Some brief ideas, that I had to answer from my reading professor Richard Dawkin’s The Ancestor’s Tale book. Some answers may be incomplete.
(1) Briefly, what is evolution?
Ans: The process by which different kind of living organisms have developed and diversified from their earlier forms during the history of the earth. Evolution is generally a gradual development towards something complex from something simple. Evolutionary history can be represented as branching from one species to other species.
(2) There is geologic time, which relies on the rock record; and “absolute” (or numerical or “linear”) time, which relies on calibrated clocks.
Which one was emphasized most in “The Ancestor’s Tale” when discussing the events in the history of life, and Why?
Ans: “Absolute dating” (Putting absolute age on the fossils using Radioactive dating, Dendrochronology, Paleomagnetism, Molecular clock) is emphasized. Geologic dating requires vertical piecing together of rocks from different parts of the world and then determine ages like solving puzzles. The different rendezvous ages are determined by absolute age.
(3) The fossil record WAS used for the dating of major divergences of types of life, and the “beginning to extinction” range of a family.
What are some general problems with relying entirely on this fossil record? [Hint: Explain why “lowest known occurrence” of a new family type is usually an underestimate; and similarly “highest known occurrence”.]
What major types of abundant multi-cellular life would not leave a useful fossil record?
….. Ans: There are lots of gaps or incomplete records in the collective fossil records. Moreover, not every type of organism gets fossilized. Relying only on the fossil record can lead to false conclusion. For example, if we only found large, big-boned dinosaur fossils and no small-light boned vertebrate, can we conclude that only large animals lived there? We can not, because light boned vertebrates did not turn into fossils.
. .Most of the time only bones, shells and teeth get fossilized. The mazor types of abundant multi-cellular lives are Amphibians, Annelida, Mollusca which don’t leave any fossils as they are soft bodied and have delicate or no bones. We only learn of their existence with fossilized burrows, trackways or impressions left on the soft sediment.
(4) “Molecular clock” is NOW used for the dating of major divergences of types of life (including some of the Ancestor’s Tale estimates, especially for soft-bodied life that doesn’t leave shells in the sediment record).
What is this concept of a “molecular clock”, and What are some important major requirements and assumptions for the “clock” part?
What major types of abundant multi-cellular life would not leave a useful molecular-clock record?
Ans: This technique uses the count of discrepancies in molecular sequences between surviving species.
The assumption is that the close cousins with recent common ancestor have fewer discrepancies. After the counting, scientists calibrate the arbintrary timescale of molecular clock and translate it into real years. They use known available fossil age for a few key branch points in the calibration process.
(5) Molluscs has twice as many species as vertebrates; but, even these are minor compared to another type of animal in diversity.
What type of life has at least 3/4ths of all animal species, and probably dominated the land since the Silurian?
What does that fact, plus related ones imply about the famous “family diversity through time” plots that are common in every textbook?
Ans: Arthropoda (insects, crustaceans, spiders, scorpions, centipedes, millipedes etc.) has at least 3/4ths fo all animal species. With their exosecleton and jointed leg and evolved segmented body, they dominated the land during Silurian (430 Ma).
The diversity of families and species have started from Cambrian, then dropped a bit, then it steadily grow throughout Ordovician before the end Ordovician mass extinction, then again grew through Silurian and Devonian before the end Devonian extinction. Most Paleozoic fauna were at these periods and most of them were arthropods. After end Ordovician mass extinction, there was no sudden drop, rather stable before the P/T boundary. And then the modern fauna started to grow.
(6) Ediacaran (ca. 590 Ma) = “the biggest split of animals” into “Protostomia” (“mouth first”) and “Deuterostome” (“mouth second”), based on the divergence in the way the embryo develops. All animals fall in one or the other; and we are a “Deuterostome” branch. It is easy from the Ancestor’s Tale book to know what are in the Deuterostome group.
But what are some main organisms in the Protostomia group?
Ans: The main organisms in Protostima groups are Athropods, Mulluscs, flat worms, round worms, annelid worms, Nematode, Brachyozoa, Bryozoa etc.
(7) earliest Silurian (ca. 440 Ma) = “a big one” split of “teleosts” from what would become amphibian-reptile-mammal (after a minor split-away of Coelacanths). Other than the fact that these are “ray-finned fish” (all fish that are not shark-ray); what is the major life-style divergence?
