Charles Darwin and Jean-Baptiste Lamarck were two prominent biologists who helped develop the field of evolutionary biology. Lamarck was a believer in individual heredity as a driver of evolution. He believed that animals made small, incremental modifications to their bodies to better adapt to their environment. These modifications were passed on to their offspring and over the course of many generations the species would evolve into something different than its ancestors. An example would be short-necked giraffes slowly stretching their necks to reach higher branches and passing this change on to their offspring. Darwin believed in natural selection. He agreed with Lamarck that species change and evolve over time to better adapt to their environments but he believed that the population, not the individual, was the driver of evolution. Organisms are always born with slight variations and those with variations that are beneficial will survive and pass the trait on to their offspring. Those with non-beneficial changes will die off and not reproduce. So by his reasoning, giraffes were always born with a slight variance in neck length and the individuals with the longer necks flourished and passed the trait on to their offspring.