Human beings are the most advanced life forms and the reproduction cycle invariably takes the better genes of both the partners. The newer generation is an hybrid combination of the previous one. The strong genes continue to propagate to the next generation... But in lower life forms, this is not the case. Nature has to externally filter out weaker genes before getting into next generation... One of the most effective example of this rule of elimination is the reproduction cycle of Salmons.
Salmons are one of the species of fish which are born in fresh water and then spend majority of their life in the sea. These fish are mature at around the age of 5 years. The matured male & female salmons start their journey from the ocean towards the stream. The fish travel miles upstream (of course, against the flow of water) to reach to the highest point of the stream where the water is calm. This is usually high up in the mountain ranges, where that stream particularly originates. This is where the reproduction actually happens.
Going upstream for miles isn't easy. The fast flowing water against the fish is a daunting task. In addition to the stream, the fish encounter enormous enemies like birds, other fresh water fish and the lethal Grizzly Bears. Most of us must have seen these scenes on TV earlier.
Salmons are one of the species of fish which are born in fresh water and then spend majority of their life in the sea. These fish are mature at around the age of 5 years. The matured male & female salmons start their journey from the ocean towards the stream. The fish travel miles upstream (of course, against the flow of water) to reach to the highest point of the stream where the water is calm. This is usually high up in the mountain ranges, where that stream particularly originates. This is where the reproduction actually happens.
Going upstream for miles isn't easy. The fast flowing water against the fish is a daunting task. In addition to the stream, the fish encounter enormous enemies like birds, other fresh water fish and the lethal Grizzly Bears. Most of us must have seen these scenes on TV earlier. The weaker fish, get killed by the bears or tire off to death, and only the stronger fish make it till the higher points of the stream, exactly the same place where they were born. Here the females lay eggs and the males fertilize the eggs. Thus only the genetically strong fish mate and the next generation would eliminate the defects in the previous genes.
Most of the fish die after the reproduction stage due to exhaustion of the journey. The eggs then hatch into fishes and the stream water flows the juveniles back to the ocean.
PS: Image courtesy http://student.britannica.com/eb/art/print?id=55550&articleTypeId=0
