09-01-08, 11:22 AM #1
Some specific questions about evolution
I have a basic, high-school biology, level of knowledge about evolution. I think it makes good sense and all, but I do have a few questions.
1:What was the evolutionary impetus toward developing sexual reproduction?
2:How did facial expression aid in survival?
3:What inspired the change from single-celled to milticelled life?
4:Is Human evolution at a dead-end due to the interference of technology?
09-01-08, 11:59 AM #2
1. I don't know what impetus means
2. It might have been initially for for something other than communication
4. No, nothing stops evolution
I know I didn't help you in any way, and I'm probably wrong on many things. Don't take my word for anything.
09-01-08, 12:08 PM #3
09-01-08, 12:17 PM #4
1. Sexual reproduction has the advantage of providing a greater variety of genes sets which can be selected by natural selection. In this way, a species can adapt more readily to a wider variety of situations. Call it, the evolution of evolvability.
2. Facial expressions provide valuable information to your peers in a silent way, useful while hunting, and a precursor to actual speech.
3. Multi-celled life has the advantage of being able to create highly specialized structures within the organism. Sponges still bridge the gap between single-celled and multi-cellular creatures.
4. No. We are still subject to selection pressures, most of them typical of animals in general, but some new ones due to civilization and technology.
09-01-08, 12:31 PM #5
1. Sexual reproduction began initially at the unicellular level. As single cells evolved, they developed a reproductive method that became increasingly complex, involving spindle apparatus to aid in the separation of the complex chromosomes. This process is now called mitotic division, and is present in all eukaryotic cells in essentially the same process. It is the asexual division of one cell into two.
Somehow, over time, a second type of cellular division also developed in those cells [now called meiosis]. It utilizes the same spindle apparatus, and begins similarly to mitotic division, but undergoes a second division so that four cells develop, instead of two, but they only have half a full-complement of chromosomes. A full complement is two chromosomes [of one type]. Having two is like always having a spare. If one section [gene] of the DNA on a chromosome goes bad, it is unlikely that its corresponding section [gene] will also go bad, so the cell can continue to function.
So, when a cell undergoes meiosis and forms four cells, one of those cells can then combine with another cell [of the same species] that also has a half-complement [called sexual union], merging to form one cell that now has the full-complement.
The impetus for that appears to be to allow for the ability of merging of those two cells, which allows for greater diversity in the cell of variations in the genes.
How exactly that occurred is difficult to answer, of course, because there are no 'fossils' -all we have now are the descendants of that ancient process, highly modified.
If you're truly interested in this area, there should be numerous treatises on meiosis and mitosis that explains this far better than this brief overview.
Eventually, over time, even the meiosis evolved to form two types of cells with half-complements [haploid], compared to the full-complement [diploid] cells. Those, of course, are called sperm and egg cells.
Eventually, over time, cells that had sexual reproduction absorbed prokaryotic photosynthetic cells, but failed to digest them so they became symbiotic, and developed several lineages we call brown algae, red algae, green algae, diatoms, etc., and those lineages also became multicellular [sea weeds; land plants].
Others that did not have that photosynthetic capability developed other lineages, some of which became single and multi-cellular fungi, and others that became single and multicellular animals.
Anyway, that is a very quick synopsis.
I will leave it for others to answer your other questions.
09-01-08, 12:32 PM #6
spidergoat-I understand the advantages, I guess my questions are unclear-
The first time sexual reproduction occured-how did it occur? Did a male and female of a species evolve at the same time, then find each other and reproduce? What would cause such an evolution?
The first face-How did this help whatever creature had it? Did a creature with an unmovable face mate with a creature with a movable face because the movement was seen as attractive?
Multi-cellular life-What made two cells join together and work in concert as one organism?
09-01-08, 12:40 PM #7
09-01-08, 12:45 PM #8
Yes, google meiosis, mitosis, haploid, diploid.
09-01-08, 12:47 PM #9
Hammy, one of things you need to apply to the concept of evolution is that it involves small changes over great periods of time, hence you need to understand that events such as you're describing do not leap from one to the other, but occur over long periods of time.
09-01-08, 01:19 PM #10
Q-I understand. It takes a long time. Just to use the face as an example, what happened to go from-no face to facial expression? Take a fly, a salamander, and a cat. They ALL have faces. I know cats have very slight facial movements, but don't know for sure if these denote communication. Does a salamander have expression? What about a fly? Is facial expression limited to verbally social animals?
09-01-08, 01:47 PM #11
Take a fly, a salamander, and a cat. They ALL have faces. I know cats have very slight facial movements, but don't know for sure if these denote communication. Does a salamander have expression? What about a fly? Is facial expression limited to verbally social animals?
So, facial expressions and the ability to recognize them are based on those species that have followed those branches of evolution.
