epic

my brother, a creationist, asked, in regards to evolution, why they don't find any evidence of a particular species turning into another... like, fossils with "half species" kinda thing... i said it was because of the time involved and then pointed out how they've found homoerectus and whatnot, also the whale with the legs... but i wanted to know, seeing i think this is a pretty common question from theists, what is the best answer to give... i think the problem is a misconceptipn in regards to how evolution works, but i'm having a hard time putting it into words for some reason.

so, if you were asked this question, what would you answer with?

also, what is the best, simplest, defination of evolution and how it works? i want to really help him understand the concept...

if this is R, apologies.

Oolon Colluphid

Hi epic, welcome to E/C!
Ask him what exactly he thinks we should be finding. What, for instance, should a 'transitional' between an ape and a human look like?
Then don�t put it into words. Show him this picture:



... and ask him which ones are the apes and which are the humans, and why he thinks so. Then bring any answers back here for us to eviscerate, if you have trouble doing so on your own.
Evolution is merely a change in the heritable characteristics of a population over time.

Which may or may not help . What might help is to say that:

1. individuals vary

2. some of that variation is inheritable

3. some of that heritable variation can aid or hinder the individual�s chances of actually passing on that variation.

4. any variation that makes the individual more likely to leave offspring than its contemporaries will, by definition, find itself in more descendants.

5. such advantages will therefore become more and more common in subsequent generations -- till they become the �norm�.

--> The population will have evolved.

The other bit to remember is that the environment, the circumstances the individuals are in, is what �decides� what lives or dies, reproduces or dies childless. Lineages will therefore, blindly, automatically and inevitably, become adapted to �fit� their lifestyle.

That, in a nutshell, is evolution by natural selection. Which might better be termed evolution by blind sieving of naturally occurring variation. Selection suggests intent, and there�s no intent -- some organisms just happen to fit their environent better than others, and they leave more descendants. Their heritable material therefore makes it through that round of the game, that generation�s sieve, better than the others� does. After many many generations of this, after many many sievings, what you get is stuff that�s good at getting through sieves: organisms that are good at living in that particular way.

The only other bit to add for now is to note that some of the variation will be due to unavoidable mistakes in the genetic copying system: random mutations. Many will mess the organism up... and these will not make it through the sieve. Many more will not actually make a difference -- there�s actually several versions of the genetic code for each protein, or the mutation may fall in the heaps of unused DNA most living things carry around. But some -- and there are examples if you need them -- will be advantageous to their owners. And these will spread through the population, automatically and inevitably, just as above.

Basically -- and there�s rather more to it than this of course -- evolution by natural selection is down to different reproductive success between varying individuals; it is, therefore, the non-random passing on (or not) of variation and random novelty.

Hope that helps!

Cheers, Oolon

Herakles

Species don't just turn into other species. Instead certain populations of a species will diverge off of the main one and slowly become different enough genetically to warrant a different species. There is really no such thing as a half-species. In the case of humans, for example, we came from an ancestor that shared both modern African ape and hominid characteristics. This original species diverged to have many branches, but for this purpose we need only include two. The apes evolved to be more suited to life in the trees and the hominids evolved to lead a social life on the ground. (BTW, humans are just one group of apes; they are not separate)

Evolution is simply the change of a population's gene pool in response to the forces of its environment.

In essence this is how it works:
1. All species have variability. This can come from the mixing up of genes by sexual reproduction or random mutations.
2. Most variation is passed on.
3. Organisms die.
4. Those less evolved to their environment are more likely to die off quicker.
5. Those species better adapted to their environment are more likely to survive and have more offspring.

RufusAtticus

Evolution is both a fact and a theory. The fact of evolution is that the characteristics and properties of populations of organisms change over generations. The theory of evolution explains this fact by identifying mechanisms responsible for the change. Mechanisms responsible for evolution include mutation, selection, drift, gene flow, and the mating system.

Mutations occur during DNA replication due to the fact that the molecular machinery is not 100% perfect. This causes offspring to differ genetically from their parents. Overtime, as the population grows and reproduces mutation ensures that no two individuals will be alike.

Selection happens when in varied populations, certain types of individuals leave more decendents than other types of individuals. Genes that underly the less fecund (worse) types will go extinct and genes that underly the more fecund (better) types will become common. What types of individuals are better than the others depends on the environment. When populations lose their worse types/genes and their better types/genes become common, we say that they have adapted to their environment.

Drift happens when. through chance (reproductive sampling), certain genes become more common and other genes become less common. This can cause genes to go extinct even if they are not selected against or sometimes if they are.

Gene flow is where through the migration of individuals and/or gametes. Genes from one population move to another population. Speciation is ususally said to have occured when through evolution populations are no longer physically capable of freely exchanging genes.

The mating system also influences evolution, but it is a little more complicated than is necessary to discuss here.

Since evolution occurs when populations change, to study it requires comparing things. The distinction between microevolution and macroevolution is an artifact of what are being compared. Microevolution is evolution apparant within a species or lower taxa, and macroevolution is evolution apparant between species or higher taxa. There is no fundamental mechanistic difference between them.

There I hope I covered the bases.

simian

To put the answer in a different context than the others:

Each new "half-way point" creates 2 new gaps.

Think in terms of numbers. If our numbering system is truely continuous, then there should be a number halfway between 1&2. Yes, there is: 1.5. Now you have to show there is a number half way between 1 and 1.5, and between 1.5 and 2. Which, of course, there is. Now you have 4 gaps to fill. Then 8. Then 16. Then 32. 64. 128. 256. 512. 1024. 2^n gaps. (Ah, but then n has to be discreet, not continuous, in the way I gave the example..)Success means creating new gaps.

Simian