Species and evolution?

Question

I am trying to conceptualise how evolution happens , I have read a few answers and it is a bit fuzzy.

Someone says that a new species doesnt just materialise overnight and 1 species does not give birth to a new species but gradual small changes occur within the species and over time this somehow creates a new species.

This sounds to me like there are no clear boundries between species.

How does evolution happen, how did an ape evolve into a human.

Answer 1

GGs absolutely right in that the essential ingredient is reproductive isolation. Isolation is the cause of speciation not just the result. Take the arboreal rabbit example. The rabbits could evolve to be better tree climbers but whilst they're freely interbreeding they won't split. Now if a female rabbit living in a forest starts to fancy an adept tree-climbing male rabbit and turns her nose up at a ground rabbit, whilst a few miles away in the savannah the reverse is true you could start moving towards speciation. Real genetic isolation could still be a long way down the road.

Similarly if one group of rabbits drifted off to an island the genetic isolation has been enforced and they could diverge into a new species over a long period of time.

You're abolutely spot on when you observe that there are no clear boundaries between species. Even a real definition of a species that works for all cases is hard to find. Check out the wiki link below for an elegant example of how difficult it can be.

No creationist entries yet. It is but a matter of time.

Answer 2

Wiggy's right that 'species' is a fairly arbitrary concept, but GG is wrong about the "fertile offspring" bit; that's a very common misconception. In fact the key is isolation under normal circumstances. Closely related species may be able to hybridize and have their offspring breed successfully (look at Blue-winged/Golden-winged Warblers, for an example), but they don't usually do so. Some species are easy to define apart, but some are tricky; most natural sciences have some sort of nomenclature committee that periodically reviews the information and makes taxonomic changes as seem appropriate. Birds are kind of notorious for this - some birds have gone from being a separate species to being a race and then back to a separate species within a fairly short period of time. The birds didn't change; the committee met a couple times and changed their minds..
Evolution is simply the change that happens over time as the orgaanism responds to natural pressures. It can be directed, as when farmers breed crops or animals to produce desired combinations of traits, or it can be simply a response to changes in the environment or the result of mate choices. Whatever the cause, if the result is that one sort of organism produces more offspring than another slightly different sort, then evolution is happening. The population will gradually come to be more like the first, and less like the second, sort of organism. If the population is somehow separated into parts, and the pressure on one part is not enough to drive the preference for that first sort of organism, then eventually you may end up with two different populations. If the differences are sufficient (as determined by taxonomists) then those two populations may be called separate species.

Answer 3

There is a very clear boundary between species -- Reproductive Isolation. If two animals can reproduce together and produce fertile offspring, then they are of the same species.

Evolution is caused by natural selection. Genetic mutations exist within all populations of organisms. Those organisms whose mutations are most beneficial for survival and reproductive success pass on their genes more than the others. This causes microevolution to occur within the population. Over time, the genetic differences within the population can become so great that members of the population can no longer all reproduce together, and thus become separate species. This is called macroevolution.

Let's use rabbits as an example. Say you have a population of rabbits that are mostly solid-colored, but a new predator moves into their area, and it is easier for spotted rabbits to hide from them. The predator would eat the solid rabbits first, since they were the easier prey. The spotted rabbits would escape from the predator, live longer, and reproduce more successfully than the solid rabbits. So now the population that used to be mostly solid has become mostly spotted. Now let's say it becomes advantageous for the rabbits to climb trees. Those rabbits that are able to do so are going to survive and reproduce more than those that are not. Let's throw in a third twist... A new herbivore has moved into the area, and is eating all the plants the rabbits used to eat. It has now become advantageous for the rabbits to eat insects instead. Those that are able to hunt, eat, and digest insects become more successful than those that are not.

...So now you have a population of rabbits that is solid-colored, ground-dwelling, and plant-eating. From that group evolved a population that is spotted, tree-climbing, and insect-eating. Changes such as this continue to happen until they become so different that they can no longer reproduce with the rabbits, and thus become a new species.

Answer 4

Evolution in Action
See how salamanders in California are evolving, just as Darwin might have predicted.

http://www.pbs.org/wgbh/nova/id/extr-evol-i.html

This is it. The thing we can't grasp is the length of time evolution has had to operate (or, if you're a creationist, you ignore the evidence for the age of Earth). With that much time, the accumulation of small changes can amount to great differences.