What does this imply about what may have been happening in the sea/land and the atmosphere environments? [Note: think about what had to change to allow the split between the fish and the lungfish-tetrapod groups.]
Ans: Sharks mainly live in sea water. The Ordovician period had cold sea. During Silurian, we got shallow warm water, high mountain lakes, acid stream, marshes, saline lake rivers. These teleosts (Ray finned fish) managed to live in these diverse habitats. Teleosts lived in many levels of underwater, both salt and fresh water. Sharks always had to maintain the same level in the water, they didn’t have bone, rather only cartilage. But ray finned fish have bones. The descendant of rendezvous 19 was the lung fish. Humans, tetrapods, coalecant, lungfish all evolved from love-finned fish.
(8) late Carboniferous (ca. 310 Ma) = big split of amniotes (tetrapods producing membrane-eggs, even if some develop inside the body) into “sauropsids” (I hate that obscure name for the group) and “mammal-like reptiles” (a name that Richard Dawkins hates, so he suggests “mammal-like reptiles”).
What are the apparent main distinctions (features that imply the separation) between the earliest “reptile-like mammals”, such as “Dimetrodon” from the “sauropsids”? [Note: consider what is grouped into the large “sauropsid” cluster.]
Ans: Pelycosaurs like Dimetrodon are less mammal like the other branch where Therapsids evolved into Cynodont and then into modern mammals. Dimetrodons were more lizard like, sprawled their bellies, legs were spreaded in both sides. However, these reptile like mammals gradually raised their bellies progressively higher off the ground, legs more vertical and gradually evolved into modern mamals. Distance from the ground is probably the biggest difference.
(9) Cretaceous = Mammal divergence (ca. 100 Ma). An important part of “mega-evolution” is isolation, then re-mixing. We looked at “World’s apart” evolution on isolated New Caledonia and New Zealand after they split from Gondwana. However, Pangea supercontinent also split into South America, Laurasia (joined North America and Europe), Africa and Australia during the Cretaceous as the South Atlantic and the Antarctic oceans opened. [Later, due to closure of Panama strait, the South America and Laurasia fauna mixed; but not Australian; and when Arabia closed with Eurasia, there were migrations into and out of Africa.] These 4 large landmasses underwent different evolutionary paths, that are grouped as “Laurasia-theres“, “Afro-theres“,”Xenarthrans“, and “Marsupial/Monotreme” mammals. Essentially, mammal evolution went into four paths during the last days of the dinosaurs, and the survivors of the end-Cretaceous catastrophe evolved to occupy the new niches independently in each regions.
Briefly describe the range of types in each of the “Laurasia-theres”, of “”Afro-theres”, of “Xenathrans” and of “Marsupials”– that together comprise these 4 main evolutionary groups of placental mammals.
Ans: Laurasia-theres include a) shrews, b) bats, c) camels, pigs, deer, sheep, hippos, whales, d) Horses, tapirs, rhinos, e) cats, dogs, bears, weasels, hynas, seals, walrus
Aftrotheres include elephants, manatees, dugongs, aardvark, golden moles, elephant shrews.
Xenarthrans include sloths, armadillos.
Marsupials include American and true opossum, shrew opossum, marsupial mole, Tasmanian devil, numbat, Manito del monte, Wombat, Kangaroos, possums, koala.
(10) Follow-up to the previous: As a speculation, before Africa contacted Eurasia to mix with the “Laurasia-theres” — What major differences would there have been with the African ecology? [for example, What would have been the “top predator” and the most abundant herbivore?] Why?
Ans: Africa didn’t have the carnivores, mainly herbivores. Carnivores came into aftrica from great northern continent of Laurasia. The trees were higher, elephants, giraffes were the herbivores which had to reach high from the ground and therefore developed the large tall bodies. So, Africa was greener and habitable for the herbivores to diversify, where in Eurasia, carnivores depend on their preys.
(11) Another follow-up to the previous: What does this “World’s Apart” concept imply about using diversity indices for larger land organisms?
Would you expect similar aspects for shallow-marine life, which dominates the fossil record? Why?