09-01-08, 04:36 PM #12
so is there a recorded first face? Or perhaps a better question, what is the most primitive face in the fossil record?
09-02-08, 08:13 PM #13
I know cats have very slight facial movements, but don't know for sure if these denote communication.Does a salamander have expression? What about a fly?Is facial expression limited to verbally social animals?
Humans have something like a hundred little muscles in our faces to make all those expressions. Even the other great apes don't have a fraction of that many.
Most mammals are limited to baring their teeth or flaring their nostrils. The primates can do a little better and our closest relatives, the chimps, bonobos, orangutans and gorillas, can do a little better than the rest of them, but still they can't come close to our range of expression. Parrots are intelligent, social and good communicators, but they have to get by with no facial muscles at all. Oddly, they have control over their pupils; hand a parrot an interesting new toy and watch his pupils dilate and contract rapidly.
So the first "face" as we know it had to be one of our recognizably human ancestral species of hominoids. They've gotten pretty good at reconstructing musculature from the patterns in bones, so perhaps they can tell us how many facial muscles the earlier species had. But I don't know if they can tell us whether they had the huge expanses of bare skin that make those muscles useful. Notice that even on men, almost all of the parts of our face that can move are the parts that don't have hair.
09-04-08, 05:19 PM #14
Many creatures have faces, one can imagine a mammal making a warning sound if a predator approaches, eventually the animals can recognize the facial movements associated with the sound. Perhaps an animal throws up if it tastes something bad, eventually, the facial movements of preparing to throw up then express disgust.
Multi-cellular life - There was an advantage. One can imagine two one-celled animals cooperating on something, eventually that relationship becomes more formal and streamlined into one body. Sponges are examples of this, you can break them up into their individual parts which still live, but put them in the same place, and they will organize into specialized structures.
09-04-08, 06:36 PM #15
all of this is unendingly fascinating, so I'll venture a bit further. Why haven't any primates developed flight? This seems to me to be an obvious advantage. Why haven't octopedal invertebrates made the transition to land? With 8 appendages, it seems like they would have an automatic advantage. I know these seem like silly questions, but I have always wondered this stuff. Why did we develop a liver, for example? OR more to the point, the appendix. Has it ever had a use? I can flare my nostrils, and roll my tongue upside down, do I have a long line of ancestors who were also able to do this? What is the advantage of holding the egg on the inside, rather than laying it and having it fertilized?
09-04-08, 06:40 PM #16
Mammals did develop flight, they are bats. Some squirrels do glide. I imagine most primates that live on fruit and vegetables are too heavy to fly very well. Evolution doesn't design things from scratch, it can't go backwards or adapt a solution of another animal. Some octopi do work very well on shore, but their lack of bones is a limitation.
Eggs on the inside cannot be eaten by a predator, and it's warm. You can still hunt for food instead of sit on an egg.
09-05-08, 03:49 PM #17
Energetically flight is very costly - so in many cases and in many environments it is most certainly not an advantage.
It helps to think of evolutionary advantages in similar terms to engineering problems and solutions, there's always a trade-off or compromise somewhere - flight requires compromises in size and diet, strength and size requires compromises in speed or agility, camouflage can restrict mobility etc etc. All of these strategies can be very successful - but they have a price nonetheless.
09-05-08, 05:34 PM #18
1:What was the evolutionary impetus toward developing sexual reproduction?
See the best biology book in the history of the universe: http://books.google.com/books?id=fHn...um=1&ct=result
09-06-08, 04:04 PM #19
An entire order of birds, the ratites, have evolved in exactly the opposite direction, and they have been fabulously successful. The ostriches, cassowaries, etc., gave up flight, grew to gigantic sizes, and use their long legs for running away from predators or kicking the crap out of the ones they can't outrun.
The psittacines evolved lethal hooked bills for fighting, prehensile claws for climbing, flock-social behavior for defense and primate-level intelligence for strategy. Many parrot species fly only incidentally and spend more time clambering. In aviculture, African Greys are noted for "flying like rocks."
Flying is perhaps not such an ideal ability.Why haven't octopedal invertebrates made the transition to land?
The cetaceans have taken a route similar to the ratites: lost their legs, returned to the sea and reached enormous sizes, becoming the apex predators in their ecosystems. In fact virtually every warm-blooded air-breathing animal that tries its luck in the water finds an easy life there. Penguins, ducks, seals, otters, polar bears... DNA analysis recently discovered that the cetaceans are merely the descendants of primitive hippopotamuses who swam all the way down the river to the sea, liked what they found, and kept going.With 8 appendages, it seems like they would have an automatic advantage.I know these seem like silly questions, but I have always wondered this stuff. Why did we develop a liver, for example?OR more to the point, the appendix. Has it ever had a use?What is the advantage of holding the egg on the inside, rather than laying it and having it fertilized?
09-07-08, 08:05 AM #20
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