Why is population the smallest unit that can evolve?

Question

Need some people strong in biology/evolution!

Here are the choices: I've looked up this question for hours online and have read my books. Really interested to know. Need to know for my assignment.

a. Species from different populations do not interbreed.
b. All methods of evolution require chromosomes from more than one organism
c. Offspring of organisms within two populations provide sufficient genetic material to permit evolution of the species to occur.
d. Mutations can only occur across multiple population members.
e. Multiple diploid gamates are required to provide a foundation for the change.

Thanks for everyone's help!!!!

Answer 1

Wow. This is a tough one as I don't like any of the answers. (Are you sure you typed them exactly?)

The question is basically two-fold: First, why is the next smallest unit (the individual) *insufficient* to support evolution ... i.e. an individual cannot "evolve" ... we require a population of many individuals to evolve? And second, why is a single population *sufficient* (i.e. a single isolated population can evolve without any contact from a second population)? Some of these responses address the first question, others the second. Let's consider each one in turn.

(a), as written, is true but nonsensical. The phrase "species from different populations" makes no sense, as a population is a subset of a species. Are you sure it didn't say "individuals from different populations", or perhaps "specimens from different populations"? If so, that would be false, as individuals from different populations can interbreed (as long as they are the same species). But as written, (a) is true, as species cannot interbreed ... but irrelevant, as the fact that two different species cannot interbreed does not explain why the smaller unit of the population can evolve.

(b) seems to be false, but it may be the correct answer. As a trivial example, evolution also occurs with creatures that use asexual reproduction, which only involves the chromosomes of a single individual (followed by intense competition with siblings). But even in sexually reproducing organisms, mutation in a single individual's chromosomes are sufficient to instigate some change that results in evolution. However, (b) may mean that evolution cannot be considered to have occurred until it propagates into the chromosomes of more than one individual.

(c) is true ... but it doesn't explain why the population is the smallest evolvable unit. I.e. it explains why *species* evolve, but not why the smaller unit of a single population can evolve.

(d) is both false and irrelevant. Mutations don't have to happen only among multiple members, they could occur in a single member. In any case, that's all that's required for that mutation to propagate among the population.

(e) Is also false, for the simple reason that "diploid gametes" are not required, much less "multiple diploid gametes". Gametes are generally haploid, not diploid. And asexual evolution does not involve gametes at all.

So (b) seems to be the only candidate ... but only if we give it a somewhat trivial interpretation ... i.e. because evolution, by definition, is the propagation of a change into the genotype of a substantial percentage of individuals. (One thing that bothers me is that it refers to "more than one organism" rather than "more than one individual" .... "organism is such an imprecise term (as it can mean either species or individual).)

So I would go with (b) ... but please check that you have the wording for all of these exactly right.

Answer 2

The reason why populations tend to evolve is because they are typically isolated. To have a poulation, you take an already existing species and break it up into subsets of the whole....this form populations. These populations can be isolated on an island, can be seperated from the main group by a mountain range or a water body, all sort of divisions. And, the key to evolution is specieation by isolation.........thats why Darwin noticed all sorts of pecultiar animals on the Galapagos, and Madigascar, because they are island that broke away fromthe main group and were now left free to inetrbreed and adapt.
Isolation increades the amount of selective pressures on an organism, this causes higher levels of mutation, and due to interbreeding with other isolated mambers of your species, these mutations are more easily expressed in the following generations. This makes it quite easy for evolution to occur to populations.
I hope that helps!

Answer 3

The best answer is "b," although it is terribly phrased.

"a" sets the upper limit, "c" mentions two populations and is therefore wrong, "d" is completely untrue, and "e" talks about "diploid gametes" when you should know gametes are haploid.

Answer 4

Yes, while true, a "population" can be as small as about 50 and have enough genetic diversity to allow the mutation to prosper.

Answer 5

Too much complicated