http://www.wasdarwinright.com/TheoryofEvolution.asp
"One case - that of sickle cell anaemia - provides some protection
against malaria. However, apart from that one asset, the condition is
not recommended. Sickle cell anaemia represents an assault on the way
blood cells work. There is one beneficial effect, but this is
counteracted by harm done to the human physiology system. A vivid
demonstration of this claim has come from observations of humans (with
sickle cell anaemia) operating under extreme conditions, where some
have been known to collapse and die. All examples of supposedly
`beneficial mutations' fit the general pattern: the trend is downward.
Organisms experience the process of `death by installment' . Our
conclusion is this: the first Darwinistic assumption is retained, not
by scientific evidence, but by appealing to chance over extended
periods of time - `given long enough, favourable mutations must
occur'"
http://www.ecotao.com/holism/conc_argue2.html
"An indigenous form of malaria in parts of Africa has led to the
increased frequency of the mutated haemoglobin in some African
communities, providing immunity to this parasite. Sickle cell anaemia
in human beings originates in about one in 100,000 people each
generation. In areas with the malarial parasite, Plasmodium
falciparum, which invades and consumes red blood cells, between five
and 20 percent of the population can have the sickle cell condition.
It is the inherited result of the replacement of one amino acid
(glutamic acid) by another (valine) in two positions on the
haemoglobin molecule. 574 amino acids make up the haemoglobin
molecule. Haemoglobin is found in the red blood cells and carries
oxygen from the lungs to the tissues via the blood. When these mutated
molecules release oxygen, they change their shape and realign into
long spindles."
"Sickle-cell anaemia also provides protection from malignant malaria,
a parasite-induced anaemia. If too many people in the population have
the sickle-cell condition, the occurrence of the potentially lethal
homozygous condition increases in their progeny. Two parents with the
homozygous sickle cell condition have all their genes in the mutant
form and can only give birth to children with both their gene pairs
with the mutant gene and severe hereditary anaemia. Parents
heterozygous for this condition can give birth to a child without
sickle cell anaemia, or with it, according to the laws of genetics.
Where malaria is killing people without sickle-cell anaemia, people
with the heterozygous condition survive and reproduce and so the
incidence of sickle cell anaemia increases. A balance in the
population occurs with malaria killing people without sickle-cell
anaemia and people dying from hereditary anaemia (Wilson, 1992)." |
