Darwin proposed that organisms change over time due to the process of natural selection, not due to artificial selection, climate change, adaptation, or genetic engineering.
Here's a breakdown of why Darwin proposed this:
1. Natural Selection: Darwin's theory of evolution by natural selection suggests that organisms best adapted to their environment are more likely to survive and reproduce. Over time, these advantageous traits become more common in a population, leading to changes in species.
2. Variation in Traits: Darwin observed that individuals within a species have variations in their traits. These variations can be inherited and passed down to offspring. Through natural selection, traits that offer a survival or reproductive advantage are more likely to be passed on to future generations.
3. Adaptation to Environment: Organisms that are better adapted to their environment have a higher chance of surviving and reproducing. This leads to the gradual accumulation of beneficial traits in a population, driving the process of evolution over time.
4. Fossil Record: The fossil record provides evidence of how species have changed over millions of years, supporting the idea that organisms have evolved and diversified over time.
In summary, Darwin proposed that organisms change over time as a result of natural selection, where advantageous traits lead to better survival and reproduction, ultimately shaping the characteristics of populations and species through generations.
