I wish to keep these questions purely academical please.
1. The characteristic of intelligence seems to benefit most species favourably, much more so than some other supposedly evolved traits. What prevents all animals and organisms from progressively becoming smarter?

2. How did the cross over happen between animals and plants happen (or even another kingdom of animals?) Did they evolve completely in another chance of nature, or did they both spawn from the original source of life? How did they cross-over

3. Why is the X-chromosome in humans slowly dissapearing? How did it evolve in the first place and why has it decided to go again?

I have more questions that I would love an answer to, but I don't want to give you too much.

Thanks in advance, Matt

Hello Matt,

1. "Intelligence" is recently describe to be an emergent property of a large organ, the brain. Generally speaking, greater intelligence requires a higher proportion of your body to be accounted for by brain tissue. Brains, especially large brains, are very complicated and energetically expensive and we divert a disproportionately large fraction of our total daily calories to just maintaining them. In addition to more food, humans pay for our large brains with a slow birth rate compared to many other mammals and high parental investment; The size of the birth canal places an upper limit on head size, requiring much earlier births and helpless young.

If intelligence can be considered a selectable trait, then, like all other traits, it is not always of benefit in all contexts. Therefore, it only arises and comes to fixation in a population which both has the potential AND the correct context for it to be beneficial. For humans and the niche we occupied at the right moment, this worked quite well; our social groups were able to cope with helpless young, and intelligence also greatly aided survival. We certainly had the potential, as you can surmise by recognising some kind of consciousness in our mammalian cousins. For something like an ant, or a rosebush or a jellyfish, the selection forces and context are quite different and therefore the drive towards something you might call intelligence may be weak, non-existant or even negative.

2. I'm not sure about plants and animals "crossing over", I don't think that happened. Plant cells are differentiated from animals primarily in that their ancestors acquired two intracellular symbiotes (symbiogenesis) which eventually became mitochondria and chloroplasts, whereas animal and fungal cells only acquired mitochondria. How exactly all this happened isn't exactly known, but the idea is that one bug tried to eat another, and they ended up doing better together when the eating failed. I suspect that the various invasions of proto-mitochondria happened millions of times before it stuck, and the same is probably true with chloroplasts. Generally speaking it is thought that since plants are the only clade with chloroplasts, they acquired them after mitochondria, which can be found in all eukaryotic cells. Since the mitochondria in all clades of eukaryotes are fundamentally the same (apart from a few hundred million years of very slow evolution), it is consistent with the evidence if this happened in only one population, which then diversified into animals, plants and all the rest.

3. The X chromosome is not disappearing. You may be confused, because according to some recent reports, the Y (male) chromosome is slowly losing genes and therefore getting smaller. This trend is controversial to say that least, and is only a problem if one assumes that there are no natural forces which will cause this trend to halt. Anyway, this isn't terribly interesting; organisms gain, lose and move genetic material around all the time. That it is happening to us is a reassuring reminder that we continue to evolve:)

Matt, here's some (academic) references to the points John makes on the Y-chromosome -

Is the Y-chromosome ‘vanishing’?: http://www.scientificamerican.com/artic … -vanishing

Recent article on Y-chromosome diversity and natural selection: www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1004064

Last edited by Steve Lolait (28th Aug 2014 09:19:57)