I am refering to times before the modern human existed.
2007-05-14 13:17:26 · 5 answers · asked by richard n 2 in Science & Mathematics ➔ Biology
Variation. All life forms have variants that are resistant to pathogens. This resistance is heritable. Pathogens are also co-evolving to new forms. Virulence is controlled somewhat by natural selection, also. You would not be a successful pathogen if you were always killing the organism you were in.
2007-05-14 13:39:31 · answer #1 · answered by Anonymous · 1⤊ 0⤋
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2016-05-18 02:25:53 · answer #2 · answered by ? 4 · 0⤊ 0⤋
Well polio did kill lots of people- but you still have to come into contact to get it, and in past societies we weren't all close together like we are now. A tribe may have contracted it, wiped out the tribe, and that was it. Same with anthrax.
HIV is actually a very recent disease, only jumped to humans in the last 200 years! That is also why it is so deadly- because it has yet to adapt to not kill its host so it can spread better. Again, it hasn't spread everywhere because of condoms etc- but look at some parts of africa, it IS killing everyone.
2007-05-14 14:02:52 · answer #3 · answered by Anonymous · 1⤊ 0⤋
Many plagues have managed to wipe out large portions of civilisation. Between 1/3 and 2/3 of the population of Europe was wiped out in the 14th century by the Black Plague. This was not an even spread across the countryside, some towns had no deaths, some had 100% deaths. Entire species have probably been wiped out, but, if it happened before humans had encountered them, how are we to know. Perhaps the Neanderthals were wiped out entirely but a disease for which we are immune. They certainly became extinct without adding to our gene pool.
2007-05-14 14:45:37 · answer #4 · answered by Labsci 7 · 1⤊ 0⤋
They are being contained. Also there are very few selected few people who are immune and can never get one particular infection!?
2007-05-18 12:06:50 · answer #5 · answered by Vicky 2 · 0⤊ 0⤋