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Author Topic: What is Darwin’s explanation of how new species arise in simple terms?  (Read 13734 times)

Offline echochartruse

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Populations change over time.  Given enough time and enough pressure (and things like the founder effect/bottleneck effect), these populations will become no longer able to breed with one another.  We then call them new species.

It honestly is that simple.

After looking back over this forum, I find that I am still confused.

The word species is very confusing.

Different species/ populations cant breed together or if they do then they can not reproduce any further. But if they do and their offspring can reproduce then we call it a new species?

My interpretation of 'species' was that each group had different heritage but if we all came from the same single cell .........where did this inability to breed with each different population come into it?
A. afarensis, H. habilis, H. erectus, archaic H. sapiens, Neanderthal man and finally Cro-Magnon or modern man are all varients of the human race or are they labeled by us a different species?
 

Offline BenV

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After looking back over this forum, I find that I am still confused.

The word species is very confusing.

It is!  In my zoology degree we spent weeks discussing the different definitions of "species" and what the implications were.

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Different species/ populations cant breed together or if they do then they can not reproduce any further. But if they do and their offspring can reproduce then we call it a new species?
I think you've pretty much got it, but lets try another example.

There's a species called A.

There are lots of groups of A, living in a field.  A flood creates a river that splits A into two groups, 1 and 2.

This geographical barrier stops the movement of genes from 1 to 2 and vice versa.

Over time, the foundation effect (the fact that 1 and 2 started with slightly different genes),  gene flow, mutations and natural selection (especially if 1 and 2 have different pressures - maybe there's not much food on 1's side, but snakes on 2's side) will alter the DNA of each population.

Given enough generations, it's possible that 1 and 2 will no longer be able to have viable offspring (or may refuse to mate, as maybe the ladies of population 2 are very picky, and will only mate with the males who are best at killing snakes).

By the broadest of definitions, we would now say that 1 and 2 are different species.

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My interpretation of 'species' was that each group had different heritage but if we all came from the same single cell .........where did this inability to breed with each different population come into it?

Not quite the right interpretation of species.  All extant species share some heritage, with varying degrees of separation.
 
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A. afarensis, H. habilis, H. erectus, archaic H. sapiens, Neanderthal man and finally Cro-Magnon or modern man are all varients of the human race or are they labeled by us a different species?

Good question.

The problem here is that we only have fossil data, as only one species of human is extant (so it's not like comparing wolves to dogs, or even grass to wheat).  It's easiest to think of this as the "humanoid" branch of the evolutionary tree.

The evidence for each of these (A. afarensis, H. habilis, H. erectus, archaic H. sapiens,) shows morphological differences between each other - each would seem to be a branch on the tree of which modern homo sapiens sapiens is currently the only twig left.

It's worth having a look at the wikipedia page for human evolution - that gives some timelines and geographical distributions that might help.
 

Offline norcalclimber

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There have been a lot of good answers to this question so far, but I'd like to give a go at it. 

First off I'd like to point out that when people are referring to differing environmental factors between separate populations of the same species, they aren't just referring to things like weather and terrain.  A huge component of the "environment" is the different predators and competitors which geographically separate/genetically isolated populations may have to deal with.

As I understand it, the first component involved in the evolution of a new species, is distance or separation.  A successful species tends to produce more offspring than a particular region can handle.  What ends up happening, is either a predator moves into the area or the offspring migrate.  Often, the migration ends up cutting off the offspring from the original genetic pool.  As different species migrate, they come in contact with other species which they had never encountered before which can be either predator or competitor.  This competition means that certain mutations will be favored over others, and spread throughout the local populations.  When prey mutates better defense, predator then mutates better offense.  Populations of the same species which are cut off from each other genetically are often also subject to vastly different predator/competitor combination's which take them down very different evolutionary paths.  Eventually, the two groups are genetically incompatible and labeled a new species, but eventually often takes thousands if not millions of years.

The speed at which a host organism can evolve into a new species is a direct reflection of the lifespan of each generation.  Since only a few mutations are "allowed" in each new generation, it takes a lot of generations to develop enough differences to prohibit reproduction with the "original" species, as well as the requirement that the two groups are completely isolated from each other.
 

Offline echochartruse

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...................Eventually, the two groups are genetically incompatible and labeled a new species, but eventually often takes thousands if not millions of years.

The speed at which a host organism can evolve into a new species is a direct reflection of the lifespan of each generation.  Since only a few mutations are "allowed" in each new generation, it takes a lot of generations to develop enough differences to prohibit reproduction with the "original" species, as well as the requirement that the two groups are completely isolated from each other.

So basically and not so unscientific as I once thought....Mother Nature, Father Time do have a roll to play in evolution.
 

Offline echochartruse

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Domestic cats are a different species than their wild counterparts, as far as I know.  (Dogs, however, can interbreed with wolves and therefore aren't a separate species.)  Other domesticated animals or plants might be separate species from their wild counterparts as well.
I was told that separate species can't mate but here are a few that seems to have mated.
http://www.messybeast.com/genetics/hybrid-cats.htm

The Savannah Cat is a result of breeding an African Serval with a spotted domestic short hair cat.
the Characat is bred from a Caracal lynx sire and an Abyssinian domestic cat dam.see link above for more.

There's also a new field called synthetic life, where the goal is the creation of life (and new species) by building single-celled organisms in a lab.

WHY?


 

Offline kckuhns

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After reading through this thread, I don't think the original question has been answered specifically. Darwin observed complex behavior and species/sub species differentiation due to environment ,and he described this process as 'natural selection'. He then *inferred* that this process eventually gives rise to new species. He did later work on his 'transmutation of species' again proposing that species mutate over time into new species. I have a general problem with this theory of transmutation.

