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Scars of evolution

Evolutionary baggage

Normal features of organisms that are problematic today. One would not initially expect such problems to exist, as evolution is commonly imagined to weed out all problems. One also would not expect serious design flaws if there was an intelligent designer creating life.  Why, then, does this “baggage” exist?<
Evolutionary theory predicts that they exist, because they came from part of the genome that was advantageous in past individuals, but is disadvantageous under the pressures exerted by natural selection today.

The mammalian eye

The mammalian eye has evolved over time. In evolution, natural selection allows new structures to be built from an adaptation of an old structure, which lets things get done, but not ideally. The process leads to a numerous defects.
An overview of how eyes has evolved is shown below:

{ http://en.wikipedia.org/wiki/Evolution_of_the_eye }

EyeEvolution

Defects from this process are illustrated here:

Image from: Evolution of the Eye, Scientific American, Trevor D. Lamb, July 2011

Eye Scars of Evolution scientificamerican0711-64-I4

{ Wikipedia contributors. “Evolutionary baggage.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 20 Dec. 2013. Web. 2 Jan. 2015. }

crossover between respiratory and ingestion tubes

“Adapting an ancestral fish into a land dwelling mammal necessarily involved many changes of function and led to some elements of poor design, such as the crossover between respiratory and ingestion tubes resulting in a maladaptive lung/esophagus arrangement (one that leads to almost 3,000 choking deaths in America each year). “

http://www.zo.utexas.edu/courses/THOC/Natural.Selection.html
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Natural selection is not a perfect process; if an organism is “fit enough” to survive a particular environment and reproduce, its genes are passed on to the next generation. Some of these genes may increase an organism’s fitness while some may even be slightly disadvantageous. This seeming paradox is the origin of evolutionary baggage, which is the collectively inherited traits that evolved in a different environment from the present.

Type I diabetes

It has been hypothesized that genetically-linked type I diabetes was advantageous during the extreme cold temperatures of the Ice Age 14,000 years ago. Type I diabetes is deleterious now, but would have conferred an advantage for individuals to survive extremely cold temperatures; this condition prevents production of insulin, keeping blood sugar levels high in the blood, which lowered the freezing point of the blood and protected the individuals with the condition.

Vestigial structures

Leftover parts of anatomy that have no function now, but did have a function when the organism existed millions of years ago. Examples include:

* Wings on flightless birds

* Eyes in cave-dwelling animals that are blind

* The pelvis in snakes such as the python. While snakes today don’t have hips and legs, their ancestors did, as their ancestors were four legged.

* Dandelions reproduce without fertilization, yet they retain flowers and produce pollen – both are plant sexual organs normally used for sexual fertilization.

* Flightless beetles which retain perfectly formed wings, housed underneath fused wing covers.

* Human wisdom teeth.

Our ancestors were largely herbivorous: molar teeth are required for 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. These useless teeth can cause significant pain, increased risk for injury, and may result in illness and even death. But these teeth played a role many generations ago.

* Human tail bone –  the coccyx.
This is made from four fused vertebrae at the base of the spine, which is exactly where most mammals and many other primates have external tails. Humans and other apes are some of the only vertebrates that lack an external tail as an adult. The coccyx is a remnant of the embryonic tail that forms in humans. Our internal tail is unnecessary for sitting, walking, and elimination.

Atavisms

An atavism is the reappearance of a lost character, which used to be part of a distant evolutionary ancestor. An atavism is not observed in the parents or recent ancestors of the organism.  They have several essential features:
(1) presence in adult stages of life,
(2) absence in parents or recent ancestors, and
(3) extreme rarity in a population

Examples:

* Living whales and dolphins with rear legs!
Here are the hind-flippers of a bottlenose dolphin found in Japanese coastal waters. Y
hindf lippers

* Humans born with tails.
X-ray image of an atavistic tail found in a six-year old girl.
human tail

http://www.talkorigins.org/faqs/comdesc/

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