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April 12, 2007

Animal Aging

I am posting this on the very moment of my birth. Luckily, I now live in the same time zone as the one when I was born which made it easier. I think it would be perfect if we hadn't changed our daylight savings policy this year. Oh, well. It's for our own good.

Anyway, I had great plans on talking about animal aging. I was going to calculate my age in human, dog, cat and any other animal years I could calculate. However, I was in for a surprise. The dog years thing is basically completely untrue. It's not a 7-to-1 ratio like I was always told.

So basically, I'm 30 (+/- 1 hour) and I've been living a lie.

I came up with a new plan: I was going to estimate animal ages myself based on my knowledge of certain mammal's weaning age, sexual maturity and lifespan. Like, for example, elephant seal years. But it's not as easy as I thought it would be since males rarely live past 14yrs but females can live to 20. But they reproduce basically until they die, and human women generally don't. Also, I would have to determine the sexual maturity of humans, and at 30 (+/- 1.25 hours), I am not quite sure I'm there yet.

Blast. So there goes my idea of estimating my relative female northern elephant seal age. I can safely say I'd be over 5 and under 18, and probably more like.. 10 because I'm basically in the middle of my plausible breeding years, so to speak.

Animals certainly age, but as you can see, its pretty complicated. Mammals like dogs and cats relative "years" vary greatly by breed, but its mostly about the size of the animal. Genetic diversity, especially regarding inherited defects and diseases, also play a significant role.

So a mouse's lifecycle is going to be shorter (and therefore faster) than a dog's. Dogs are a terrible example, though, since many of the breeds suffer from inbreeding and congenital disorders. Irish Wolfhounds are considered one of the largest (tallest) dog breeds but they have very short lifespans (7 yrs) whereas the yappy little Jack Russell Terrier lives an average of 14 years. Why? Jack Russell gene pool is strong, and they haven't suffered from heavy inbreeding, whereas the Irish Wolfhound suffered from a genetic bottleneck during the 1800's.

Live To Breed

One of the other issues with age estimation is that most animals do not age linearly. They rapidly reach sexual maturity and stay there. Life expectancy is different in the animal kingdom, where one is hunted. You want to grow up fast and perpetuate your species.

Weaning age varies greatly amongst species. We wean our children at various ages from just after birth through childhood, depending on our life plans, our class, our culture, and the available food. The Northern elephant seal weans her pup after about four weeks, whereas the sea lions nurse their pups for up to a year.Why so different? The elephant seal mother fasts while she nurses, her food source is far away. The sea lion nurses her pup for a few days, and then goes hunting, coming back and nursing more. Incidentally, this difference in behavior explains why vocalization is so much more important for sea lions - when mom comes ashore, she has to find her pup amongst all the others, whereas the elephant seal mother-pup bond is mostly (but not exclusively) due to proximity.

Let's look at something bigger. A female African Elephant may live to be more than 70 years old, if she's not poached first. It takes over a decade for her to reach sexual maturity, but she can reproduce until she's almost 60. She may let a calf nurse for upwards of two years if she does not have another calf right away.

Posted by sorsha at April 12, 2007 6:29 AM