Evolution Lesson

[tansy]

The simple answer is that members of a species can produce fertile offspring. That's not a perfect definition, though.

Is a mule a separate species because from what I understand they are infertile (at least the male is, though apparently the female mule can occasionally, with difficulty, get pregnant)? From what I read a horse and donkey are separate species, but together produce mules, which are hybrids. So, if not a species, what do they count as?

 

[Speedwell]

Is a mule a separate species because from what I understand they are infertile (at least the male is, though apparently the female mule can occasionally, with difficulty, get pregnant)? From what I read a horse and donkey are separate species, but together produce mules, which are hybrids. So, if not a species, what do they count as?

They're a separate species, but still very close together. They can mate and produce offspring, but the offspring are sterile--a well-known intermediate step in speciation.

The fact of the matter is, that there is no hard, qualitative line between species--just a gradual diversion of type over time.

 

[PsychoSarah]

I didn't learn about evolution at school, so lots of things puzzle me. I do remember at primary school looking at a picture of humans developing from more ape like creatures and gradually becoming upright - and thinking...that is ridiculous! Made no sense to me, but then again I had no explanation as to why that would happen.

That type of diagram specifically is not a good representation of evolution. Heck, a good portion of them even put humans as evolving from chimpanzees, which is incorrect.

But anyhow, one of my questions is, how on earth did different 'sexes' arise? If we all started from single-celled creatures and many creatures like amoeba and spyrogyra just split in two, so to speak, to multiply...well, how did creatures after that start getting male and female organs, not to mention wombs and female breasts or various forms of udders etc, to reproduce and feed their young? I mean, I can't see that there would suddenly be an animal (however 'primitive') suddenly develop a penis and close by, there is one that develops a vagina etc etc etc. So presumably, this would have to develop gradually, but I just don't understand how.

I don't know if you can explain the process in any way?

It is explainable, and actually rather simple. Even today, there are single celled organisms that reproduce both by "splitting into two cells" by themselves, and via sexual reproduction. Many are hermaphrodites entirely, but as can be seen in other species, the split begins with populations having ones that solely produce the "male" gametes (sex cells) mixed in with the hermaphrodites. The benefit of being male is that less energy has to be used up making sex cells, as these individuals only make one type. However, as you might note, the hermaphrodites still exist to keep reproduction going. An example of populations like that are certain stages of fern life cycles. Now, with sufficient males in the population, there can be a selective force on the remaining hermaphrodites to dedicate more of their cellular function to the female sex cells rather than making both. But, there is a give and take with that, hence why the mixed hermaphrodite and male populations still exist as well as male and female. With making male gametes, it makes it easier to spread genes without expending the energy of serving as the female, even as a hermaphrodite. However, energy is conserved far more with making only one type of sex cell. So, if conditions favor reducing energy consumption, there will be selective pressure for the remaining hermaphrodites to gradually dedicate more and more to making only the female sex cells. If conditions do not favor reducing energy consumption, then the selective pressure will be for them to remain hermaphrodites.

To summarize in brief:
1. Start with asexual reproduction
2. Sexual reproduction with hermaphrodites and asexual reproduction
3. Sexual reproduction with hermaphrodites, asexual reproduction ceases (it's less effective at producing healthy offspring, but more reliable at allowing survival when very few individuals remain in a population, hence why many organisms still use asexual reproduction)
4. Sexual reproduction with hermaphrodites and males
5. Sexual reproduction with males and females.

 

[PsychoSarah]

You know the 2LOT has zero to do with ToE, right? Right?!

Based on your ignorant comment/question, I'll assume you've never read or studied the laws of thermodynamics, let alone the second one. So here, save yourself some future embarrassment and take a moment to read this:

Second law of thermodynamics - Wikipedia

Hey, no, try at least to be polite.

 

[PsychoSarah]

Sorry Sarah, I bet you were expecting better informed questions, and not the PRATT tripe creationists sites spew.

No, I had no expectations for the quality of the questions. Some people really don't know that much about biology or evolution, others know a bit, and their questions will reflect their knowledge accurately as long as they aren't asking them to be snide. I'd rather you not insult the questions or those asking them. Curiosity is a good thing, and I don't want people to be deterred from asking questions by making them face condescension.

 

[HitchSlap]

Hey, no, try at least to be polite.

Sorry ... I think I've been around too long, and I'm tired of seeing these tired old PRATT's paraded one after the other.

Have at it.

 

[PsychoSarah]

How did new biochemical pathways, which involve multiple enzymes working together in sequence, originate?

