Beginner question regarding evolution

[Monique]

Yes, if you mate with a wild boar your offspring is going to look like a wild boar!

 

[mitchell porter]

What I cannot grasp is that, let's say, these birds would have very similar beaks. Some would eventually get the "a bit longer beak" trait, but what are the odds of that happening? If mutations vary from a single gene in a cell located in the foot and to an extra limb being attached, what are the odds of getting a beneficial trait? Aren't they extremely small?

It might help to think about how DNA works and why mutations have effects.

DNA is a very long molecule stored in the cell nucleus. Sections of DNA (the genes) get copied and moved out of the nucleus to other parts of the cell, where small molecules called "transfer RNAs" which have amino acids attached to them, line up along the copy of the DNA sequence. This is how proteins are assembled from a DNA blueprint. Those proteins then go and do whatever they're supposed to do.

A mature multicellular organism has the same DNA sequence in every cell, but different cells are expressing different parts of that sequence, and that is why some are brain cells, others are muscle cells, others are blood cells, and so on. There's a genetic cause for everything.

A mutation is a change in the DNA. This can be a small change in one gene that affects the shape and other properties of the protein that it codes for, or it can be a big change like the complete deletion of a gene, or the duplication of a gene. Duplication events are good raw material for evolution because one copy of the gene can mutate while the other copy preserves the original function. Let's say you have a gene that produces an important digestive enzyme. If it mutated you might lose the ability to digest certain substances and that would be bad for your survival prospects. But if the gene is duplicated, now evolution has a chance to experiment on one copy while the other one still keeps you alive.

In the human genome (and other species) there is actually a lot of redundancy, a lot of old genes that are no longer used but not yet completely deleted, and so on. The human body and the genes that build it are extremely intricate, but they are not perfectly streamlined in how they work. It's even likely that the genome has evolved to be a little sloppy, precisely so evolution can occur. Some species mutate much more than others. This has advantages and disadvantages, and comparative advantage is what evolution is all about.

Anyway, what actually happens when a mutation makes a bird with a longer beak? First, the mutation has to happen in a "germ cell", like an egg cell, so the offspring will inherit it and manifest it. The direct cause of the mutation might be a toxic molecule that damages the DNA a little, or it might be a rearrangement or duplication of several genes caused by the machinery that normally copies genes for readout or checks for errors. Some genes contain repetitive subsequences ('repeats'), and if they correspond to protein structure, duplication of repeats can literally change the shape of the protein that the gene produces. That will change the way the protein interacts with other proteins, and ultimately it can add up to a big change of form. For example, if the protein controls how much growth hormone gets produced, a change in the protein may mean that it stimulates the production of growth hormone much more, which in turn means that certain tissues will grow bigger. That is the sort of mutation that produces a longer beak. The size and shape of organs is due to the way that their constituent tissues grow, and that growth consists of cell divisions, and cell divisions are controlled by internal and external signals like the growth hormone, which in the end is just another protein produced from a specific gene or two.

So I'm trying to sketch how it is that a change in the DNA turns into a change in the offspring. You can see variation in human beings all the time - height, weight, strength, as well as less visible qualities like personality, intelligence, or the way you respond to diet and environmental conditions. There is a basic human genetic blueprint, more or less, and then all the individual people are variations on that blueprint. The variations we see are mostly produced by sex, and the way that the child's chromosomes are a mix of the parents'. But maybe you can see how a mutation in that genetic system is not so different to sexual recombination - it's another way of playing with the blueprint. If the variation is really bad, then the fetus won't even develop properly and there will be a natural abortion. But if the mutation is mild enough to lead to an organism that can live and function in the world, then the new quality has a chance to prove itself in the world of survival and reproduction.

There are genes which control really basic things like the number of limbs. Mutations there are responsible for the big changes to what is called the body plan, the general organization of the organism. Again, most mutations like that (two heads, one eye, etc) are simply fatal, or at least not life-enhancing. Nonetheless, the basic supposition is that the history of evolution over *millions* of years consists mostly of small variations on a settled blueprint, with most big mutations being lethal or maladaptive, but very occasionally getting an extra limb, losing a limb, or rearranging a limb really does allow an organism to do something new and useful in its environment, and it's those events which add up to the big differences in the tree of life - between a worm, a fish, a rat and so on.

What I just wrote is not exactly scientific quality discussion, but I hope it conveys some more of the details.

 

[ThomasEdison]

Hi,

I.

Why are the ears on the same spot in almost all human beings? I understand that if the human is too weird looking, he might not be able to get a mate. But a little weirder looks would happen if it would happen randomly, right?


Thanks.

Mutation does happen in humans all of the time and in some very extreme ways (more extreme than missing ears or extra ears (and i'll bet those do happen.))
As far as ears go, a cat was actually born with four ears in Germany and humans would not be a surprise.
http://creation.com/a-cat-with-four-ears-not-nine-lives

We may not call them 'mutations' per se they might even be labeled genetic abnormailities or even birth defects or genetic differences. Perhaps it is only a semantic distinction. In some cases the mutations like the continued lactose digestion for adult humans have great advantages. Not all humans can digest lactose properly but the ability to do so as an adult probably started as mutation. In my opinion it's a very important adaptation considering it relates to the domestication of animals (the start of civilization) Its an adaptation directly relating to technology no different than say the eye or skin changing this century in office workers to better adapt to flourescant light. The point I make though is that not all humans share this trait of lactose digestion and its a major one-- a huge adaptation. We are not as homogenous as we like to assume and that is probably controversial. We are not that different than your scenario where some birds have longer beaks than others within the same species and in the same niche.

