19 May 2005 18:02:02 GMT

Source: Reuters

By Maggie Fox, Health and Science Correspondent

WASHINGTON, May 19 (Reuters) - The evolutionary path that separated
humans from chimps 5 million years ago may have made human sperm survive
better but paradoxically may have made humans prone to cancer.
A comparison of chimpanzee genes to human genes shows a concentration of
genes unique to people in areas associated with sperm production and
cancer, and suggests the changes that make humans unique also make us
uniquely prone to cancer.
"If we are right about this, it may help explain the high prevalence of
cancer," said Rasmus Nielsen of the University of Copenhagen in Denmark,
who led the study while at Cornell University in New York.
Nielsen and colleagues were studying the chimpanzee genome, the
collection of all DNA, for clues about what make chimps and humans
different. They used genetic sequences published by Maryland-based
Celera Corp. <CRA.N>
For the report, published in the journal Public Library of Science
Biology, Nielsen's team at Cornell studied the 13,731 genetic sequences
that are the most different between humans and chimps.
They knew that genes having to do with smell, making sperm and fighting
bacteria and viruses were likely to be different.
"While we expected to find genes involved in olfaction, spermatogenesis,
and immune defense among the 50 annotated genes ... we were surprised to
find a very large proportion of cancer-related genes, especially genes
involved in tumor suppression, apoptosis, and cell cycle control
sequences," they wrote.
"It is surprising to find such a large proportion of genes that may be
related to tumor development and control."
In cancer, cells lose their ability to self-destruct when they become
faulty, a process called apoptosis. Cell cycling -- the process by which
cells activate, divide, and grow into two separate cells -- is also
disrupted in cancer.
"Eliminating cancer cells by apoptosis is one of the main processes used
by the organism to fight cancer," Nielsen said.
"The connection that we saw that these genes involved in proliferation
may be involved in spermatogenesis," Cornell's Andrew Clark, who worked
on the study, said in a telephone interview.
Apoptosis also kills many developing sperm cells before they mature. But
evolution could have interfered with this process, allowing more sperm
to reach maturity, thus carrying the mutation into the next generation.
Clark said chimpanzees get cancer, too, but no one has been able to
study enough of them in captivity to see if they do so at the same rate
and in the same ways as humans do.
Cancer in people usually occurs in late adulthood, after they have
reproduced, and thus has not been removed by natural selection -- the
process that leads to evolution.

knowledge is power - growing old is mandatory - growing wise is optional    
"Many more men die with prostate cancer than of it. Growing old is
invariably fatal. Prostate cancer is only sometimes so."
http://community.webtv.net/PALMER_ENT/doc