Friday, July 8, 2011

I use this blog to save my favorite evidences for evolution.

Written by Human Evolution

The Origin and Evolution of Primates
Millions of Years Ago
65MYA - Proto-primates (which looked somewhat like squirrels)
55MYA - Prosimians
34MYA - Monkeys
23MYA - Apes (humans, chimps, gorillas, orangutans, gibbons, and extinct species)
7MYA - Hominids (bipedal apes, ancestral to humans) [1]

Scientists create phylogenies (tree of life) to categorize species and place them in certain groups by how closely related they are. By using mountains of anatomical and genetic evidence some phylogenies can be accurately constructed. As in the case of humans. We are still in the ape family (hominidae) in nearly every way we are still intrinsically connected to the other great apes. Since the early 1800’s (before The Origin of Species) we have been discovering hominid fossils. Our hominid family tree goes back approximately 7 million years. Within this timeframe we have discovered thousands of specimens from well over 100 individual hominids. [2] When we date fossils with various and accurate methods which are all cross referenced, we find that these creatures are transitioning from quadrupeds to bipeds. Other features that we see morphing are, the brain size which has tripled in the last 3 million years, the face becoming less protruding, and curved fingers (which were used for climbing.)

To go along with the thousands of chronologically dated transitional fossils above, we have homologies. Homologies between humans and nonhuman apes include, grasping hands with opposable thumbs, flat fingernails instead of claws like most mammals have, and we usually only give birth to one offspring instead of a litter like most animals. [3] Further evidence can be found in vestigial structures which are anatomical or genetic remnants from an organisms ancestral past that have lost their original function our are altogether useless. The ancestors of humans are known to have been herbivorous, and molar teeth are required for chewing and grinding plant material. Over 90% of all adult humans develop third molars (otherwise known as wisdom teeth). Usually these teeth never erupt from the gums, and in one third of all individuals they are malformed and impacted [4] These useless teeth can cause significant pain, increased risk for injury, and may result in illness and even death. [5] Another vestige from our herbivore ancestors is the vermiform appendix, “The appendix is a rudimentary tip of the caecum and is useless as a normal, cellulose-digesting caecum.” [6] Closely related to vestigial structures are atavisms which are rare but a great piece of evidence for common ancestry. In an organisms genes is information to build it’s body, the information from it’s ancestral past is buried away in the DNA. Sometime this genetic material gets switched on in development and we see bizarre characteristics from an organisms past. Examples of documented atavisms are, the rear limbs on whales and dolphins, and toes on horses. In humans we find babies born with tails, [7] and extra nipples that follow the milk line like other nonhuman mammals. [8]

As the genius Darwin once stated, embryology is one of the best examples of common descent via natural selection. Sometimes in embryological development an organism in certain stages will grow structures from it’s evolutionary past and then loose them before birth, this is known as recapitilation. Examples of recapitulation in humans are, “in early in development, mammalian embryos temporarily have pharyngeal pouches, which are morphologically indistinguishable from aquatic vertebrate gill pouches” [9] This indicates that mammals were once aquatic gill-breathing vertebrates because these same pharyngeal pouches in fish develop into gills. Another example in humans is once again, the tail, one distinctive thing that separates apes from other mammals is the lack of tail. But since we ultimately and recently came from monkeys the tail is there as a vestige, sometimes an atavism, and always in embryonic development. “At between four and five weeks of age, the normal human embryo has 10-12 developing tail vertebrae which extend beyond the anus and legs, accounting for more than 10% of the length of the embryo. By the eighth week of gestation, the sixth to twelfth vertebrae have disappeared via cell death, and the fifth and fourth tail vertebrae are still being reduced.” [10]

Our primate phyletic branches can be accurately constructed alone by the anatomical evidence above, but to confirm everything and perhaps even stronger evidence is that in which we can find in our genes, and nonhuman genes. Since anatomy has shown us that we are in the ape family, we would expect that comparative genetics would corroborate with the conclusions. And that is exactly what we find, we now know with the genetic sequencing of the human and chimpanzee genome that we are more than 95% identical.[11] We are genetically closer to chimps than they are to the other great apes, some even say we should change the Pan genus of chimps to Homo and change our ethical views on their treatment. Like the anatomical features listed above we also have vestiges, in our DNA, as Ken Miller eloquently described with the chromosome 2 fusion. The list for genetic evidence goes on and is perhaps the most impressive in all.

As Spencer Wells proved with ‘The Journey of Man’ in 2003, we are all from Africa, and all humans are closely related. Not only that, we are all animals and if it was not for other humans domesticating us and teaching us what it is to be human, we would not be much different than the wild apes we see in the jungles today. [12]

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