What was one of the most important steps in the evolution of early
living things?

the development of the enzyme Rubisco and evolution of oxygenic photosynthesis.

Explanation: One can pick many key steps in early evolution: the development of the first cells, oxygenic photosynthesis, endosymbiosis leading to eukaryote organisms.

One important step was the mutation to the enzyme ribulose bisphospate carboxylase oxygenase (Rubisco) which enabled oxygenic photosynthesis.

The cyanobacteria that had Rubisco changed the planet’s atmosphere by producing oxygen as a by-product of photosynthesis. They were the most successful organisms of the time and have continued as a successful and ubiquitous group of organisms for billions of years.

The production of oxygen changed the direction of evolution profoundly. Later endosymbiosis led to the evolution of plants, with cyanobacteria the ancestors of chloroplasts, making Rubisco one of the most common enzymes on the planet.

fertilization, pictured in figure 24.23a is the process in which gametes (an egg and sperm) fuse to form a zygote. the egg and sperm each contain one set of chromosomes. to ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. in mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. when a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. in placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in figure 24.23b. the fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. the nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

explanation:

the two answers are a, the population of birds with large beaks will increase on the island, and c, the trait for large beaks will be passed on to future generations through natural selection. the reason for that is because if the birds that have beaks developed for eating small seeds lose all of their food, they will go hungry and eventually starve because they physically cannot eat the large seeds, therefore making the population of large beaked birds higher. also, if the trait of large beaks are dominant on the island over small beaks, then over time the large beaked birds will reproduce more and more, while the smaller beaked birds will reproduce less and less because they can't survive with the food provided. that leads to the trait of small beaks disappearing and the trait of large beaks taking over the island.