Evolution

The great angiosperm radiation of the mid-Cretaceous, the dramatic explosion of flowering plant species that occurred about 100 million years ago, is thought to have been good news for evolving mammals, providing them with new options for food and habitat. 

Previous literature suggested the spread of angiosperms, along with the evolution of pollinating insects, may have spurred an increase in the diversity of mammals. The idea made sense: The radiation would likely have resulted in more food sources from seeds, fruits, leaves and insects.

Not always. 


Before there was life on Earth, there was a primordial soup of molecules, and at some point a specialized molecules began replicating. This self-replication kick-started a biochemical process that would lead to the first organisms.

How those molecules began replicating has been one of science's enduring mysteries.

In the early 1980s, researchers found that ribozymes — RNA enzymes — act as catalysts. It was evidence that RNA can be both the blueprints and the chemical catalysts that put those blueprints into action. This finding led to the "RNA World" hypothesis, which posits that RNA alone triggered the rise of life from a sea of molecules.


A genetic phenomenon that allows for the selection of multiple genetic mutations that all lead to a similar outcome - a 'soft selective sweep' such as the ability to digest milk- has been characterized for the first time in humans.

This soft selective sweep was described in the population of Ethiopia by a team of geneticists from University College London, University of Addis Ababa and Roskilde University and reveals that individuals from the Eastern African population have adapted to be able to digest milk, but via different mutations in their genetic material.


The ancient closest relatives of mammals, the cynodont therapsids, not only survived the greatest mass extinction of all time 252 million years ago, they thrived in the aftermath.

The first mammals arose in the Triassic period, more than 225 million years ago. These early fur balls include small shrew-like animals such as Morganucodon from England, Megazostrodon from South Africa and Bienotherium from China.  They had differentiated teeth - incisors, canines, molars - and large brains and were probably warm-blooded and covered in fur; all characteristics that stand them apart from their reptile ancestors, and which contribute to their huge success today.

Females select the 'right' sperm to fertilize their eggs when faced with the risk of being fertilized by wrong sperm from a different species and researchers recently set out to investigate salmon and trout, which fertilize externally in river water, because the two species occasionally hybridize in the wild.

Since hybrid offspring become reproductive dead-ends, females of both species are under selection to avoid hybrid fertilizations, and instead promote external fertilization by their own species' sperm.


Two papers published this week have proposed explanations regarding the evolution of social monogamy among mammals and especially primates.  Of three competing hypothesis, one proposes that a driving force in establishing social monogamy was the protection of offspring by preventing male infanticide, while the other proposes that social monogamy is the result of female intolerance towards each other and a low population density that simply prevents males from adequately "guarding" females from other males (1).

A study of mortality and fertility patterns using seven species of wild primates (apes, monkeys etc.) compared with similar data from hunter-gatherer humans found that menopause sets humans apart from other primates.


Most mammals aren't monogamous, nor are most anything except birds, where it happens in about 90% of cases. 

It's actually quite rare in mammals (5%), so why did it evolve? Was it to be better parents together, to protect offspring from being killed by other males or instead to protect women from competitors? Well, it depends on who you ask.

Being a solitary individual who can't run all over the place protecting females from other males wins the prize, according to Cambridge zoologists Lukas and Clutton-Brock, who looked at 2,000 species of mammals and determined that when breeding females didn't like each other and female density was low, a monogamous mating strategy developed because males were unable to defend multiple females from other males.

Male guppies must not be very sexy, because they have evolved an extreme way to hold on to a female that interests them, even if that affection is unrequited: claws on their genitals to make it more difficult for unreceptive females to get away during mating.