Gorilla genome sequenced - Page 2

Thank you for continuing the discussion! And thanks for the further info about chimps. She is an old gal to be a mom again.

I'm reminded of a paper I read for my Psychobiology of Reproduction class by Gould back in the 1970's that argued against the "trait-evolution" mindset, seeking instead to view the whole individual organism as the unit of selection. While his arguments often leaned toward using the "straw-man" argument, I did understand something he was getting at which relates to this discussion. Not all things we observe in anatomy or behavior are traits selected by evolution. Some are simply by-products of another development (the human chin was used as an example -- we have a prominent chin, but Neanderthals didn't, but is a prominent chin something that was selected, or merely the by-product of differences in jaw structure?). As such, menopause might be a by-product of something else -- perhaps pregnancy for humans incurs more wear-and tear than it does for chimps, and the menstrual cycle suffers from "early burnout."

Or perhaps there was a benefit to menopause -- the grandmother hypothesis is one possibility. Perhaps some women had fewer children but managed to ensure the survival of more grandchildren because their own reproductive lives ended earlier. Remember, it's not just about the number of babies parents crank out -- it's how many of those babies survive and make babies of their own that counts for genes being passed down.

Another might simply be the increased length of time in humans compared to our ancestors until an infant reaches independence. If you look at the average age of onset for menopause, and imagine that a woman's last child was born just before then, how old would that child be when it's mother reached the end of an average life span? Would it be independent at that point? I'm guessing it would be just about entering puberty. If the mother did not enter menopause, how many years before average age of death would be necessary to raise another offspring?

I'd be very interested in finding out what has been tested thus far.

Quote:

Originally Posted by Matthew3590 

I always get confused when they say we share 98% of DNA.  Does that just mean that we have 98% of the same possible genes?

Most of our DNA is not genes. The old-school definition of a gene is a segment of DNA that gets transcribed and translated to produce a protein. In terms of our total DNA, that's in the single-digits percentage. The rest is what used to be called "junk DNA" -- because, until recently, if DNA didn't make a protein, it was considered "junk" or merely "structural." We now know that there is a lot more to our DNA than just "genes" and "not-genes." Some stretches of DNA may not code for a protein themselves but affect the rate that other genes are expressed. And within a gene, only some parts may actually be translated into a protein -- there are many genes that stretch on and on and on, but only a minor portion of the gene actually makes it to the ribosome to direct amino acid sequence to build a protein. It's a more complicated system than originally thought.

Mutations are errors that occur during DNA replication at mitosis and meiosis. When a mutation occurs in a section of DNA that does not code for a protein or affect another section that codes for a protein, there is no negative result in the organism -- a "harmless" or "neutral" mutation. As such, these will vary more between lineages, since there isn't a selective pressure to maintain a non-mutated version.

Genes, however, tend to vary less down a lineage, so differences in genes between related species are more significant than differences in DNA overall between related species. Those differences found in the genes will have effects that are related to the differences seen in the related species when we look at them.

Differences found in the rest of the DNA is what's used in "genetic clocks" to measure divergence between species since the differences are mutations which are calculated to occur at regular intervals. When you read research that states how long ago two different species shared a common ancestor based upon DNA studies, it is often based on measuring differences at particular regions on chromosomes that have a steady mutation rate, and then doing some math to determine how long it's been since the differences diverged.

See below for a more in-depth explanation:

http://www.talkorigins.org/faqs/molgen/

And, if you read someone's attempt at dismissing the work above, the author posted a response which I (in my geekiness) find somewhat amusing.

http://www.talkorigins.org/faqs/molgen/plaisted.html

ETA -- oh, and another response

http://www.talkorigins.org/faqs/molgen/wieland.html

Quote:

Originally Posted by redhen 


What about female dogs in heat? They do bleed when they are ready to mate/reproduce..

There are differences that occur beyond the similarities of a "bleed". Other species have an estrous cycle.

Oh, and now I'm confused, and emailed my prof for clarification. In "human" classes I've taken, menstruation was stated as being unique to humans, that other species have an estrous cycle. But now that I'm looking further (to find a link or two to explain it better and post it here...), I see some references stating that menstruation is also found in the great apes...then another broadens that to include old world monkeys...Now I'm wondering if the "human" classes are more specific about how they define "menstrual cycle" versus "estrous cycle", and the "mammal" classes are a bit fuzzier with the distinctions, and lump things together. I'll let you know tomorrow -- I have my PsyBio of Repro class in the morning.