Evolution Questions (NOT a Creationist Thread)

Factual Questions
1

For the record I am a firm believer in evolution and don’t buy creationist theory one bit. Even so I have a few questions that have bothered me:

  1. If todays current species evolved from other ones why don’t we see this in the fossil record (or de we and I’ve missed it)? For example, if birds evolved from dinosaurs why don’t we ever see a half bird/half dinosaur…like a Chickagator (chicken + alligator). While I know birds and dinos share some traits (such as bone structure) that led to the conclusion of dinos being bird ancestors it seems as if one day there aren’t any birds and then the next we have feathered friends all over the place.

  2. I understand random mutations slowly pushing species to better adapted/higher life forms but can this explain everything? How do you go from an egg laying creature to a live birth creature with random mutations? It’s one thing to suggest a mutation allowed an animal to run faster or see a little better or be a little smarter but it’s something else entirely to suggest an egg laying creature had a mutation that developed a uterus and all the attendent things necessary to make it work (hormones, placenta, gestation time, pelvic adaptations to accomodate live birth vs. an egg, etc.). How do you get from there to here?

2

  1. Only a tiny percentage of creatures that lived are preserved as fossils as it takes an extremely narrow set of conditions for them to form.

  2. Fundimentally different branches such as placenta and marsupial split from each other at a very primitive stage. A modern Canada goose did not evolve into a duck billed platypus or vice versa.

3

  1. I understand that fossils are relatively few and far between but do ever find a middle stage? Something that’s in the middle of evolving from the ‘old’ form to the new form?

  2. I realize that branches of the evolutionary tree split ages ago and that a star fish has practically no relationship to a human. Still, there are a few items, such as a uterus, that I don’t see evolving over eons. Maybe the uterus was tweaked for better performance over time but it seems like the first one pretty much had to pop-up complete and functional out of the gate. What use to an organism is a quasi-uterus that isn’t quite functional yet? Seems like nature would kill off the animal with a proto-uterus as it’s just one more thing to go wrong and provides no discernable benefit to the animal till it’s functioning and starts conferring its benefits to the animal that possesses it.

4

I’ll attempt to answer these.

We do. In the past 20 years, there have been a bunch of half-bird, half-dinosaur creatures, several of which have showed various types of “feathers” Remember the “velociraptors” from Jurassic Park? Some theorize these may have had feathers. Some obvious relatives of Velociraptor have had them.

Oh, and I’ll reitterate what Padeye says: fossils are VERY VERY VERY rare. It is quite likely that less than 1% of the total number of species (not of individuals, but of species) have left a fossil record for us to find, never mind that we have found only a small portion of even that.

Higher life forms? Better adapted is a correct term, but there is no “higher” there is only “well adapted to its environment” If the environment changes, then the species is no longer well adapted, and it probably dies off. There is no “higher” or “lower.”

Well, it’s easy to see that egg laying takes a lot of energy because you have to lay a LOT of eggs to guarantee that some of your offspring will live. Especially since the egg is outside of the body. If a species came along where the egg stayed inside the body until it cracked, it would fill an econiche not currently being filled, its young would survive better because they stayed better protected until they were mobile themselves. There are some species of snakes and lizards that do this. (and it’s important to note that just because there are these snakes, does not mean we directly decended from these snakes. It could just be coincidental evolution: two different species fill their niche in the similar way). Now that the egg stays inside the whole time, the shell becomes superfluous, and so species that don’t waste resources making shells do better. Now, its easy to see that species that evolve modern mammalian “birthing equipment” for lack of a better term, do better than species before them. Which is not to say that the previous species did badly, and some of these earlier species still exist (like say, the platypus) because they continued to fill a niche not exploited by another species.

5

Hate to sound like a broken record on this, but “The Blind Watchmaker” by Richard Dawkins is a very worthwile read, and has many words on this subject. If you look close, you generally CAN find incremental paths for complex structures. His detailed example is development of the eye. I find his writing a good bit better than the other well known “evolution for the laymen” writer, Stephen Gould.

