In 1859, Charles Darwin published a paper, On the Origin of Species, which talked about the newly introduced concept of evolution. Evolution is the change in the genetic composition of a population through generations. The evolutionary processes of natural selection, mutation, genetic drift, and gene flow can change the gene frequency (allele frequency) which is the relative frequency of an allele in a population. Gene frequencies show the genetic diversity of a population.
In natural selection, the organisms that have inherited traits bettersuited to their environments are more likely to survive and reproduce than the organisms without those traits.
Eventually this will cause the population to change, with the amount of organisms with beneficial traits increasing and the amount of other organisms decreasing. These beneficial inherited characteristics are called adaptations. These adaptations are caused through mutation.
In natural selection, the organisms that have inherited traits bettersuited to their environments are more likely to survive and reproduce than the organisms without those traits.
Eventually this will cause the population to change, with the amount of organisms with beneficial traits increasing and the amount of other organisms decreasing. These beneficial inherited characteristics are called adaptations. These adaptations are caused through mutation.
Mutations are changes in the nucleotide sequence of organisms’ DNA. They result when DNA is not replicated properly in synthesis, when an organism is exposed to external influences like chemicals or radiation, or when there are errors in meiosis. Mutations are completely random and most of the time these mutations pose no noticeable effect on the organism or they effect it negatively but sometimes these random mutations are advantageous to the organism, helping it survive in its environment. Organisms with these beneficial mutations will survive and reproduce at a higher frequency than other individuals which will eventually result in a changed population that has many organisms with this mutation. These mutations cause greater genetic variation, which is the variation of alleles in genes, by adding new alleles to the gene pool.
Genetic drift is a process in which chance events cause random changes in allele frequencies from one generation to the next. It is prominent in small populations. Two situations that result in genetic drift are the founder effect and the bottleneck effect. The founder effect occurs when a few individuals become isolated from a large population and form a new population with a different gene pool than the original population. The bottleneck effect occurs when the size of a population is reduced and the surviving population, like the result of the founder effect, does not reflect the original population. Genetic drift can cause allele frequencies to change quickly and randomly, and it can lead to a loss of genetic variation, with some alleles becoming fixed in the population.
Gene flow is the transfer of alleles/genes into or out of a population. This happens when fertile organisms or their gametes overlap with organisms/gametes from another population and reproduce with them. Sexual reproduction, in which two organisms each contribute one gamete, a haploid cell (sperm in male, egg in female), and produce offspring that have a mix of both parents’ genes, increases genetic variation as well. The offspring’s genes are completely random due to recombination (crossing over), the process in which two homologous chromosomes exchange DNA during meiosis.
Traits that are beneficial at one point aren’t necessarily beneficial at another. Environments change over time from natural disasters, the movement of tectonic plates, climate changes, and human interference (although this particular one is irrelevant to the dinosaurs). These changes could result in environments that can no longer support the organisms previously living there. If the genes of the species no longer help the species survive, they will become extinct. Other genes, arisen from mutations, that were maybe even harmful to the organism in the past, might prosper in this new environment.
Genetic drift is a process in which chance events cause random changes in allele frequencies from one generation to the next. It is prominent in small populations. Two situations that result in genetic drift are the founder effect and the bottleneck effect. The founder effect occurs when a few individuals become isolated from a large population and form a new population with a different gene pool than the original population. The bottleneck effect occurs when the size of a population is reduced and the surviving population, like the result of the founder effect, does not reflect the original population. Genetic drift can cause allele frequencies to change quickly and randomly, and it can lead to a loss of genetic variation, with some alleles becoming fixed in the population.
Gene flow is the transfer of alleles/genes into or out of a population. This happens when fertile organisms or their gametes overlap with organisms/gametes from another population and reproduce with them. Sexual reproduction, in which two organisms each contribute one gamete, a haploid cell (sperm in male, egg in female), and produce offspring that have a mix of both parents’ genes, increases genetic variation as well. The offspring’s genes are completely random due to recombination (crossing over), the process in which two homologous chromosomes exchange DNA during meiosis.
Traits that are beneficial at one point aren’t necessarily beneficial at another. Environments change over time from natural disasters, the movement of tectonic plates, climate changes, and human interference (although this particular one is irrelevant to the dinosaurs). These changes could result in environments that can no longer support the organisms previously living there. If the genes of the species no longer help the species survive, they will become extinct. Other genes, arisen from mutations, that were maybe even harmful to the organism in the past, might prosper in this new environment.
Around 230 million years ago (during the Triassic period), dinosaurs evolved from lizards. Lizards had (and still have) sprawling bent legs but during this period they evolved as a population until some of them eventually had legs directly under their bodies. The change was gradual and most likely started with a few lizards having slightly different legs and these lizards passing on this advantageous trait to their offspring, with the population of lizards progressively having legs more and more different from their predecessors until it changed so much that there was a new species with completely different, straighter legs. These straight legs benefited the individuals that had them, whether it was to help them reach higher food or escape predators, so they flourished. Other genes evolved as well which eventually led to the dinosaurs, which within itself had different species, all evolved for different environments. The brontosaurus probably evolved in an area with very tall trees, which would explain its long neck, while the tyrannosaurus rex probably evolved in an area where there were only large animals to feed on.