That's getting more into abiogenesis than evolution, which only works with existing life. However, existing biochemical pathways are often altered with genetic mutation. As to how the biochemical pathways originated, I can speculate, but the understanding of that is far lesser than the knowledge of how existing life changes over time in a population over generations.

Many proteins and most if not all amino acids are molecules that are generated in nature without any influence from life, so the first enzymes used in these processes weren't generated by the proto-cells that were the precursors to living cells. Rather, they got caught in the cell membranes (a structure of cells that can easily form; you can do it yourself by mixing oil in water and shaking it up a bit, something that currents and undersea vents would do in nature) or caught inside of them. While DNA controls the generation of enzymes and proteins, that is all it does; they perform their various functions with no other input. The oil bubbles that caught proteins that aided in their continued existence and helped them reproduce succeeded, while the remainder eventually fell apart.

You could also take into consideration early DNA molecules, and that those which directed the production of helpful proteins would also persist better than those that did not. With free flowing amino acids all over, and simpler membranes, they wouldn't have to produce the building blocks of proteins, just the proteins themselves. Which is a very slow process without a metabolism, which is why it took hundreds of millions of years for even simple life to form on this planet.

Charles Darwin admitted that the available fossil evidence didn’t support his theory of evolution. But he expected that plenty of evidence would be found in the coming years. Now, more than a century and a half later, the evidence still fails to support his theory. Where are the, expected, countless millions of transitional fossils?

Every fossil is transitional, because evolution is a continuous process. Your generation is among many generations that transition from human to some future species. Due to the rarity of fossils, it is uncommon to see species to species transitions represented in them, but genus to genus and on higher orders of classification are very common.

 

[PsychoSarah]

Is a mule a separate species because from what I understand they are infertile (at least the male is, though apparently the female mule can occasionally, with difficulty, get pregnant)? From what I read a horse and donkey are separate species, but together produce mules, which are hybrids. So, if not a species, what do they count as?

Mules themselves are considered species hybrids, and are not functional as a species in their own right.

This classification remains for all species hybrids, even ones that can breed, because they aren't true-breeding for the hybrid traits.

 

[Loudmouth]

Is a mule a separate species because from what I understand they are infertile (at least the male is, though apparently the female mule can occasionally, with difficulty, get pregnant)? From what I read a horse and donkey are separate species, but together produce mules, which are hybrids. So, if not a species, what do they count as?

They count as hybrids.

 

[John Hyperspace]

Their fossils though tell us enough that we know they're different enough to be separate species for the purposes of classification.

There's the problem. You say "different enough to be separate species" like your use of the word "species" in that statement has meaning, but since your definition of "species" has nothing to do with "appearances" and everything to do with "fertile offspring": you're using a word with no inherent contextual meaning like it has meaning. What you're actually wanting to say is "we define a species by the way it looks" or "species is based on a system of morphology", true? Because clearly we don't know anything about the biology of fossils let alone the fertility of the offspring.

 

[John Hyperspace]

It gets even worse

True that.

 

[PsychoSarah]

True that.

That wasn't even the full sentence.

 

[Loudmouth]

There's the problem. You say "different enough to be separate species" like your use of the word "species" in that statement has meaning, but since your definition of "species" has nothing to do with "appearances" and everything to do with "fertile offspring": you're using a word with no inherent contextual meaning like it has meaning. What you're actually wanting to say is "we define a species by the way it looks" or "species is based on a system of morphology", true? Because clearly we don't know anything about the biology of fossils let alone the fertility of the offspring.

Morphological differences are used in the context of fossil species.

Gene flow is used to determine species boundaries in the context of living sexual species.

Function and morphology are used to determine species in the context of asexual species.

The fact that biology doesn't fit into neat little boxes that humans prefer is not a problem.

 

[PsychoSarah]

There's the problem. You say "different enough to be separate species" like your use of the word "species" in that statement has meaning, but since your definition of "species" has nothing to do with "appearances" and everything to do with "fertile offspring": you're using a word with no inherent contextual meaning like it has meaning. What you're actually wanting to say is "we define a species by the way it looks" or "species is based on a system of morphology", true? Because clearly we don't know anything about the biology of fossils let alone the fertility of the offspring.

Species will have a degree of conformity in their physiology. It's enough to reliably distinguish most fossils from each other, but it can get difficult at times, and lead to arguments.

 

[Loudmouth]

The analogy of language may be useful in this discussion.

Most people agree that the Romance languages arose from an earlier form of Latin. If we start with modern French and trace it back to the Latin, will there be a single generation that started speaking modern French and their parents did not? Of course not. The language changed slowly over time, and there is no objective place in time where everyone was suddenly speaking modern French. There wasn't a generation that was suddenly speaking a different language that their parents didn't recognize.

