How do & did animals evolve?

Question

How do & did animals evolve?

Answer 1

To put it simply, evolution is driven by two basic factors: mutation and natural selection.

Answer 2

Through s*x.  Every time a male and female have offspring, some of the genetic information comes from each parent -- but the copying process is not perfect, and occasionally an error is made.  Depending on the nature of the error, this can have anywhere from no effect at all on the offspring, all the way up to a profound effect -- and the resulting offspring may or may not be viable.  Most of these copying errors are unfavorable, and the offspring (if it survives at all) will be deficient in some way.  But some are favorable, and will provide an improvement in survivability.  Usually, the error is in a part of the genetic information which doesn't affect the descendant in any visible way (about 98% of human DNA is in this category -- called introns).  Sometimes, the difference becomes visible, and the resulting organism may have survival assets in excess of those of its parents.  For more on the mechanics of this, see Ref. 1.  For a history of the evolution of life on earth, see Ref. 2.

Answer 3

To put it simply, evolution is driven by two basic factors:  mutation and natural selection.  

Every time something or someone is born, it possesses several or many random genetic mutations which may or may not exhibit themselves.  These mutations are also passed down from generation to generation and accumulate over time.  

The two major factors in natural selection ('climate change' and 'sexual selection') influence which individuals pass down their genetic material to future generations.  Basically, as the mutations build up, some animals within a given population are better suited to, say, a colder climate, so as there is a general cooling trend over a great length of time, the animals not as well suited to the cold cannot pass their genetic material down to the future generations.

As these two factors build up over time, a population can begin to look and even behave differently from how they looked and behaved previously.  There are also two major theories as to how this process exhibits itself in the fossil record, or indeed in animals living today.  One is called 'Darwinian gradualism', and this is basically that the change in a population due to evolution exhibits itself at a constant rate, so every species would be continuously changing.  The other theory is 'punctuated equilibrium', which is basically that, though these mutations build up over time, they do not exhibit themselves until a major climatic shift kills off a great many of the population - which is called a 'speciation event'.  This increases the frequency of the mutations within the population which are selected for by the speciation event, basically making it more prevalent and thus more noticeable.

That is evolution in a nutshell.