What exactly causes evolution?

Question

Like bears from thousands of years ago to turn into polar bears. Is it because of the environment? if so then what causes evolution?

Answer 1

Mate selection and survival of the fittest. Mate selection determines what genes are available to the next generation. Survival of the fittest weeds out the week in favor of the strong, weeds out the stupid in favor of the brains, weeds out the lazy in favor of the ambitious . . . oh no . . . here comes the weed whacker . . .!!!

Answer 2

The genetic component of evolution comes from slight variances in the genetic makeup of the individual. If a particular trait in a given individual allows it to survive better than its counterparts, then it has a better chance of mating with a member of its opposite sex. The trait then has the chance to be carried over to the next generation. While changes in biology occur at the individual level, the unit of evolution is the population since the trait in question is carried over between individuals to allow for the propogation of the species.

There is no exact environmental cause for evolution in regards to any specific need. Evolution occurs whether there is a need for a trait or behavior or not. Not all evolutionary changes are successful and evolution is not a linear path. Some changes allow an animal or group of animals to exploit new areas that most other organisms could not reach. Other changes allow for adaptations that would cause a major development of a new family of organisms.

Environmental circumstances may have some argue that the environment is a crucial factor in evolution. However, the environment has exterminated far more organisms off this planet than man has even tried to kill (major global land shifts through plate tectonics have wiped out ~90% of all life on earth more than a few times). In those instances, luck was more of a factor than biological design.

Evolution starts at the genetic level through the development of a mutation in the DNA coding. This could either assist or hinder the organism in question.

Answer 3

Evolution is fueled by changes, called mutations, in organisms. For example, if a species lives in an environment where it would be extremely advantageous to be green, because they'd be eaten less, then a greener-shaded lizard would be less likely to be eaten, and therefore more likely to reproduce and make another lizard that is greener. This is called natural selection. Over time, nature selects FOR certain traits, like camoflage, and against others, like blindness in areas where an organism needs to see.

There also certain instances of "natural" selection caused by humans. We usually see this in breeders, where humans tend to breed animals with traits we like, such as dairy cows that produce a lot of milk, much more than animals we don't like, and over time, the species changes.

Macroevolution, the idea that species change over time into entirely different species, is hotly contested, mostly by religious groups, although the evidence of microevolution, the idea that species change over time to have different characteristics, is incontrovertable and in evidence all around us.

I don't believe that we can really argue that there is NO evolution in its strictest sense, although I am willing to keep an open mind mind about the theory of macroevolution.

In the end, though, it's all about the initial mutations. These can take almost any form, and can be positive or negative, although Darwin's hypothesis, laid out in Origin of the Species, states that the negative mutations are selected against. This means that an offspring with a mutation that does not assist it in its environment is less likely to find a mate, and therefore less likely to pass on that mutation.

Answer 4

Sure, environment has to be a primary factor. As you mention, bears are a good illustration of this. Polar bears evolved with heavy fur coats for warmth. The coats became white probably for camouflage and to reflect sunlight. Bears in warmer climates did not need these features, and so their coats are different.

Answer 5

Evolution is the study of change of allele frequencies in a population.

What you are describing isnt evolution of a populations allele frequencies, it is mutation of alleles to cause a new behavior in the animals body.. white fur. Polar bears have much more than white fur.. they have huge paws (for swimming), they have thick surface fat deposits, they have incredible senses, and incredible speed. They are very highly adapted for where they live.

Answer 6

It's not triggered or anything. It's just the accumulated change one can observe after a significant number of generations have passed. It is influenced by anything that affects whether a creature dies or lives to procreate, but significant factors are the environment and the climate, which changes a lot over millennia.

Answer 7

In biology, evolution is the change in the heritable traits of a population over successive generations, as determined by changes in the allele frequencies of genes. Over time, this process can result in speciation, the development of new species from existing ones. All contemporary organisms on earth are related to each other through common descent, the products of cumulative evolutionary changes over billions of years. Evolution is thus the source of the vast diversity of life on Earth, including the many extinct species attested to in the fossil record.

According to the theory of evolution, the basic mechanisms that produce evolutionary change are natural selection (which includes ecological, sexual, and kin selection) and genetic drift; these two mechanisms act on the genetic variation created by mutation, genetic recombination, and gene flow.

An outline of the theory of natural selection was jointly presented to the Linnean Society of London in 1858 in separate papers by Charles Darwin and Alfred Russel Wallace. Detailed support for the theory was then set out in Darwin’s 1859 book, On the Origin of Species. Natural selection is the process in which individual organisms best adapted to their circumstances are more likely to survive and successfully reproduce. If the adaptations are passed on to the offspring, the favorable traits become more common in succeeding generations. In time, cumulative adaptations can result in a new species being formed.

In the 1930s, Darwinian natural selection was combined with the theory of Mendelian heredity to form the modern evolutionary synthesis, also known as "Neo-Darwinism". The modern synthesis describes evolution as a change in the frequency of alleles within a population from one generation to the next. With its enormous explanatory and predictive power, this theory has become the central organizing principle of modern biology, relating directly to topics such as the origin of antibiotic resistance in bacteria, eusociality in insects, and the biodiversity of Earth's ecosystem.

Answer 8

simply put, survival of physiological traits that increase an organism's chance of survival, causes those traits, of the survivors, to become more pronounced in a community, as they pass their traits onto their offspring.

AKA survival of the fittest!
Note: that is an oversimplified description.

Answer 9

Survival of the fittest.
Environmental changes.
Availability of resources and competition with other species .
Female preferences.