Hubris and the Tree of Life: [excerpted from Huffington Post article]
….Prior to Darwin, it was common to classify animals in a linear sequence. Aristotle had proposed a scala natura, a rank order of animals in terms of perfection, by which he meant similarity to humans. He had humans at the top of the scale, and formless creatures like sponges way down below, and all other organisms that he knew about in between. Christian theologians later refined this notion, changing the meaning of perfection…
Modern genetics has greatly aided the process of animal classification. Biologists today accept a version of the tree metaphor (a version with fewer major branches) for organisms with eukaryotic cells, that is, all the creatures we call animals. If we trace human origins backwards towards the major branch and then the trunk, we get a clear picture of which animals are in our past and which are not.
First of all, we are vertebrates, animals with a vertebral column that surrounds the spinal cord, and a bony skull case that houses our cephalic ganglion, or brain (cephalic has to do with the head, and a ganglion is a collection of cells). All mammals, birds, reptiles, amphibians, and bony fish are vertebratesHumans are mammals, specifically primates, and like all mammals our ancestors were a particular kind of reptile that is no longer with us. Their ancestors, in turn, were bony fish. So where did the original bony fish, the first vertebrates, come from? The simple answer is, from invertebrates. But there’s more.
Yes, ancient ancestors of starfish, through zillions of cycles of natural selection, are believed to be the root of fish-like creatures that lacked bones, and that were the origin of bony fish, the primordial vertebrates, from which other vertebrates, including humans, sprang.
Body parts change during evolution to help organisms cope with their environment in new ways. There are certain things that have to be accomplished in order to survive. For example, you have to be able to meet nutritional demands, keep your fluids up to date, and defend against danger. And for your species to survive you have to reproduce. This list probably applies to all organisms, and, to some extent, even to simple single cell creatures like bacteria.
Each bacterium is responsible for its own survival. It has to take in sustenance from its surroundings to keep its internal machinery going.…Through the long course of evolution, during which single cells combined to form multicellular life forms, and these combined to form complex organisms with multiple systems (for example, digestive, respiratory, reproductive, and nervous systems), more sophisticated solutions to these problems arose. But at a very basic level the fundamental problems faced by living things are fairly universal.
For vertebrates, the brain mechanisms that help solve these problems are remarkably similar. … all adhere to a common scheme.
The hindbrain is necessary for life (damage there stops you from breathing), the midbrain for basic reflexes (like orienting towards a sudden sound)the forebrain for all the stuff we think of as complex behavior and thought.
Not surprising is the fact that the forebrain differs the most between mammals and other vertebrates, and the hindbrain the least.
Particularly relevant in the present context are the highly conserved systems within the mammalian forebrain that regulate behaviors involved in feeding, drinking, defense, sex and other functions necessary for the survival of the individual and species.
There are of course differences in size and complexity in brain areas across mammals, but these differences are mostly variations on a common theme.
One important violation of the mammalian status quo is the human neocortex, and especially the prefrontal cortex, which does allow us to have some fairly sophisticated cognitive capacities. This justifies the common assumption that we are unique in our ability to think, reason, imagine, and create.
But when we creatively imagine we are somehow special, standing on the top rung of a ladder of nature or near the heavenly end of a chain, we ignore the complexity of the natural world, and our place in it. We are part of a process, not its goal or final state. Just a branch point, a distal twig, on a continuously branching limb of the tree of life.
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