In the case of placental mammals, we actually have a couple of surviving non-placental “midway points” - monotremes, which are egg-laying mammals, and marsupials. Marsupials have a shell membrane - essentially, they hatch the eggs internally, then the very undeveloped young finish developing in the pouch.

There are species of snakes which have live birth as well. I would guess that they have eggs very similar to the egg laying species which are hatched internally.

One could imagine approaching the internal hatching of eggs incrementally. Then the shell membrane slowly disappears, and the yolk eventually becomes a placenta.

6

Thanks guys…that helps.

As for…

I was using ‘higher’ as short hand for more highly evolved, not necessarily better. I’ll stick by saying humans are more highly evolved than a flat worm. We may not be better but we are certainly a more complex organism.

7

For an evolutionist you make very creationist sounding arguments. Seriously, critical thinking does make for good science. I make a good devil’s advocate myself, probably my Catholic upbringing.

Evolution theory doesn’t have all the answers as the raw data is hard to come by. It’s a fill-in-the-blanks framework with a lot of blanks. Soft tissue items like eyeballs and uteruses don’t make good fossils so we’re unlikely to ever make a find that makes clear how they evolved. Evolution theory is the best explanation of how things got to be the way they are unless you cross that gulf to G*d miracling everything into existence.

8

Padeye has covered question 1 as well as I could; it’s a mighty big mosaic, and we’re missing most of the tiles. As for question 2…it’s complicated, and no one really knows the details, but here is a conceivable (NPI) scenario:

Egg-layer to live-birther–The ela (egg-laying-animal) shares an environment with predators and scavengers that like to steal eggs; it has no practical way to hide or conceal its eggs. Therefore, the best it can do is reduce the window of opportunity for egg-theft. Two options present themselves: reduce the gestational period (hurry up and hatch, already!) or carry the eggs longer before laying them (the ela can move to avoid predators, and may be too large for some of the scavengers). Reducing the gestational period is tricky–it takes time for a complex organism to develop and grow from a single cell to a viable creature, and it can’t always be rushed safely. Holding the eggs, on the other hand, is a relatively minor adjustment, and can offer the same benefits. IIRC, this can be seen in some species of snakes–they develop eggs, but actually hold them internally until they hatch in an approximation of live birth <hangs head in shame…can’t provide cite…saw it on a nature show a long time ago>. Now, if the eggs remain internal until they hatch, there’s no need for that hard shell to protect the embryo from dehydration, elements, etc, and the shells will tend to encumber the mother’s movements. Thus the hard shells are selected against whenever a soft-shell mutation arises. Eventually, they evolve into a sort of life-support sack–can anybody say “placenta”?

I’ll leave the hypothetical converse (live-birther --> egg-layer) as an exercise for someone else.

9

Not exactly.


<disclaimer>

I am not a biologist,


</disclaimer>

but as I understand it natural selection is a complete opportunist. Most mutations are detremental to the to the survival or reproductive success of an individual but that, in no way means that it’s an all or nothing deal. A “proto-uterus”, could (and I guess probably would) serve some purpose completely unrelated to its derivitive. Later mutations might change the “proto-uterus” such that it gets “tweaked” until it essentially functions as a bona fide uterus.

As far as speciation is concerned, we have transitional fossils. The reason why this seems to be such an issue with folks is simply the way we like to categorized things like “ant” or “dog”. Nature is not obliged to lend herself to our categories and doesn’t to check out a good source on speciation check this out

http://www.talkorigins.org/faqs/faq-speciation.html

10

An excellent website explaining evolution & answers to your questions…
http://www.talkorigins.org

11

How do chromosone numbers change? Most changes in chromosone number result in severe defects (e.g., Down’s syndrome), but I can see that every once in a while, a viable change would occur. The problem is, even if, say, a perfectly healthy 48-chromosone person, say, were to be born, and that person would be interfertile with other such varients, from what I understand of biology, a 48er wouldn’t be interfertile with a normal 46er (the pairs couldn’t match up), and being surrounded with 46ers, would hence be unable to reproduce at all. What am I missing here?