So, if transmutation is true, then from a critical view, there is a rather fantastic set of events that leads to a new species. We know that species are defined by their DNA that is organized into chunks, chromosomes. The the ape to man jumped happened at some point when a single individual [ape] with 48 chromosomes, mutated to a human having 46 chromosomes. At this point, that particular individual would have no one with whom he/she could successfully mate, so there must have been two...? Adam and Eve..? But a viable population must have more than just a single set of individuals to genetically propagate, it seems to me. So there was this mutation that happened to a whol large group of apes, simultaneously..?

I just don't understand the mechanism of this most necessary mutation that would give rise to speciation.

Anyone able to help me out here?

Kevin

 

Offline norcalclimber

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After reading through this thread, I don't think the original question has been answered specifically. Darwin observed complex behavior and species/sub species differentiation due to environment ,and he described this process as 'natural selection'. He then *inferred* that this process eventually gives rise to new species. He did later work on his 'transmutation of species' again proposing that species mutate over time into new species. I have a general problem with this theory of transmutation.

So, if transmutation is true, then from a critical view, there is a rather fantastic set of events that leads to a new species. We know that species are defined by their DNA that is organized into chunks, chromosomes. The the ape to man jumped happened at some point when a single individual [ape] with 48 chromosomes, mutated to a human having 46 chromosomes. At this point, that particular individual would have no one with whom he/she could successfully mate, so there must have been two...? Adam and Eve..? But a viable population must have more than just a single set of individuals to genetically propagate, it seems to me. So there was this mutation that happened to a whol large group of apes, simultaneously..?

I just don't understand the mechanism of this most necessary mutation that would give rise to speciation.

Anyone able to help me out here?

Kevin



Let me see if I can help here.... First off, humans didn't evolve from apes, rather apes and humans have a common ancestor.  So Humans didn't have to "lose" two chromosomes, it's possible that apes "gained" two chromosomes.  I have had similar issues with the fantastic circumstances required for purely "random" mutations, but I feel that recent science has answered that problem.  We have learned that in order for large phenotypic changes to happen, we actually don't need to have changes to the genome, we can have changes to the epigenome instead.  Epigenomic changes are a direct response to environmental changes, and therefore are present in an entire local population.  I believe these epigenomic changes can eventually become genomic changes, and this is likely to be the foundation for most of the genetic diversity we see on Earth today.  I believe that this probably evolved ~750 million years ago, and that is why we see almost no evolution prior to ~750 million years ago and then all of a sudden thousands of new species evolving at a much faster rate. 

Please see my post here for more detailed information on Epigenetics and what I feel probably happened: http://www.thenakedscientists.com/forum/index.php?topic=30685.0
 

Offline echochartruse

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Ok so I have still some questions and have searched out some answers.

Quote from: http://www.digitaljournal.com/article/263378
The genetics of speciation are extremely difficult to figure out. The reason for that is simple enough. Since speciation means that interbreeding is not possible, it becomes very hard to interbreed the different species an use the findings to determine the speciation genes. That is the opinion of Nitin Phadnis, a geneticist at the Fred Hutchinson Cancer Research Center in Seattle........
"What this work shows you is that speciation can happen not only because of adaptation to the external environment, but also because of adaptation to the internal genomic environment," Phadnis says.

transposable elements are jumping genes. Epigenetics can play a large roll in where abouts your genes sit in relation to your DNA. Previously Junk DNA are now considered TE transposaable elements and is thought to be responsible for our individuality among our group/species.

I have always thought 'random mutation' to be unscientific. Mutations in DNA cause disease.

Quote from: http://www.nature.com/scitable/topicpage/genetic-mutation-1127 
 However, the idea that mutations are random can be regarded as untrue if one considers the fact that not all types of mutations occur with equal probability. Rather, some occur more frequently than others because they are favored by low-level biochemical reactions. These reactions are also the main reason why mutations are an inescapable property of any system that is capable of reproduction  in the real world. Mutation rates are usually very low, and biological systems go to extraordinary lengths to keep them as low as possible, mostly because many mutational effects are harmful........
Finally, still other sources of mutations are the many different types of transposable elements, which are small entities of DNA that possess a mechanism that permits them to move around within the genome. Some of these elements copy and paste themselves into new locations, while others use a cut-and-paste method. Such movements can disrupt existing gene functions (by insertion  in the middle of another gene), activate dormant gene functions (by perfect excision from a gene that was switched off by an earlier insertion), or occasionally lead to the production of new genes (by pasting material from different genes together)......
Many direct and indirect methods have been developed to help estimate rates of different types of mutations in various organisms. The main difficulty in estimating rates of mutation involves the fact that DNA changes are extremely rare events and can only be detected on a background of identical DNA. 

So could the environment cause the shuffling of genes within our DNA (DNA being the store room for information)as well as switching genes on and off and this leads to variations and adaptation, which makes more scense to me than 'random' mutation.

Quote from: http://shapiro.bsd.uchicago.edu/Shapiro_1999_Genetica.pdf
The thrust of this presentation has been to point out how the discovery of transposable elements as agents of genome restructuring has brought the question
of evolutionary change into the realm of cell biology, where regulation and biological information
processing are major factors. We are entering the next century with an increasingly computational view of cells and how they make important decisions. The argument here is that evolutionary change is not exempt from this new perspective. Evidence from a variety of systems indicates that transposable elements can interact in a molecularly plausible way with signal transduction networks, the key information processing entities in the cell. Biological feedback can play a critical role in genomic responses to emergencies (McClintock, 1984). Thus, organisms have a farmore powerful evolutionary potential to generate integrated genomic networks and ensure the survival of
their descendants than predicted by current theories of gradualism and random mutation.
 

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