Sometimes, you feel like something is wrong. Most of the time, it’s just a feeling; it doesn’t mean anything. But, every now and then, something is wrong, you really are in danger, you really should be afraid.
Here are some articles on how humans can react to the unconsciously sensed smell of fear in the perspiration of others.
To suppose that the eye, with all its inimitable contrivances… could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree… Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist… and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered a real1.
Charles Darwin (1809–1882)
Darwin included a section in his book, “On the Origin of Species,” called, “Problems With the Theory.” It included the Cambrian explosion, covered in the previous episode, and the development of complex organs like the eye. Today, using things we’ve learned since Darwin’s time, we look at how eyes evolved.
Here are a number of articles with further information.
Between 520 and 550 million years ago, a sudden explosion of animal types appear in the fossil record. This example of rapid evolution is known as the Cambrian explosion. Theories of how and why it occurred range from the notion that it didn’t happen at all, to a spike in oxygen levels, to the advent of the sense of vision.
Here’s an article that includes an animation of some of the oddball animals that appeared and disappeared during the Cambrian period.
In today’s rather short episode, we talk about the first creatures to have developed a centralized nervous system, though not a central nervous system as of yet. It was a simple worm like creature, with a nerve cord running along the length of its body, and an extra-large bundle of nerves toward its mouth. For worms and other invertebrate animals, like crabs, lobsters, octopuses, squid, slugs and snails, the nerve cord runs along the belly of the creature. For what would become vertebrates, including us, the main nerve cord runs along the back. Apparently, for reasons unknown, some of the worms flipped over, and decided to live their lives upside-down.
This month has included some unusually long episodes. To leave room for the upcoming Halloween special, this and the next couple of episodes are unusually short. Check back on the 31st for, “Be Afraid.: when reason can get you killed.”
A stun gun works by passing electricity through your muscles, causing uncontrollable contractions. An electric eel, which is actually a type of fish, can do the same thing. There is a single celled creature that can conduct electrons from hydrogen sulfide in the soil, to oxygen dissolved in the water. Almost every living cell has an electric charge. Multicellular life has found a way to use electricity to send long distance messages from one part of the organism to another. Today, we talk about electricity, life, and some slightly grotesque experiments that have been done with the relationship between the two.
Here’s an article on electric currents applied to recently deceased human body’s, that caused them to move.
Here’s an article about experiments done that altered the electrical properties of cells that changed the way the organism grew. This included eyes on the tales of tadpoles, and hints of being able to regrow severed limbs in creatures that do not normally possess such a capacity.
Darwin originally published “On the Origins of Species” in 1859. At the time, the mechanism of inheritance wasn’t well understood. Inheritance and the implication that lifeforms could change over time stood in contrast to the popular notion that God had created all things in perfect and unchanging forms. His theory only considered traits that come from parents, in the case of sexual reproduction, and mutation, in asexual reproduction. It turns out that organisms, especially single celled forms, can and do snag genetic information from other organisms that they aren’t related to in the least. Today we look at some of the mechanisms of horizontal gene transfer, and some examples.
Bacteria are very successful. They’ve been around for billions of years, as compared to hundreds of millions for multicellular creatures. They have survived mass extinctions that wiped out things like the dinosaurs and others. Today, we look at salpingoeca rosetta, which can live as either a single celled creature, or in a multicellular colonial form. We compare that to the experimentally evolved multicellular colonies of yeast we introduced in the previous episode, episode 72; and examine how the multicellular creatures came about, and how and why they are no longer able to return to a single celled lifestyle.
Here’s an article about work by Nicole King, that introduced me to salpingoeca rosetta.
Take life, put it in the right environment, and give it between 3.5 and 4 billion years. We take the time to review what we’ve covered since “How to make a mind—part1,” episode 35; and “How to make a mind—part2,” episode 59. This sets us up nicely to talk about the way we evolved from simple creatures, into the oh so very complicated animals we are today.
There are creatures that do not seem to have a natural limit on their life span. They only die when they are killed by accident or the action of sickness parasites and pathogens. Other creatures are apparently programmed to die at a given time, and under a given set of conditions. So why do we die? What is death for?