There is also Italian and Spanish. They also arose from Latin. Today, a native speaker of Italian will have a hard time understanding a native speaker of French. There is almost no information traded between them. However, there probably was a time in the distant past where people from those two regions spoke different dialects, but could still understand each other today. In the same way, an American, Aussie, and Scot can all talk to one another and be understood (mostly). Was there a single minute of time in history where the populations of those two regions could understand each other, and then suddenly not? Of course not. It was a slow process of divergence.

The very same things exist in biology. There isn't an objective point in history where one species becomes another, just as There wasn't a single day in history where people began speaking modern French when no such language existed the day before. Species also slowly diverge from one another. There isn't going to be a single generation event where one species splits into two completely separate populations that can no longer interbreed. There can be a period where there is some interfertility and interbreeding, but that dwindles over time until there is no interbreeding.

The real problem is human bias, where we expect there to be hard lines between species. Biology just doesn't work that way. Due to evolution, there shouldn't be hard lines between closely related species, and there isn't a hard line.

 

[John Hyperspace]

Morphological differences are used in the context of fossil species.

Okay and how do we determine when morphology is a different "species"? Are the criteria of "morphology" a little more precisely defined? Or are we still at vague? In other words, how are we determining that a change from one species to another (in the past) is actually taking place?

The fact that biology doesn't fit into neat little boxes that humans prefer is not a problem.

Talking about "species" with a vague definition of "species" is a problem. The first step in any form of meaningful communication is to properly define the terms so we know what we're actually saying. It doesn't appear that we can actually talk about "species" with any meaningful logical ability. Is there any other science that has this much problem defining the terms?

 

[John Hyperspace]

Species will have a degree of conformity in their physiology. It's enough to reliably distinguish most fossils from each other, but it can get difficult at times, and lead to arguments.

Okay I get that morphology can distinguish between a small many armed thing and a large biped. But how do we determine when a species has actually changed into another species? Since morphology is defined by what criteria? In other words, if I look at two biped fossils, how do I determine if they are the same species, or, different species? If you say "This one evolved from that one" I ask "Based on what criteria do you claim this?"

 

[PsychoSarah]

Okay and how do we determine when morphology is a different "species"? Are the criteria of "morphology" a little more precisely defined? Or are we still at vague? In other words, how are we determining that a change from one species to another (in the past) is actually taking place?

One of the interesting benefits of fossils being rare is that they normally depict species that are thousands of years apart or more, so the morphological differences even between "closely" related species in the fossil record can be easily seen through side-by-side comparison. So much so, that teeth or a part of a skull is usually enough to at least get to the genus level, if there are other fossils of that species already found. When you have very few pieces to start with, they can be kept in categorical limbo until enough are found to make a classification.

Talking about "species" with a vague definition of "species" is a problem. The first step in any form of meaningful communication is to properly define the terms so we know what we're actually saying. It doesn't appear that we can actually talk about "species" with any meaningful logical ability. Is there any other science that has this much problem defining the terms?

Psychology.

 

[Loudmouth]

Okay and how do we determine when morphology is a different "species"?

Usually through statistical tests such as means, standard deviations, and multivariate analyses. They use physical measurements of bones and muscle placements in order to have concrete numbers to work with.

In other words, how are we determining that a change from one species to another (in the past) is actually taking place?

You can't, unless you can extract DNA from the fossils. Only DNA can give you direct evidence of ancestry and relatedness.

What we can do is test hypotheses. If humans and apes share a common ancestor, and humans evolved from that shared ape ancestor, what should we see in the fossil record? At some point in the last 5-7 million years there should have been individuals that had a mixture of more basal ape features and more modern human features. We can then look in the fossil record to see if those fossils exist, and they do.

Talking about "species" with a vague definition of "species" is a problem.

The terms "young" and "old" are vague terms, but you can still arbitrarily define young to be below 40 and old to be over 40. As long as you define your terms for a specific case and context, then it isn't a problem.

Scientists do the same thing for fossils. They set out a specific description of what features a fossil species has. They then look at each new fossil and see if it fits that defined description.

It doesn't appear that we can actually talk about "species" with any meaningful logical ability.

We absolutely can talk about species. We just need to agree to a specific definition in each case.

 

[Loudmouth]

Okay I get that morphology can distinguish between a small many armed thing and a large biped. But how do we determine when a species has actually changed into another species?

How do we determine when someone has changed from being young to being old? Is there an exact microsecond in their life when they stop being young and become old, and is this change objective and easily identifiable?