Ans: World’s apart means isolation. In the case of Australia, giant island like Madagaskar, Galapagos, in isolation, from few small population of animals, a new class of diversified animals have come into existence. Even in shallow marine life, from fish or marine individual’s perspective, there are small islands of habitats where organisms grow and evolve. Possibly the lack of external predators help the diversity.
(12) Paleogene (ca. 50 Ma) – Monkey divergence. There are “Old World Monkeys” (Africa-Eurasia), “New World Monkeys” (originally only South America) and “Lemurs” (mainly Madagascar). When these three monkey-types diverged, there was no land connections, and monkeys don’t swim.
Which place seems to be the evolutionary “home” of the original monkeys; and
How did those ancestors of monkey types then inhabit (and evolve to fill niches) in the other 2 regions separated by ocean seaways?
Ans: Africa seems to be the evolutionary home of the original monkeys.
West Africa and south America were close. There were possibly chains of islands in between.. A small founding population of monkeys probably rafted across, perhaps on fragments of mangrove swamps which kept them alive and then they floated from Africa to south America. They were lucky to have the sea current towards the right direction.
(13) Briefly explain Why a “massively improbably event” is often nearly inevitable in geologic time.
Ans: Extremely improbable events are common in nature. Given enough opportunities, the probabilities of even very unlikely events can mount up to be almost certain. For example, the probability of one particular mutation during evolution may be very little, but there are billions of mutations happening continuously with the help of natural selection. So, therefore one single mutation is not very unlikely. David Hand proposed his improbability principle which is the combination of laws of truly large numbers, laws of inevitability and the laws of near enough. The law of near enough tells that we tend to identify similar but not identical event as identical event. It’s also a perception issue as we tend to pay attention to the improbable things that do happen and completely ignore the even large number of improbable things that does not happen. So, in nature, one in a million event happen all the time. When we are looking at geological time, where we mostly care the span of millions or billions of years, massively improbably event is thus easy to find.
(14) Neogene (ca. 15 myr) – Ape families “out of ?where?”. Dawkins explores the divergence between early hominids, chimpanzees, gorillas, orangutans, and gibbons; and the problems in explaining why some of them have fossils only in Eurasia, whereas others have fossils only in Africa (and neither has a complete fossil record in either location). He then contrasts “out of Africa” with “out of Asia” and other debate ideas.
Briefly summarize his preferred model (with which direction) for how small “founding populations” of apes and their relatives seem to have migrated between Africa and Asia, and then evolved and diverged.
Ans: Dawkins support the model of “Hopping to Asia from Africa and then back again to Africa from Asia”. It matches with the facts of drifting continents and fluctuations of sea levels. Steward Disotell created the family tree and if the tree is correct then according to this model
- A population of ape migrated from Africa to Asia around 20 Ma and became all the Asian ape including the living gibbons and orang utans
- A population of apes migrated back from Asia to Africa, became todays African ape (Gorillas, Chimanzees, Humans) including us.
(15) Quaternary (ca. 2 myr) – Hominids. What is the main “defining difference” between “Australopithecus” and “Homo” genus of hominids?
For the “Homo” species, what is the evidence that there were at least two “out of Africa” events?
Ans: The main difference is in the size of the brain. Compared to Austalopithecus, the brain started to expand beyond the normal size. It’s more of the brain size to body ratio than just the brain size.
(16) Late Pleistocene (ca. 40 kyr) — Humans and cousins. Could Neanderthals talk to each other?
What was the “Great Leap Forward” for Homo sapiens sapiens?
Ans: Neanderthals are our closest cousin and they might have spoken with each other. They had social communities with complex lifestyle. They had clothing, jewelry and even bigger brain than ours.
Jared Diamond coined the term “Great Leap Forward” which basically points to the flowering and flourishing of human mind which drove the evolutionary process. All the modern cultural, industrial changes have happened very rapidly. Before 40K, the things were very slow. The development of intellect in the brain was a great leap for mankind. Some points to the origin of language or written language, but Dawkins and Steven Pinker argues that the great leap may not be the language as the history of language seem older. It may be how we started using our brain critically or the ability to store or extrapolate or predict future.
(17) In retrospect, what is required for surges in evolution of new types of life?
How can we use databases of first/last fossil ranges to try to identify such surges, and their potential causes?
Ans: I guess, appropriate environment, genetic mutation, possible interbreeding.