Evolution Lesson

[PsychoSarah]

No I'm not embarrassed at all, exposing the equivocation fallacy at the heart of Darwinian presuppositional logic is a reasonable first step.

Save it for another thread; this is for people curious about aspects of evolution and biology as a whole, not a place to debate.

 

[PsychoSarah]

Darwin found the definition of species elusive but that's really an ongoing issue for taxonomy. The Troglodytes and Bonobos can still interbreed but they are still distinct species.

Uh... you wouldn't refer to Homo sapiens as just "sapiens", so don't refer to Pan troglodytes as just "troglodytes". And if you are going to try to refer to chimpanzees using taxonomy, you should refer to bonobos using taxonomy too. Though I can't fathom why you wouldn't just use their common names. The reason you can't just refer to a species without its genus name too is because entirely different organisms can have the same species name if they aren't in the same genus. For example, the Eurasian wren's taxonomic name is Troglodytes troglodytes.

I've always thought it wasn't so much arbitrary as it was a matter of convenience. Maybe the Dewey decimal system works fine in most Libraries but I've found some of my favorite books in some odd places. I found Zen and the Art of Motorcycle Maintenance in the travel section once.

For the term "species" to be useful, it actually can't be the same for every Kingdom of organism. It's an entirely different definition when applied to bacteria than when applied to plants, for example.

 

[mark kennedy]

Uh... you wouldn't refer to Homo sapiens as just "sapiens", so don't refer to Pan troglodytes as just "troglodytes". And if you are going to try to refer to chimpanzees using taxonomy, you should refer to bonobos using taxonomy too. Though I can't fathom why you wouldn't just use their common names. The reason you can't just refer to a species without its genus name too is because entirely different organisms can have the same species name if they aren't in the same genus. For example, the Eurasian wren's taxonomic name is Troglodytes troglodytes.

My point was there are two species, yet they can still interbreed.

For the term "species" to be useful, it actually can't be the same for every Kingdom of organism. It's an entirely different definition when applied to bacteria than when applied to plants, for example.

Taxonomy is organized largely for convenience.

 

[PsychoSarah]

My point was there are two species, yet they can still interbreed.

Being able to interbreed is not the only measure for if two different populations are the same species. Such is why horses, donkeys, and zebras are not the same species, nor are tigers and lions. For example, barriers to reproduction, such as the river that separates bonobos from chimpanzees and keeps the populations from intermingling, are also kept in consideration. Basically, although bonobos and chimpanzees are capable of interbreeding, this is rare in the wild, and they are genetically distinct enough from one another to warrant being labelled as different species.

Taxonomy is organized largely for convenience.

Absolutely, with guidelines, otherwise it'd be entirely pointless. Unfortunately, life rarely fits into the neat little boxes we try to make for it, making taxonomy one of the most continuously contested and debated aspects of biology.

 

[xianghua]

Because it's the only explanation for the lifeforms that we know exist, and there is nothing to suggest that it's wrong.

are you sure? have you heard about the flafellum motor?:

 

[mark kennedy]

Being able to interbreed is not the only measure for if two different populations are the same species. Such is why horses, donkeys, and zebras are not the same species, nor are tigers and lions. For example, barriers to reproduction, such as the river that separates bonobos from chimpanzees and keeps the populations from intermingling, are also kept in consideration. Basically, although bonobos and chimpanzees are capable of interbreeding, this is rare in the wild, and they are genetically distinct enough from one another to warrant being labelled as different species.



Absolutely, with guidelines, otherwise it'd be entirely pointless. Unfortunately, life rarely fits into the neat little boxes we try to make for it, making taxonomy one of the most continuously contested and debated aspects of biology.

I found a brief article on the offspring of a female grizzly and a male polar bear. You would think as distinct as those two species that couldn't happen.

 

[Shemjaza]

I found a brief article on the offspring of a female grizzly and a male polar bear. You would think as distinct as those two species that couldn't happen.

The various bear species are very closely related. Both genetics and structure of their bodies show that polar bears, brown and grizzly bears have been separate for a similar time to humans and Neanderthals. (Similar circumstances too, populations isolated and some needing to adapt to a cold environment).

 

[Ophiolite]

I found a brief article on the offspring of a female grizzly and a male polar bear. You would think as distinct as those two species that couldn't happen.

Correction: you would think that it couldn't happen. I would not. I would be interested. I would reflect on the nature of species classification as more a matter of convenience than reality. Convenience, that is, both for nature and the taxonomist. But, no I wouldn't think it couldn't happen.

