils are "completely ape" because some fossils are so strongly intermediate in their morphology.
I will look at brain sizes in particular. As you can see from the following chart, the brain sizes of fossil hominids run the spectrum between those of Australopithecines (which creationists consider to be apes) and modern humans. The fossils intermediate in morphology between Australopithecines and modern humans are also intermediate in chronology.
Name - Brain size in cubic centimeters - Age
Australopithecines - 375 to 550 cc - 2,500,000-4,200,000 years old
Homo habilis - 500 to 800 cc - 1,500,000-2,400,000 years old
Homo georgicus - 600 to 680 cc - 1,800,000 years old
Homo erectus - 750 to 1225 cc - 300,000-1,800,000 years old
Homo heidelbergensis (aka Homo sapiens archaic) - 1200 cc average - 800,000-200,000 years old
Homo sapiens sapiens - 1400 cc average - 0-200,000 years old
( Source: http://www.talkorigins.org/faqs/homs/species.html )
[ Note: Creationists often disregard radiometric dating techniques, but the evidence for their accuracy is very compelling. For more information you can go to http://www.asa3.org/ASA/resources/Wiens.html ]
Many creationists have drawn the line between "completely human" and "completely ape" between Homo habilis and Homo erectus, with disagreement over some Homo habilis fossils. However, the Homo georgicus fossils found in 2002 are intermediate in morphology between Homo habilis and Homo erectus and it is still uncertain whether most creationists will classify them as apes or humans.
In this image you can visually see the evolutionary progression of hominids from our ape-like ancestors to modern humans. Skulls B-N proceed in choronological order, with skull B being the oldest and skull N being the youngest. Skull A is that of a modern chimpanzee for comparison. You can see why creationists have such a hard determining whether these fossils are "completely ape" or "completely human."
For more information about fossil hominids, you can go to http://www.mnh.si.edu/anthro/humanorigins/index.htm or
http://www.talkorigins.org/faqs/homs/
II. Genetic evidence
A. Pseudogenes
A pseudogene is a defective segment of DNA that is very similar to or identical to a gene but either cannot be transcribed or cannot be translated. Because pseudogenes are largely non-functional and their sequences are complex, it is highly unlikely that two or more species would have identical psuedogenes if they are unrelated.
An example of a pseudogene is the L-gulano-gamma-lactone oxidase gene, the gene required for L-ascorbic acid (Vitamin C) synthesis, found incapable of functioning in humans, apes, and monkeys. This pseudogene is also found in guinea pigs, but the mutations that rendered it functionless are very different from the mutations that caused the pseudogenes in humans, apes, and monkeys to become functionless ( http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=10572964&dopt=Abstract ).
Another example is the 21-hydroxylase pseudogene. Humans and chimpanzees, who are our closest relatives, share the same eight base-pair deletion in this pseudogene ( http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1550121&dopt=Abstract ).
III. Anatomical Vestiges
A vestige is "a degenerate anatomical structure or organ that remains from one more fully developed and functional in an earlier phylogenetic form of the individual" (Dictionary of Bioscience, 1997). An example of an obvious vestige is the eye that remains in blind species. This indicates that the ancestors of these species were able to see and this ability has since been lost. In the same way, vestiges found in humans provide evidence of our own evolutionary history.
A. Arrectores pilorum
Arrectores pilorum are tiny muscles under the skin that cause hair to become erect. Our fur-covered ancestors would have used these in the same way that modern primates use them: to make themselves appear larger and more frightening. Modern humans do not have enough body hair for this to be effective.
B. The Appendix
The appendix is a vestige of the end of the large cecum of our herbivorous ancestors. The large cecum found in many herbivorous animals contains specialized bacteria that secrete cellulase, an enzyme that digest cellulose (which is a common plant molecule). However, the cecum of hominoid apes (including humans) has lost this function and the appendix and the cecum remain as a rudiment of our evolutionary history.
For a comprehensive look at the vestigial nature of the appendix, you can go to http://www.talkorigins.org/faqs/vestiges/appendix.html
B. Endogenous retroviruses
Endogenous retroviruses convert their RNA into DNA and insert this DNA into their host's genome. This retrogene can be inherited if it happens to a sperm or an egg cell. Because this process is rare and somewhat random, two or more species having genomes with the same retrogenes in the same location strongly suggests that the two species have a common ancestor. There are many known instances of retrogene insertions that are common between humans and monkeys (and several that are common only among humans and chimpanzees) ( http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=10655035&dopt=Abstract ).
IV. The Human tail
A normal human embryo develops a tail after about 4 to 5 weeks of age, as you can see:
This tail is composed of complex tissues, including developing vertebrae, notochord, and mesenchyme. Normally, this tail is removed through a process of apoptosis (programmed cell death). However, in rare cases, it is retained and humans are born with tails. This tail "contains adipose and connective tissue, central bundles of striated muscle, blood vessels, and nerves and is covered by skin" and "can move and contract." ( http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=6373560 )
Here are a few pictures of a baby born with a functioning tail:
In biology, this reappearance of a characteristic found in an evolutionary ancestor is known as an atavism. Another extraordinary case of atavisms is living whales found with legs.
The muscle which enables these people to contract their tails is the extensor cocygis. This muscle has no practical purpose in normal humans and it is not always present. http://education.yahoo.com/reference/gray/subjects/subject?id=115
If humans and monkeys were unrelated, we certainly wouldn't expect any humans to be born with functioning tails. Nor would we expect to find human embryos developing complex tails only to later destroy them.
http://www.talkorigins.org/faqs/comdesc/
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