Selective breeding definatly changes the appearance of dogs and the aim is always to breed good features in and bad ones out - however it isn't that easy!
This rule applies to any animal - natural selection in the wild ensures that only the healthiest animals breed to produce the best off spring. Humans intervene to try and artificially create this - as in using the best meat producing bull to service the cows. This was seen when they started to ship herefordshire bulls out to America to mate with the native cows. The herefordshire bulls had been bred over the years to produce meat. The american cattle were less meaty - put the two together and beef burgers all round! However the Herefordshire bulls were less hardy than their american counterparts and alot of them died in the harsh conditions. However their off spring benefited from their mothers genes and were more suited to survival on the plains. How do i know - my GGGG grandfather shipped the bulls over!
Natural selection even occurs in humans - we are not naturally designed to be monogomous!!!! Surprise surprise girls! How do we know??? Well a mans sperm is made up of two kinds - the swimmers and the fighters!! When he does the biz(ahem) the swimmers go for it and head off for the goal (should we say) while the fighters stay back and guard!!!! (euch!) So if the female mates again the fighters are ready to attack any new sperm to prevent it from getting to the goal first - the healthyest sperm wins and gets to reproduce - survival of the fittest!!!.
God my brain is full of rubbish facts!!