 

[PsychoSarah]

I found a brief article on the offspring of a female grizzly and a male polar bear. You would think as distinct as those two species that couldn't happen.

Here's a far more extreme one: all members of the genus Nepenthes are physically capable of cross-breeding, they are generally separated physically by distance to much to make but a few hybrids exceedingly rare in nature. People like myself that grow them as a hobby certainly enjoy making our own hybrids of them.

And don't even get me started on orchid hybridization.

 

[pat34lee]

Evolution isn't "truth". That's the sort of verbiage philosophers and theologians love, but it's meaningless in a scientific discussion. Evolution is a fact. The theory of evolution explains that fact. You may not like this. You may reject this. But your thoughts and feelings on the subject won't change this.

You're mixing up facts, theories and conclusions. Evolution is not a fact. Fact: grass is green. glass is transparent. Evolution is an extrapolation of facts and theories. You see A and B and conclude C. The problem is, A and B are unrelated.

 

[pat34lee]

Since your question doesn't ask about an aspect of biology or evolution in a specific way (example: what is natural selection and how does it work?), I feel no need to answer that. I answer that question in literally every other thread under this subforum that I participate in.

Maybe this question will be more pertinent. Science has supposedly calculated the number of mutations necessary to go back from man to the nearest simian ancestor. How can that number of mutations be broken down into individual changes, such as the restructured pelvis, vocal cords, feet instead of grasping paws, lack of fur, intelligence, self-awareness, language, etc? I think they would fall far short of the number necessary only through haphazard changes to DNA.

 

[pat34lee]

PsychoSarah,

This is sort of a "What am I missing?" question. I will not debate any answer.

Evolution depends on changes to DNA to move forward. The problem is, a program can only work within its hardware. Think of all the computer systems in different fields. Computer-run robots build cars, cars use computers to run more efficiently, cell phones use computers, probably thousands of discrete devices today are run by or with computers. Now, when you break down the programs, they are mostly very similar, no matter what function they serve. So, what changes? The hardware that decodes the software. I could upload a program made for controlling a robot to a different type of robot. It may even do something, but the chances are that it would crash and possibly damage or destroy the robot (depends on built-in safeties).

In living beings, that means changing the DNA wouldn't give anything that wasn't there to begin. You have to change the hardware to accept new commands, and to create new templates to build by. Templates, as every cell's DNA has a full plan of the organism it represents, whether bacterium or man. Otherwise, you could never get from a single fertilized cell to a complex organism.

 

[USincognito]

You're mixing up facts, theories and conclusions.

Actually, I'm not the one mixing them up. I actually know what I'm talking about.

 

[PsychoSarah]

Maybe this question will be more pertinent. Science has supposedly calculated the number of mutations necessary to go back from man to the nearest simian ancestor. How can that number of mutations be broken down into individual changes, such as the restructured pelvis, vocal cords, feet instead of grasping paws, lack of fur, intelligence, self-awareness, language, etc? I think they would fall far short of the number necessary only through haphazard changes to DNA.

First off, "simian" can refer to apes or monkeys, so I don't know what ancestor you are trying to refer to. As far as mutations being broken down into individual changes in physiology, remember that it is entire populations that evolve, not individuals. However, I'll try to answer your question to the best of my ability regardless.

So, to begin with, you have fundamentally misunderstood what "science has supposedly calculated". It's an approximation of a likely evolutionary path. We can't quantify the number of mutations between us and, say, Homo habilis, because we don't have access to Homo habilis DNA and thus we can't determine how genetically distant that species is from our own. In fact, any claim that the fossil species we discover are definitively ancestral to us is flat out wrong. Without DNA, we'd never be able to know that for sure.

