A test for claimed knowledge of how macroevolution occurs

Rule 10. The sincerely held beliefs of other members deserve your respect. Please keep discussion civil. Argue the position, not the person. The question is whether or not you can provide an example of the kind of post you want to read. It's your choice.Enjoy

Let's start again, but with the basics... First off let's take a standard scientific definition of Macroevolution:

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Macroevolution is evolution on a grand scale ” what we see when we look at the over-arching history of life: stability, change, lineages arising, and extinction.

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Here, you can examine the patterns of macroevolution in evolutionary history and find out how scientists investigate deep history.

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It is the study of the natural history of life over many generations, the long term results of individual populations evolving (by microevolution) generation after generation after generation, accumulating changes in traits over time.There are 4 basic Patterns in macroevolution that result from continued (micro)evolution and all have been observed:

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You can think of patterns as "what happened when." All of the changes, diversifications, and extinctions that happened over the course of life's history are the patterns of macroevolution.

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However, beyond the details of individual past events ” such as, when the beetle radiation began or what the first flowers looked like ” biologists are interested in general patterns that recur across the tree of life:

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1. Stasis: Many lineages on the tree of life exhibit stasis, which just means that they don't change much for a long time, as shown in the figure to the right.
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2. Character change: Lineages can change quickly or slowly. Character change can happen in a single direction, such as evolving additional segments, or it can reverse itself by gaining and then losing segments. Changes can occur within a single lineage or across several lineages. In the figure to the right, lineage A changes rapidly but in no particular direction. Lineage B shows slower, directional change.
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   Trilobites, animals in the same clade as modern insects and crustaceans, lived over 300 million years ago. As shown below, their fossil record clearly suggests that several lineages underwent similar increases in segment number over the course of millions of years.
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3. Lineage-splitting (or speciation): Patterns of lineage-splitting can be identified by constructing and examining a phylogeny. The phylogeny might reveal that a particular lineage has undergone unusually frequent lineage-splitting, generating a "bushy" tuft of branches on the tree (Clade A, below). It might reveal that a lineage has an unusually low rate of lineage-splitting, represented by a long branch with very few twigs coming off (Clade B, below). Or it might reveal that several lineages experienced a burst of lineage-splitting at the same time (Clade C, below).
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4. Extinction: Extinction is extremely important in the history of life. It can be a frequent or rare event within a lineage, or it can occur simultaneously across many lineages (mass extinction). Every lineage has some chance of becoming extinct, and overwhelmingly, species have ended up in the losing slots on this roulette wheel: over 99% of the species that have ever lived on Earth have gone extinct. In this diagram, a mass extinction cuts short the lifetimes of many species, and only three survive.

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+ Note that #2 - Character change - shows two variations on anagenesis (blue and red lineages) and that #3 - Lineage-splitting (or speciation) - shows cladogenesis with daugher-clades nested inside parent clades. /+(Micro)evolution in isolated populations diverges over time due to mutations and genetic drift, resulting in both anagenesis and cladogenesis. The speciation events occur within clades forming a branching pattern with nested hierarchies, as seen in 3 above.So the next questions are what is speciation, how do speciation events it occur and how frequent are they?See Population Dynamics - the math behind the evolution of species, which I'll cover in the next reply.EnjoyEdited by RAZD, : + clrty

Having covered the scientific definition of macroevolution in Message 772, involving anagenesis, cladogenesis, genetic drift, basic microevolution effects over multiple generations. Now let's look at speciation, what it is and how it happens.Speciation occurs when two reproductively isolated daughter populations diverge over time until they are sexually incompatible.From Population Dynamics - the math behind the evolution of species, Message 6

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THE BASIC MODEL

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The central assumption of the DOBZHANSKY-MULLER model of speciation is that alleles cause no sterility or inviability on their normal “pure species” genetic background. Instead, an allele can lower fitness only when brought together with genes from another species. Any particular hybrid incompatibility might cause partial or complete hybrid sterility or inviability. For most of this paper, I assume that hybrid incompatibilties involve interactions between pairs of genes, as in DOBZHANSKY and MULLER’S verbal models. Later, I consider three-locus and higher interactions. I also assume that multiple substitutions do not occur at the same locus, an assumption that is reasonable during the early divergence of taxa. I assume nothing about the evolutionary causes of substitutions. The DOBZHANSKY-MULLER model of speciation requires only that substitutions occur and assumes nothing about whether they are brought about by natural selection or genetic drift.

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Because I consider the cumulative effects of interactions between many loci -- which quickly gets complicated -- it is useful to picture this process diagramatically. Figure 1 offers a simple way to picture the accumulation of complementary genes between two haploid populations. Each of the two heavy lines represents a lineage descended from a common ancestor. The two allopatric populations begin with identical “ancestral” lowercase genotypes at all loci (a b c . . .). Time runs upward, with the first substitution occurring at the a locus, the second at the b locus and so on.

