I don't understand NATURAL SELECTION and EVOLUTION. Biologists...PLEASE EXPLAIN!!! ?

Question

I just got done reading/studying The Cell Theory...and I understood all of that.

Now, I'm reading The Theory of Evolution by Natural Selection ... I looked up the definitions but they're so confusing... Can someone please explain all of this in SIMPLE words or as simply as possible...

thanks... and if you know any websites that might help. = )

Answer 1

Okay this is the version you get in Yr 7, so forgive me if it is a little simplistic.

Natural selection:  There are some traits and mutations which may be benefical to a particular species or population of organisms/animals/people etc.  Some examples of this are colour mutations in moths which make their camoflague more effective (and makes them safer from predators), darker pigmented skin in people who live in more sun exposed climates, a larger proportion of body fat in animals that live in colder climates etc etc etc.  Any trait or mutation can be more desirable...  e.g. sharp claws or teeth, dislocating joints, a big mouth, gills etc etc etc.

Basically certain traits and mutations in particular areas can make survival easier and increase the chance of the organism/animal or person making it to maturity or mating age.  The ones that do not carry these traits may not make it to mating age and as a result there will be less of the genes that carry the less desirable traits in teh mating/gene pool.  This makes it more likely that the desirable traits be passed on and over time this increases until the desirable trait or mutation is the most dominant.

Answer 2

So you have your organism, whose developmental processes (think going from egg to fetus) and adult properties are encoded in DNA.  This DNA, when it changes in sequence in reproductive cells, either harms, helps, or has no effect on the organisms of the next generation.  The majority of harmful changes result in death for an organism before it can reproduce itself.  The majority of the other mutations have no significant short-term benefit or harm.  There are a few kinds of mutations that can really enhance what we call fitness in a short period of time (note 1).  

Now we switch from looking at individual organisms to looking at populations of the same species of organism.  Individuals cannot evolve.  Populations evolve.  

So now you have a group of individuals whose developmental processes and adult properties are encoded in DNA.  This group has a distribution of, let's say arm length, for the sake of argument.  There's a suite of genes and a developmental pathway that cause each individual to develop the same arm, but there must be some differences between the genes of individuals when each does not have the same length arm.  The variation in arm length is a neutral mutation if, over time, the average arm length of the population does not change.  

Let's say, for example, fellows with longer arms of this species have access to more food.  If this advantage allows them to live longer, and if living longer aids their fitness (note 1), then they will have shifted the average arm length in their children's generation.  

Now we switch to looking at the time scale over which these changes result in discernable speciation.  There are two dominant views on this topic:

1. Over a long period of time, through many twists and turns through ecological landscapes, (some of which may favor shorter arms!), and through many mutations, one species may evolve into one or more species. 100s of millions of years

2. Alternatively, over a very short period of time, one species may encounter an environment in which the selection pressures are extremely strong and varied.  These pressures would fragment the population, favoring radical shifts in body plan over a very short period of time.  10s of millions of years, or less.

Notes

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1. Fitness is a measurement of an individual organism's ability to produce as many offspring as possible.  It is usually measured as a value from 0 to 1, relative to the individual who is reproductively most successful in a population.

2. Hardy Weinberg equilibrium is the theoretical baseline against which to measure evolutionary change.  It is an equilibrium

Answer 3

Any trait can be a survival trait--to run fast, to have a slow metabolic rate which conserves food for longer periods in the body, the ability to go without water, etc.  Whenever some trait helps the organism survive to reproductive age, and it reproduces the trait, usually reinforced by both parents; that trait grows stronger until the organism's DNA has separated out the less favorable traits.  So, deer that run fast live long enough to reproduce, while deer that run slow end up being a mountain lion's meal.  When two fast deer reproduce, the offspring usually inherit the gene sequence that makes them fast runners.  Good swimmers survive better near and in watery areas, but animals that can go without much water survive better in arid places.  Red squirrels survive better where there is more red coloring to the trees and ground, and grey squirrels survive better where the tree bark is grey and the ground has grey slate--makes them harder to spot by predators.  That's natural selection of certain genetic strands.  When enough changes have occurred, a new species develops because the differences make reproduction very unlikely.  Look at the birds on the Galapagos Islands.  Different traits were reinforced for so long, and the birds were basically isolated, so they grew differently than their mainland relatives.

Answer 4

As simple as I can put it...there are 5 major points to the theory of evolution....

1. organisms within a population must compete for resources to survive. (Food, water, space, breeding partners, etc)

2. organisms within a population exhibit variations (size, shape, color, resistance to disease, etc)

3. some variations will enhance a particular organisms ability to compete for resources or survive adversity.

4. Those organisms with beneficial variations are more likely to survive and pass their characteristics on to their offspring. (natural selection)

5. Over time these variations will spread through each generation to a larger and larger portion of the population thus gradually changing the population as a whole.

Of course Darwin did not know about DNA genetics etc. (Making his work all the more remarkable)

It was the re-discovery of Mendels work on heredity and later work by men such as Watson and Crick on DNA as the genetic material that allowed us to flesh out the details of Darwins' theory

Answer 5

You've heard the phrase "survival of the fittest"?  That pretty much sums it up.  The idea is that an organism with characteristics that make it better equipped to survive its environment and successfully mate and produce offspring will pass on those superior traits and that other organisms that are not well equipped to survive and mate will fail to do so and die without passing on their genetic traits.  Over a very long period of time, mutations and adaptations that work well with the environment prevail.

Evolution should not be confused with adaptation, where an organism adapts to the environment within its own lifetime.  Over time though, these adaptations can impact evolution if they are key to survival.

Answer 6

This web site has videos for students: http://www.pbs.org/wgbh/evolution/

This web site is put together by Berkeley University.  It is excellent: http://evolution.berkeley.edu/evosite/ev...