Since time immemorial doomsayers have predicted the end of the world. But every time these predictions have been proved false and they would do so forever.I have gone through an article on Wikipedia on this topic and found it too pedagogic. Many of the so called threats listed in the article are in the realms of science fiction rather than reality.
Yes, there are a few events that may actually lead to the extinction of the human race, but they are very few and would be occurring in too distant a future and need not be considered as a threat at all.
I am separating the likely possibilities for human extinction into two streams; CONJECTURAL and INEVITABLE. These are listed below.
CONJECTURAL:
All these threats are imaginary and have no strong foundation whatsoever. These are generalized predictions which may or may not happen. No credence may be given to such baseless hypothesis’s which lack scientific foundation. One can just read and forget about them.
1. Widespread breaking out of disease resistant to medicines. This certainly would not affect the entire humanity.
2. Loss of oxygen due to changes in atmosphere on account of cataclysmic events.
3. Extreme ice age leading to Snowball Earth. An ice age can be a result of a nuclear winter. Ordinary ice ages have occurred in the past and may occur again but they lack the power to wipe out humanity.
4. Evolution of humanity into a different life-form or existence by means of technology, leaving no trace of original humans.
5. Genetic change of humanity to replace its ancestral predecessor.
6. Genetic engineering could lead to a species unable to inter-procreate, accidentally resulting in extinction.
7. Mutation of genes among humanity resulting in a less intelligent species.
8. Evolution of another species that out-competes humans for food, habitat or hunts as prey.
9. Solar flares may suddenly heat the earth, or the light from the sun may be blocked by dust, slowly freezing it.
10. A disruption, chemical, biological, or otherwise, in humans' ability to reproduce properly or at all.
11. Within a million years, the star Eta Carinae, which is 7500 light years from the Sun, may become a hypernova and explode. This would (may???) send dangerous radiation to earth.
12. In 1.4 million years the star Gliese 710 will be only 1.1 light years from Earth and this might disturb the comet belt, possibly resulting in a comet shower.
INEVITABLE:
I am again splitting these into two a) MANMADE and b) NATURAL.
MAN MADE:
All these events can be controlled by man and hence there is no reason to believe that mankind would cause self extinction.
1. Warfare, whether nuclear or biological, or conventional.
2. Preference for fewer children; if developed world birthrates are extrapolated they would lead to extinction of the human species before 3000 AD.
3. Infertility: Caused by hormonal disruption from the chemical/pharmaceutical industries, or biological changes.
NATURAL:
These are threats that are likely to occur and cannot be evaded. However, except for threat number 5 each of them would occur in too distant a future and one need not lose any sleep over them.
1. In about 3 billion years, our Milky Way galaxy is expected to collide with the Andromeda galaxy as Andromeda is approaching our galaxy. The consequences of this event is unlikely to be predicted-Certainly this event would cause great changes but one should remember that it would happen only after 300 crore years and one need not even bother about it.
2. In 5 billion years time Sun' would reach the red giant stage in its evolution, and it will expand and engulf Earth. 500 crore years too long a period even to bother about it.
3. Evolution of humanity into another hominid species. Humans will continue to evolve via traditional natural selection over a period of millions of years, and homo sapiens will gradually transition into one or more new species.
4. Gamma-ray burst in our part of the Milky Way (Bursts have been observed in other galaxies). The lack of fossil record interruptions, and relative distance of the nearest Hypernova (exploding star 7500 light years away) makes this a long term (rather than imminent) threat.
5. Major impact events where objects from space crash into the earth.
Threat number 5 is very real and has occurred in the past. However, it would not be sufficient to wipe out humanity from the face of the earth and there may be localized damage.
Considering all the above factors humans can feel comfortable about the existence of their species and need not worry about a doomsday.
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