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The first substitution involves the replacement of the a allele by the A allele in population 1 (uppercase letters indicate only that an allele is “derived”; no dominance is implied). The A allele cannot cause any hybrid sterility or inviability: because A is obviously compatible with the genetic background of population 1, it must be compatible with the identical background of population 2. The second substitution, at the B locus (in population 2), could be incompatible with only one locus: A, as the B allele has not been “tested” for compatibility with A. The third substitution, at C, could be incompatible with the B or a alleles. As we continue this process, it is clear that we can identify all possible (i.e., evolutionarily allowed) incompatibilities by drawing an arrow from each derived allele to each “earlier” (lower) allele carried by the other species. Thus D can be incompatible with c, B, and a. This arrow-drawing device will repeatedly prove useful.

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Several other less trivial facts also emerge from Figure 1:

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• All incompatibilities are asymmetric. For example, although B might be incompatible with A, b cannot be incompatible with a.
• Evolutionarily derived (uppercase) alleles are involved in more potential incompatibilities than ancestral (lowercase) alleles.
• Later substitutions cause more possible incompatibilities than earlier ones (e.g., although the substitution of B produces one possible incompatibility, the later substitution of D produces three). This suggests that the strength of reproductive isolation might increase faster than linearly with time.

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Note that this means that ancestral (lowercase) alleles cannot on their own cause speciation, and that at least two derived/mutated (uppercase) alleles are needed to cause reproductive incompatibilities.From Population Dynamics - the math behind the evolution of species, Message 7

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THE RATE OF SPECIATION

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Later substitutions cause more potential incompatibilities than earlier ones (Figure 1). As already noted, the first substitution at the A locus cannot cause any hybrid incompatibility, while the second substitution could be incompatible with only one locus: the B allele has not been tested with the A allele. In general, the Kth substitution can be incompatible with K-1 loci from the other population. It is obvious, then, that the total number of incompatibilities separating two taxa increases faster than linearly with the number of substitutions that have occurred between them. This, in turn, implies that the strength of reproductive isolation -- or the probability of speciation -- between two taxa increases faster than linearly with time. This important effect is easily quantified. I consider two cases. First, I assume that complete reproductive isolation results from a single incompatibility between two complementary genes. Second, I assume that reproductive isolation results from the cumulative effects of many small incompatibilities. As we will see, both cases yield similar results.

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Considering the cumulative effects of all K substitutions,

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where L is the strength of reproductive isolation (or the fitness “load” among hybrids due to complementary gene interactions). Thus, early in the divergence of two taxa (L << l), the strength of reproductive isolation increases as the square of the number of substitutions:

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Thus the chance of speciation increases much faster than linearly with K (or time) whether speciation typically results from a very small number of genes of large effect (as in the first model) or a large number of genes of smaller effect (as in the second). The number of substitutions having a substantial effect on reproductive isolation also increases faster than linearly with time. Thus, if one were to double the time since divergence, one would more than double the number of genes having a large effect on hybrid fitness. ...

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The role of early vs. late substitutions: The above discussion might seem to imply that a gene of known large effect on hybrid fitness was more likely a later than earlier substitution. This is incorrect. Although the probability that a substitution causes hybrid sterility or inviability increases with time, any gene afflicting hybrids is just as likely to have been the first gene to diverge as the last. This is because a late diverging gene must be incompatible with something, in particular with some locus that diverged earlier.

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The bottom line is that speciation is caused by multiple (at least 2) mutations, and the longer populations are isolated the higher is the probability that incompatible mutations or mutation combinations arise in either of the daughter populations.

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These incompatibilities need not be enough to cause speciation on their own, and it may take several mildly incompatible mutations to build up to the point of speciation, but the probability increases with the square of the number of mutations. The longer population are isolated the more probable incompatibilities will arise.This tells us how speciation occurs. This causes the nested hierarchies of species, as predicted by the ToE.Enjoy.Edited by RAZD, : No reason given.

This confusion is all your doing by NOT using the scientific definitions for the scientific terms. ++ If I were you I would stick to "kind" and define that for how you want to use it.+ I think we can assume that meddle was using the scientific definition, so you only confuse yourself with your non-standard use of the term species.+ We also know, btw, that it takes at least 2 mutations to develop reproductive incompatibilities. Your insistence on ignoring the roll of mutations in the diversification of life on earth is also your loss.+ See Population Dynamics - the math behind the evolution of species, Message 6 and Message 7 which show that it is not possible to develop reproductive incompatibilities without mutations.EnjoyEdited by RAZD, : +Edited by RAZD, : ++

Curious, Faith: Can you define what you mean by this method?Curious.

FWIW, I think you mean ... you wouldn’t expect less variation between humans and chimps than between chimps and gorillas ... ( and not less variation overall).or ... you would expect more variation between humans and chimps than between chimps and gorillas ...Good job.Enjoy