Evolution & critical thinking. What's your opinion(see below)?

Question

If there is no variation in a population, or if the only variation is acquired and not inherited, or if all of progeny survive to equally reproduce, will evolution occur? What's your opinion?

Answer 1

Despite 16 answers, I think everyone is missing two key parts of the question.

The first is that it is a *critical thinking* question. It is a given than the theory of Natural Selection requires three ingredients: variation, inheritance, and competition (selection). But the question is *WHY*. I think your assignment is to look at each of those three ingredients and explain *WHY* natural selection cannot occur if that ingredient is absent.

The second point is that these are three ingredients needed for *natural selection*, but are they necessary for *evolution*? It turns out that evolution can occur without natural selection ... through a second mechanism called 'genetic drift.' This is where the percentage of the population that has a certain gene (or more correctly put, the frequency of an allele) can increase or decrease just by random drift. Variation and inheritance are still necessary for this process, but competition (selection) is not. Genetic drift is usually a factor in a small population (like a small group of individuals introduced to a new environment without any resource stress) ... but eventually the population will reach the capacity of the environment, and natural selection will kick in, and take over as a much stronger process. Genetic drift also explains how neutral, recessive, or even harmful genes, can spread into a population even when there is no selection pressure to do so. Genetic drift is much slower than natural selection ... but technically, it is still "evolution" (change in the allele frequency of a population).

Of the two, I don't know if the second one (genetic drift) is something your class is covering. But I think the first one is definitely part of your assignment. Saying "no" to all three is correct ... but your assignment is to say *WHY*. Just stop and think about each one for a couple of minutes, and it should be fairly obvious. The brilliance of Mr. Darwin is that he put all three *together* ... but once he did so, *many* scientists just thumped themselves on the head and said "That's so obvious! Why didn't I think of that!"

Answer 2

No variation=no evolution. Acquired variation=no evolution. Equal probability of reproduction=no evolution. Here's why:

Evolution relies on 3 things: (1) That reproduction (the inheritance of traits from a parent organism) occurs; (2) that variation occurs (through crossing-over events, mutation, etc.); and (3) that natural selection forces act on these variations in terms of how long the organism lives and how many offspring they will produce. All 3 of your "if's" throw all these things out the window. Without these three things, evolution won't occur.

Answer 3

Here's the closest thing to your scenario I can think of. The population is a pair of identical twin men and a pair of identical twin women. Even if each man mates with each woman, the children will not be genetically identical. You will see exactly as much genetic variation among all their children as would see among the children of any couple. If those children intermarry, you would have an increased risk of genetic anomalies. That's why incest isn't a good idea. The possible variations designed into human DNA are immense.

Most genetic variations don't affect survival in the short term. It usually takes hundreds of generations to see that kind of effect. It's remarkable that so few genetic variations are harmful or even fatal.

Answer 4

If there is no genetic variation, there is no way for changes to be introduced into the genome, and therefore no evolution. I think you can still get evolution without distinct survival advantage if there are other selection or sorting mechanisms at work. For example, if some sneetches are born with stars on their bellies, and preferentially mate with others like them, you will get a stable population of star-bellied sneetches that will over time genetically drift away from the plain-bellied population, even though both survive. Also, populations that become separated from each other tend to drift apart over time. In both cases, the differences would certainly develop faster in the presence of different survivability issues, but even without that, random genetic drift would probably cause the populations to diverge.

Answer 5

Or .. if .. maybe ...
Those are unrealistic circumstances.
But when circumstances are very benign, then there is not much pressure on the population, and there is not much evolution.

Evolution happens quickly when the population is under stress - but not so much stress that it is wiped out.

Evolution means: the circumstances favor some members over others, because those members are better suited to the environment. But if everyone is equally well suited, then evolution is not going to happen much. I say "much" instead of ruling it out entirely because no situation is perfect - there will always be some differentiation that favors some members over others, even if it is not many or by much.

Answer 6

Well if you define-out any evolution, of course there will be none. This is like 2 + 2 = 4, it isn't a matter of opinion. The only posibility of evolution would come from random mutations which, in all likelyhood, would kill off the population before mutating in a positive direction.

Answer 7

Are you including the introduction of viral outbreaks? Viruses cause genetic mutations.

Evolution can occur with enviromental stresses, not just genetic variations.

Also no population variation in a closed small scale system eventually causes genetic problems too. See genetic problems in Amish community.

Answer 8

Under the entirely hypothetical (and unrealistic) conditions you posit - no. No evolution will occur.

Evolution depends on three things: Mutation, Heredity, and Selection.
In your example, there is no mutation to introduce variance into the population. There is also no heredity (as any acquired changes are not inherited). And as a result, there is no selection. So no evolution.

Answer 9

No; evolution would not occur under these circumstances.

Evolution relies on mutations of genes throughout generations; without variance, genes will be copied perfectly and no changes will ever occur.

However, our genetic material does not always copy perfectly. Sometimes these mis-copies give our sons and daughters enhanced ability to survive and reproduce. With this variance, we have evolution.

Answer 10

Evolution in humans stopped when we began to change our environment to suit us (clothes, housing, agriculture and animal husbandry) rather than adapting to changes in the environment.
Medical science has also removed the 'survival of the fittest' rule. We now regularly pollute the human gene pool by allowing genetic deficients to grow to adulthood and breed.