Evolution by Spencer

What is evolution? Evolution is a process in which animals slowly change over time to suit their environment.

Natural selection is when traits are passed down, not by choice, but survival. Animals with more desirable traits, tend to be the ones that survive. To reproduce, you have to be alive. An example of natural selection is a giraffe. The giraffes with longer necks were able to eat more leaves, because they were higher up. The giraffes with shorter necks, were unable to reproduce, because they didn’t have as much food to eat. The giraffes with longer necks were able to survive and reproduce. The offspring with longer necks were more likely to breed, unlike the ones with shorter necks. Over time giraffes with longer necks became the majority, causing most giraffes with shorter necks to die out.

* See teachers note

Mutation is when there is a change in DNA. When a mutation occurs the outcome can be good, bad, or neither. An example of mutation is the ice fish. Over time it slowly started to get rid of its red blood cells. This made the blood thinner, and took less effort to circulate in the body. The fish also produced its own type of antifreeze. It lived in waters that were -1.8 degrees celsius. It’s  body mutated to live not have, and to live without red bloods cells.

Here is a picture a its blood compared to a normal fish.

            Gene flow is the exchanging of genes between a population. During the early 1800’s there were only 20 elephant seals left in the world. We have tried to bring back their population. Today there are 30,000 elephant seals. All elephant seals are closely related, because there were only 20 elephant seals left, and who knows how many were female or male. This is a lack of gene flow, and kind of the opposite of evolution.

*Teachers note: The picture chosen actually show's Lamarck's theory of change, which was later disproved. Organisms cannot wish into existence a trait they need. Instead, there is variation in traits in a given population, and those with traits more suited to the environmental conditions are more likely to survive and reproduce. Spencer explains this in his post, but the picture might be a bit confusing.