DISCLAIMER: I am not a fundamentalist creationist, and like Jeff_42, I believe that the theory of evolution is true. I ask this in the context of assuming that there is a scientific answer, but that I don’t know what it is.

12

Padeye said:

I PROMISE I’m not a creationist in evolutionist clothing. I just want to have my Platypi (Platypusses?) in a row for the next time I run into a creationist :).

On a related but slightly differnt topic…

What’s the current thinking on the speed at which evolution takes place? I know the common thinking is that it is something that takes place over eons but I’ve heard of some speculation that evolution may occur in leaps. I.e. a change that takes place on the order of a few generations as apposed to thousands of generations.

BTW–I don’t think the ‘quick’ version precludes the ‘long’ version. I see no reason why they can’t co-exist (i.e. animals with flight slowly evolved over millenia from animals that needed to jump far, to gliding further to flying while maybe an extreme intelligence jump happens in a few hundred years).

Any merit to this or is it pure bunk and takes millions of years all the time?

13

There is support for the idea of (relatively) rapid bursts of speciation, particularly following mass extinctions and colonization events. In an environment where many niches are unfilled (because prior occupants have either died off or never existed), a wider variety of mutations can prove beneficial. Mutations that tend to push an isolated group into a new niche are usually selected against if there’s competition for that niche, and selected for if the niche is empty. Massive overgeneralization, of course, but you can see the logic in it. Anyone got hard data on this?

14

Look up “punctuationism” or “punctuated equilibrium”.

15
  1. I have a picture of a fossil of the Archeopteryx on this page http://www.angelfire.com/oh4/cooling/arch.html It is evidence of a transition between birds and reptiles.
16

The division of animals into nice neat species, orders, etc. is an artificial division invented by man. These divisions are not honored by nature. If the record of something between dinosaur and bird were found, we would classify it as one or the other, because we like to have things in nice neat boxes even if they don’t fit exactly.

17

Several species of rattlesnakes and sharks develop a type of placenta. The eggs actually embed themselves into the wall of the cloaca and blood vessels grow over them from the mother, providing nutrients and disposal of waste.

As there are no hard parts to fossilize, this is speculation, but if one type of monotreme developed this type of egg retention we would be 75 percent of the way to placental mammals. The only other modification would be to split off the egg-implantation section of the cloaca into a functional uterus.

Others have already mentioned that we have plenty of dinosaur-to-bird transitionals. I would like to point out that the distinguishing characteristics of various lineages are usually acquired after the different groups have split. For instance, the last common ancestor of dogs, cats, and sea lions looked like a weasel. One (or more) populations of this weaselly critter took to group hunting and what we recognize as canid characteristics were encouraged in their gene pool. Another group got better at hunting rodents and developed a “hide and pounce” method. Their descendants were moulded by natural selection to become what we call cats. Etc.

My point is that the parent group or species that we can find in the fossil record rarely show the characteristics developed by their daughter groups. It is only in retrospect that we can recognize the incipent signs of later differentiation.

18

Jeff_42 said:

Really? I disagree. If anything, flatworms are probably more evolved than we are. But that’s a whole new thread.

As for Chronos’s question, chromosome numbers are interesting. Bananas are edible because they’re triploid. In wild bananas, the part we eat is filled with large hard seeds, with little fruit. But because domestic bananas are triploid, meiosis is a mess, as you suggest. Consequently, the seed pod contains abortuses rather than seeds, and we get a snack. Seedless watermelons are similar, IIRC.

The easiest way to change chromosome number is to double it. If you get a nondisjunction early enough, you end up with a gamete with 2 copies of the genome rather than one. have 2 of these gametes mate, and you have a tetraploid. As long as you have an even ploidy, everything will have something to pair up with, and you’ll be able to reproduce.

