Hows does evolution take place? I understand that its an accumulation of changes to adapt to an environment, but how does it change generation to generation? Is the set of traits that will be passed down to an offspring predetermined or does it change depending on how my environment is? Its seems too fascinating that my environment may change the set of dna that is passed down, or is that not the case?
In: Biology
They start as random mutations in the DNA. The process of copying DNA isn’t perfect, so occasionally mistakes make it in. A lot of these mutations are bad or don’t affect anything, but some them help you survive and make babies. If you get one of these mutations, you’re more likely to pass it down to your children, and they’ll pass it to their children and so on.
Basically, every individual has slight genetical variation compared to its parents. One slight modification, mutation, can sometimes lead to a different caracteristic. Mutations can provide an advantage (e.g make you more robust), be neutral or be disadvantageous (e.g makes you genetically ill). Now the interesting part is that if one individual has a disadvantageous mutation, they will be less likely to transfer this mutation to offspring. Imagine a mutation that makes a rat flashy green : the poor rat will be easily seen and eaten by predation, thus he dies and its mutation as well. On the opposite, a mutation that makes the color of a rat change and that increases its ability to hide will makes it more likely that the rat survives, reproduces, and transmits its mutation. The non-mutant type, with time, would then disappear. This is natural selection. Other type of selection exist, like sexual selection.
The mutations that are transmitted depend of the environment in which they appear. But the mutations themselves do not depend of the environment.
Now you add different evolutive mechanisms like natural selection, you keep in mind that multiple mutations can be selected at the same time, and you remember that this process occurs over the course of hundreds of generations, and you understand how evolution works.
A bug has a hundred children. Some have thicker skeletons, some have thinner skeletons. The ones with thicker skeletons are slower, so they are much more likely to get fly-swatted by angry humans.
So now the thicker-skeletoned bugs are dead and the thinner-skeletoned bugs are alive. They then have whole families themselves, and on average their children will also have thinner skeletons. This repeats generation after generation, with the more successful genes being passed along while the less successful genes die with their host.
Evolution is defined as changes in how often alleles appear in the gene pool. There are five ways this happens. Natural selection, non-random mating, gene flow, genetic drift, and mutations. When a population is reproductively isolated, that is they are no longer interbreeding with other communities of their species, these five ways a gene pool can change will cause their gene pool to drift away from other members of their species. When the accumulated differences in these genes is great enough, the reproductive systems of these species will no longer work together to create viable off spring. This is what we call a “speciation event”, where a new species has derived from the original species.
DNA mutations are at the heart of evolution. That’s how you get variety, and natural selection requires there to be variation in traits among organisms. Mutation is random. Mutation rates can be increased by stresses to the body/cells, but in general DNA mutations will be random and usually have a neutral impact, but occasionally will cause a harmful or beneficial change for the organism. When it DOES result in beneficial traits, it may give the organism a higher chance of having offspring and passing those genes down. The “mutated” DNA will become more prevalent through the population over generations as a result.
The environment can’t change DNA with any “intention” but it can put selective pressure on the variety of life that is currently living there. With competition for resources, organisms with better traits will be more likely to survive, reproduce, and pass down those traits. There is some luck involved too, of course, and “drift” is another mechanism of evolution that accounts for the luck/lottery component of how genes get passed down (for example if a population is small and spread out, luck may play a bigger role in which mating pairs find each other).
The set of genes that will be passed down isn’t really “predetermined”, but environmental stressors can influence which genes are turned on/off. So a gene might become dormant and functionally inactive, and that “on/off setting” can get passed down to the offspring. We’re only just barely starting to understand this process (epigenetics), but it’s a way for traits to change quickly between generations without the actual DNA itself necessarily being altered. Even small tweaks to gene expression can have large effects on how an organism looks/functions.
> but how does it change generation to generation
Randomly. 999,999,999,999 random mutations that happen in a species are either inconsequential or even detrimental. But then one randomly happens that actually gives that animal an advantage. That animal is going to have an easier go of survival, and therefore have an easier time reproducing. If that mutation is hereditary, then its offspring will enjoy the same advantages too. Over a long period of time, across a broad population, the ones with that advantageous gene that gets passed down to them will do better than those who didn’t, and the ones with the gene will eventually be the entire population.
> Is the set of traits that will be passed down to an offspring predetermined
Just straight up dominant and recessive genes just like any other genetic trait.
> does it change depending on how my environment is?
The environment can’t change your DNA. Pollution can *damage* DNA but that’s different. That’s just damage.
> Its seems too fascinating that my environment may change the set of dna that is passed down, or is that not the case?
Not like you’re thinking. No. Why is that tundra full of white rabbits? Well there used to be all kinds of colors of rabbits. All of their fur colors were totally random circumstances of their birth. Well the rabbits that just so happened to have white fur like the snow didn’t get eaten nearly as much so they reproduced more and more compared to the darker rabbits. **The tundra didn’t CHANGE anyone’s fur.** Those who *happened* to have white fur just did better, for obvious reasons. They did better for so long that none of the other colored rabbits are left. They all got eaten faster than they could reproduce.
>Is the set of traits that will be passed down to an offspring predetermined or does it change depending on how my environment is?
These two ideas were actually theories that competed with Darwin’s natural selection! Jean-Baptiste Lamarck suggested that the actions an organism takes during its life introduce new traits in its offspring – that giraffes come from horses stretching their necks out, or that a bodybuilder would have beefier kids because of his bodybuilding. Others believed that change happened through divine direction, or that there was just a natural progression from “primitive” to “advanced” organisms that was built into nature.
No one knew how genes worked back then, and Darwin himself wasn’t able to answer where new traits come from within a population. These two ideas were more popular than natural selection for decades because of that, although we now understand things like mutations and horizontal gene transfer.
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