A non-harmful mutation as an example:
Blue Eyes.
http://www.sciencedaily.com/releases/2008/01/080130170343.htm


There are even people born without irises. Wiki "Eye color" and you will see some strange variances in eye color like red, no iris (black) etc.
If these differences were considered the height of human attractiveness I don't see why they wouldn't become more common.

I will conjecture that the first Blue eyes ever to appear were considered attractive and thus that trait survived. This is a guess.
In my opinion, whatever strays too far from the norm will be shunned, eye color was simply not a great enough difference for the other people in the village to stake and burn the blues.

I just want to make the point that there is great variety in human beings right now and there are people with unique traits who did not inherit them from their parents (this is alluded to in the cat link) some can appear "out of the blue" (a random mutation never before seen to happen) we could call them errors or mutations but in modern society they are probably just called birth defects.

There was a book in the 1970's called something like "Special People" or something or other (sadly I can not remember it.) Within its pages were many vastly different looking humans from short to tall, thin, wide, extra limbs, missing limbs, hirsuite or without hair, a seemingly endless amount of drastic variation. This still happens with humans today but its important to make the distinction that many of the differences mentioned are inherited (like hirsuitism or the many variations of dwarf) and so they are not mutation at all but some of it is random mutation, at other times it can be from a direct source (a defect from a poison like thalidamide) which does not qualify as random mutation or it could be from a disease which makes a person look different or a behavior (like extreme morbid obesity) not a mutation at all... but this does not mean that drastic human mutations are not out there and there were certainly some in that book.

For an inheritable difference it would be the first occurance ever that I would consider the 'random' mutation not the following generations. Like with blue eyes.


Perhaps I simply should have said: "There are people with random mutations walking about even odd ears."

..whew.

 

[bobze]

Hi,

I stumbled on your website when looking for a good place to ask educated professionals.
I'm 16, I have a question on evolution.

Ok so let's say there are these birds on an island with a food source that require long pecks, but these birds have smaller pecks than needed. So after a long time, I'm not sure to say how long, the birds have developed a longer peck, enabling them to reach the food source.
Now, as I understand, mutations happen every day and most of them are harmless, and some of them don't even matter. Perhaps some small mutation in a stomach cell.
I also recall that mutations happen randomly, and not in any particular part of the body for any animal. Just completely randomly.
So how can these birds develop with themselves this long peck, even if they have millions of years to do it? A single, a single part in their body being transformed beneficially? And how come the animals don't have extremely weird shapes (within each species) if mutations happen completely randomly? Why are the ears on the same spot in almost all human beings? I understand that if the human is too weird looking, he might not be able to get a mate. But a little weirder looks would happen if it would happen randomly, right?

Don't think I'm against evolution, this is just something I can't grasp. I'm a pantheist, so I believe in evolution.
Thanks.

I only skimmed the topic, so if this was addressed (I didn't see it anywhere) then I apologize. However I didn't see anyone mention some very important things for understanding evolution.

First evolution cannot happen to individuals. Evolution is a process which can only happen on populations. Make sure you drill that into yourself when studying biology-Its a very common misconception.

Why?

Because, biological evolution is the change in allele frequencies over time. Individuals are born with a set genes, live with those genes and die with them. Populations however are like shifting clouds of alleles. Over time selection drives this cloud in a direction that best fits the population to their environment.

Think about it as an analogy like this;

Think about a population of organism and all their different alleles for each gene as a cloud, which can represent with a color. Over time, that color gradually shifts reflecting which alleles are passed on more than others.

[PLAIN]http://img641.imageshack.us/img641/9906/genepool.jpg

Another thing I'd like to point out, that seems a very big misconception about evolution is it is not a random process. Often times people that mean well trying to explain it say this, but it is not true. You can't have adaptive evolution that is random-The probabilities involved are staggering.

People tend to misunderstand this because evolution does involve some 'chance', namely mutation. However, who lives and reproduces isn't a random event. Some variants in a population are better suited to a given environment, thus more likely to survive and reproduce.

The next misconception seems to be 'most mutations are harmful'. Again, not true. Most of your genome isn't given to coding DNA (DNA which makes proteins). So mutations in these other areas are largely unnoticeable-That is neutral.

Because multiple codons also code for the same amino acids many times mutations which do change amino acids in proteins are again, neutral.

And only specific parts of proteins play their specific roles in their functions. Changes to amino acids outside of these sites are again, neutral.

In biology we use the term 'fitness' to describe an organisms ability to pass on its genes. Remember that the ability to do so isn't random, in other words its not equiprobable that all males in a generation will sire offspring or that all females in a generation will birth the same number of offspring over their life.

Organisms that are less fit, are 'weeded' out by natural selection and their genes don't make it into the next generation, or maybe make it in a lower proportion.