This is also a good way to get fertile hybrids. A hybrid has one copy of species A’s genome, and one of species B’s. While it’s still one-celled, just have the DNA replicate without splitting the cell, and boom. You have 2 copies of both genomes, and all is well.

In humans and other animals, this does usually cause immediate spontaneous abortion, so you don’t see it. Plants and (I think) reptiles and amphibians seem to be much more tolerant of extra genetic material than we are.

In order for me to have a normal child with an extra chromosome, here’s what would have to happen: my chromosome #2 (let’s say) becomes split in two and both halves become full-on chromosomes. This means that the half without a centromere would have to get one. From somewhere. Any DNA not attached to a centromere is usually quickly lost. Also, the two broken ends would have to be capped by telomeres before exonucleases begin chewing them up. The odds of that are not good, to say the least.

So it never happens? No, but it’s rare. One of our chromosomes (#2, actually, I think) looks just like it was made by taking two ape chromosomes and sticking them together. But death is much more likely than a happy accident like that - and I would think combining is easier than splitting.

But anyway, this post is already way too long and has taxed my feeble memory. I will allow others to expound.

19

Couple of points: first, we are not likely to find a ‘half this / half that’ of anything. The pace of evolution is one aspect of the theory that is still somewhat up in the air. Add to this the fact that different traits may not (indeed, need not) evolve at the same rate, and we wind up with organisms that are a mosaic of traits inherited by its ancestors, rather than a gradual transition from one species to another.
Another thing to consider is that evolution is more a tree than a ladder. Species A does not gradually evolve into Species B. Typically, Species A and Species B share a common ancestor, Species C, which we may never find as a result of holes in the fossil record. How similar Species A and B are depends upon how long ago they diverged from Species C. The more recent the split, the more similar they will be. Thus, since certain dinosaurs (e.g., Velociraptor) are more bird-like than others (e.g., Triceratops), it is hypothesized that the dino-bird split took place closer to the Velociraptor lineage than the Triceratops lineage. And, since Velociraptors and their ilk are VERY bird-like (or, perhaps, birds are VERY Velociraptor-like), it is likely that the velociraptor-like dinosaurs share a fairly recent common ancestor with ‘true’ birds. And it is very likely, therefore, that this common ancestor was a ‘true’ dinosaur. Any such ancestor, then, we would expect to have characteristics common to both dinosaurs and birds. Whether or not we ever actually find one, such a creature must have existed.

(Note: I have made any number of generalizations in the above in order to not make this post any longer than it will already be!)

As to why we never find these ‘ancestors’, well, the fossil record is like a giant flip-book with most of the pages missing - the further back we go, the more pages are missing. Further, fossilization in general is a rare event, as others have pointed out. Add to this the idea that speciation might be a fairly rapid event, followed by long periods of ‘stasis’ for the resulting species (this is Punctuated Equilibrium in a nutshell, and the odds of finding even one of these true ancestral species is virtually nil. The best we can hope for in the fossil record, usually, is to find something fairly close to the split. However, we do find living organisms that appear to be intermediate forms - for example a ‘fish’ that has both lungs and gills.

You are quite correct in stating that “it’s something else entirely to suggest an egg laying creature had a mutation that developed a uterus and all the attendent things necessary to make it work”. But, there is no reason to assume that this transition happened in just one speciation event! Macro-evolution of this sort can operate over tens of millions of years. Random mutations occur all the time. Many of these are harmful to the organism (since they are ultimately the result of a ‘fault’ in the transcription of DNA), and are thus weeded out. Some of these mutations turn out to be neither harmful nor beneficial and can ‘hang around’. Still further mutations turn out to be actively beneficial to the organism and are kept (that is, passed on to the offspring).

Keep in mind that ORGANISMS do not evolve. An egg-layer is not going to give birth to a placental. Even if we accept Punctuated Equilibrium, speciation is not believed to happen overnight - it can still take a few million years, which is a phenomenally long time in an absolute sense, but still only a drop in the bucket of the geological sea of time.

20

I mean, ‘inherited FROM its ancestors’.

:eek: