123

This is a interesting question and for a long time it was thought that they do not age. In the meantime there are some new papers which say that bacteria do indeed age. Aging can be defined as the accumulation of non-genetic damages (for example oxidative damage to proteins) over time. If too much of these damages are accumulated, the cell will eventually ...


74

Why do we age is a classical question in Evolutionary Biology. There are several things to consider when we think of how genes that cause disease, aging, and death to evolve. One explanation for the evolution of aging is the mutation accumulation (MA) hypothesis. This hypothesis by P. Medawar states that mutations causing late life deleterious (damaging) ...


69

Crystallin proteins are found in the eye lens (where their main job is probably to define the refractive index of the medium); they are commonly considered to be non-regenerated. So, your crystallins are as old as you are! Because of this absence of regeneration, the accumulate damage over time, including proteolysis, cross-linkings etc., which is one of ...


22

This is a very good question. There is a big ongoing field of research called "evolution of aging/senescence" that tackles this question. I won't give you a complete overview of the different hypothesis the could explain why we age but here is a fundamental concept that is to know. We'll assume that there is some extrinsic mortality, mortality against ...


22

I like Mowgli's answer, because it is a non-obvious example. However I would also point out that there are many, many protein-based structural components in the body that we know do not regenerate due to associated pathologies; so presumably these structural proteins are as old as from when they first arose in developemnt. Take the stereocilia on hair cells ...


20

The immortal jellyfish can revert back to its immature polyp stage after reaching maturity, then mature again, over and over. You can read more on the wikipedia page, but this ability means it can potentially avoid senescence altogether.


17

The answer(s) to this question can fill libraries. But I can give a few pointers here, as the question is relevant and timely, giving the tendency to an ever increasing life expectancy of the general populace in developed countries (notable exception: US). I think your question can broadly be answered by the fact that degenerative processes in the brain ...


15

I now found this Wikipedia article on biological immortality. It's pretty much what I was looking for. Wikipedia describes the phenomenon as follows: Biological immortality refers to a stable or decreasing rate of mortality from cellular senescence as a function of chronological age. Various unicellular and multicellular species may achieve this ...


15

The HeLa cell line is undoubtedly the most used and investigated human immortal tumor cell line. Extracted from a cervical tumor from Henrietta Lacks in 1951 at Johns Hopkins hospital, Baltimore, MD these cells proved immortal and are still used in many, many labs worldwide today. It is the oldest human cell line in use and, therefore, the oldest human ...


14

Because evolution isn't about individuals: it's about species. What matters to natural selection isn't how long you live, but how many grandchildren you have. A long lifespan can be an evolutionary advantage, but like any trait, it's only an advantage to the extent that allows you to reproduce more. It would seem that a longer lifespan would be advantageous ...


13

Yes. The Bristlecone Pine, Pinus longaeva, is one example. This species boasts the oldest individual living organisms, and also has been convincingly argued by Lanner and Connor (2001) to show no evidence of senescence. While the Wikipedia page on Biological Immortality (as of June 2013) unfortunately ignores plants, the pages on Negligible Senescence and ...


13

Actually, genetically, there is no reason for animals to continue to exist after they have procreated. If you look at salmon, they die immediately after procreating, which is probably the most efficient way to carry the best genes to the next generation. In the case of mammals, they need to teach their offspring where to find food, where to find water and ...


12

Short answer Large animals do get cancer. They may contract cancer with an incidence less than that estimated by absolute cell numbers, but there seems to be a lack of data on cancer rates in large animals to support this hypothesis conclusively. Background Whales contract cancer (Martineau et al, 2002). There does, however, seem to be a lack of correlation ...


10

Gametes (sperm and ovum), which fuse to form a zygote, arise from germ cells (spermatogonia and oogonia). Germ cells, like stem cells, are maintained carefully i.e the genome is preserved and transposition/recombination events are tightly controlled via different mechanisms. So these germ cells don't have shortened telomeres. Also, during early embryonic ...


9

Interesting question. My answer is no, but it requires a rather science-fiction style answer - at least it's beyond current technology, but here goes: My Assumptions I make the simplifying assumption that ageing is only related to telomere length. Thus by "avoid ageing" I assume you mean "avoid telomere shortening". Also to clarify things for others, I'll ...


