The Common Ancestry Thread
by cantleave 271 Replies latest members adult
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still thinking
The view that the zub-zero environment of Siberia would cause animals to evolove to deal with that cold is incorrect then?
My understanding of this, is that you have this the wrong way around. You are still trying to say that the animal evolves to fit the end result.
Cells mutate, some good, some bad. The ones that mutate in a way that help the animal survive in its environment are the ones that are passed on. Because the animal survives...but not only survives, does so in abundance. As cantleave pointed out. If the animal happens to evolve a thicker fur or thicker skin, or the abiltiy to carry more fat...it is THEN able to move into colder harsher environments to take advantage of the food supply there, and the ones that do not evolve these traits cannot. It doesn't change itself specifically to do this. Like there is an unspoken plan. The animal purely takes advantage of the changes that have happened. I'll try to use the giraffe as an example of what I am trying to say (hopefully successfully ). A Giraffe doesn't plan to grow a long neck because it can see that there is an abundance of food in the tops of the tree. That would be planned mutation. Which never occurs. Some girraffes may have slightly longer necks than others. A gene could have mutated which gave the giraffe a slightly longer neck. If the ones with longer necks breed with each other, there is a CHANCE that they will have offspring with still longer necks. This enables the giraffe to reach some of the higher branches in the trees that they couldn't reach before. Maybe food is scarce on the ground and this becomes a real benefit to the giraffe. So having a longer neck becomes genetically appealing to a breeding female. She sees the longer necked male as more attractive now. So he gets to do more breeding than the shorter necked variety. Eventually, the mutations that occured benefit the giraffe because they can now reach a food source they couldn't reach before. They weren't designed to eat from high branches. A combination of mutation and benefit and survival ensured that the giraffes neck became longer and longer until it reached a point where the supply of food (energy) didn't support the neck growing any longer. A fine balance between supply and demand. If the food supply on the ground had been abundant for them they may never have evolved this way, because those genetic changes wouldn't have been appealing for sexual reproduction and survival. Having a long neck could have been a hinderace to the offspring. And the female giraffe could have selected shorter necked males as good breeding specimens. The long neck genes would simply have died out. -
frankiespeakin
climate change + enviroment change + selective mutations that enhance survival = progressive evolution of surviving species
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cantleave
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The organism will use an inherited phenotypic trait to exploit the enivronment. That trait is random, a happy accident as it were, that can be used to provide an advantage. The useful trait is random, It hasn't been designed because of the environment, it just so happens to be useful in that environment.
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jgnat
stillthinking, I would consider that there were giraffes with longer and shorter necks. The long-necked giraffes did better.
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frankiespeakin
Yeah but when the necks of giraffes get too long they might die prematurely before sharing dna so thier must be some optimum limit in this long neck race.
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jgnat
Yeah, frankie. Like the finches I was looking at. Scientists speculated that there was no upper limit to the big-beaked finch, but nature took care of that. The island suffered a drought and the finches with lighter beaks did better. The big beaked finches survived, but it seems to have settled to a size.
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still thinking
stillthinking, I would consider that there were giraffes with longer and shorter necks. The long-necked giraffes did better.
So what happened to the shorter necked giraffes do you think? Were they just bread out? They must have been. If their environment changed and lets say there were no more trees. How would the giraffe fair then? Surly the shorter neck would be more beneficial and sexual attraction would start to include mates with shorter necks so that ground feeding was easier and better for survival. The giraffes neck would either evolve through natural selection...or it would become extinct because it couldn't evolve fast enough.
Yeah but when the necks of giraffes get too long the might die prematurely before sharing dna so their must be some optimum limit in this long neck race.
There is a trade off isn't there? How long is too long and detrimental to survival? Those that are too long simply don't survive.
Just like the gazelle having long thin legs. They help it to run fast and get away from predators. But if they were too long or too thin they would break easily. If their legs are too thin they don't survive to breed. Thus enabling the optimum variety to continue it's species.
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cofty
I wanted to understand a little more about psuedogenes - tornapart
I have writen you some more stuff about pseudogenes you may find helpful.
A pseudogene is simply a gene that doesn't get transcribed. They are bits of code that first appeared in the genomes of our ancestors for a number of possible reasons.
1. Processed Pseudogenes.
A few pages back I posted about retrotransposons which are pieces of text that get themselves copied and pasted back into our genome multiple times. 30% of our 3 billion base pairs consist of these parasitic bits of code and comparisons of these LINES and SINES are used to provide evidence of paternity and of the common ancestry of species.
This malfunctioning of cell replication depends on the enzymes reverse transciptase and integrase. In a similar way these enzymes can act on any RNA transcript including that of a functional gene resulting in additional copies. These gene copies lack the regulatory sequences that signals to the copying mechanism to start transcribing so they are not expressed.
2. Gene Duplication
During the process of meiosis the two copies of each chromosome are reduced to a combined single copy in the making of a sex cell. Sometimes this process goes wrong resulting in the copies of the same gene. According to researchers at the University of Michigan the human genome contains 15 000 duplicate genes - 2/5 of all genes.
3. Redundant Genes
Some of our pseudogenes no longer get transcribed because they are broken. Changes in environment sometimes mean that some genes are no longer important and there is no selection pressure to maintain them. For example we have the genes to produce vitamin C but at least one of those genes is broken. A relic of our distant past. With vitamin C readily available in our environment there was no disadvantage to our ancestors who suffered mutations in these genes.
The insertion of pseudogenes and the precise ways in which they suffer mutations is a random process. There is no reason apart from common ancestry why different species should have the same pseudogenes with identical mutations.
The evidence confirms beautifully the relationships between species that evolution predicted.
Just one specific example illustrate the point.
The steroid 21-hydroxylase pseudogene is shared by humans and primates. It doesn't function in humans because of a deletion of 8 neucleotides - 8 letters of DNA.
When the genome of chimps was examined precisely the same 8 letters were missing in exactly the same location.
Duplicate genes do provide raw material that can prove useful. Later I intend to post about how duplication of the opsin gene resulted in our colour vision.
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still thinking
And speaking of predators and prey...there is a reason both are very fast. Both have evolved to either chase and kill...or run and get away. Without the predator...the gazelle may have had more benefit in some other area of evolution instead of investing so many of its resources in speed. Maybe they would develop long necks if they had time to stand around eating leaves off trees.
It is no coincidence that they have both evolved the ability to run fast. Those that couldn't were eaten. So those that could run fast lived to breed another day passing on those genes to their offspring. So the successful predators in turn also passed on those genes.
Of course some predators just have a burst of speed which can't be maintained. So the smarter ones survived. The ones that figured out how to get close enough to their prey to catch them without running for miles. This was then also passed on to their offspring. The trade off between speed and intelligence is finely tuned in some prey animals. But if their particular food supply changed. They would have to change too. Maybe speed might not be needed. Maybe they would need more smarts. Choosing a mate may no longer include how fast they can run. But how smart they are.
