Humans have a definite “vertebrate” bias in their thinking. When we picture an “animal,” almost all of us immediately picture mammals, birds, and other things with backbones. Few human minds immediately picture an octopus or hornet, an earthworm or a jelly. But about 95% of animal life lack the backbone of which we are so proud.
Biases such as our deceptive concept of proportions of vertebrates in nature, often originate in our differential awareness of large land organisms, and our innate preference for things more like ourselves. (Face it: We give people medals and positive recognition for running into a fire to save a human or a cat. We’re less impressed with the rescue of a goldfish. We are likely to apply the label of “crazy” to anyone who runs into a fire to rescue a spider or a snail.)
The following Trees of Life show how animal life is perceived by science today and over 100 years ago. Lots of our ideas have changed over time. As our tools improve and our awareness of our biases and self deceptions has become more keen, we get have asymptotically approached better approximations of what happened.