Why did the amount of tinkering done by evolution decrease?

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RRL
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Why did the amount of tinkering done by evolution decrease?

Post #1

Post by RRL »

For those with a better understanding of evolution than me, why was there a ton of "tinkering" and experimenting before the Cambrian explosion, with strange, nightmarish ocean creatures with 6 eyes on top of their flat heads, but then today, you see relatively stable populations with very little tinkering and experimenting, from humans, to lions, to otters? The chance of a human with 5 arms growing out of their back is astronomically improbable, and yet, if evolution is a blind, tinkering process taking shots in the dark, I don't see any reason why the amount of tinkering it does would slow down. If it tinkered at one point in the past, what is the reason or reasons that the amount of tinkering decreased?

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Re: Why did the amount of tinkering done by evolution decrea

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Post by Divine Insight »

RRL wrote: and yet, if evolution is a blind, tinkering process taking shots in the dark
That's not how evolution works. It may appear to you to be shots in the dark but it's not.

Also you are aware the humans are mammals? Right? So it should come as no surprise that humans are going to have a lot in common with other mammals.

Another thing to consider is that in terms of timelines, mammals, and humans in particular, are extremely recently evolved critters. If you look at the timeline of life on earth as a 24 hour clock.

Image

You can see that humans have only been around for a few seconds. Not a lot of time to evolve in comparison with other critters.

The tinkering that you were referring to would have occurred over several hours on this scale. Humans and mammals simply haven't been around long enough to evolve as diversely.

So it's not that "tinkering" has decreased. It's simply that there hasn't been enough time for tinkering to have occurred in more recently evolved critters like humans.
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Post #3

Post by Difflugia »

Another factor is that, in a nutshell, the Cambrian involved the radiation of species into niches with very low competition. By the end of the Precambrian, shallow areas of the oceans were full of algae waiting to be eaten and a successful survival strategy required nothing more than being able to eat algae that nobody else was eating yet. The "Cambrian explosion" is essentially the period during which slight modifications often resulted in tapping a new source of algae. Are the competition passive filter-feeders? Burrowing or free-swimming gets a new source of food with no competition. By the end of the Cambrian, most of the available niches (the "low-hanging fruit" if you will) were taken. Anything new moving in had to either be better at getting someone else's food or had to eat one of its neighbors. It's not a coincidence that the latter part of the Cambrian is marked by fossils of animals with hard shells.

Fast forward to now, most organisms are really good at what they do because they have to be. Differences from one's parents are more likely to get one eaten than to be a survival advantage.

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Re: Why did the amount of tinkering done by evolution decrea

Post #4

Post by Menotu »

[Replying to post 1 by RRL]

The tinkering timeline you propose seems to be yours alone (at least I haven't seen any evidence to suggest this timeline).
That said, I haven't seen anything saying evolution has to act in a timely fashion as outlined by human beings.
Maybe we're looking for patterns when it's not necessary?

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Tinker's Dam

Post #5

Post by Gracchus »

Consider the coelacanth (Latimeria sps.), living in the abyssal ocean. It has existed virtually unchanged for millions of years. Its environment is very stable, and it has evolved to fit that environment. Any random mutation is likely to make it more unfit, and so be naturally culled, selected out. Thus, the mechanism of evolution, which adjusts species to environment resists "tinkering".
Now, consider a valley into which is introduced a species of small furry mammals. This is a new environment. Suppose it to be cooler than the environment from which they were introduced. There is natural variation in the species. Some have more or less body fat, some have longer or shorter limbs, larger or smaller ears. and thinner or thicker. In the cooler environment, those with longer more gracile limbs, larger ears less body fat, and thinner fur will be selected out, less likely to breed, because they radiate heat more rapidly and so need more food and have to be more active, exposing them more to predation. Soon most of the species have more body fat, shorter, stubbier limbs, and thicker fur. They are noticeably different from their immigrant ancestors.
That's how evolution "tinkers", and why it slows in stable environments.

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Post by Gracchus »

Consider a valley into which is introduced a species of small furry mammals. This is a new environment. Suppose it to be cooler than the environment from which they were introduced. There is natural variation in the species. Some have more or less body fat, some have longer or shorter limbs, larger or smaller ears. and thinner or thicker fur. In the cooler environment, those with longer more gracile limbs, larger ears less body fat, and thinner fur will be selected out, less likely to breed, because they radiate heat more rapidly and so need more food and have to be more active, exposing them more to predation. Soon most of the species have more body fat, shorter, stubbier limbs, and thicker fur. They are noticeably different from their immigrant ancestors. Within a few generations, the species has evolved, become adapted, to a colder environment.

Now, consider the coelacanth (Latimeria sps.), living in the abyssal ocean. It has existed virtually unchanged for millions of years. Its environment is very stable, and it has evolved to fit that environment. Any random mutation is likely to make it more unfit, and so be naturally culled, selected out. Thus, the mechanism of evolution, which adjusts species to environment resists "tinkering".

That's how evolution "tinkers", and why it slows or stops in stable environments.

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Re: Why did the amount of tinkering done by evolution decrea

Post #7

Post by Diagoras »

RRL wrote:... strange, nightmarish ocean creatures with 6 eyes on top of their flat heads...
Did you mean this? It only has five eyes, though - not six.