What we can do is distinguish the physical traits and genes we do and don't share with other modern ape species besides ourselves, and give approximations as to how long ago our evolutionary paths split. Remember, chimpanzees are our evolutionary cousins; we didn't evolve from chimpanzees. Basically, the traits we do share existed prior to the evolutionary split, such as the fact that humans and chimps have the same blood types. The ones we don't came after. Since we know the average mutation rates in apes, and we know the modern similarities and differences, we can roughly calculated how long ago the split was mathematically. That is, we start out knowing how many sequences in our DNA are shared between us and our closest modern relatives (bonobos and chimpanzees) and work backwards to find the time. So, the difference between human and chimp DNA is about 1.2%. For simplicity sake, I am going to use the number of base pairs in human DNA for calculations (3 billion) and the low end for the average number of mutations per person that is born (40). Multiplying 3 billion by 0.012 (1.2%) makes for approximately 36,000,000 differences in the base pairs. Divide that by 40, and I get 900,000 individuals as the minimum to be born for humans and chimps to diverge (obviously, more individuals were born than that and this isn't all in one generation). So, let me be very cynical, and say that each of those individuals represents an entire generation, and that each generation is 15 years apart. My result is that human and chimpanzee evolution diverged about 13.5 million years ago.Now I'll use Google to check the actual estimate for that... 12.1 million years ago. Not too bad, considering that I purposely used worst case scenarios.

As for self-awareness, uh, humans and chimps share that trait. In fact, all apes are self-aware, as well as dolphins, many birds, and elephants, to name a few. And even bees and ants have language. How we utilize these aspects is a matter of our intelligence. What makes our minds so advanced compared to a chimpanzee? Not much, it's mostly a matter of size, since chimps share most of the same brain structures as us. You can attribute most of that difference to the fact that there are 2 groups of genes which serve functions in other apes, but have mutations in humans that leave them non-functional. 1 group of genes functions for the generation of a muscle that attaches to the skull and jaw (and has the secondary effect of restricting the expansion of the skull and brain case, limiting the size it can achieve). The other group of genes are regulatory genes for brain cell division and growth. And that's about it. Some broken genes made our jaws weaker but gave our skulls more room to grow, and other broken genes caused our brain tissue to grow and divide at ridiculous rates; almost cancerous rates, which is why we are so much more prone to brain cancers than other apes.

Addressing the other traits you mentioned, they vary from just a few mutations to dozens, and mutations often impact more than one part of the body, so there is overlap. Furthermore, while mutations are mostly random, natural selection is not. Individuals with traits that help them survive and reproduce will pass those traits down to the next generation, and those that have traits that kill them or significantly reduce reproductive success will not contribute so much to the next generation. Intelligence is such a beneficial trait to survival that our increased cancer risk and weak jaws don't outweigh it. Walking upright and having the hands freed up to manipulate objects is such a beneficial trait that the fact that this method of locomotion wears our bodies down and inflicts us with back pain and spinal problems doesn't outweigh it.

 

[xianghua]

. For simplicity sake, I am going to use the number of base pairs in human DNA for calculations (3 billion) and the low end for the average number of mutations per person that is born (40). Multiplying 3 billion by 0.012 (1.2%) makes for approximately 36,000,000 differences in the base pairs. Divide that by 40, and I get 900,000 individuals as the minimum to be born for humans and chimps to diverge (obviously, more individuals were born than that and this isn't all in one generation). So, let me be very cynical, and say that each of those individuals represents an entire generation, and that each generation is 15 years apart. My result is that human and chimpanzee evolution diverged about 13.5 million years ago.Now I'll use Google to check the actual estimate for that... 12.1 million years ago. Not too bad, considering that I purposely used worst case scenarios.

lets try to do that with the lung fish- coelacanth molecular clock. they both split of about 400my. lets say that every species add about 100 new mutations to the genome per generation. if a generation is about 10 years then we are talking about 40 milion generations*100 new mutations=4 bilion bases difference for each lineage. if those numbers are true then they should be different in about 75% of their genome. but actually they are very similar and belong to the same group (lobe-fins fishes).

 

[pitabread]

if those numbers are true then they should be different in about 75% of their genome. but actually they are very similar and belong to the same group (lobe-fins fishes).

Two things :

1) There is discordance between changes to genotype and phenotype. IOW, you can have lots of changes to a genome with minimal changes to the phenotype and vise-versa.

2) You also have to take into selective pressures and environment. Ultimately evolution is about adapting organisms in response to environmental change; in some cases this could mean few changes to the phenotype.

 

[PsychoSarah]

lets try to do that with the lung fish- coelacanth molecular clock. they both split of about 400my. lets say that every species add about 100 new mutations to the genome per generation. if a generation is about 10 years then we are talking about 40 milion generations*100 new mutations=4 bilion bases difference for each lineage. if those numbers are true then they should be different in about 75% of their genome. but actually they are very similar.

Just so you know, mutation increases in populations are not all the same... or linear. Basically, natural selection plays a role in the future genetic diversity of a species to an extreme extent. If a species has been in a relatively consistent environment, adapted to it over the course of millions upon millions of years without significant selective pressures for change, it won't change very much, because it is already as biologically suited to its environment as it's going to get.

