Listen to part of a lecture in a biology class.

Listen to part of a lecture in a biology class.
So over long periods of time, thousands or millions of years, most animal species undergo significant changes involving their physical appearance, various environmental challenges typically force the species to physically adapt and change or face extinction. However, scientists have found that there are certain species that have actually changed very little over time. Modern members of these species look remarkably similar to their ancestors from millions of years ago, which scientists can tell from looking at fossilized evidence. So why have certain species managed to survive so long without any significant changes? Let's discuss a couple of reasons. One is that the habitat where these species have lived has remained stable and seen little change over time because of its extreme or remote location. Few predators lived there to begin with, and no new ones were introduced over the years because of it being so difficult to access, thus no pressure to adapt to environmental change, like developing protections against new predators was ever present. So generation after generation, the native species remains basically the same. For example, a species of fish has occupied the same deep sea caves off the coast of Africa, and because the caves are so very deep underwater and isolated from other forms of life, this fish looks pretty much the same today as it did during the time of the dinosaurs according to fossil records. Scientists think other species have persisted without much change because they have extremely flexible dietary requirements. They are generalists in what they eat, meaning they don't have specialized food needs and can survive on a variety of different foods. Not being picky eaters better enables them to withstand dramatic environmental shifts like the loss of significant food sources, without having to adapt and change or face extinction. For example, one little furry mammal called the possum has survived difficult periods, like ice ages without changing when there were very few plants or other foods around. This is in part because possums can eat just about anything, various plants, small animals, dead organisms, even in the modern day, garbage produced by humans.