Evolution and Birth Premature Birth

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					                                    Evolution and Birth
                                         Kayla Manzi
                          Massachusetts Academy of Math and Science

        A newborn baby is the subject of admiration and wonder to all who are in his or her
presence because the infant is helpless and innocent. Why is it that when one of our closest
evolutionary relatives, chimpanzees, reproduce, their young surpass human newborns in agility
and body control? In contrast, it takes about a year for human offspring to learn how to walk
upright on their own. Throughout evolution, the birth canal has drastically changed, which has
led to our survival as a species, but also to our vulnerability when we are first born.

       The human species was first set apart from its ancestors when the population began to
walk upright. Some believe this change in gait occurred because it made mobility more efficient
in open areas, such as the savanna. The bipedal characteristic could have also occurred due to the
emergence of gathering as a food source. Evolving from moving on all fours to only two legs
caused some changes in the shape and anatomy of the pelvis, which resulted in a narrower birth
canal for women. Less space in the birth canal causes a more difficult and painful birth for the
mother (Bock, 2009).
        The anatomy of the human pelvis is perfectly suited for walking upright. The pelvis
balances the effects of gravity on the organs caused by walking on two legs by tilting towards the
front of the body. The pelvic bones must keep the internal organs from falling right out of the
human body; therefore, the bones are linked by a series of rings all attached at the coccyx, or
tailbone. The degree of tilt of the pelvic openings varies throughout the birth canal, leaving a
difficult path for the infant to follow. The mother’s body does adapt to prepare for childbirth,
which makes the journey a little easier. The ligaments holding together the pelvic bones soften so
the openings can increase in size to let the baby through (Mitchell, 2006).
        Once walking upright, humans began to work on problem solving and social interactions,
which led to larger brains. Eventually, through natural selection, humans with superior brains
survived to pass on their genes. As brain size increased, it became more dangerous and difficult
for mothers in childbirth because the larger heads did not fit through the birth canal as easily.
This tight fit could almost definitely kill the mother and child (Bock, 2009).
        Because of the confined space, infants’ heads compress as they pass through the bones in
the pelvis. A fully developed, mature brain could not fit through the birth canal; therefore, human
brains and bodies continue developing outside the womb, unlike other mammals. The
undeveloped brain, tiny structure, and immature skull bones and body result in the necessity of
constant care for the newborn. Human offspring are far more helpless than other primate infants
(Bock, 2009).
       Even though humans have adapted to give birth successfully with larger brains, there are
many other complications that can occur. Premature infants, who are becoming more common,
are babies born before the 37th week gestation, or more than 3 weeks early. In the United States,
premature births account for 8 to 10% of all pregnancies. Premature infants, also called
preemies, weigh much less than infants carried for full term and are born without fully developed
organs. These newborns must reside in a neonatal intensive care unit until their organ systems
can function on their own (U.S. National Library of Medicine, 2009).
        Speculated causes of women’s delivering prematurely include excessive maternal stress
from exhaustion, tension, or abuse and fetal trauma from low blood supply or a birth defect can
trigger preterm labor. For example, emotional stress or tension can trigger the release of
hormones that cause contractions. Medical conditions also contribute to stress, such as an
unhealthy diet, anemia, or diabetes. Other causes of preterm labor can be infections or bleeding.
The body’s instinctual immune response to some bacterial infections has been shown to trigger
premature labor, most commonly with infections concerning the genital and urinary tracts or
fetal membranes. Similarly, certain proteins released during blood clotting may prompt the
beginning of labor contractions. Placenta abortion, separation of the placenta from the uterine
wall, causes bleeding which releases the proteins. When the uterus is carrying multiple infants,
as in the case of twins or triplets, it has to stretch much larger than if only carrying one child,
which can also cause the mother to go into labor early (March of Dimes, 2009).
        Being a preemie can affect a child for the rest of his or her life. A common disease
caused by premature birth is Retinopathy of Prematurity (ROP), which is a potentially blinding
disease of the eyes. It is most common in children born weighing less than 2 ¾ pounds, but the
risk of ROP increases significantly as the weight of the newborn decreases. ROP can lead to
lifelong visual impairment or even blindness, and it usually develops in both eyes. Most cases
diagnosed improve and cause no permanent damage on the child. The majority cases of ROP in
children are mild enough to not permanently damage the child’s vision or require medical
treatment; however, about 10% of infants develop a more serious case of ROP which leads to
permanent vision impairment or blindness. Premature birth can have lasting effects on infants
(National Eye Institute, 2009).
       The first hospitals for premature infants were built at the turn of the twentieth century.
These hospitals demonstrated the success of the care for infants using incubators. Before the
invention of the incubators, care for all infants, including premature infants, was the
responsibility of the mother. Due to the poor medical conditions and care for these immature
newborns, not many survived. The incubators and better medical conditions are allowing infants
weighing less and less to survive; therefore the risk of ROP is increasing in relation to the
increases in premature survival rates. Negative consequences always come with the bettering of
human kind (Lieberman, 2001).

                                         Literature Cited
Bock, J. (2009, September). Are our Brains the reason newborns can't walk?. Scientific American
       Mind, Retrieved from
Lieberman, H. (2001). Incubator baby shows: a medical and social frontier. The History Teacher,
       35(1), Retrieved from
March of Dimes. (2009). Pregnancy and newborn health education center. Retrieved from
Mitchell, E.M. (2006, November 15). Evolution of childbirth?. Retrieved from
National Eye Institute. (2009, October). Retinopathy of prematurity. Retrieved from
U.S. National Library of Medicine. (2009, December 2). Premature babies. Retrieved from

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