Human evolution is a good example of an evolutionary speed run; how fast evolution can be in a land mammal. Although we take a long time to mature and have offspring, since we care for our offspring, they have far higher survival rates than the hundreds of eggs fish might lay at a time. Furthermore, we are a fairly recent species, so we aren't heavily adapted to any specific environment, making natural selection pressures very high between modern humans and the point at which the lineage of human and chimp diverged.

However, coelacanths and lungfish are derived from ancient species, and the respective environments they have adapted to haven't changed all that much, despite hundreds of millions of years passing. Basically, they've adapted to their respective environmental niche about as far as it can go, so for them, practically all further mutations that impact physiology are going to negatively impact their survival. Unless their environment changes in such a way that change in coelacanth biology will start to become advantageous or even necessary to avoid extinction, they just aren't going to change much.

In summary, if a specific set of adaptations remains that which is best suited to an unchanging environment, then selective pressures dictate favoring no change over any change, causing the buildup of mutations to slow to a crawl. It's also worth noting that organisms that live underwater regularly have slower mutation rates than organisms on land.

 

[xianghua]

Just so you know, mutation increases in populations are not all the same... or linear. Basically, natural selection plays a role in the future genetic diversity of a species to an extreme extent. If a species has been in a relatively consistent environment, adapted to it over the course of millions upon millions of years without significant selective pressures for change, it won't change very much, because it is already as biologically suited to its environment as it's going to get.

Human evolution is a good example of an evolutionary speed run; how fast evolution can be in a land mammal. Although we take a long time to mature and have offspring, since we care for our offspring, they have far higher survival rates than the hundreds of eggs fish might lay at a time. Furthermore, we are a fairly recent species, so we aren't heavily adapted to any specific environment, making natural selection pressures very high between modern humans and the point at which the lineage of human and chimp diverged.

However, coelacanths and lungfish are derived from ancient species, and the respective environments they have adapted to haven't changed all that much, despite hundreds of millions of years passing. Basically, they've adapted to their respective environmental niche about as far as it can go, so for them, practically all further mutations that impact physiology are going to negatively impact their survival. Unless their environment changes in such a way that change in coelacanth biology will start to become advantageous or even necessary to avoid extinction, they just aren't going to change much.

In summary, if a specific set of adaptations remains that which is best suited to an unchanging environment, then selective pressures dictate favoring no change over any change, causing the buildup of mutations to slow to a crawl. It's also worth noting that organisms that live underwater regularly have slower mutation rates than organisms on land.

ok. but i actually refer to the genetic level. the genetic level is constant and therefore we can calculate the number of generations since their suppose diverge. do you think that lungfish and coelacanth are only about 25% similar in their genome?

 

[USincognito]

ok. but i actually refer to the genetic level. the genetic level is constant and therefore we can calculate the number of generations since their suppose diverge. do you think that lungfish and coelacanth are only about 25% similar in their genome?

Mutation rates are known to vary by taxa. In the case of sarcopterygians and and their descendants, basal sarcopterygians mutate at a slower rate than terrestrial tetrapods.
The African coelacanth genome provides insights into tetrapod evolution : Nature : Nature Research

 

[PsychoSarah]

ok. but i actually refer to the genetic level. the genetic level is constant and therefore we can calculate the number of generations since their suppose diverge. do you think that lungfish and coelacanth are only about 25% similar in their genome?

No, I don't, however, I fail to find any paper that actually quantifies how genetically similar they are to each other to begin with, so I don't exactly have much to comment on.

Also, I just told you that divergence at a genetic level is NOT constant. As species evolve, their mutation rates can change (which is why humans and chimpanzees don't have the same mutation rates). Furthermore, when selection pressures are such that no change is the most beneficial path for survival, changes on the genetic level will be selected against almost entirely, leaving the population genetics pretty consistent despite the passage of time. Thus why the ancestors of modern sharks from millions of years ago appear so similar to modern sharks, while human ancestors from millions of years ago are highly distinct from modern humans.

In such cases where genetic change is selected against, only neutral mutations that have no impact are liable to be passed down and show a divergence. So, only mutations that keep non-coding areas non-coding, and ones which do not change the effects of coding genes even though they might change a base pair or two, prevail in such circumstances. Evolution doesn't stop, sure, but it slows to such a crawl that a species can remain functionally unchanged for thousands of generations easily.