Evolution: Lamarck vs. Darwin

Influential Scientists in Evolution

• Jean Baptiste Lamarck proposed the theory of inheritance of acquired characteristics in the early 1800s.
• Lamarck believed organisms could alter their traits during their lifetime based on use or disuse.
• An example of Lamarck's theory is giraffes stretching their necks to reach higher leaves.
• Lamarck thought these acquired changes would be passed to offspring.
• Modern science discredited Lamarck's theory because only genetic information can be inherited.
• Genetics research, especially DNA and mutation, proved traits are inherited through genetic material, not physical changes.
• Darwin's theory challenged the dominant religious views that species were created in their current form.
• Darwin could not explain how traits passed to the next generation because inheritance mechanisms were unknown.
• Some scientists believed in alternative theories like Lamarckism or creationism.
• The idea of slow, gradual change over millions of years was difficult to accept without fossil or genetic evidence.
• Darwin's theory gained acceptance later, especially after Mendel’s work on genetics was rediscovered.
• Alfred Russel Wallace independently developed a theory of natural selection while studying species in the Malay Archipelago.
• Wallace wrote to Darwin in 1858, describing strikingly similar ideas.
• This prompted Darwin to publish his research that he had been developing for over 20 years.
• Both Wallace's and Darwin's ideas were presented together at the Linnean Society of London in 1858.
• Wallace is recognised as a co-discoverer of natural selection, though Darwin’s research gave him more recognition.

Mechanisms of Evolution

• Mutation involves random and permanent changes in the DNA sequence.
• Mutations can introduce new alleles and lead to new traits.
• Some new traits from mutations may improve survival.
• Meiosis involves processes like crossing over and independent assortment that mix genetic material during gamete formation.
• Meiosis leads to new combinations of traits in offspring.
• Sexual reproduction involves offspring inheriting half of their genes from each parent.
• The mixing of genes during sexual reproduction increases genetic diversity in populations.
• Natural selection requires variation where individuals in a population differ from one another.
• Organisms exhibiting overproduction create more offspring than can survive.
• Limited resources cause competition and a struggle for survival.
• Adaptation relates to individuals with advantageous traits being more likely to survive and reproduce.
• Descent with modification means beneficial traits become more common over generations.
• Speciation occurs when populations of the same species become genetically distinct enough that they can no longer interbreed.
• Geographical isolation, like mountains or rivers, is a common cause of speciation by separating populations.
• Reproductive isolation can occur through changes in mating behavior or timing.
• Over time, genetic differences accumulate due to mutation, natural selection, and lack of gene flow.
• Speciation results in the emergence of new species.
• Darwin’s finches on separate islands with different food sources are an example of speciation, leading to different beak shapes.

Types of Evidence for Evolution

• Homologous structures have similar anatomy but different functions in different species.
• Homologous structures show that species share a common ancestor.
• An example of homologous structures is the forelimbs of humans, whales, birds, and cats having the same bone structure but different purposes.
• Embryology, the study of embryos, shows that different species have similar early developmental stages.
• Similarity in embryonic development indicates common ancestry.
• All vertebrate embryos have gill slits and tails during early development.
• Vestigial organs are structures that no longer serve a function but were useful to ancestors.
• Vestigial organs provide evidence of evolutionary change over time.
• Examples of vestigial organs are the human appendix and pelvic bones in whales.
• The fossil record shows progression and changes in species over time via preserved remains.
• Fossils reveal transitional forms that link different groups of organisms.
• Archaeopteryx, a fossil, shows features of both reptiles and birds.
• Molecular biology/DNA comparisons reveal that closely related species have more similar DNA and protein sequences.
• Similarity in DNA confirms evolutionary relationships on a genetic level.
• Humans and chimpanzees share approximately 98% of their DNA.
• Biogeography studies the distribution of species across the world.
• Isolated regions often contain unique species not found elsewhere.
• The unique finches of the Galápagos Islands evolved in isolation.
• Direct observation demonstrates evolution in real-time, especially in species with short life cycles.
• An example of direct observation is bacteria developing resistance to antibiotics after exposure.