9

First of all, in eukaryotes (as far as I'm aware), older cells can be distinguished from younger cells due to telomere shortening, so there is an ageing process. HeLa cells mentioned by @Gary Chou have a more active telomerase which mitigates telomere shortening, allowing cells to continue to divide indefinitely. I think it's a very interesting question ...


9

A very interesting example are the cohesin molecules holding sister chromatids together in the oocytes (so only applicable to females, sorry!). Cohesion is established in utero, and these molecules are not recycled throughout life (AFAIK only shown directly for mice, not humans - https://www.ncbi.nlm.nih.gov/pubmed/20971813, https://www.ncbi.nlm.nih.gov/...


8

I can find no examples of immortal plants, but then again immortality is rather hard to prove, it's rather like trying to prove that space will never turn in to a pony - as long as time exists it could still occur, only if you go beyond the end of all time would you be able to say that it has or has not happened but then time would no longer exist and nor ...


8

Good question. There are many organisms that are technically biologically immortal. However, I would like to point out that the definition of biological immortality is this: ...cells that are not limited by the Hayflick limit, where cells no longer divide because of DNA damage or shortened telomeres. (That's from here.) So biological immortality ...


7

If you take the line of "The Selfish Gene - Richard Dawkins". Evolution doesn't care about individuals, it cares about genes. So as long as the genes are passed along reliably into the future, evolution may do it with 4 generations per 100 years or 100 generations per 100 years.


7

There is no color code for the leafs - the color results from biochemical reactions. Basically there are three colors: Green, yellow and red. Green color is caused by the chlorophyll inside the chloroplasts, when the leafs are active in photosynthesis. Yellow color is caused by Carotenoids, which are present in the leafs all the time, but are masked by the ...


6

Yes, at least some fishes have intrinsic lifespans and deaths that are related to their own life-history and not to external forces such as predation or disease. Fishes show three types of senescence. Lampreys, eels and pacific salmon exhibit rapid senescence and sudden death at first spawning. The guppy, red panchax, medaka, platyfish, Indian murrel ...


6

First of all, it will be practically impossible to make an estimation of how long a transplanted organ will live and how many times it could be transplanted. However, it is relatively safe to say that it will not live forever. To be able to receive an organ transplantation, the HLA MHC-complexes of donor and receiver need to be matched very carefully, to ...


6

Short answer: Yes, we do shrink with age. The most important reason is that the cartilage in the joints between our bones gets worn out and thinner, as well as disks between the vertebrae of the spine. This results in a compression of the spine and also to a loss in height. Shrinking bones due to osteoporosis can also play a role, as well as muscular ...


6

You have a very interesting question there! In order to answer, however, we must examine the most widely accepted "reason" for why we age and eventually die. Most scientists agree that it is because of mass cell death. Normally you and I would be able to deal quite well with mass cell death (such as a very large injury), the problem comes in when we are ...


6

Second law of thermodynamic and ageing The second law of thermodynamic applies to closed system. Organisms are not closed system. The second law of thermodynamic is a fundamental principle of our universe and any biological processes do follow the principles of physics. However, stating that biological ageing is (partially) caused by the second law of ...


5

The answer is that the majority of the cells were frozen from very early in their Hayflick lifetimes e.g. after 9 population doublings. They have been thawed out judiciously and only as needed thus preserving a lot of frozen stocks. When an ampule of cells frozen at, for instance 9 population doubling, is thawed, the cells pick up where they left off and ...


5

Telomeres do not "cause" ageing as such - although you are right that they limit the number of times a somatic cell can divide. Each time a cell divides the chromosomes are replicated in an imperfect way, and as such a small amount of DNA is lost from the end of the chromosome during each round of cell division. Telomeres are just extensions to the ...


5

The immortal jellyfish (Turritopsis dohrnii) is capable of biological immortality. It's one of few known species capable of reverting completely to a sexually immature, colonial polyp stage after having reached sexual maturity as a solitary (free-floating) individual (called a medusa). Theoretically, this process can go on indefinitely, effectively ...


5

In men, gout is associated with a higher risk of death from all causes. This would imply that their life expectancy is shorter. From a review by Kim et al. (1): Among men who did not have pre-existing coronary heart disease, the increased mortality risk is due primarily to an elevated risk of cardiovascular death, particularly from coronary heart ...


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