Our world and species in it can be very fascinating and to understand it, we need to do a lot of reaearch work. There are a lot of exciting species in our world like the Adactylidium mite which gives birth to already pregnant young ones that feeds to ensure their eggs hatch inside them. The eggs contain numerous females and a male and the mating occurs inside the mother. These young ones eat mum to find their way to the outside world and the females come out pregnant ready to repeat the cycle again.
That is extremely amazing but there is more when we talk about our word and the species living there. Codfishes are able to lay million of eggs while kiwi bird lay only one egg which is about two third of its entire weight. Compared to these two some animals can take years before they reach maturity such as the greenland shark which reaches maturity when it is 150 years and its young ones spend 8 years in the belly before they are born.
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If we study life history, we will learn a lot about so many organism, why they are the way they are, why they shed their energy towards growing and living long or why they allocate it to fast growth with shorter lifespan. When we mention evolution or natural selection, there is a point to it and if is to be able to pass genes to young ones and whatever traits make the organisms successful at it is transferred to their young or the next generation.
In other to maximize fitness in organisms, there are usually tradeoffs and these are usually taken into consideration. Having more offspring will reduce an organisms lifespan and their rate of survival would be put to a teat as there will be high competition. Fast maturity and early reproduction can affect the size of the organisms as it can remain small.
Now humans. Compared to our closest relatives apes, that die at 30 or 40 years, humans are one of the species with backbones that live long. A lot of animal young ones especially mammals can fend for themselves immediately they are done with breastfeeding but this is not the same with humans but that’s not all that it has to do with humans. Why do male have an active reproductive year all round their life but females reach the end of rheir reproductive years in their 40s and 50s?
Sexual maturity occurs during puberty which can be around age 8 years to age 13 years in females and later in males. In females, they can experience a ton of changes in hormones which lead to their menstrual cycle and this cycle is split into the follicular phase which is from day one of cycle to day 14 and the luteal phase where the ovulation site becomes a corpus luteum which makes progrsterone and once the corpus luteum dies, progesterone levels will drop which leads to a withdraw bleed known as the menstrual cycle.
Do you know that your grandma isn’t the only one that love grandchildren? Elephants and a few species of whales also have their grandmothers care for their grandkids including providing food and passing down knowledge to them. This has led to the grandmother hypothesis which says that as a result of menopause and long post reproductive lifespan, older female stop to care about their young ones and start to care about the young of others thereby improving the odds of survival.
Scientists are still arguing this as it is someone peculiar to us and a few mammals like elephants and whales. So are we saying other animals do not have this evolutionary trait?
Reference
https://www.sciencedirect.com/science/article/pii/S0092867423010802
https://www.pnas.org/doi/full/10.1073/pnas.1903844116
https://www.nature.com/articles/s41586-024-07159-9
https://pmc.ncbi.nlm.nih.gov/articles/PMC2625386/
https://content.csbs.utah.edu/~hawkes/Hawkes_al00gramsHumanEvolution.pdf
https://onlinelibrary.wiley.com/doi/10.1017/S1464793103006432
https://pmc.ncbi.nlm.nih.gov/articles/PMC5768312/
https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2016.00222/full