NationStates Jolt Archive

Links to information sites would be great, or explanations you typed. Failing that, if you could link me to a site that might have people with the knowledge I'm looking for, that would be good too.

1: What is the process of developing from a monocelular organism to a multicellural microscopic organism, and from there to an organism with various cell cluster specializing on certain activities? What are some examples of species at about this stage? How does a multicellular microscopic organism reproduce?

2: How and why does a species go from bisexual (like plants, and, I presume, the common ancestor between animals and plants) to monosexual?

3: What is the evolutionary cause of the predominance of certain aspects of individuals that appear to have no benefit whatsoever--for instance right-handedness?



EDIT: Please disregard 2 now.

1) Examples of multicellular life forms that don't have differentiated cells include green algae like Volvox, which forms a hollow sphere of identical algae cells, and Ulva (sea lettuce). Their cells lack differenciation and if separated from the whole will survive, reproduce, and grow a new multicellular structure. They can reproduce like any unicellular algae through the cells splitting, or by breaking the multicellular unit into pieces.

2) It could have happened in a species like hydra, which reproduces both by budding off a clone of itself, and through sexual reproduction. One would assume budding would come first, and an accumulation of genetic modifications would have eventually led it to be capable of sexual reproduction. Later as the creature became more complex budding wouldn't work too well to reproduce a complete clone, so the organism would rely totally on sexual reproduction.

3) Things that have no benefit, but also do no real harm to the continuation of the species are to be expected in evolution. Sometimes they come about through random mutation, sometimes they're a byproduct of a beneficial change. Right handedness, the example you gave, comes about becase humans' brains are organized according to a division of labor that gives parts of the brain specific functions.

BTW, I'm not a biologist, so you might want to do some research. Maybe what I posted will give you some ideas for stuff to look up.

Thanks. I expect a google for the species names will give me a good bit of the information I'm looking for.

3: What is the evolutionary cause of the predominance of certain aspects of individuals that appear to have no benefit whatsoever--for instance right-handedness?

I'm no biologist but I think that qualities such as left-handedness are probably recessive alleles so you need one from each parent to be left handed, so they're less common but at no disadvantage. The same applies to eye and hair colour.

2: How and why does a species go from bisexual (like plants, and, I presume, the common ancestor between animals and plants) to monosexual?

I think you may have switched this one around and you were actually looking for going from asexual to bisexual.

However, we do have one example of a species that seems to have gone from a species with two sexes to a species with only one - the Whiptail Lizard. Whiptail Lizards are all female. They all lay eggs. They all fertilze their own eggs. However, they can only do it after simulated copulation with another whiptail lizard. Their hormones cycle on a basis that causes some lizards to sometimes be acting as the "male" in the copulation and others to act as the "female".

In short, the female fertilizes and lays her own eggs, but she has to get humped by another female to do so. =)

3: What is the evolutionary cause of the predominance of certain aspects of individuals that appear to have no benefit whatsoever--for instance right-handedness?

This has been pretty well explained, but I'll give a little more detail. Any aspect of an individual can get propogated across a species in evolutionary theory. This is true if the trait seems to be harmful, seems to be beneficial, or seems to be neutral, although the mechanisms may be different. A harmful trait is most likely something which has never had an alternative, or a recessive trait of some sort. A beneficial trait is expected to propogate by natural selection - that is, the organism with the trait is better suited to its environment, and will thus, over time, outperform those without it.

A neutral trait, like right-handedness, will appear rather random. This is because it most likely arose out of a random mutation that was propogated simply because there was no alternative, better or otherwise, to outperform it. Either that, or the organisms with the beneficial trait also had the neutral trait, and it was distributed in that way.

On question 2, it becomes apparent that not only was I unclear in my question, but I made a stupid assumption. I assumed that the plants, being "less advanced" should be a close match with the common ancestor, rather than being as different from it as I am, and that therefore the common ancestor had the sexual aspects of plants: sexual reproduction with each organism able to take either role in the sexual process, pluss asexual reproduction.



The tree in my yard is a flowering plant. Like nearly all other flowering plants, they have both male and female sex organs: the pestol and stamen (spelling errors notwithstanding). It reproduce sexually through crospolination as well as reproducing asexually.

However, my cat has only female sex organs. She reproduces (or would reproduce were it not for an operation about a decade ago removing her pre-emptively from the gene pool) only sexually, and only with another member of the same species with opposite gender.

My cat, however, is related, through a common ancestral species billions of years ago, to the tree.

At this point it becomes apparent that the common ancestor was almost certainly a very simple sexually reproducing multi- or mono-cellular microorganism. Evolutionary development, going from that, would follow two different paths, one leading to plants, which follow a more free-form structure based on seeking the light, and one leading to animals, which rely on fast, intelligently-controlled action to capture food or escape hazards. The distinction, presumably, would be between "hunter" microorganisms and "colony" microorganisms, of the sorts that can be observed in any puddle of pond water with a $50 microscope.

As to question 1, I'm still hoping for an answer to how a multicellular microscopic with differentiated cells/ cell groupings reproduces, and how the transition between homogenous to heterogenous cells/cell groupings occurs.

As to question 3, it is sufficiently answered I think: "the organisms with the beneficial trait also had the neutral trait, and it was distributed in that way" -- it just takes some deeper searching for the benefitial neutral trait and/or confirmation of the absense of better or equal alternatives. (In the case of handedness, presumably a side-effect of a more-benefitial pattern of nerve-wiring combined with the sidedness of the the brain)

Links to information sites would be great, or explanations you typed. Failing that, if you could link me to a site that might have people with the knowledge I'm looking for, that would be good too.

1: What is the process of developing from a monocelular organism to a multicellural microscopic organism, and from there to an organism with various cell cluster specializing on certain activities? What are some examples of species at about this stage? How does a multicellular microscopic organism reproduce?

2: How and why does a species go from bisexual (like plants, and, I presume, the common ancestor between animals and plants) to monosexual?

3: What is the evolutionary cause of the predominance of certain aspects of individuals that appear to have no benefit whatsoever--for instance right-handedness?

1: The best explanation that I've heard comes from a Zoobook: early cells divided, but some divided incompletely, remaining stuck together but each containing the same components. These groups were larger and therefore harder to eat, so they multiplied. Eventually once simple multicellular organisms those cells nearer food got more adept at processing it and those farther away got more adept at channeling it.

2. Plants are not really a good example of what you're talking about because they do have differentiation, just within themselves. Sex was an early invention used to increase diversity that probably came from some method of exchanging genes to improve individuals, but I don't know when sexual differentiation started.

3. Why is there more right handedness than left? Why is there more black hairedness than blonde? There are probably two answers to this: first, certain traits are simply recessive or dominant. Second, there was probably some degree of sexual selection involved (something on the order of: uses different hand. Strange.)