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Post #8

Post by PeterPan »

Limbs

All mammals and birds have four limbs (if wings are counted as limbs) whereas simpler animals have widely differing numbers of limbs,
even among closely related millipedes.

This is because the limbs of mammals and birds are so complex that it is extremely unlikely for a mammal or bird to simultaneously have a mutation that produces an extra limb and have all the mutations needed to make the limb useful. Whereas simpler animals - especially the animals of the precambrian era - often have a number of similar or identical segments, and it is easy for a mutation to change the number of segments without decreasing fitness.

Symmetry

A complex, bilaterally but not radially symmetric animal cannot have viable radially symmetric offspring. The genetic changes that would cause radial symmetry would turn off the chemical gradient in the embryo that tell cells which side is the front and which side is the back. Cells use this gradient to help them decide which cell type to differentiate into, so without this gradient cells will differentiate into the wrong cell types and the organs will grow in the wrong places.

The first animals to evolve had fewer different cell types than most modern animals, so messing up cell differentiation was less devastating.
Most echinoderms (such as starfish) are radially symmetric. Echinoderms evolved from ancestors that were not radially symmetric. It most be noted, though, that all echinoderm larvae are have bilateral rather than radial symmetry and they later metamorphose into radially symmetric adults.

Competition

Over time, animals become more complex and have developed more specialised body plans. In the Precambrian era an animal with a mutation that made it lose all its legs might have had a small chance of surviving, whereas today any such animal would be unable to compete with all the legless animals that have had millions of years to adapt to being legless.

This is also why animals living on islands can evolve to look quite different from their ancestors rather rapidly, whereas those on continents evolve more slowly. Animals on islands only have to compete with the limited number of species which have managed to reach their island, so with more unfilled niches there is a higher chance of a mutation allowing an animal to fill one of these niches.

Homeobox genes

I was going to add a few paragraphs on homeobox genes but I've run out of time. Homeobox genes specify the basic body plan of an animal, and if there is one piece of advice I would give to anyone seeking to understand evolution it is to learn about homeobox genes.
https://embryo.asu.edu/pages/homeobox-g ... d-homeobox

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Post #9

Post by William »

PeterPan wrote: Limbs

All mammals and birds have four limbs (if wings are counted as limbs) whereas simpler animals have widely differing numbers of limbs,
even among closely related millipedes.

This is because the limbs of mammals and birds are so complex that it is extremely unlikely for a mammal or bird to simultaneously have a mutation that produces an extra limb and have all the mutations needed to make the limb useful. Whereas simpler animals - especially the animals of the precambrian era - often have a number of similar or identical segments, and it is easy for a mutation to change the number of segments without decreasing fitness.

Symmetry

A complex, bilaterally but not radially symmetric animal cannot have viable radially symmetric offspring. The genetic changes that would cause radial symmetry would turn off the chemical gradient in the embryo that tell cells which side is the front and which side is the back. Cells use this gradient to help them decide which cell type to differentiate into, so without this gradient cells will differentiate into the wrong cell types and the organs will grow in the wrong places.

The first animals to evolve had fewer different cell types than most modern animals, so messing up cell differentiation was less devastating.
Most echinoderms (such as starfish) are radially symmetric. Echinoderms evolved from ancestors that were not radially symmetric. It most be noted, though, that all echinoderm larvae are have bilateral rather than radial symmetry and they later metamorphose into radially symmetric adults.

Competition

Over time, animals become more complex and have developed more specialised body plans. In the Precambrian era an animal with a mutation that made it lose all its legs might have had a small chance of surviving, whereas today any such animal would be unable to compete with all the legless animals that have had millions of years to adapt to being legless.

This is also why animals living on islands can evolve to look quite different from their ancestors rather rapidly, whereas those on continents evolve more slowly. Animals on islands only have to compete with the limited number of species which have managed to reach their island, so with more unfilled niches there is a higher chance of a mutation allowing an animal to fill one of these niches.

Homeobox genes

I was going to add a few paragraphs on homeobox genes but I've run out of time. Homeobox genes specify the basic body plan of an animal, and if there is one piece of advice I would give to anyone seeking to understand evolution it is to learn about homeobox genes.
https://embryo.asu.edu/pages/homeobox-g ... d-homeobox

William: It is important to understand that when we place constraints around understanding nature and natural process through use of language, we tend to distort the truth about it.

Removing that distortion allows for us to understand that there is no 'more' or 'less' complex depending on the construct of the thing being examined. Those are simply additional and unnecessary comments/opinions.

Removing those opinions allows for the understanding to increase. There is intelligence behind the process. That is undeniable once the opinions are placed to one side.

Categorizing 'this and that' might aid in formulating understanding of the intricacies of the process.

Such method is unhelpful to understanding if it is then not placed to one side. These are not in fact separate unrelated processes. This is - altogether - one intelligent process.

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Post #10

Post by Difflugia »

William wrote:There is intelligence behind the process. That is undeniable once the opinions are placed to one side.
You haven't supported this and it's not self-evident. So far, it's only undeniable because I don't know from what part of the process you infer the intelligence.

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